Recon (THR and TKR)

Question 1

Hip Osteoarthritis

1. Definition
2. Epidemiology:

• incidence
  
  • hip OA (symptomatic)
  • knee OA (symptomatic)

Answer 1

1. Definition

◦degenerative disease of synovial joints that causes progressive loss of articular cartilage

2. Epidemiology: incidence

◾hip OA (symptomatic)

◾88 per 100,000 per year

◾knee OA (symptomatic)

◾240 per 100,000 per year

Question 2

Hip Osteoarthritis: Risk factors 1. Modifiable 2. Non-modifiable

Answer 2

1. Modifiable ◾articular trauma ◾muscle weakness ◾heavy physical stress at work ◾high impact sporting activities 2. Non-modifiable ◾gender (females >males) ◾increased age ◾genetics ◾developmental or acquired deformities ◦ Hip dysplasia ◦ Slipped capital femoral epiphysis ◦ Legg-Calvé-Perthes disease

Question 3

Osteoarthritis : Pathophysiology Articular cartilage: 1. > OR < water content 2. eventual < OR > in amount of proteoglycans 3.Collagen abnormalities a) __________ b) __________

Answer 3

1. increased water content 2. decrease in amount of proteoglycans 3. collagen abnormalities a) organization and orientation are lost b) binding of proteoglycans to HA

Question 4

Osteoarthritis : Pathophysiology Change to synovium and capsule 1. Early phase of OA 2. Middle phase of OA 3. Late phases of OA

Answer 4

1. early phase of OA: ◾mild inflammatory changes in synovium 2. middle phase of OA: ◾moderate inflammatory changes of synovium ◾synovium becomes hypervascular 3. late phases of OA ◾synovium becomes increasingly thick and vascular ◾bone changes occur: ◾subchondral bone attempts to remodel ◾forming lytic lesion with sclerotic edges (different than bone cysts in RA) ◾bone cysts form in late stages

Question 5

Osteoarthritis: Cell biology Proteolytic enzymes: 1. Matrix metalloproteases (MMPs) Effect and examples 2. Tissue inhibitors of MMPS (TIMPs): Effects 3. Inflammatory cytokines Effect and examples

Answer 5

1. matrix metalloproteases (MMPs): responsible for cartilage matrix digestion ◾examples: stromelysin; plasmin; aggrecanase-1 (ADAMTS-4) 2. Tissue inhibitors of MMPS (TIMPs) ◾control MMP activity preventing excessive degradation ◾imbalance between MMPs and TIMPs has been demonstrated in OA tissues 3. Inflammatory cytokines: secreted by synoviocytes and increase MMP synthesis ◾examples: IL-1 ; IL-6 ; TNF-alpha

Question 6

Osteoarthritis: Genetics 1. inheritance 2. Genes potentially linked to OA ? (3

Answer 6

1. non-mendilian 2. Genes potentially linked to OA: ◾vitamin D receptor ◾estrogen receptor 1 ◾inflammatory cytokines -> IL-1 - leads to catabolic effect; -> IL-4 -> matrilin-3 -> BMP-2, BMP-5)

Question 7

Osteoarthritis: Radiographs 1. recommended views 2. optional views Findings 3. OA 4. Pelvic obliquity? 5. Acetabular retroversion

Answer 7

1. ◾standing AP pelvis ◾AP + lateral hip 2. optional views = false profile view (e.g. hip dysplasia) 3. Findings i) OA (joint space narrowing / osteophytes / subchondral sclerosis / subchondral cysts) 4. may be secondary to spinal deformity; may cause leg-length issues 5. makes appropriate positioning of acetabular component more difficult intraoperatively

Question 8

Osteoarthritis: Studies Histology findings in OA (4)

Answer 8

Histology 1. Loss of superficial chondrocytes 2. Replication and breakdown of the tidemark 3. Fissuring 4.Cartilage destruction with eburnation of subchondral bone

Question 9

Hip Osteoarthritis: Treatment (Nonoperative) Treatment options Controversial treatments

Answer 9

1. NSAIDs and/or tramadol 2. Walking stick 3. Weight loss, activity modification and exercise program/physical therapy ◾ind= BMI > 25 4. corticosteroid joint injections ◾indications ◾can be therapeutic and/or diagnostic of symptomatic hip osteoarthritis ADDIT: Controversial treatments ◾acupuncture ◾viscoelastic joint injections ◾glucosamine and chondroitin

Question 10

Hip Osteoarthritis: Treatment (Operative)

Answer 10

1. arthroscopic debridement: ◾indications= controversial ; degenerative labral tears) 2. Periacetabular osteotomy +/- femoral osteotomy ◾indications = symptomatic dysplasia in an adolescent or young adult with concentrically reduced hip and mild-to-moderate arthritis ◾outcomes = mixed results ; literature suggest this can delay need for arthroplasty 3. Femoral head resection ◾indications= pathological hip lesions ; painful head subluxation 4. Hip resurfacing ◾indications = young active, male, patients with hip osteoarthritis 5. Total hip arthroplasty (THA) ◾indications = end-stage, symptomatic or severe osteoarthritis arthritis note: preferred treatment for older patients (>50) and those with advanced structural changes

Question 11

Knee Osteoarthritis: presentation 1. History 2. Symptoms

Answer 11

1. History ◦identify age, functional activity, pattern of arthritic involvement, overall health and duration of symptoms 2. Symptoms ◦function-limiting knee pain (effect on walking distances) ◦pain at night or rest ◦activity induced swelling ◦knee stiffness ◦mechanical ◾instability, locking, catching sensation

Question 12

Knee Osteoarthritis: presentation Physical exam 1. inspection 2. range of motion 3. ligament integrity

Answer 12

1. inspection ◾body habitus ◾gait (often an increased adductor moment to the limb during gait) ◾limb alignment ◾effusion ◾skin (e.g. scars) 2. range of motion ◾lack of full extension (>5 degrees flexion contracture) ◾lack of full flexion (flexion <110 degrees) 3. ligament integrity

Question 13

Knee Osteoarthritis: Treatment (Operative) Options (3) 1. 2. 3. 4. CR vs PS outcome? 5. Patella resurfacing vs not outcomes ? 6. Drain or no-drain

Answer 13

1. high-tibial osteotomy ◾indications = younger patients with medial unicompartmental OA ◾outcomes - AAOS guidelines: limited evidence for 2. unicompartmental arthroplasty (knee) ◾indications =isolated unicompartmental disease ◾outcomes ◾TKA have lower revision rates than UKA in the setting of unicompartmental OA 3. total knee arthroplasty ◾indications =symptomatic knee osteoarthritis ; failed non-operative treatments 4. TKR cruciate retaining vs. crucitate sacrificing implants show no difference in outcomes 5. patellar resurfacing ◾no difference in pain or function with or without patella resurfacing ◾lower reoperation rates with resurfacing 6. Drains are not recommended

Question 14

Hip Osteonecrosis

Epidemiology

1. incidence: accounts for __% of total hip arthroplasties performed
2. demographics - gender predominance ?
3. demographics - av age at presentation is __to__yr
4. bilateral hips involved ___% of the time
5. How is multifocal osteonecrosis defined

Answer 14

1. 10%
2. male > females
3. is 35 to 50
4. 80%
5. Disease in three or more different joints (3% of patients with osteonecrosis have multifocal involvement)

Question 15

HIP AVN: Risk factors

1. direct causes (6)
2. indirect causes (8)

Answer 15

1. direct causes
   - irradiation
   - trauma
   - hematologic diseases (leukemia, lymphoma)
   - dysbaric disorders (decompression sickness, “the bends”) - Caisson disease
   - marrow-replacing diseases (e.g. Gaucher’s disease)
   - sickle cell disease
2. Indirect causes
   - alcoholism
   - hypercoagulable states
   - steroids (either endogenous or exogenous)
   - systemic lupus erythematosus (SLE)
   - transplant patient
   - virus (CMV, hepatitis, HIV, rubella, rubeola, varicella)
   - protease inhibitors (type of HIV medication)
   - idiopathic

Question 16

AVN: Pathophysiology

i. idiopathic AVN
ii. AVN associated with trauma
- due to injury of femoral head blood supply, in particular the __________________ artery ?

Answer 16

Pathophysiology

i. idiopathic AVN = intravascular coagulation is the final common idiopathic pathway

pathoanatomic cascade

1. coagulation of the intraosseous microcirculation →
2. venous thrombosis →
3. retrograde arterial occlusion →
4. intraosseous hypertension →
5. decreased blood flow to femoral head →
6. AVN of femoral head →
7. chondral fracture and collapse
   ii. medial femoral circumflex

Question 17

AVN Hip : Associated conditions

1. AVN rates of specific traumatic injuries
   a. femoral head fracture: __to__%
   b. basicervical fracture: ___%
   c. cervicotrochanteric fracture: ___%
   d. hip dislocation: __to__%
   e. intertrochanteric fracture: ____
2. higher risk of AVN with_____ initial displacement and _____ reduction
3. decompression of ______ _______may reduce risk
4. ___________ reduction may reduce risk

Answer 17

1. AVN rates of specific traumatic injuries
   a. 75-100%
   b. basicervical fracture: 50%
   c. cervicotrochanteric fracture: 25%
   d. hip dislocation: 2-40% (2-10% if reduced within 6 hours of injury)
   e. intertrochanteric fracture: rare
2. higher risk of AVN with greater initial displacement and poor reduction
3. decompression of intracapsular hematoma may reduce risk
4. quicker time to reduction may reduce risk

Question 18

Hip AVN: Classification

1. Eponymous name and description

Answer 18

1. Steinberg (modification of FICAT)

Six stages/grades (0 - VI)

Question 19

AVN Hip : Prognosis

risk of femoral head collapse with osteonecrosis is based on the modified Kerboul combined necrotic angle

1. How is this calculated ?
2. what angles indicate Low vs Mod vs High risk ?

Answer 19

Kerboul combined necrotic angle

1. Calculated by adding the arc of the femoral head necrosis on a mid-sagittal and mid-coronal MR image
2. Risk categorisation
   - > Low-risk = combined necrotic angle less than 190°
   - > Moderate-risk= combined necrotic angle between 190° and 240°
   - > High-risk= combined necrotic angle of more than 240°

Question 20

AVN Hip : Presentation

1. Symptoms [3]
2. Physical exam [2]

Answer 20

1. Symptoms
   - insidious onset of pain
   - pain with stairs, inclines, and impact
   - pain common in anterior hip
2. Physical exam
   - mostly normal initially
   - advanced stages similar to hip OA (limited motion, particularly internal rotation)

Question 21

AVN Hip: Imaging

1. Radiographs: recommended views
2. MRI Findings
3. When should MRI be ordered ?
4. presence of bone marrow edema on MRI is predicitve of______ and future ______
5. other imaging

Answer 21

1. recommended views: AP hip / frog-lateral of hip / AP and lateral of contralateral hip

NOTE: classification systems based largely on radiographic findings (see below)

2. MRI [highest sensitivity (99%) and specificity (99%)]
   - double density appearance= T1: dark (low intensity band); T2: focal brightness (marrow edema)
3. order when radiographs negative and osteonecrosis still suspected
4. presence of bone marrow edema on MRI is predicitve of WORSENING PAIN and future PROGRESSION OF DISEASE
5. Bone scan in some cases - replaced by MRI largely

Question 22

AVN HIP: Treatment

1. Nonoperative

Answer 22

1. Nonoperative

bisphosphonates

• indicated for precollapse AVN (Ficat stages 0-II)
• trials have shown that alendronate prevents femoral head collapse in osteonecrosis with subchondral lucency (However, other studies have also shown no benefit of preventing collapse with bisphosphonates)

Question 23

AVN HIP: Treatment

Operative options [7]

Answer 23

1. core decompression with or without bone grafting: indications = early AVN, before subchondral collapse occurs; reversible etiology
2. rotational osteotomy: indications = only for small lesions (<15%) in which the lesion can be rotated away from a weight bearing surface
3. Curettage and bone grafting through Mont trapdoor technique or Merle D’Aubigne lightbulb technique: indications = preferably pre-collapse
4. vascularized free-fibula transfer: indications = for both pre-collapse and collapsed AVN in young patient

reversible etiology preferred

5. total hip replacement: indications
   i. younger patient with crescent sign or more advanced femoral head collapse, +/- acetabular DJD
   ii. irreversible etiology (chronic steroid use)
   iii. patients >40 with large lesions
6. total hip resurfacing: indications
   i. in advanced DJD with small, isolated focus of AVN
   ii. requires adequate bone to support resurfacing component
   iii. contraindicated in underlying disease process or chronic steroid use causing AVN (poor bone quality) and renal disease (metal ions from metal-on-metal implant)
7. hip arthrodesis: indications= only consider in the very young patient in a labor intensive occupation

Question 24

Adult Dysplasia of the Hip

Introduction

1. define
2. Adult and adolescent dysplasia can come in two forms
   a. _____
   b. _____
3. Outcome if left untreated ?
4. Pathoanatomy = acetabular __________ is most common factor
5. Epidemiology: dysplasia is attributable to ___%of all cases of hip osteoarthritis

Answer 24

1. Hip dysplasia is a disorder of abnormal development or dislocation of the hip secondary to capsular laxity and mechanical factors
2. Adult and adolescent dysplasia can come in two forms
   a. dysplasia that was previously treated
   b. dysplasia that was not treated
3. If left untreated it can progress to early arthritis
4. Acetabular retroversion is most common factor
5. 33% (one third)

Question 25

Adult Dysplasia of the Hip

1. Crowe classification

Grade 1

Proximal displacement = <10% vertical height of pelvis

Femoral head subluxation= proximal migration of head neck junction from inter-teardrop line <50% of femoral head vertical diameter

Grade II

• Prox displacement = 10-15%
• Fem Head Sublux = 50-75%

Grade III

• Prox displacement = 15-20%
• Fem Head Sublux = 75-100%

Grade IV

• Prox displacement = >20%
• Fem Head Sublux = >100%

Answer 25

treatment based on crowe grade

Question 26

Adult Dysplasia of the Hip

1. Hartofilakidis Classification

Answer 26

Dysplasia (Type A)

Femoral head within acetabulum despite some subluxation. Segmental deficiency of the superior wall. Inadequate true acetabulum depth.

Low dislocation (Type B)

Femoral head creates a false acetabulum superior to the true acetabulum. There is complete absence of the superior wall. Inadequate depth of the true acetabulum.

High dislocation (Type C)

Femoral head is completely uncovered by the true acetabulum and has migrated superiorly and posteriorly. There is a complete deficiency of the acetabulum and excessive anteversion of the true acetabulum.

Question 27

Adult Dysplasia of the Hip : Presentation

1. Symptoms
2. Physical exam

Answer 27

1. Symptoms

• hip or groin pain, especially in flexion activities
• often insidious onset

2. Physical exam

• increased int rot before arthritis sets in (due to increased femoral anteversion)
• decreased internal rotation may represent osteoarthritis
• increased external rotation with ambulation
• positive anterior impingement test (pain with passive flexion, internal rotation and adduction)
• may have instability with extension, abduction and external rotation

Question 28

Adult Dysplasia of the Hip : Imaging

Radiograph findings [7]

Answer 28

1. decreased femoral head sphericity
2. crossover sign (see image)
   - results from increased retroversion

Question 29

Adult Dysplasia of the Hip

https://www.orthobullets.com/recon/5008/adult-dysplasia-of-the-hip?expandLeftMenu=true

Answer 29

3. acetabular protrusio decreased lateral center-edge angle < 20° (image)

• angle between vertical line + line from femoral head to lateral acetabulum
• assess on AP view
• normal 25-40°

Question 30

Adult Dysplasia of the Hip : Imaging

4. increased tonnis angle > 10°
5. decreased head-neck offset ratio

https://www.orthobullets.com/recon/5008/adult-dysplasia-of-the-hip?expandLeftMenu=true

Answer 30

4. increased tonnis angle > 10°

• angle between horizontal line + line along superior acetabulum
• measures inclination of weightbearing zone
• assess on AP view
• normal 0-10°

5. decreased head-neck offset ratio

• distance between line parallel to femoral neck through anterior femoral neck + anterior femoral head divided by diameter of femoral head
• assess on lateral view
• normal > 0.15

Question 31

Adult Dysplasia of the Hip : Imaging

6. increased femoral neck-shaft angle
7. decreased vertical center anterior margin angle (anterior center edge angle)

Answer 31

6. increased femoral neck-shaft angle

• angle created by anatomic axis of the femur and the femoral neck
• coxa valga

7. decreased vertical center anterior margin angle (anterior center edge angle)

• obtained on false profile radiograph
• angle between the vertical line through the center of the femoral head to the lateral acetabulum
• assessment of anterior undercoverage

Question 32

Adult Dysplasia of hip

Treatment : Non-op

Answer 32

Nonoperative

• supportive measures
  
  • indicated as first line of treatment

Question 33

Adult Dysplasia of hip

Treatment : Operative Options (4)

Answer 33

1. Periacetabular osteotomy +/- a femoral osteotomy

• indications
  
  • symptomatic dysplasia in an adolescent or adult with
  • concentrically reduced hip
  • congruous joint with good joint space

2. salvage pelvic osteotomy (chiari, shelf)

• indications
  
  • unreduced hip
  • recommended for patients with inadequate femoral head coverage and an incongruous joint (a salvage procedure)

3. hip resurfacing

• indications
  
  • can be used for Crowe type I or II disease

4. total hip arthroplasty (THA)

• indications
  
  • treatment of last resort for those with severe arthritis
  • preferred treatment for older patients (>50) and those with advanced structural changes
  • in a patient with bilateral hip dysplasia, there are significant technical challenges that need to be addressed to ensure a successful total hip arthroplasty.

Question 34

Adult Dysplasia of hip

Treatment : Operative

1. Complications [4]

Answer 34

1. Sciatic nerve palsies

• 10 times increased incidence of sciatic nerve palsy (5-15%)
• lengthening of greater than 4 cm can lead to sciatic nerve palsy that will present clinically as a foot drop.

2. Hip Dislocation
   * increased risks of hip dislocation after arthroplasty (5-10%)
3. Periprosthetic femur fx
4. Infection

Question 35

Prosthetic Joint Infection

Epidemiology

1. incidence:
   - in primary joint replacement (TKA vs THA)
   - in revision

Answer 35

1. incidence
   - primary joint = 1-2% TKA vs. 0.3-1.3% THA
   - revision joint = 5-6% TKA vs. 3-4% THA

Question 36

Prosthetic Joint Infection : Risk factors

1. pre-operative [2]
2. postoperative [3]

Answer 36

1. pre-operative

• active infection
  
  • local cutaneous, subcutaneous, deep-tissue or joint infection
  • systemic septicemia
• previous local surgery/prior local infection

2. post-operative

• immune suppression
  
  • immunosuppressant drugs
    
    • anti-TNF agents (e.g. infliximab, etanercept, adalimumab, certolizumab, golimumab)
    • antimetabolites (e.g leflunomide)
    • corticosteroids
• immunosuppressive conditions (dysplasia or neoplasia)
  
  • poorly controlled diabetes mellitus (HBA1c >7)
  • chronic renal disease
  • acute liver failure
  • malnutrition (eg. albumin <3.5; total serum leukocytes <800)
  • HIV (CD4 counts <400)
• inflammatory arthropathy
  
  • rheumatoid arthritis
  • psoriasis
  • ankylosis spondylitis
• lifestyle factors
  
  • morbid obesity
  • smoking
  • excessvice alcohol consumption
  • intravenous drug use
  • poor oral hygiene

Question 37

Prosthetic Joint infection

Pathophysiology

1. most common bacterial organism include: [3]
2. most common fungal pathogen [1]

Answer 37

1. most common bacterial organism include

• staphylococcus aureus
• staphylococcus epidermidis
• Coagulase-negative Staphylococcus (chronic infections)

2. most common fungal pathogen
   * Candida species (e.g. Candida albicans)

Question 38

Prosthetic joint infection

Prophylaxis

1. screening
2. operatively
3. post-operatively

Answer 38

1. screening

• screen and optimize risk factors
• nasal mupirocin for decolonization of nasal MSSA/MRSA
• routine urine cutures NOT warranted pre-operatively, unless history or symptoms of UTI
• stop DMARDs 4-6 weeks prior to surgery
• revision joint replacement
  
  • normalized ESR, CRP off antibiotics

2. Operatively

• pre-operative skin cleansing with antiseptic wash
• systemic antibiotics
  
  • administered within 30 minutes to incision, and >10 minutes prior to tourniquet
  • continued for 24 hours after surgery
• operative room
  
  • vertical laminar airflow systems
  • limit hospital personal OR traffic in-and-out of room

3. Post-operatively
   * antibiotics prior to dental work is dependant on host risk factors

Question 39

Prosthetic joint infection

Classifcation

Timing of onset

1. Acute
2. Chronic

Answer 39

1. Acute infection

• infection within 3-6 weeks from surgery
  
  • CDC definition < 90 days from date of joint replacement
• biology
  
  • usually confined to joint space
  • no invasion into prosthetic-bone interface
  • no biofilm production
• S. aureus commonly associated with acute THA PJIs

2. Chronic infection infection

• more than 3-6 weeks from surgery
  
  • CDC definition > 90 days from date of joint replacement
• biology
  
  • biofilm created by all bacteria forms on implant within four weeks
  • biofilm composition = 15% cells and 85% polysaccharide layer (glycocalyx)
  • glycocalyx allows biofilm to adhere to prosthesis and sealoff infection and protect bacteria from host immune system
• S. epidermidis most common organism in chronic THA PJIs

Question 40

Prosthetic joint infection

Imaging: Radiograph findings

Answer 40

findings

periosteal reaction

scattered patches of osteolysis

generalized bone resorption without implant wear

transcortical sinus tracts

implant loosening

Question 41

Prosthetic joint infection

Bone scan

• modalitity
• indications
• sensitivity and specificity

Answer 41

modalitity

• Tc-99m (technetium) detects inflammation and In-111 (indium) detects leukocytes
• triple scan can differentiate infection from fracture or bone remodeling

indications

• if infection is suspected, but cannot be confirmed by aspiration or blood wor

sensitivity and specificity

• 99% sensitivity and 30% to 40% specificity

Question 42

Prosthetic joint infection : MSIS Criteria

Musculoskeletal Infection Society (MSIS) analyzed the available evidence to propose a new definition for prosthetic joint infections:

1. Major criteria [2] (diagnosis can be made when [1] major criteria exist)
2. Minor criteria [6] (diagnosis can be made when [4/6] of the following minor criteria exist)

Answer 42

Major criteria (diagnosis can be made when [1] major criteria exist)

1. sinus tract communicating with prosthesis, or
2. pathogen isolated by culture from 2 separate tissue/fluid samples from the affected joint

Minor criteria (diagnosis can be made when [4/6] of the following minor criteria exist)

1. elevated ESR (>30mm/h) or CRP (>10mg/L)
2. elevated synovial WBC (>1,100cells/ul for knees, >3,000cells/ul for hips)
3. elevated synovial PMN (>64% for knees, >80% for hips)
4. purulence in affected joint
   
   • this finding alone is insufficient
     
     • fluid from metal-metal articulation, gout, etc. can resemble pus
5. pathogen isolation in 1 culture
6. >5 PMN per hpf in 5 hpf at x400 magnification (intraoperative frozen section of periprostehtic tissue)

Question 43

Prosthetic Joint Infection

1. ESR and CRP

Serum interleukin-6 (IL-6, normal <10pg/mL)physiology

peaks 8-12h after surgery

returns to normal 48-72h after surgery (3 days)

less commonly followed, but can monitor and follow the progress of infection

outcomes

has been shown to have the highest correlation with periprosthetic joint infection

sensitivity 100%, specificity 95%

false positives

RA

multiple sclerosis

AIDS

Paget’s disease of bone

Answer 43

CRP physiology

• peaks 2-3days after surgery
• returns to normal at 21 days (3 weeks)

normal range CRP

• acute (< 6 weeks from surgery) = <100 mg/L
• chronic (> 6 weeks from surgery)= <10 mg/L

ESR physiology

• peaks 5-7 days after surgery
• returns to normal 90 days (3 months)

normal range ESR

• acute (< 6 weeks from surgery) = no consences
• chronic (> 6 weeks from surgery)= <30 mm/hr

Serum interleukin-6 (IL-6, normal <10pg/mL)physiology

• peaks 8-12h after surgery
• returns to normal 48-72h after surgery (3 days)
• less commonly followed, but can monitor and follow the progress of infection

outcomes IL-6

• has been shown to have the highest correlation with periprosthetic joint infection
• sensitivity 100%, specificity 95%
• false positives
  
  • RA
  • multiple sclerosis
  • AIDS
  • Paget’s disease of bone

Question 44

Prosthetic joint infection

Joint aspirate

Answer 44

cell count and differential

• lowest serologic values suggestive of infection
  
  • synovial WBC >1,100 cells/ul and PMN >64% in knees
    
    • synovial WBC >27,800 cells/ul in the first 6 weeks after TKA suggestive of infection
  • WBC >3,000 cells/ul and PMN >80% for hips

gram stain

• stain for bacteria in sample
• specificity > sensitivity
  
  • positive test would be indicative of infection, however a negative test does not rule out infection

repeat aspiration

• indicated in cases of inconclusive aspirate and peripheral lab data

other tests

• alpha-defensin immunoassay test
• leukocyte esterase colorimetric strip test

Question 45

Prosthetic joint infection

Peri-operative micro/aspirate analysis

microbiology

1. definitive diagnosis can be made if the same organism is obtained by: ________
2. complications: false-positive rate is__% [tissue sample better than swabs]

Histology

• Intraoperative frozen section
  
  • indications

Answer 45

microbiology

1. definitive diagnosis can be made if the same organism is obtained by repeat aspirations or at least 3 of 5 periprosthetic specimens obtained at surgerycomplications
2. false-positive rate is 8%

HistologyIntraoperative frozen section

• indications
  
  • equivocal cases with elevated ESR and CRP or suspicion for infection
  • sensitivity 85% and specificity 90% to 95%
  • >5 PMNs/hpf x 5 hpf is probable for infection

Question 46

Prosthetic Joint Infection

https://www.orthobullets.com/topicview?id=5004

Treatment: Nonoperative

• Chronic suppressive antibiotic therapy
  
  • indications: [3]
  • outcomes

Answer 46

Indications:

• unfit for surgery
• refuse surgery
• systemic spread and maintain joint motion with symptomatic relief

Outcomes

• 10% to 25% success rate of eradication
• 8% to 21% complication rate

Question 47

Prosthetic Joint Infection

https://www.orthobullets.com/topicview?id=5004

Operative

1. Polyethylene exchange with component retention, IV abx for 4-6 weeks
   * indications

Answer 47

Indications:

• acute infection (<3 weeks after surgery)
• acute hematogenous infection (weak literature, ideally <48-72hrs from symptom onset)

Question 48

Prosthetic Joint Infection

https://www.orthobullets.com/topicview?id=5004

1. one-stage replacement arthroplasty
2. two-stage replacement arthroplasty

Answer 48

One-stage replacement arthroplasty

indications:

• used more commonly in Europe for infected THA
• no sinus tract, healthy patient and soft tissue, no prolonged antibiotic use, no bone graft
• low-virulence organism with good antibiotic sensitivity

outcomes

• 75-100%

Two-stage replacement arthroplasty

indications

• gold standard for an infected joint >4 weeks after arthroplasty
• must be medically fit for multiple surgeries
• requires adequate bone stock
• requires confirmation of microbial eradication
  
  • benign clinical exam
  • normal labs (WBC, ESR, and CRP)
  • negative aspiration cultures
    
    • obtain repeat cultures at least two weeks after planned antibiotic course has been completed

Outcomes

• bilateral TKA resection arthroplasty followed by 6 weeks of antibiotics and bilateral reimplantation has excellent results at 2-year follow-up
• early reimplantation within 2 weeks has 35% success rate
• delayed reimplantation >6 weeks has a 70-90% success rate
• cementless reimplantation in the hip has better outcomes than cemented

Question 49

Prosthetic Joint Infection

Operative treatment (card 4 of 4)

1. resection arthroplasty
2. arthrodesis
3. amputation

Answer 49

1. resection arthroplasty

• indications
  
  • poor bone and soft tissue quality
  • recurrent infections with multi-drug resistant organisms
  • medically unfit for multiple surgeries
  • failure of multiple previous reimplantations
  • elderly nonambulatory patients
• outcomes
  
  • total knee success rate is 50% to 89%
  • total hip success rate is 60% to 100%

2. Arthrodesis

• indications
  
  • reimplantation is not feasible due to poor bone stock
  • recurrent infections with virulent organisms
• outcomes
  
  • 71% to 95% success rate with bony fusion and infection eradication

3. amputation

• indications
  
  • total knee infections recalcitrant to other options
  • severe pain, soft tissue compromise, severe bone loss, or vascular damaged

Question 50

Wear & Osteolysis Basic Science

Introduction

1. define
2. Steps in the process include [4]

Answer 50

Osteolysis represents a histiocytic response to wear debris.

Steps in the process include (see below)

1. particulate debris formation
2. macrophage activated osteolysis
3. prosthesis micromotion
4. particulate debris dissemination

Question 51

Wear & Osteolysis Basic Science

Step 1: Particulate Debris Formation

1. types of wear [5]

Answer 51

Types of wear

1. adhesive wear

• most important in osteolytic process
• microscopically PE sticks to prosthesis and debris gets pulled off

2. abrasive wear
   * cheese grater effect of prosthesis scraping off particles
3. third body wear
   * particles in joint space cause abrasion and wear
4. volumetric wear

• main determinant of number of particles created
• directly related to square of the radius of the head
• volumetric wear more or less creates a cylinder
  
  • V=3.14rsquaredw
  • V is volumetric wear, r is the radius of head, w is linear head wear
  • head size is most important factor in predicting particles generated

5. linear wear
   * is measured by the distance the prosthesis has penetrated into the liner

Question 52

Wear & Osteolysis Basic Science

Step 1: Particulate Debris Formation

Wear leads to particulate debris formation

Wear rates by material

1. polyethylene
2. ceramics
3. metals

Answer 52

1. polyethylene

• non-cross linked UHMWPE wear rate is 0.1-0.2 mm/yr [linear wear rates greater than 0.1 mm/yr has been associated with osteolysis and subsequent component loosening]
• highly-cross linked UHMWPE generates smaller wear particles and is more resistant to wear (but has reduced mechanical properties compared to conventional non-highly cross-linked)
• factors increasing wear in THA
  
  • thickness < 6mm
  • malalignment of components
  • patients < 50 yo
  • men
  • higher activity level
• femoral head size between 22 and 46mm in diameter does not influence wear rates of UHMWPE

2. ceramics

• ceramic bearings have the lowest wear rates of any bearing combination (0.5 to 2.5 µ per component per year)
• ceramic-on-polyethylene bearings have varied, ranging from 0 to 150 µ.
• has a unique complication of stripe wear occurring from lift-off separation of the head gait
• recurrent dislocations or incidental contact of femoral head with metallic shell can cause “lead pencil-like” markings that lead to increased femoral head roughness and polyethylene wear rates.

3. metals

• MoM produces smaller wear particles as well as lower wear rates than those for metal-on-polyethylene bearings (ranging from 2.5 to 5.0 µ per year)
• titanium used for bearing surfaces has a high failure rate because of a poor resistance to wear and notch sensitivity.
• MoM wear stimulates lymphocytes
• MoM serum ion levels greater with cup abduction angle >55 degrees and smaller component size

Question 53

Wear and osteolysis in THA

Step 2: Macrophage Activated Osteoclastogenesis and Osteolysis

Answer 53

1. Macrophage activation

• results in macrophage activation and further macrophage recruitment
• macrophage releases osteolytic factors (cytokines) including
  
  • TNF- alpha
  • osteoclast activating factor
  • oxide radicals
  • hydrogen peroxide
  • acid phosphatase
  • interleukins (Il-1, IL-6)
  • prostaglandins

2. Osteoclast activation and osteolysis

• increase of TNF- alpha increases RANK
• increase of VEGF with UHMWPE inhances RANK and RANKL activationRANKL mediated bone resorption
  
  • an increase in production of RANK and RANKL gene transcripts leads to osteolysis

Question 54

Wear & Osteolysis Basic Science

Step 3: Prosthesis Micromotion

Answer 54

Osteolysis surrounding the prosthesis leads to micromotion

• micromotion leads to increase particle wear and further prosthesis loosening
• N-telopeptide urine level is a marker for bone turnover and are elevated in osteolysis

Question 55

Wear & Osteolysis Basic Science

Step 4: Debris Dissemination

Answer 55

Increase in hydrostatic pressure leads to dissemination of debris into effective joint space

• increased hydrostatic pressure is result of inflammatory response
• dissemination of debris into effective joint space further propagates osteolysis
• circumferentially coated prosthesis limits osteolysis in the distal femur

Question 56

Catastrophic Wear & PE Sterilization

1. Define
2. Catastrophic failure is most commonly seen in ___ in contrast to osteolytic failure that is usually seen in ____
3. Primary variables that lead to catastrophic wear include [5]

Answer 56

1. Refers to macroscopic premature failure of polyethylene (PE) due to:

• excessive loading
• mechanical loosening

2. Catastrophic failure is most commonly seen in TKA, in contrast to osteolytic failure that is usually seen in THA
3. Primary variables that lead to catastrophic wear include:

• PE thickness
• articular surface design
• kinematics
• PE sterilization
• PE machining

Question 57

Catastrophic Wear & PE Sterilization

PE Thickness

1. define
2. causes of failure
3. Solution

Answer 57

1. PE insert width is usually defined as the maximal thickness of the PE insert and metal tray
   * therefore a PE insert labeled as 8mm, may only have a “true” PE of only 4-5 mm at the thinnest point, assuming the metal tray is ~ 2 mm thick
2. Cause of Failure

• PE thickness <8mm
  
  • leads to loads transmitted to localized area of PE which exceed PE’s inherent yield strength
  • thickness of < 8mm associated with catastrophic PE failure

3. Solution
   * keep thinnest portion of PE >8mmavoid having to use a PE insert of less than 8mm by making a more aggressive tibial cut

Question 58

Catastrophic Wear & PE Sterilization

Articular surface design

1. define
2. causes of failure
3. Solution

Answer 58

1. two general designs in TKR prosthesis include:

• A deeper congruous joint (deeper cut PE) without rollback
  
  • less anatomic
  • maximizes contact loads
  • decreases contact stress
• A flat tibial PE that improves femoral rollback and optimizes flexion,
  
  • more anatomic
  • PCL sparing
  • increases contact stress and catastrophic failure

2. Cause of Failure

• flat designs of tibia PE
  
  • low contact surface area leads to high contact stress load in areas of contact

3. Solution

• increase congruency of articular design
  
  • higher contact surface area leads to lower contact stress load
  • newer prosthesis designs sacrifice rollback and have a more congruent or “dished” fit between the femoral condyle and the tibial insert in both the sagittal and coronal plane in order to decrease the contact stress

Question 59

Catastrophic Wear & PE Sterilization

Kinematics

1. define
2. causes of failure
3. Solution

Answer 59

1. Variables that affect kinetics include

• knee alignment
  
  • varus alignment of knee associated with catastrophic PE failure
• femoral rollback
  
  • optimizes flexion at the cost of increasing contact stress and increased risk of catastrophic failure

2. Cause of failure

• excessive femoral rollback
• dyskinetic sliding movements of femur on tibia causes surface cracking and wear

3. Solution

• Perform medial release to avoid varus malalignment
• Decrease contact stress by minimizing femoral rollback
  
  • use a more congruous joint design
  • increase posterior slope of tibia
  • use PCL substituting knee for incompetent PCL or dyskinetic femoral rollback
  • to compensate for the lack of rollback, newer designs move the point of contact (where femoral condyle rests) more posterior and have a steeper posterior slope to aid with flexion

Question 60

Catastrophic Wear & PE Sterilization

PE Sterilization

Radiation

1. _______ radiation is the most common form of polyethylene sterilization
2. oxidation vs. cross linking
3. Solution

Answer 60

1. gamma radiation is the most common form of polyethylene sterilization

2. oxidation vs. cross linking

• presence of oxygen determines pathway following free radical formation
  
  • oxygen rich environment
    
    • PE becomes oxidizedleads to early failure due to
      
      • subsurface delamination
      • pitting
      • fatigue cracking
  • oxygen depleted environment
    
    • PE becomes cross linked
      
      • improved resistance to adhesive and abrasive wear
      • decrease in mechanical properties (decreased ductility and fatigue resistance) and is at greater risk of catastrophic failure under high loads

3. Solution

• irradiate PE in inert gas or vacuum to minimize oxidation

Question 61

Idiopathic Transient Osteoporosis of the Hip (ITOH)

Answer 61

• ITOH also known as
  
  • bone marrow edema syndrome
  • regional migratory osteoporosis
  • migratory osteolysis
• Epidemiology
  
  • demographics
    
    • men >women (3:1)
    • 2 groups
      
      • middle aged (40-55y) men
      • women in 3rd trimester of pregnancy
    • rare in Asians
  • location
    
    • usually unilateral
    • may recur
• Pathogenesis
  
  • local hyperemia and imparied venous return with marrow edema and increased intramedullary pressure
• Prognosis
  
  • resolves spontaneously in 6-8mths

Question 62

Pelvis Anatomy

Osteology

Intro: Pelvic ring formed from 2 innominate bones

• articulate posteriorly with the sacrum and anteriorly through pubis symphysis
  1. Each innominate bone is composed of three fused bones:
  2. Ilium - prominences [5]

Answer 62

1. Each innominate bone is composed of three fused bones: ilium, ischium, and pubis
2. Ilium - prominences

• ASIS
• AIIS
• PSIS
• iliopectineal eminence - region union between ilium and pubis
• sciatic notch

Question 63

Pelvis Anatomy

Ligaments & Stability

Ligament complexes [3]

Answer 63

No inherent stability of articulations; stability comes from ligament complexes

Ligament complexes

1. posterior complex
   
   • sacroiliac ligaments
     
     • posterior stronger than anterior
   • iliolumbar ligaments
     
     • posterior stronger than anterior
2. anterior complex
   
   • pubis syphysis
     
     • fibrocartilaginous disc between innominate bones
3. pelvic floor complex
   
   • sacrospinous ligament
     
     • transversely oriented
     • resists external rotation
   • sacrotuberous ligaments
     
     • longitudinally oriented
     • resists vertical translation

Question 64

Pelvic Anatomy

Blood Supply

1. Abdominal aorta
   a. bifurcates at ___
2. External iliac artery
   a. courses along _______
   b. branches into ______artery (distal to _____)
3. Internal iliac artery
   a. divides____ and ____ near the SI joint into:
   b. posterior division which leads to _______ artery and other branches, and :
   c. anterior division which leads to ______ artery
4. Corona mortis ?
5. Significance of the posterior venous plexus

injury in pelvic fractures can account for majority of blood loss

Answer 64

1. Abdominal aorta bifurcates at L4 into common iliac system
   2a. courses along pelvic brim
   2b. branches into common femoral artery (distal to inguinal ligament)
   3a. divides distal and posterior near the SI joint into
   3b. superior guteal artery
   3c. obturator artery
2. Corona mortis
   * connects iliac and obturator systems
3. Injury in pelvic fractures can account for majority of blood loss

Question 65

Pelvic Anatomy

Nerves

1. Lumbosacral plexus
2. Lateral femoral cutanous nerve
3. Obturator nerve
4. Femoral nerve
5. Sciatic nerve

Answer 65

Lumbosacral plexus

• L1-S4 nerve roots

Lateral femoral cutanous nerve

• L2-L3 nerve roots
• deep to inguinal ligament near ASIS

Obturator nerve

Femoral nerve

Sciatic nerve

Question 66

Pelvic Anatomy

Imaging

.

Answer 66

Imaging

• AP pelvis
  
  • standard radiograph for all trauma patients
• Inlet view
  
  • beam perpendicular to the S1 end plate (caudal tilt)
• Outlet view
  
  • cranial tilt
  • demonstrates cranial-caudal displacemnt of the pelvic ring and sacral morphology

CT

• provides excellent detail of bony anatomy and can confirm pelvic ring / acetabular fractures that are not always visible on plain radigraphs.

Question 67

Knee Biomechanics

The knee is comprised of 2 joints:

• tibiofemoral joint
• patellofemoral joint

1. PFJ Function
2. PFJ Biomechanics

Answer 67

1. Function

• transmits tensile forces generated by the quadriceps to the patellar tendon
• increases lever arm of the extensor mechanism
  
  • patellectomy decreases extension force by 30%

2. Biomechanics

• patellofemoral joint reaction force
  
  • up to 7x body weight with squatting
  • 2-3x body weight when descending stairs

Question 68

Knee Biomechanics : PFJ (card 2)

3. PFJ Motion

4. PFJ Stability

Answer 68

3. Motion

• “sliding” articulation
  
  • patella moves 7cm caudally during full flexion
• maximum contact between femur and patella is at 45 degrees of flexion

4. Stability

• passive restraints to lateral subluxation
  
  • MPFL
    
    • primary passive restraint to lateral translation in 20 degrees of flexion
    • 60% of total restraining force
  • medial patellomeniscal ligament
    
    • 13% of total restraining force
    • medial retinaculum
    • 10% of total restraining force
• dynamic restraint
  
  • quadriceps muscles
• Q angle
  
  • definition= line drawn from the anterior superior iliac spine –> middle of patella –> tibial tuberosity
  • normal Q anglein extension
    
    • males =13 degrees
    • females = 18 degrees
  • in flexion = 8 degrees

Question 69

Knee Biomechanics : Tibiofemoral joint

1. Function
2. Biomechanics
3. Motion in sagittal plane

Answer 69

Function

• transmission of body weight from femur to tibia

Biomechanics

• tibiofemoral joint reaction force
  
  • 3x body weight with walking
  • 4x body weight with climbing

Motion in sagittal plane

• range of motion
  
  • 3 degrees of hyperextension to 155 degrees of flexion
  • thigh-calf contact is usually the limiting factor to full flexion
  • normal gait requires ROM from 0 to 70 degrees

Question 70

Knee Biomechanics : tib-femoral joint

(card 2 of 2)

4. Rotation
5. Stability

Answer 70

4. Rotation

• Instant center of rotation = point at which the joint surfaces are in direct contact
  
  • relevance
    
    • posterior rollback
      
      • as the knee flexes, the instant center of rotation on the femur moves posteriorly
      • allows for increased knee flexion by avoiding impingement
• “screw home” mechanism = tibial externally rotates 5 degrees in the last 15 degrees of extension
  
  • cause
    
    • medial tibial plateau articular surface is longer than lateral tibial plateau
  • relevance
    
    • “locks” knee decreasing the work performed by the quadriceps while standing

5. Stability

• varus stress
  
  • lateral collateral ligament
• valgus stress
  
  • superficial portion of MCL
• anterior translation
  
  • ACL
    
    • function = primary static restraint to anterior translation
    • also plays a roll in axial rotation
• posterior translation
  
  • PCL
    
    • function = primary static restraint to posterior translation
• external rotation
  
  • PLC is the primary stabilizer of external tibial rotation

Question 71

Hip Biomechanics

Question 72

Hip Biomechanics

Question 73

Hip Biomechanics

Question 74

Hip Anatomy

Overview

1. Type of joint ?
2. Stability provided from ?
3. Acetabulum ossification centers ?
4. _________ portion has thicker cartilage for weightbearing purposes

Answer 74

1. Ball-and-socket type of diarthrodial joint
2. Stability

• conferred by bony architechture
• augmented by acetabular labrum and hip capsule

3. Acetabulum formed from three ossification centers

• ilium
• ischium
• pubis

4. Posterosuperior portion has thicker cartilage for weightbearing purposes

Question 75

Hip Anatomy: Osteology

Acetabulum

1. anteverted ___ degrees
2. abducted ___ degrees (caudal tilt)

Divided into four quadrants (image)

i. posterior-superior

• contains which nerves and vessels?
• Safe for screw placement ?

ii. posterior-inferior

• contains which nerves and vessels?
• safe for screw placement ?

iii. anterior-inferior

• contains which nerves and vessels?
• safe for screw placement ?

iv. anterior-superior

• contains which nerves and vessels?
• safe for screw placement ?

Answer 75

1. anteverted 15 degrees
2. abducted 45 degrees (caudal tilt)
3. Divided into four quadrants line drawn from ASIS through center of acetabulum

i. posterior-superior

• contains superior gluteal nerve and vessels and sciatic nerve
• safest zone for screw placement

ii. posterior-inferior

• contains inferior gluteal nerve and internal pudendal vessels
• second safest zone for screw placement

iii. anterior-inferior

• contain the obturator vessels
• unsafe for screws

iv. anterior-superior

• contains external iliac artery and vein
• unsafe for screws

Question 76

Hip Anatomy: osteology

Proximal Femur

Proximal femur

1. Femoral head
   * center of femoral head should be at the level of _____________?
2. Femoral neck

• anteverted ___ degrees (in relation to femoral condyles)
• neck shaft angle of ____ degrees

Answer 76

1. femoral head

center of femoral head should be at the level of the tip of the greater trochanter

2. femoral neck

• anteverted 15 degrees (in relation to femoral condyles)
• neck shaft angle of 125 degrees

Question 77

Hip Anatomy :

Capsule & Ligaments

Hip joint capsule

1. attaches anteriorly to ________
2. extends posteriorly only ________
3. three ligaments [3]
4. Ligamentum teres?
5. Transverse acetabular ligament

• the most inferior portion of labrum
• provides anatomic landmark for reaming

Answer 77

1. attaches anteriorly to the along the intertrochanteric crest
2. extends posteriorly only partially across the femoral neck [image]
   * basicervical and intertrochanteric regions are extracapsular
3. three ligaments

• iliofemoral ligament (Y ligament of Bigelow)
  
  • strongest ligament
  • AIIS to intertrochanteric line
  • taut in full hip extension
  • prevents anterior dislocation / hyperextension
• ischiofemoral
  
  • reinforces posterior capsule
• pubofemoral

4. Ligamentum teres

• cotyloid notch to fovea of femoral head

5. Transverse acetabular ligament

• the most inferior portion of labrum
• provides anatomic landmark for reaming

Question 78

Hip Anatomy : Blood Supply

(Card 1 of 2)

Blood supply to femoral head changes with age

1. birth to 4 years of age - supplied by ?
2. 4 years of age to adult - supplied by ?
3. adult age - supplied by ?

Answer 78

1.) birth to 4 years of age

• medial and lateral circumflex and ligamentus teres

2.) 4 years of age to adult

• posterosuperior and posteroinferior retinacular vessels from medial femoral circumflex
• piriformis start nails
  
  • damage posterosuperior retinacular vessels
  • can cause AVN of femoral head

3.) adult age

• medial femoral circumflex
• avoid transection the quadratus during posterior approach and damaging the MFC artery

Question 79

Hip Anatomy : Blood Supply

Aorta and branches

1. external iliac artery

• common femoral artery
  
  • at risk during screw placement in _______quadrant during THA
• profunda femoris
  
  • lateral femoral circumflex
    
    • ascending branch at risk during ______approach
  • medial femoral circumflex
    
    • major blood supply to head
    • at risk during _____ tenotomy
• femoral artery perforators
  
  • supply _________ muscle

2. internal iliac artery

• obturator (posterior branch)
  
  • supplies _______ ligament
  • at risk with screw placement in _____ and _______ retractors
• superior gluteal
• inferior gluteal
  
  • supplies ____ muscles [3]
• internal pudendal
  
  • re-enters pelvis via ______ notch

Answer 79

Abdominal aorta

• common femoral at risk during screw placement in anterosuperior quadrant during THA
• profunda femoris - lateral femoral circumflex
  
  • ascending branch at risk during anterolateral approach
• medial femoral circumflex
  
  • at risk during psoas tenotomy
• femoral artery perforators
  
  • supply vastus lateralis

INTERNAL ILIAC

• obturator (posterior branch)
  
  • supplies transverse acetabular ligament
  • at risk with screw placement in anteroinferior acetabulum and acetabular retractors
• superior gluteal
• inferior gluteal supplies short external rotators and gluteus maximus
• internal pudendal
  
  • re-enters pelvis via lesser sciatic notch

Question 80

Hip Antomy : blood supply

1. Branches of External iliac
2. Branches of Int Iliac
3. Corona mortis

Answer 80

1. External Iliac artery

• common femoral artery
  
  • profunda femoris
    
    • lateral femoral circumflex
    • medial femoral circumflex
  • femoral artery perforators

2. Internal iliac artery

• obturator
• superior gluteal
• inferior gluteal
• internal pudendal

3. Corona mortis

• connection between inferior epigastric branch of the external iliac vessls and the obturator vessels

Question 81

Hip Anatomy : Nerves

Lumbosacral plexus [nerve roots / relation to psoas]

Answer 81

Lumbosacral plexus

• T12-S4 nerve roots
• lies posterior to psoas muscle

Question 82

Hip Anatomy : Nerves

1. Sciatic nerve

• posterior division branches [5]
• anterior division branches [5]

2. Other main branches [4]

Answer 82

1. Sciatic

• posterior division
  
  • peroneal
    
    • runs deep to long head of biceps femoris
  • superior gluteal
  • inferior gluteal
  • piriformis
  • posterior femoral cutaneous
• anterior division
  
  • tibial
  • nerve to quadratus femoris
  • nerve to obturator internus
  • pudendal
  • coccygeus

2. Obturator nerve

3. Femoral nerve (between iliacus and iliopsoas)

4. Lateral femoral cutanous nerve [L2-L3]

5. Genitofemoral nerve

• pierces iliopsoas and runs on its anteromedial surface

Question 83

Hip Anatomy : Muscles

1. External rotators [7]

2. Hip abductors [3]

3. Hip extensors [4]

Answer 83

1. External rotators

• gluteus maximus
• piriformis
• obturator externus
• obturator interus
• superior gemellus
• inferior gemellus
• quadratus femoris

2. Hip abductors

• gluteus medius
• gluteus minimus
• tnesor fasciae latae

3. Hip extensors

• gluteus maximus
• hamstring tendons
  
  • semitendinosis
  • semimembranosus
  • long head of the biceps femoris

Question 84

Hip Anatomy : Muscles

1. Hip flexors [5]

2. Hip adductors [4]

Answer 84

1. Hip flexors

• iliopsoas
• rectus femoris
• sartorius
• pectineus
• iliacus

2. Hip adductors

• posterior adductor magnus
• adductor longus
• adductor brevis
• gracilis

Question 85

THA Prosthesis Design

Designs include

1. Femoral component [2]
2. Acetabular components [2]
3. Bearing surfaces [3]

Answer 85

femoral component

• cemented
• press-fit (uncemented)
  
  • tapered stems
  • extensively porous coated stems
  • modular stems

acetabular components

• cemented
  
  • polyethylene
  • metal
• press-fit (uncemented)
  
  • metal

bearing surfaces

• polyethylene
• metal
• ceramic

Question 86

THA Prosthesis Design

Femoral Stems

Press-fit Femoral Stems

1. rely on ______ fixation
2. compression _______ provide initial stability
3. Types [3]
4. Unique complications

https://www.orthobullets.com/topicview?id=5033

images of examples on website if required

Answer 86

1. rely on biologic fixation
2. compression hoop stresses provide initial stability
3. Types

• tapered stems
  
  • most are proximally coated stems that taper distally
  • examples: Tri-Lock (DePuy) / M/L Taper (Zimmer)
• extensively coated stems
  
  • porous coating extends into the diaphysis for distal engagement
  • eg. AML (DePuy) /VerSys Full Coat (Zimmer)
• modular stems
  
  • distal stem and proximal body can be “mixed-and-matched”
  • eg. S-ROM (DePuy) / ZMR (Zimmer)

4. Unique complications

• intraoperative fracture
  
  • more likely in press-fit through lateral approach
  • typically due to underreaming
• loosening
  
  • high loosening rate when used in irradiated bone (due to lack of ingrowth)
• junctional corrosion
  
  • seen in modular components (including cemented modular components)

Question 87

THA Prosthesis Design

Cemented Femoral Stems

1. Rely on cement fixation

• _______ remodeling potential
• preferred for _____ bone due to limited ability for ingrowth

2. composition [2]

3. Unique complications

Answer 87

1. Rely on cement fixation

• limited remodeling potential
• irradiated bone

2. composition

• cobalt-chrome
  
  • most common / reduce cement stresses
• titanium
  
  • may be prone to micromotion and debonding

3. Unique complications

• stem breakage cemented stems are smaller than press-fit stems and unable to tolerate as much cantilever bending
  
  • may occur in cementless stems as well

Question 88

THA Prosthesis Design

Bearing Surfaces

1. Metal on Poly

• Benefits [3]
• Disadvantges [2]

2. Metal on metal

• Benefits [2]
• Disadvantges [4]
• Contraindications [3]

Answer 88

1. Metal-on-polyethylene:

• benefits
  
  • longest track record of bearing surfaces
  • lowest cost
  • most modularity
• disadvantages
  
  • higher wear and osteolysis rates compared to metal-on-metal and ceramics
  • smaller head (compared to metal-on-metal) leads to higher risk of impingement

2. Metal-on-metal

• benefits
  
  • better wear properties than metal-on-polyethylene
    
    • lower linear wear rate
    • decreased volume of particles
  • larger head allows for increased ROM before impingement
• disadvantages
  
  • more expensive than metal-on-polyethylene
  • increased metal ions in serum and urine (5-10x normal)
    
    • serum metal ion concentration highest at 12-24 months
      
      • correlates with the initial “wear in” or “run-in” phase of increased particle generation, but then followed by a “steady state” phase of decreased particle generation
    • no proven cancer link
• may form pseudotumors
• hypersensitivity (Type IV delayed type hypersensitvity)
  
  • mediated by T-cells
    
    • metals sensitize and activate T-cells (nickel > cobalt and chromium)
    • however, most participating cells are macrophages (only 5% are lymphocytes)
  • antigen-activated T-cells secrete cytokines that activate macrophages
    
    • activated macrophages have increased ability to present class II MHC and IL-2, leads to increased T-cell activation
    • the cycle continues

Question 89

THA Prosthesis Design

Bearing Surfaces

1. Ceramic-on-ceramic

Benefits [3]

Disadvantges [5]

2. Ceramic-on-Poly

Disadvantges [1]

Answer 89

1. Ceramic on Ceramic

• benefits
  
  • best wear properties of all bearing surfaces
  • lowest coefficient of friction of all bearing surfaces
  • inert particles [no concern for cancer risk]
• disadvantages
  
  • more expensive than metal-on-polyethylene
  • worst mechanical properties (alumina is brittle, low fracture toughness)
    
    • small 28mm heads only exist in zirconia because of alumina’s inferior mechanical properties
  • squeaking
    
    • increased risk with:
      
      • edge loading
      • impingement and acetabular malposition
      • third-body wear
      • loss of fluid film lubrication
      • thin, flexible (titanium) stems
  • less modularity & fewer neck length options
  • stripe wear
    
    • caused by contact between the femoral head and rim of the cup during partial subluxation
    • results in a crescent shaped line on the femoral head

2. Ceramic on polyethylene

• disadvantages
  
  • zirconia undergoes tetragonal to monoclinic phase transformation with time increased with:
    
    • prolonged in vivo implantation >8yr
    • pressure
    • temperature

Question 90

THA Templating

1. Importance [3]
2. Accuracy
3. Steps

Answer 90

1. Importance

• allows surgeon to anticipate potential difficulties
• to reproduce hip biomechanics
• minimizes leg length inequality

2. Accuracy

• 52-98% accurate +/- one size
• related to experience and practice

3. Steps

• obtain appropriate radiographs
• record vital patient information on template (age, height, weight, etc)
• establish radiographic landmarks
• establish limb length discrepancy
• template acetabular component
  
  • do this first to determining center of rotation of new hip
• template femoral component

NB: Tips

• best to achieve a good template with sizes in the middle range of the component system
• different system may be a better choice if this cannot be achieved

Question 91

THA Templating

1. Radiographic Analysis - Necessary radiographs?
2. Magnification
3. Secondary assessment of radiographs

Answer 91

1. Necessary radiographs

• AP pelvis
  
  • centered over pubic symphysis
• AP hip taken with 10-15 degrees of IR
  
  • places femoral neck parallel to cassette
  • external rotation on radiographs will:
    
    • falsely decrease offset
    • create valgus appearing femoral neck
    • falsely decrease femoral canal diameter
• Frog lateral hip

2. Magnification

• 20% is standard
  
  • most templates account for this
• magnification markers are helpful

3. Secondary assessment of radiographs

• pelvic obliquity
  
  • may be secondary to spinal deformity
  • may cause leg-length issues
• acetabular retroversion
  
  • makes appropriate positioning of acetabular component more difficult intraoperatively

Question 92

THA Templating

Establish Limb Length Discrepancy

1. Steps [3]

2. Alternatives

Answer 92

1. Steps

• on AP pelvis, draw horizontal line connecting the ischial tuberosities
  
  • ensure the line extends beyond the medial femoral cortices bilaterally
• mark the top (proximal-most point) of both lesser trochanters on the AP pelvis radiograph
• measure the distance between the inter-tuberosity line and the line drawn at the most proximal aspect of the lesser trochanters

2. Alternatives

• a line connecting the teardrops may be used instead of the ischial tuberosity line
  
  • this may be more accurate

Question 93

THA Templating

Template the Acetabulum

1. steps

2. alternatives

Answer 93

1. Steps

• place appropriately sized acetabular template with roughly 40 degrees of abduction
  
  • medial border of cup should approximate the ilioischial line and lie close to the teardrop
  • inferior border of cup should be at level of inferior teardrop line
• mark center of rotation of acetabular component

Question 94

THA Templating

Radiographic Landmarks

1. Femoral side [4]
2. Acetabular side [2]
3. Pelvis [1]

Answer 94

1. Femoral side

• medullary canal
• greater trochanter
• lesser trochanter
• saddle point
  
  • most distal part of the junction between the superior aspect of the femoral neck and the greater trochanter

2. Acetabular side

• acetabular roof
• tear drop
  
  • created by superposition of the most distal part of the medial wall of the acetabulum and the tip of the anterior/posterior horn of acetabulum

3. Pelvis ischial tuberosities

• important to determine limb length discrepancy

Question 95

THA Templating

Template the Femur

1. steps

Answer 95

Steps

• choose an appropriate sized femoral implant to fill medullary canal
• insertion depth is determined to optimize limb length inequality
  
  • placing the new femoral head center of rotation superior to the acetabular center of rotation will lengthen the limb
  • placing the new femoral head center of rotation inferior to the acetabular center of rotation will shorten the limb (example shown here )
  • mark the intended femoral neck resection level
    
    • use lesser trochanter for posterior approach
    • use saddle point (see above) for anterior approaches
• restore offset
  
  • may be restored by:
    
    • choosing a stem with more or less offset
    • choosing a stem with a different neck-shaft angle
    • modifying the length of the femoral neck

Question 96

THA Stability Techniques

Four important variables that help determine the stability of THA

Answer 96

Four important variables that help determine the stability of THA

• component design
• component position
• soft-tissue tensioning
• soft tissue function

Question 97

THA Stability Techniques

Component Design

Femoral component design [2]

• [1] large femoral heads decreased dislocation rates due to:
  
  • head-neck ratio increased
    
    • definition
      
      • diameter of femoral head/diameter of femoral neck
    • importance
      
      • larger head-neck ratios allow greater arc range of motion prior to impingement
• skirts can be avoided
  
  • definition
    
    • skirts are attachments used to extend the length of the femoral neck
  • importance
    
    • skirts decrease the head-neck ratio
• jump-distance is increased
  
  • definition
    
    • amount of translation prior to dislocation
  • importance
    
    • large femoral heads are seated deeper within the acetabulum, increasing jump-distance
    • increase in jump-distance increases joint stability
• [2] femoral offset
  
  • see “soft tissue tensioning” below

Acetabular component design [2]

• elevated rim liner
  
  • a posteriorly placed elevated rim liner may increase joint stability
• lateralized liner
  
  • increases soft-tissue tension by increasing offset
  • has been shown to increase the risk of acetabular component loosening

Answer 97

Femoral component design [2]

• [1] large femoral heads decreased dislocation rates due to:
  
  • head-neck ratio increased
    
    • definition
      
      • diameter of femoral head/diameter of femoral neck
    • importance
      
      • larger head-neck ratios allow greater arc range of motion prior to impingement
• skirts can be avoided
  
  • definition
    
    • skirts are attachments used to extend the length of the femoral neck
  • importance
    
    • skirts decrease the head-neck ratio
• jump-distance is increased
  
  • definition
    
    • amount of translation prior to dislocation
  • importance
    
    • large femoral heads are seated deeper within the acetabulum, increasing jump-distance
    • increase in jump-distance increases joint stability

Acetabular component design [2]

• elevated rim liner
  
  • a posteriorly placed elevated rim liner may increase joint stability
• lateralized liner
  
  • increases soft-tissue tension by increasing offset
  • has been shown to increase the risk of acetabular component loosening

Question 98

THA Stability Techniques

Component Position

1. Acetabular position

2. Complications

a) excessive retroversion
b) excessive anteversion
c) excessive abduction (high theta angle, vertical cup)
d) excessive adduction (low theta angle, horizontal cup)

Answer 98

Acetabular position

• anteversion = 5° - 25°
• abduction =
  
  • 30° - 50°
• caveats
  
  • surgical approach may affect optimal position of implants
    
    • posterior approach should err towards more anteversion
    • anterior approach should err towards less anteversion
  • Hypertrophy of the anterior inferior iliac spine may cause component impingement and instability

Complications

2a) posterior dislocation
2b) anterior dislocation
2c) posterior superior dislocation ; eccentric polyethylene wear and late instability
2d) impingement in flexion; inferior dislocation

Question 99

THA Stability Techniques

1. Femoral stem position

2. Combined version

Answer 99

1. Femoral stem position

• recommendations = 10°- 15° of anteversion
• caveats
  
  • more difficult to adjust femoral component version in uncemented femoral components

2. Combined version

• definition
  
  • femoral component anteversion plus acetabular component anteversion
• recommendations = 37 degrees

Question 100

THA Stability Techniques

Soft Tissue Tensioning

Answer 100

1. Restoration of offset

• definition
  
  • perpendicular distance from femoral head center of rotation to the axis of the femur
• importance
  
  • increased offset leads to:
    
    • increased soft-tissue tension
    • decreased impingement
    • decreased joint reaction force
  • decreased offset may lead to:
    
    • instability
    • abductor weakness
    • gluteus medius lurch
  • increasing offset improves hip stability
• techniques to increase offset
  
  • increasing length of femoral neck
  • decreasing neck-shaft angle
  • medializing the femoral neck while increasing femoral neck length
  • trochanteric advancement
  • alteration of the acetabular liner (see “component design” above)

Question 101

THA Templating

Soft Tissue Function

1. Three main factors

Answer 101

1. central nervous system

• pathology that affects the central nervous system
  
  • stroke
  • cerebellar dysfunction
  • dementia
  • MS
  • Parkinson’s
  • myelopathy
  • delirium
  • alcoholism

2. peripheral nervous system

• pathology that affects the peripheral nervous system
  
  • spinal stenosis (gluteus medius is L5)
  • peripheral neuropathy
  • radiculopathy
  • paralysis/paresis

3. local soft tissue integrity

• trauma
• myoligamentous disruption
• deconditioning
• aging process
• poor health
• irradiation
• osteolysis
• collagen abnormalities
• myopathy
• malignancy
• infection

Question 102

THA Implant Fixation

1. name the 2 types of fixation
2. What is PMMA ?
3. Name two types of cementless fixation

Answer 102

1. Types of fixation

• cement fixation
• biologic fixation

2. Polymethylmethacrylate (PMMA)
3. Biologic fixation (cementless fixation)

• bone ingrowth
• bone ongrowth

Question 103

THA Implant Fixation

Dorr classification attempts to guide indications for cemented or uncemented femoral component fixation.

1. describe Dorr Classificaiton

Answer 103

Dorr Classification bsed on:

• Ratio (inner canal diameter at midportion of lesser trochanter divided by diameter 10 cm distal)
• Characteristics

Type A = ratio <0.5 / Characteristics = cortices seen on both AP and lateral XR (Suggest Uncemented)

Type B = ratio 0.5-0.75 / Characteristics = thinning of posterior cortex on lateral XR (Suggest Uncemented)

Type C = ratio >0.75 / Characteristics = thinning cortices on both AP lateral XR (Suggest Cemented)

Question 104

THA Implant Fixation

Cement Fixation

Indications

1. Femoral component
2. Acetabular component

Answer 104

Indications

1. Femoral component

• elderly patients
  
  • deeper penetration of cement in osteopenic patients provides excellent fixation
• irradiated bone
  
  • bone ingrowth potential is limited with press-fit components in irradiated bone
• “stovepipe femur”
  
  • also known as Dorr C femur
  • enlarged metaphyseal region and lack of supporting isthmus make cementless fixation difficult

2. Acetabular component

• controversial
  
  • cemented acetabular component fails at a higher rate than press-fit
    
    • cement resists shear poorly

Question 105

THA Implant Fixation

Cementing Technique

1. Cement fixation optimized by:

Answer 105

• limited porosity of cement
  
  • leads to reduced stress points in cement
• cement mantle > 2mm (image)
  
  • increased risk of mantle fractures if < 2mm mantle
• stiff femoral stem
  
  • flexible stems place stress on cement mantle
• stem centralization
  
  • avoid malpositioning of stem to decrease stress on cement mantle
• smooth femoral stem
  
  • sharp edges produce sites of stress concentration
• absence of mantle defects
  
  • defined as any area where the prosthesis touches cortical bone with no cement between
  • creates an area of higher concentrated stress and is associated with higher loosening rates
• proper component positioning within femoral canal
• varus or valgus stem positioning increases stress on cement mantle

Question 106

THA Implant Fixation

Biologic Fixation

Mechanism = 2 different types

• ingrowth: bone grows into porous structure of implant
• ongrowth: bone grows onto the microdivots in the grit blasted surface

Indications for biologic fixation

1. Femoral component:
2. Acetabular component:

Answer 106

1. Femoral component

• younger patients
• older patients with good bone stock
• revision total hip arthroplasty
  
  • cemented femoral stems have lower success rates in the revision setting

2. Acetabular component

• all situations except
  
  • poor acetabular bone stock
  • irradiated bone

Question 107

THA Implant Fixation

Biologic Fixation

Techniques

Answer 107

1. press fit technique

• slightly larger implant than what was reamed/broached is wedged into position

2. line-to-line technique

• size of implant is the same as what was reamed/broached
• screws often placed in acetabulum if reamed line-to-line

Question 108

THA Implant Fixation

Biologic Fixation

Types of coating [3]

Answer 108

1. Porous-coated metallic surfaces

• allows bone ingrowth fixation
• extent of coating
  
  • proximal coating only
    
    • less distal stress shielding
  • extensively coated stem
    
    • produces more stress shielding of proximal bone
    • useful for revision arthroplasty where proximal bone stock may be compromised

2. Grit blasted metallic surface

• allows bone ongrowth fixation
• all grit blasted stems are extensively coated
  
  • fixation strength is less than with porous coated stems, necessitating greater area of surface coating

3. Hydroxyapatite (HA)

• osteoconductive agent used as an adjunct to porous-coated and grit blasted surfaces
• may allow more rapid closure of gaps between bone and prosthesis
  
  • has shown shorter time to biologic fixation in animal models, but no advantage clinically in humans

Question 109

THA Implant Fixation

Radiographic analysis

1. Signs of a well-fixed cementless femoral component [4]
2. Signs of a well-fixed cementless acetabular component [3]

Answer 109

1. Signs of a well-fixed cementless femoral component:

• spot-welds
  
  • new endosteal bone that contacts porous surface of implant
• absence of radiolucent lines around porous portion of femoral stem
• proximal stress shielding in extensively-coated stems
• absence of stem subsidence on serial radiographs

2. Signs of a well-fixed cementless acetabular component

• lack of migration on serial radiographs
• lack of progressive radiolucent lines
• intact acetabular screws

Question 110

THA Implant Fixation

Complications

1. Aspectic loosening
   a. causes
   b. clinical presentation
   c. evaluation

Answer 110

1. Aseptic loosening

• causes
  
  • poor initial fixation
  • mechanical loss of fixation over time
  • particle-induced osteolysis
• clinical presentation
  
  • acetabular loosening
    
    • groin/buttock pain
  • femoral loosening
    
    • thigh pain
    • start-up pain
• evaluation
  
  • sequential radiographs
  • bone scan
• treatment
  
  • revision of loose components

Question 111

THA Implant Fixation

Complications

1. Stress Sheilding

2. Intraop Fracture

Answer 111

1. Stress shielding

• definition: proximal femoral bone loss in the setting of a well-fixed stem
• risk factors
  
  • stiff femoral stem
    
    • most important risk factor
  • large diameter stem
  • extensively porous coated stem
  • greater preoperative osteopenia
• clinical implications
  
  • clinical implications of proximal stress shielding unknown
• treatment
  
  • no specific treatment is necessary

2. Intraoperative fracture

• risk factors
  
  • use of press fit technique
• treatment
  
  • acetabular fracture
    
    • stable cup
      
      • add screws for additional fixation
    • unstable cup
      
      • remove cup, stabilize fracture, and reinsert cup with screws
  • femur fracture
    
    • proximal femur fracture
      
      • stable prosthesis
        
        • limit weight-bearing
        • consider cerclage cables/wires
      • unstable prosthesis
        
        • remove prosthesis, stabilize fracture, reinsert new stem that bypasses fracture by two cortical diameters

Question 112

THA Acetabular Screw Fixation

Acetabular Screw Placement and Safe Zones

Draw quadrants [image]

• first line drawn from ASIS to center of acetabulum
• second line drawn perpendicular to first line

1. Which Zone is safest for screw placement
2. What structures are at risk in each quadrant

Answer 112

1. posterior-superior quadrant

• “target zone”
• is the ideal place for supplemental component screws.
• elevating the hip center in revisions can place sciatic nerve at risk in this quadrant

2. Posterior-inferior quadrant

• “caution zone”
  
  • if screw exceeds 20mm the following structures are at risk:
    
    • sciatic nerve
    • inferior gluteal nerve and vessels
    • internal pudendal nerve and vessels

3. Anterior-inferior quadrant

• “danger zone”
  
  • obturator nerve, artery, and vein at risk

4. Anterior-superior quadrant

• “death zone”
  
  • external iliac vessels at risk

Exceptions

• in the “high hip” the structures in the anterosuperior and anteroinferior quadrants are often found in the posterosuperior quadrant

Question 113

THA Acetabular Screw Fixation

Avoiding Prosthesis Impingement

Answer 113

Avoiding Prosthesis Impingement

• Leaving the anterior rim of the acetabular component proud above the native acetabulum
  
  • may result in anterior iliopsoas tendon impingement
    
    • evaluate with cross-table lateral radiograph and anesthetic injection of the iliopsoas tendon sheath
• Causes of impingement
  
  • medializing and raising acetabulum cup center of rotation will increase risk of bone-on-bone impingement by decreasing femoral offset
  • lateralizing cup will increase risk of metal femoral neck-on-metal acetabulum impingement
  • femoral head-to-neck ratio (<2:1) will increase risk of impingement
    
    • femoral head skirts
    • small femoral head

Question 114

THA Revision

1. Indications [7]

2. Complications [8]

(significantly higher than primary THA)

Answer 114

Indications

1. osteolysis 2. loosening 3. instability
2. infection 5. mal-alignment
3. polyethylene wear 7. Fx or implant failure

Complications

1. dislocation; 2. infection; 3. nerve palsy;
2. cortical perforation; 5. fractures;
3. abductor deficiency; 6. DVT; 7. LLD

Question 115

THA Revision

Presentation

1. Location of pain and component most likely involved
2. evaluation ?

Answer 115

1. groin pain –> acetabulum; thigh pain –> femoral stem; start-up pain –> component loosening; night pain –> infection

2. Assessment

• XRAY (AP / orthogonal views / Judet views - assess columns)
• CT - lysis and component position
• Bloods: ESR/CRP/FBC
• Aspirate - if bloods equivocal

Question 116

THA Revision

Treatment Options

(more details @ https://www.orthobullets.com/topicview?id=5009)

1. Femoral revision options [6]
2. Acetabular revision options

Answer 116

Femoral revision

1. primary THA components
   
   • indications minimal bone loss, Paprosky I
2. uncemented extensively porous-coated long stem prosthesis (or porous-coated/grit blasted combination) or modular tapered stems
   
   • indications: most Paprosky II and IIIa defects; Paprosky IIIb (modular fluted tapered stem); outcomes =95% survival rate at 10-years
3. impaction bone grafting (paprovsky IIIb-IV)
4. allograft prosthetic composite (paprovsky IIIb-IV)
5. modular oncology components (bone loss+++)
6. cemented stems (ind. irradiated bone; elderly;
   low-demand patients) outcomes = high failure rate

Acetabular revision

1. porous-coated hemisphere cup secured with screws (ind. rim is competent [> 2/3 of rim remaining])
2. reconstruction cage with structural bone allograft (ind. rim is incompetent (<2/3 of rim remaining)
   
   • outcomes
     
     • allograft failure is the most common complication
     • high failure rate (40-60%) without reconstruction cage due to component migration after graft resorption

Question 117

THA Revision

Surgical Techniques

1. Femoral revision with uncemented extensively porous-coated long stem prosthesis
2. Femoral impaction bone grafting
3. Acetabular revision with porous-coated hemisphere cup with screws
4. Acetabular revision with reconstruction cage and structural bone allograft
5. Femoral head and polyethylene exchange
6. Gluteus maximus transfer in setting of irreparable abductor deficiency technique

Answer 117

1. Femoral revision with uncemented extensively porous-coated long stem prosthesis

• technique
  
  • femoral stem must bypass most distal defect by 2 cortical diameters
    
    • prevents bending moment through cortical hole
  • cavitary lesions are grafted with particulate graft
  • allograft cortical struts may be used to reinforce cortical defects

2. Femoral impaction bone grafting

• technique
  
  • morselized fresh frozen allograft packed into canal
  • smooth tapered stem cemented into allograft

3. Acetabular revision with porous-coated hemisphere cup with screws

• technique
  
  • cavitary lesions are filled with particulate graft
  • cup placement should be inferior and medial
  • lowers joint reactive forces
  • metallic wedge augmentation may be used if cup in good position and rigid internal fixation is achieved
  • jumbo cups may be used when larger reamer is needed to make cortical contact
  • structural allografts may be used to provide stability while bone grows into cementless cup

4. Acetabular revision with reconstruction cage and structural bone allograft

• Technique
  
  • polyethylene cup is cemented into reconstruction cage
  • bone graft placed behind cage

5. Femoral head and polyethylene exchange

• technique
  
  • Exchange both head and liner
  • osteolytic defects may be bone grafted through screw holes to fill bony defects

6. Gluteus maximus transfer in setting of irreparable abductor deficiency

• technique
  
  • along with the tensor fascia lata, the anterior aspect of the gluteus maximus is freed and transferred to the greater trochanter so that the fibers are similarly oriented to the native abductor musculature

Question 119

THA Dislocation

Dislocation following THA is a common reason for revision

Epidemiology

1. incidence __to__%
2. __% occur within first month
3. __to__% posterior

Mechanism

4. anterior
5. posterior
6. Risk factors

Answer 119

1. 1-3%
2. 70% occur within first month
3. 75-90% posterior
4. extension and external rotation of hip
5. flexion, internal rotation, adduction of hip
6. Risk factors

• prior hip surgery (greatest risk factor)
• female sex
• >70-80 years of age
• posterior surgical approach
  
  • repairing capsule and reconstructing external rotators brings dislocation rate close to anterior approach
• malpositioning of components
  
  • ideal positioning of acetabular component is 40 degrees of abduction and 15 degrees anteversion
  • in general, excessive anteversion increases risk of anterior hip dislocation; excessive retroversion increases risk of posterior hip dislocation
• spastic or neuromuscular disease (Parkinson’s)
• drug or alcohol abuse
• decreased femoral offset (decreases tissue tension and stability)
• decreased femoral head to neck ratio

Question 120

THA Dislocation

Treatment

Closed reduction and immobilization

1. indications

Revision THA

2. indications
3. other options [2]

Answer 120

1. indications
   * two-thirds of early dislocations can be treated with closed reduction and immobilization
2. indications

• indicated if 2 or more dislocations with evidence of implant malalignment
  
  • vertical acetabular component
  • acetabular retroversion
• implant failure
• polyethylene wear

3. Conversion to hemi with Lrg head; resection arthroplasty

Question 121

THA Dislocations

Surgical techniques for revision THA in recurrent dislocation

Answer 121

Techniques to prevent future dislocation during THA include:

• realign components
  
  • indicated if malalignment explains dislocation
    
    • retroverted acetabulum
    • vertical acetabulum
    • short femoral neck
    • lack of femoral neck offset
    • retroverted femoral component
• head enlargement
  
  • optimize head-neck ratio
• trochanteric osteotomy and advancement
  
  • places abductor complex under tension which increases hip compression force
• conversion to a constrained acetabular component
  
  • recurrent instability with a well positioned acetabular component due to soft tissue deficiency or dysfunction
• conversion to dual mobility implant
• conversion to tripolar construct

Question 122

THA Aseptic Loosening

• Macrophage-induced inflammatory response resulting in bone loss*
  1. Steps in the process include: [3]
  2. XRay findings
  3. Treatment

Answer 122

1. Steps in the process include

• prosthesis micromotion
• particulate debris formation
• macrophage activated osteolysis

2. XR Findings

• lucency > 2 mm at cement-bone or metal-bone interface
• component motion with stress views
• femoral component
  
  • subsidence > 1 cm
  • fracture of cement mantle
  • change in peg-neck angle
  • decreased distance from tip of peg to lateral femoral cortex
  • narrowing of femoral neck after 3 years or > 10%
• acetabular component
  
  • migration or change in position/inclination
  • wearing of polyethylene liner
    
    • leads to asymmetric superior location of femoral head within acetabular cup

3. If painfree and stable - observe otherwise revise

Question 123

THA Aseptic Loosening

Question 124

THA Sciatic Nerve Palsy

1. Epidemiology = uncommon (___to___%), but potentially devastating complication following THA
2. _______ division of sciatic nerve most commonly affected (80%)
3. sciatic nerve travels closest to acetabulum at level of _______
4. exercise care with __________ retraction when hip in flexed position
5. less commonly affected nerves
   include [3]

Answer 124

1. uncommon (0-3%) but potentially devastating complication following THA

2. Peroneal division (80%)

3. Ischium

4. Posterior acetabular retraction

5. Less commonly affected nerves include:

• femoral
• obturator
• superior gluteal

Question 125

THA Sciatic Nerve Palsy

1. Causes [5]
2. Risk factors [6]
3. Prognosis

Answer 125

1. Causes
   
   • direct trauma
   • stretch
   • compression due to hematoma
   • heat from PMMA (cement) polymerization
   • unknown (40%)
2. Risk factors for motor nerve palsies include

• developmental dysplasia of the hip
• revision surgery
• female gender
• limb lengthening
• posttraumatic arthritis
• surgeon self-rated procedure as difficult

3. Prognosis

• only 35% to 40% recover full strength after complete palsy

Question 126

THA Sciatic Nerve Palsy

1. Imaging

• Post-operative CT
  
  • AND/OR
• Ultrasound - may be helpful if __?__

2. Studies

• EMGs

3. Treatment

• (a) Intraoperative
• (b) Immediate postoperative
• (c) Persistent foot drop

Answer 126

1. Post-operative CT AND/OR Ultrasound may be helpful if hematoma suspected
2. EMGs may be used post-operatively to confirm level of injury and guide discussion with patient regarding prognosis

3a. Intraoperative

• adult hip dysplasia undergoing THA
  
  • subtrochanteric osteotomy
  • downsizing components

3b. Immediate postoperative

• place hip in extension and knee in flexion
  
  • indications
    
    • immediate post-operative palsy
  • technique
    
    • decreases tension along sciatic nerve
• immediate excavation in operating room
  
  • indications
    
    • post-operative hematoma

3c. Persistent foot drop

• AFO orthosis
  
  • indications
    
    • first line of treatment for persistent foot drop

Question 127

THA Leg Length Discrepancy

Introduction

- said to be most common reason for litigation following total hip arthroplasty

- operative limb lengthening most common

- functional, but transient, limb-length differences are common

1. Etiology

• contracture leads to pelvic obliquity
  
  • ABDuction contracture causes ?
  • ADDuction contracture causes ?
• weakness
  
  • weak abductors may provide the sensation of a _____ in the absence of true LLD
  • usually resolve within __to__ months post-operatively

2. Treatment ?

Answer 127

1. Etiology

• contracture leads to pelvic obliquity
  
  • ABDuction contracture causes involved hemipelvis to be lower, creating apparent LONG leg
  • ADDuction contracture causes involved hemipelvis to be higher, creating apparent SHORT leg
• weakness
  
  • weak abductors may provide the sensation of a long leg in the absence of true LLD
  • usually resolve within 3-6 months post-operatively

2. Treatment

• Nonoperative = shoe-lift
  
  • indications = most cases / wait 6 months until treatment to allow adequate relaxation of muscles
• Operative = revisions THA - rare
  
  • indications: significant LLD that affect quality of life and has not resolved over 6 to 12 months.
  • concern for dislocation with revision surgery especially if attempting to shorten limb

Question 128

THA Periprosthetic Fracture

Epidemiology: incidence

1. intraoperative fractures

• _(a)_% of primary uncemented hip replacements;
• _(b)_% of cemented arthroplasties

2. postoperative fractures

• ___%
• most common at (location)?

3. Prevention

Answer 128

1a. 3.5% of primary uncemented hip replacements
1b. 0.4% of cemented arthroplasties
2. postoperative fractures

• 0.1%
• most common at stem tip

3. Prevention

• preoperative templating reduces risk of intraoperative fractures
• adequate surgical exposure
• special care when using cementless prosthesis in poor bone (RA, osteoporosis)

Question 129

THA Periprosthetic Fracture

Postoperative Femur fracture

1. Incidence = __to___% for primary cementless total hip arthroplasties
2. etiology

• (a) early postoperative fractures
• (b) late postoperative fractures

3. Risk factors

Answer 129

1. Incidence = 0.1-3% for primary cementless total hip arthroplasties
   2a. early postoperative fractures

• cementless prosthesis tend to fracture in the first six months
• likely caused by stress risers during reaming and broaching
• wedge-fit tapered designs cause proximal fractures
• cylindrical fully porous-coated stems tend to cause a distal split in the femoral shaft

2b. late postoperative fractures

• cemented prosthesis tend to fracture later (5 years out)
• tend to fracture around the tip of the prosthesis or distal to it

3. Risk factors

• poor bone quality
• cementless prostheses
• compromised bone stock
• revision procedures

Question 130

THA Periprosthetic Fracture

Postoperative Femur fracture

Classification

1. Eponymous name
2. Considerations
3. Pros
4. Cons

Answer 130

1. Vancouver classification (postoperative)
2. Considerations

• stability of prosthesis
• location of fracture
• quality of surrounding bone

3. Pros

• simple
• validated

4. Cons
   * often difficult to differentiate between B1 and B2 fractures based on radiographs alone

Question 131

Hip Resurfacing

Indications (controversial)

Contraindications

• absolute
• relative

Answer 131

Indications (controversial)

• patients with advanced arthritis and good proximal femoral bone stock
• best outcomes in younger males with good bone stock
• patients with proximal femoral deformity making total hip arthroplasty difficult

Contraindications

• absolute
  
  • bone stock deficiency of the femoral head or neck
    
    • e.g., cystic degeneration of the femoral head
• relative\
  
  • coxa vara (increased risk for neck fractures)
  • significant LLD (resurfacing doesnt allow leg length corrections)
  • female sex of child bearing age (controversial) -> due to fact that metal ions can cross placenta
  • renal failure (functional kidneys required to excrete metal ions)

Question 132

Hip Resurfacing

1. advantages

2. disadvantages

3. outcomes

Answer 132

1. Advantages

• preservation of femoral bone stock
• better stability compared to standard small head (22- to 32-mm) THA
• improved restoration of hip biomechanics with lower risk of limb length discrepancy
• revision may be easier than an intramedullary THA

2. Disadvantages

• lack of modularity with inability to adjust length or correct offset
• requires larger exposure than conventional THA

3. Outcomes

• Variable outcome findings in the literature (79% to 98% success rate)
• Better results found in patients young, larger males with excellent bone stock treated for osteoarthritis than for dysplasia or osteonecrosis
• Some case series have shown survival comparable to conventional THA, while others have reported higher rates of early revision
  
  • some products have been removed from the market due to early failure
• More recent prospective trials have shown few differences between resurfacing and THA

Question 133

THA Complications

Heterotopic Ossification

• frequent complication that may limit functional outcome following hip replacement*
  1. risk factors [4]
  2. Treatment
  3. Prophylaxis

Answer 133

1. Risk factors

• prolonged surgical time
• excessive soft tissue handling during procedure
• hypertrophic osteoarthritis
• male gender

2. Treatment

• surgical excision
  
  • indications
    
    • severe loss of motion
    • once HO is visible on XR, only surgical excision will eradicate
  • technique
    
    • must wait 6/12 after initial procedure to allow for maturation and formation of capsule
    • perioperative prophylaxis with perioperative radiation or NSAIDs

3. Prophylaxis

• oral indomethacin
• radiation therapy
  
  • 600-800 cGy administered ideally within 24-48 hours following procedure

Question 134

THA Complications

Squeaking

1. Definition
2. Incidence

• ceramic-on-ceramic
• metal-on-metal
• incidence of revision due to squeaking=__%

3. Risks [6]

impingement

edge loading

component malposition

loss of fluid film lubrication

third body particles

thin, flexible (titanium) femoral stem

Answer 134

1. Defined as a high pitched audible sound occurring during hip movement
2. Incidence (ceramic-on-ceramic) =0.5-10%
3. Incidence (MoM) = 4-5%
4. Revision because of squeaking is 0.5%
5. Risks

• impingement
• edge loading
• component malposition
• loss of fluid film lubrication
• third body particles
• thin, flexible (titanium) femoral stem

Question 135

TKA Prosthesis Design

Introduction

1. Basic Design Concepts

Answer 135

Designs include

• Unconstrained
  
  • posterior-cruciate retaining (CR)
    
    • OR
  • posterior-cruciate substituting (PS)
• Constrained
  
  • nonhinged
    
    • OR
  • hinged
• Fixed versus mobile bearing

Question 136

TKA Prosthesis Design

Concepts in Prosthetic Design

1. Femoral rollback

• definition
• importance
• biomechanics
• design implications

Answer 136

1. definition
   * the posterior translation the femur with progressive flexion
2. importance
   * improves quadriceps function and range of knee flexion by preventing posterior impingement during deep flexion
3. biomechanics
   * rollback in the native knee is controlled by the ACL and PCL
4. design implications

• both PCL retaining and PCL substituting designs allow for femoral rollback
  
  • PCL retaining
    
    • native PCL promotes posterior displacement of femoral condyles similar to a native knee
  • PCL substituting
    
    • tibial post contacts the femoral cam causing posterior displacement of the femur (image)

Question 137

TKA Prosthesis Design

Concepts in Prosthetic Design

Constraint

1. definition
2. importance
3. design implications
   * in order of least to most constrainied ?

Answer 137

1. definition

• the ability of a prosthesis to provide varus-valgus and flexion-extension stability in the face of ligamentous laxity or bone loss

2. importance

• in the setting of ligamentous laxity or severe bone loss, standard cruciate-retaining or posterior-stabilized implants may not provide stability

3. design implications

• in order of least constrained to most constrained:
  
  • cruciate-retaining
  • posterior-stabilized (cruciate-substituting)
  • varus-valgus constrained (non-hinged)
  • rotating-hinge

Question 138

TKA Prosthesis Design

Modularity

1. definition
2. options
3. advantages
4. disadvantages

Answer 138

1. definition

• the ability to augment a standard prosthesis to balance soft tissues and/or restore bone loss

2. options

• metal tibial baseplate with modular polyethylene insert
  
  • more expensive than all-polyethylene tibial component
  • has an equivalent rate of aseptic loosening compared with all-polyethylene tibia component
• metal augmentation for bone loss
• modular femoral and tibial stems

3. advantages

• ability to customize implant intraoperatively

4. disadvantages

• increased rates of osteolysis in modular components
• backside polyethylene wear (image)
  
  • micromotion between tibial baseplate and undersurface of polyethylene insert that occurs during loading

Question 140

TKA Prosthesis Design

Constrained Nonhinged Design

1. Design
2. Indications
3. Advantages
4. Disadvantages

Constrained Hinged Design

1. Design
2. Indications
3. Advantages
4. Disadvantages

Answer 140

Constrained Nonhinged Design

1. Design = constrained prosthesis without axle connecting tibial and femoral components (nonhinged)

• large tibial post and deep femoral box provide:
  
  • varus/valgus stability AND rotational stability

2. Indications: (i) LCL AND/OR MCL attenuation or deficiency; (ii) flexion gap laxity; (iii) moderate bone loss in the setting of neuropathic arthropathy

3. Advantages

• prosthesis allows stability in the face of soft tissue (ligamentous) or bony deficiency

4. Disadvantages

• more femoral bone resection (necessary to accommodate large box)
• aseptic loosening (as a result of increased constraint)

Constrained Hinged Design

Design: most constrained prosthesis with linked femoral and tibial components (hinged); tibial bearing rotates around a yoke on the tibial platform (rotating hinge) - decreases overall level of constraint

Indications:

• global ligamentous deficiency
• hyperextension instability (seen in polio or tumor resections)
• resection for tumor
• massive bone loss in neuropathic joint

Advantages

• prosthesis allows stability in the face of soft tissue (ligamentous) or bony deficiency

Disadvantages

• aseptic loosening
  
  • as a result of increased constraint
  • large amount of bone resection required

Question 141

TKA Prosthesis Design

Question 142

TKA Prosthesis Design

Mobile Bearing Design

1. Design
2. Indications
3. Advantages
4. Disadvantages

Answer 142

1. Design

• minimally constrained prosthesis where the polyethylene can rotate on the tibial baseplate
• PCL is removed at time of surgery

2. Indications

• young, active patients (relative indication)

3. Advantages

• theoretically reduces poly wear
  
  • increased contact area reduces pressures placed on polyethylene (pressure=force/area)

4. Disadvantages

• bearing spin-out
  
  • mechanism
    
    • occurs as a result of a loose flexion gap
    • tibia rotates behind femur
  • treatment
    
    • initial = closed reduction
    • final = revision to address loose flexion gap

Question 143

TKA Prosthesis Design

All Poly Base Plates

Design: tibial plate is a solid block of polyethylene as opposed to a metal tray with a poly insert.

Indications ?

Pros ?

Cons?

Highly congruent liners

Design: medial compartment concavity allows lateral compartment to translate between flexion and extension; this creates a medial pivot

Indications ?

Pros ?

outcomes ?

Answer 143

All-polyethylene base plates

1. Indications = no clear indications

2. Advantages = less expensive AND decreased rates of osteolysis

3. Disadvantages = loose modular flexibility

4. Outcomes= studies show equivalent functional outcomes with decreased cost

Highly Congruent Liners

1. Indications = no clear indications

2. Pros = may better create native knee kinematics

3. Outcomes = studies show equivalent outcomes and survivorship in short and mid-term studies

Question 144

TKA Axial Alignment

Important considerations include: 1. pre-op planning; 2. component insertion; 3. ligament balancing; 4. prosthetic design selection

1. Normal anatomy

• distal femur is ~___ degrees of valgus
• proximal tibia is __to__ degrees of varus (anatomic axis to joint line)

2. Technical goals (4)
3. Mechanical axis of Limb - define?

Answer 144

1. Normal anatomy

• distal femur is ~9 degrees of valgus (anatomic axis compared to joint line)
  
  • 5-7 deg valgus of femur refers to difference of anatomic axis to mechanical axis
• proximal tibia is 2-3 degrees of varus (anatomic axis to joint line)

2. Technical goals

• restore mechanical alignment (mechanical alignment of 0°)
• restore joint line ( allows proper function of preserved ligaments. e.g., pcl)
• balanced ligaments (correct flexion and extension gaps)
• maintain normal Q angle (ensures proper patellar femoral tacking)

3. Mechanical axis of Limb = axis from center of femoral head to center of ankle

Question 145

TKA Axial Alignment

Question 146

TKA Axial Alignment

Femoral Alignment

1. Anatomic axis femur (AAF)
2. Mechanical axis femur
3. Valgus cut angle (~5-7° from AAF )

Answer 146

1. Anatomic axis femur (AAF)

• a line that bisects the medullary canal of the femur
• determines entry point of femoral medullary guide rod
• intramedullary femoral guide goes down anatomic axis of the femur

2. Mechanical axis femur

• defined by line connecting center of femoral head to point where anatomic axis meets intercondylar notch
• obtaining a neutral mechanical axis allows even load sharing between the medial and lateral condyles of a knee prosthesis

3. Valgus cut angle (~5-7° from AAF )

• difference between AAF and MAF
• perpendicular to mechanical axis
• jig measures 6 degrees from femoral guide (anatomic axis)
• will vary if people are very tall (VCA < 5°) or very short (VCA > 7°)
• can measure on a standing full length AP x-ray

Question 147

TKA Axial Alignment

Tibial alignment

1. Anatomic axis of tibia (AAT)

2. Mechanical axis of tibia

Answer 147

1. Anatomic axis of tibia (AAT)

• a line that bisects medullary canal
• tibia medullary guide (internal or external) runs parallel to it
• determines entry point for tibial medullary guide rod

2. Mechanical axis of tibia

• line from center of proximal tibia to center of talus
• proximal tibia is cut perpendicular to mechanical axis of tibia
• usually mechanical axis and anatomic axis of tibia are coincident and therefore you can usually can cut the proximal tibia perpendicular to anatomic axis (an axis determined by an intramedullary jig)
• if there is a tibia deformity and the mechanical and anatomic axis are not the same, then the proximal tibia must be cut perpendicular to the mechanical axis (therefore an extramedullary tibial guide must be used)

Question 148

TKA Axial Alignment

Patellofemoral Alignment

1. Q angle

2. Any increase in the Q angle will lead to increased lateral subluxation forces on the patella relative to the trochlear groove, which can lead to: [4]

3. It is critical to avoid techniques that lead to an increased Q angle. Common errors include:

Answer 148

Q angle

• Abnormal patellar tracking, although not the most serious, is the most common complication of TKA.
• The most important variable in proper patellar tracking is preservation of a normal Q angle (11 +/- 7°)
  
  • the Q angle is defined as angle between axis of extensor mechanism (ASIS to center of patella) and axis of patellar tendon(center of patella to tibial tuberosity)

2. Increased Q-angle can lead to:

• Pain
• mechanical symptoms
• accelerated wear
• dislocation.

3. Common errors include:

• internal rotation of the femoral prosthesis
• medialization of the femoral component
• internal rotation of the tibial prosthesis
• placing the patellar prosthesis lateral on the patella

Question 149

TKA Axial Alignment

Joint Line Preservation

• Goal is to restore the joint line by inserting a prosthesis that is the same thickness as the bone and cartilage that was removed*
  1. This preserves appropriate ________ ?
  2. elevating the joint line (> 8mm leads to motion problems) and can lead to: [4]
  3. lowering joint line can lead to: [2]

Answer 149

1. This preserves appropriate ligament tension

2. Elevating the joint line (> 8mm leads to motion problems) and can lead to:

• mid-flexion instability
• patellofemoral tracking problems
• an “equivalent” to patella baja
• never elevate joint line in a valgus knee until after balancing to obtain full extension

3. Lowering joint line can lead to:

• lack of full extension
• flexion instability

Question 150

TKA Coronal Plane Balancing

Definition: both medial and lateral ligaments may be stretched or contracted with time

Pathophysiology: concave side - tight ligaments that need release / convex side - stretched ligaments that need tightening / must test balancing in both flexion and extension

1. Varus Deformity - Anatomy: medial side is ______), lateral side ______
2. Goals ? [4]

Answer 150

Varus Deformity

Anatomy

• medial side is tight (concave), lateral side stretched (convex)

Goals

• create precise bone cuts
• release the tight medial ligaments
• tighten the lax lateral ligaments
• balance flexion and extension gaps by adjustment of polyethylene bearing thicknesss

Question 151

TKA Coronal Plane Balancing

Varus Deformity

1. Steps in medial release [1 to 8]
2. Lateral tightening

Answer 151

Step 1: Deep MCL Release To Mid-Coronal Plane Of Tibia

Step 2: Medial Osteophyte Removal

Step 3: Release Posteromedial Corner (Posterior Oblique Ligament)

Step 4: Medial Tibial Reduction Ostectomy

Step 5: Consider PCL Release/Substitution If Imbalance Persists At This Point (If Substitution Not Initially Chosen)

Step 6: Release Semimembranosis (Especially If There Is An Associated Flexion Contracture)

Step 7: Pie Crust Superficial MCL (Favor Use Of 18 Gauge Needle)

Step 8: Complete Superficial MCL Release / Pes Anserinus

• Rarely Required Even In Severe Cases
• Destabilizes Medial Flexion Gap / Consider A Constrained Prosthesis
• Differential release: performed with two components of superficial MCL
  
  • posterior oblique portion is tight in extension (release if tight in extension)
  • anterior portion is tight in flexion (release if tight in flexion)

2. Lateral tightening

use a prosthesis that is sized to “fill up” the gap and make the stretched lateral ligaments taut

if a polyethylene bearing thickness of >15mm is required to gain appropriate lateral ligamentous tension, consider use of a constrained prosthesis to avoid excessive joint line elevation

Question 152

TKA Coronal Plane Balancing

Valgus Deformity (lateral side is concave/tight)

• Anatomy =lateral side is tight (concave), medial side stretched (convex)*
• Goals: create precise bone cuts / release the tight lateral ligaments / tighten the lax medial ligaments / balance flexion and extension gaps by adjustment of polyethylene bearing thickness*

1. Lateral release - Steps [1 to 5]

2. Medial tightening

Answer 152

1. Lateral release in order

• Step 1 : osteophytes
• Step 2: posterolateral capsule
• Step 3: ITB if tight in extension with pie crust or release off Gerdy’s tubercle
• Step 4: popliteus if tight in flexion (release if tight in flexion)
  
  • release the anterior part of its insertion
  • for severe deformities release both the iliotibial band and the popliteus
• Step 5: LCL
  
  • some authors prefer to release this structure first if tight in both flexion and extension
  • other authors prefer to release the LCL last
    
    • if LCL & Popliteus require release, flexion gap stability is lost so consider constrained prosthesis
• Differential release: performed by differentially release the IT band and popliteus

2. Medial tightening

• Fill up medial side until medial ligament complex is taut
• In severe cases, if a polyethylene bearing thickness >15mm is required to obtain appropriate medial tension, consider a constained prosthesis to avoid excessive joint line elevation

Question 153

TKA Coronal Plane Balancing

Complications

Answer 153

Complications

1. Peroneal nerve palsy

• correction of valgus and flexion contracture deformity has highest risk of peroneal nerve palsy
• if patient presents with a peroneal palsy in recovery room then:
  
  • then take off dressing and flex the knee
  • watch for three months to see if function returns
  • if function does not return, consider nerve conduction studies or operative exploration to access for damage

2. Coronal plane deformities >20 degrees cannot be corrected by intra-articular bone cuts and soft-tissue balancing alone and require an extra-articular osteotomy

Question 154

TKA Sagittal Plane Balancing

Introduction

Goal is to obtain a gap that is equal in flexion and extension. This will ensure that the tibial insert is stable throughout the arc of motion.

balancing is complex due to two radii of curvatures (patellofemoral articulation and tibiofemoral articulation)

often requires soft tissue release and bony resection to obtain balance

1. General Rules

• adjust femur if ?
• adjust tibia if ?
• remember increasing/decreasing the size of the femoral component only changes the ___ diameter and therefore affects the ____ gap only.

Answer 154

General Rules

• adjust femur if asymmetric
  
  • distal femur cut affects extension gap
  • posterior femur cut affects flexion gap
• adjust tibia if problem is symmetric (same in both flexion and extension)
  
  • tibia cut affects both flexion and extension gap
• remember increasing/decreasing the size of the femoral component only changes the AP diameter and therefore affects the flexion gap only.

Question 155

TKA Patellofemoral Alignment

Abnormal patellar tracking is the most common complication of TKA.

1. the most important variable in proper patellar tracking is ______ ?.
2. An increase in the Q angle will lead to: [2]
3. It is critical to avoid techniques that lead to increase Q angle. Common errors include :

Answer 155

1. Preservation of a normal Q angle.

2. Increase in the Q angle will lead to:

• an increased lateral subluxation forces on the patella relative to the trochlear groove
• possible pain, mechanical symptoms, accelerated wear, and even dislocation

3. Common errors include

• internal rotation of the femoral prosthesis
• medialization of the femoral component
• internal rotation or medialization of the tibial prosthesis
• placing the patellar prosthesis lateral on the patella

Question 156

TKA Patellofemoral Alignment

Femoral Prosthesis

1. AP Axis
2. Transepicondylar Axis
3. Posterior condylar Axis

Answer 156

Question 157

TKA Patellofemoral Alignment

Tibial Prosthesis

1. The preferred rotation of the tibial component is _____?
2. Internal Rotation of Tibial Prosthesis will:
3. Medialization of tibia will ___ ?

Answer 157

1. neutral, with no internal or external rotation.

• the best way to obtain this is to have the tibial component centered over the medial third of the tibial tubercle
• this may leave a portion of the posteromedial tibia uncovered and some overhang of the prosthesis over the tibia on the posterolateral tibia.

2. Internal Rotation of Tibial Prosthesis will increase Q angle
   * internal rotation of the tibial component effectively results in relative external rotation of the tibial tubercle and an increase in the Q angle
3. Medialization of tibia will increase Q angle

Question 158

TKA Patellofemoral Alignment

Patellar Prosthesis

1. Preferred position of patellar prosthesis

2. Approach if patella subluxing intraop ?

3. Indications for resurfacing

• absolute [3]

Answer 158

1. Either centered over the patella or medialized

• medializing the patellar component is one strategy to decrease the Q angle.
• results in uncoverage of lateral facet. Consider removing to lessen risk of lateral facet syndrome.
• another alternative is use of an oval shaped patella with the apex medialized.
• Lateralization of the patellar prosthesis will increase the Q angle and increase maltracking

2. Intraoperative lateral subluxation of the patella

• deflate tourniquet and recheck before performing a lateral release

3. Indications for resurfacing -absolute:

• inflammatory arthritis
• patella maltracking
• patellofemoral arthritis as the main indication for TKA

Question 159

TKA Patellofemoral Alignment

Patella resurfacing vs. Non-resurfacing

Answer 159

Patella resurfacing vs. Non-resurfacing

• less anterior knee pain with resurfacing
• less revision rates with resurfacing
• inferior results with secondary resurfacing
• increase complications (fx, tendon injury, etc.) with resurfacing
• similar patient satisfaction rates
• trochlear design important: “patellar friendly”
  
  • thinner anterior flange
  • anatomic trochlear groove

Question 160

TKA in Patella Baja (Infera)

1. Define:
2. Etiology [2 broad groups]
3. Pathophysiology - common causes (aquired) [5]
4. Associated conditions

Answer 160

1. Patella baja is characterized by lowering of the patella relative to its normal position
2. May be congenital or acquired (this topic)
3. Pathophysiology of acquired patella baja

• common causes include
  
  • proximal tibial osteotomy
    
    • patella baja is the most common complication seen following proximal tibial opening-wedge osteotomy
    • may be caused by shortening of the patellar tendon during tibial osteotomy or from scarring of the patellar tendon post-operatively
  • tibial tubercle slide or transfer
  • trauma to the proximal tibia
  • technical error during primary total knee replacement (joint line elevation)
  • ACL reconstruction

4. Associated conditions

• total knee arthroplasty
  
  • patella infera is an important consideration when performing total knee arthroplasty
    
    • improper technique may cause patella baja
    • special techniques must be utilized when performing TKA in patients with patella baja from congenital or acquired (tibial osteotomy, prior TKA) causes

Question 161

TKA in Patella Baja (Infera)

Insall-Salvati Ratio

Treatment

Answer 161

Insall-Salvati ratio (see image)

• lateral view of the knee in 30 degrees of flexion used to measure Insall-Salvati ratio
• measures ratio patellar tendon length to patellar bone length
• normal Insall-Salvati is 1:1 between length of the patellar tendon length to patellar bone length
• Insall-Salvati ratio of < 0.8 is consistent with patella baja

Treatment

• Nonoperative: activity modifications, physical therapy
  
  • indications = mild symptoms in younger patients
• Operative: total knee replacement
  
  • indications = severe impingement in older patients with osteoarthritis

Question 162

TKA in Patella Baja (Infera)

TKR Technique in patient with patella baja

Four ways to correct patella baja in TKR

Answer 162

1. place patellar component superiorly

• indications = mild patella baja
• technique
  
  • use a smaller patellar dome placed on superior aspect of patella
  • trim inferior bone to decrease flexion impingement

2. lower joint line

• indications= moderate patella baja
• technique
  
  • add distal femoral augmentation
  • cut more proximal tibia to lower joint line (lower tibial cut)
  • avoid bone cuts that raise the joint line
    
    • raising the joint line will effectively increase the patella baja deformity
  • may require revision knee system

3. transfer tibial tubercle to cephalad position

• indications = moderate patella baja
• technique = difficult due to complexity of a tibial transfer in proximity to a cemented tibial component
• outcomes
  
  • unpredictable bone healing leads to variable, and often poor, outcomes
  • patients may be left with extensor lag

4. patellectomy

• indications = severe patella baja
• techniques
  
  • alters the tension in the anterior knee mechanism
    
    • therefore recommended to use use a cruciate substituting system
  • consider partial patellectomy in which patella is resected to a width of 10-12mm
    
    • lessens impingement & crepitus while maintaining some of the fulcrum of the patella.

Question 163

TKA Revision

Most common causes of failure [8]

(top 3 represent 75%)

Answer 163

1. aseptic component loosening (~39%)

• most common reason for late revision (>2 years from primary)
• tibial loosening more common than femoral
• femoral loosening more difficult to detect due to obscured view of posterior femoral condyles where lesions typically occur
  
  • oblique radiographs may help /detected on serial XRs
• osteolytic wear
  
  • most common in uncemented technique
  • motion between modular tibial insert and metal tray (backside wear)

2. septic failure (~27%)

• must rule out infection prior to any revision
• infection is the most common failure mechanism for early revision (< 2 years from primary)

3. ligament/flexion instability (~8%)

• MCL/LCL incompetence can to lead to laxity
• flexion instability
  
  • PCL attenuation (in CR knees)
  • unbalanced flexion gap
  • excessive posterior slope
  • undersized femoral component
  • femoral component placed in excessive extension

4. periprosthetic fracture (~5%)

• most commonly supracondylar femur region
• need for revision due to combination of excessive comminution/bone loss with loose component

5. arthrofibrosis (~5%)

• patellofemoral maltracking: most commonly caused by component malpositioning

6. abnormal joint line problems

7. patellar clunk

• fibrotic scar tissue that ‘clunks’ as the knee moves from flexion into extension and patella jumps the femoral notch / arthroscopic treatment to remove fibrotic tissue

8. metal hypersensitivity

Question 164

TKA Revision

Goals of Surgery [6]

General Steps in revision [5]

Answer 164

Goals

• extraction of components with minimal bone loss and destruction
• restoration of bone deficiencies
• restoration of joint line
• balance knee ligaments
• stable revision implants
• adequate soft tissue coverage

General Steps

• surgical exposure
  
  • should be extensile
    
    • when compared to the standard medial parapatellar approach for revision total knee arthroplasties, the oblique rectus snip approach shows no difference in outcomes
    • tibial tubercle osteotomy allows for good exposure and is especially indicated if there is patella baja as it allows proximal translation of the tibial tubercle
• removal of implants
  
  • proceed with tibial side first by establishing tibial joint line
    
    • tibial joint line should be 1.5 to 2 cm above head of fibula (use xray of contralateral knee to determine exact distance)
  • after tibia joint line established proceed with femoral side to match the tibia
• balance flexion-extension gaps
• balance medial and lateral gaps
• address patellofemoral tracking
  
  • keep patellar thickness >12mm to avoid fracture

Question 165

TKA Revision

Complications

Answer 165

Complications

• Pain
  
  • pain scores less favorable than primary TKR
  • activity related pain can be expected for 6 months
• Stiffness
• Neurovascular problems
  
  • peroneal nerve subject to injury with correction of valgus and flexion deformity
• Infection
  
  • upwards of 4-7%, double the risk of primary TKA
• Skin necrosis
  
  • prior scars should be incorporated into skin incision whenever possible
  • bloody supply to anterior knee is medially based, so lateral skin edge is more hypoxic
    
    • if multiple previous incisions, use most lateral skin incision
  • can use wound care, skin grafting, or muscle flap coverage (gastroc) for full thickness defects
• Extensor mechanism disruption
  
  • can use extensor mechanism allograft using achilles tendon bone block
    
    • residual lag due to attenuation is common
  • extensor mechanism reconstruction with mesh may offer better mid-term results in function and survivorship

Question 166

Patellar Clunk Syndrome

Introduction

1. Definition
2. Epidemiology / prevalence

Answer 166

1. Definition

• a painful, palpable “clunk” at the patellofemoral articulation of posterior stabilized TKA caused by a fibrous nodule of scar tissue at the posterior surface of the distal quadriceps tendon/superior patellar pole catching on the box of the femoral component during knee extension

2. Epidemiology

• prevalence reported at 3.5%
• even less frequent with newer component designs

3. Pathophysiology

• cause of scar tissue is unknown, but may be related to:
  
  • direct trauma to quadriceps tendon during patella resection during TKA
  • impingement of the quadriceps tendon on the femoral component due to an undersized patellar component
• scar is entrapped within the intercondylar notch during flexion
• the scar is forced out of the notch during active knee extension
• the painful snap or clunk is usually felt between 30-45 degrees

Question 167

Patellar Clunk Syndrome

Risk factors

1. Preoperative factors
2. Component factors

• patellar component
• femoral component

Answer 167

1. Preoperative factors

• preop patella baja
• valgus pre-operative alignment
• preoperative fibrosynovial proliferation at quadriceps insertion into superior pole of patella
• resect this at the time of surgery
• previous knee surgery

2. Component factors

• patellar component
  
  • small patellar component
    
    • because of decreased quads tendon contact forces against superior aspect of intercondylar box, allowing fibrosynovial proliferation and entrapment in intercondylar region of the box
  • patellar component placed low on the patella
    
    • exposes unresurfaced superior pole and quadriceps tendon to contact with femoral component
  • patellar overresection and thin patellar button
    
    • reduces offset of quadriceps tendon from top of trochler groove
  • exposure of cut patellar bone that is not covered by patellar component
    
    • resect uncovered lateral patellar facet
• femoral component
  
  • PS design
  • increased posterior femoral condylar offset
  • smaller femoral component
  • femoral component in flexed position
    
    • causes by more posterior entry point for intramedullary distal femoral cutting jig, because of anterior bow of femur
  • femoral component with higher intercondylar box ratio (trochlear groove extended more proximal and anterior)
• thick polyethylene insert
  
  • raises joint line, creates relative patella baja

Question 168

Patellar Clunk Syndrome

1. presentation / examination findings
2. Treatment

Answer 168

• Presents an average of 12 months after TKA
• Symptoms
  
  • patellofemoral knee pain
  • complaints of knee “popping” and “catching”
• Physical exam
  
  • painful, palpable “pop” or “catch” as knee extends (~40° of flexion)

Treatment

• Operative
  
  • arthroscopic vs open resection of fibrous nodule
    
    • indications
      
      • severe symptoms
    • outcomes of arthroscopic resection are good, with very low rates of recurrence and improvement in knee society scores

Question 169

TKA Peroneal Nerve Palsy

Neurologic Injury (peroneal nerve)

1. incidence ?
2. Risk factors [5]
3. prognosis: __% or more improve in time with no additional treatment
4. Anatomy

• common peroneal nerve lying on ___[a]___ at the level of the joint line
• distance from posterolateral corner of tibia to peroneal nerve is __[b]__mm at this level

Answer 169

1. incidence = 0.3%-2%

2. Risk factors

• preoperative valgus and/or flexion deformity
• tourniquet time > 120 min
• postoperative use of epidural analgesia
• aberrant retractor placement
• preoperative diagnosis of neuropathy (centrally or peripherally)

3. 50% or more improve in time with no additional treatment

4. Anatomy

• [a] lying on lateral head of gastrocnemius at the level of the joint line
• distance from posterolateral corner of tibia to peroneal nerve is 9mm-15mm at this level

Question 170

TKA Peroneal Nerve Palsy

1. Evaluation
2. Treatment

Answer 170

Evaluation

• EMG
  
  • obtain after 3 months if no improvement

Treatment

• remove dressing and place knee in flexed position
  
  • indications
    
    • initial postoperative management in all cases noted in the immediate postoperative period
• ankle-foot orthosis
  
  • indications
    
    • complete foot drop
• late nerve decompression or muscle transfer
  
  • indications
    
    • no recovery after 3 months

Question 171

TKA Extensor Mechanism Rupture

1. incidence
2. Causes
3. Presentation
4. Imaging

Answer 171

1. incidence = 0.17% to 2.5%
2. Causes

• intraoperative
  
  • avulsion from tibial tubercle
• postoperative
  
  • manipulation
  • impingement
  • trauma

3. Presentation

• Symptoms
  
  • knee pain and weakness

4. Imaging

• Radiographs
  
  • patella alta or baja

Question 172

TKA Extensor Mechanism Rupture

Treatment : non-op and operative

Answer 172

Treatment

• Nonoperative
  
  • knee immobilizer x6 weeks
    
    • indications
      
      • partial quadriceps tendon rupture
• Operative
  
  • direct repair with suture
    
    • indications
      
      • patellar tendon avulsion < 30%
      • complete quadriceps tendon rupture with adequate soft tissues
  • primary repair and augmentation with graft
    
    • indications
      
      • complete laceration of patellar tendon with adequate patellar bone stock
• extensor mechanism allograft
  
  • indications
    
    • complete laceration of patellar tendon without adequate patellar bone stock and deficient soft tissues

Question 173

Unicompartmental Knee Replacement

Surgical option for knee arthritis when only one compartment of the knee is involved

Epidemiology

1. ___% of surgeries where knee arthroplasty is indicated are unicompartmental knee replacements
2. Location: ______ compartment is most common
3. Types of implants
4. Mobile-bearing : pros [3] / cons [2]

Answer 173

1. 5% of surgeries where knee arthroplasty is indicated are UKA
2. medial compartment is most common
3. Types of implants

• fixed-bearing [historical standard of care]
• mobile-bearing

4. Mobile bearing

• Pros:
  
  • weightbearing through the meniscus increases conformity and contact without increasing constraint
  • decrease in wear pattern
  • excellent survivorship out to the second decade
• Cons
  
  • technically demanding
  • bearings can dislocate

Question 174

Unicompartmental Knee Replacement

1. indications

2. Contraindications

Answer 174

1. Indications

• controversial and vary widely
• as an alternative to total knee arthroplasty or osteotomy for unicompartmental disease
• classicaly reserved for older (>60), lower-demand, and thin (<82 kg) patients
  
  • 6% of patient’s meet the above criteria with no contraindications
• new effort to expand indications to include younger patients and patients with more moderate arthrosis

2. Contraindications

• inflammatory arthritis
• ACL deficiency
  
  • absolute contraindication for mobile-bearing UKA and lateral UKA
  • controversial for medial fixed-bearing
• fixed varus deformity > 10 degrees
• fixed valgus deformity >5 degrees
• restricted motion
  
  • arc of motion < 90°
  • flexion contracture of > 5-10°
• previous meniscectomy in other compartment
• tricompartmental arthritis (diffuse or global pain)
• younger high activity patients and heavy laborers
• overweight patients (> 82 kg)
• grade IV patellofemoral chondrosis (anterior knee pain)

Question 175

Unicompartmental Knee Replacement

Outcomes

Answer 175

Outcomes

• Fixed-bearing
  
  • 1st decade results
    
    • 10-year survivorship from studies done in 1980s and 1990s ranges from 87.4% to 96%
    • the standard faliure rate in the first decade is 1%
  • 2nd decade results
    
    • rapid decline in survivorship ranging from 79% to 90%
• Mobile-bearing
  
  • excellent clinical results with 15-year survivorship reported at 93%
• Long-term results
  
  • lateral compartment arthroplasties have equivalent results to medial
  • revision rates are worse than total knee revision rates
  • causes of late failure
    
    • other compartment degeneration (idiopathic, over-correction, more common with mobile-bearing)
    • component failure (overload due to under-correction)
    • component loosening (common in fixed-bearing)
    • patella impingement on femoral component (patella pain)
    • polyethylene wear

Question 176

TKA Stiffness

1. Definition
2. Incidence = ___to___%
3. Risk factors

• preoperative factors [4]
• technical factors [6]
• postoperative factors [5]

Answer 176

1. Definition :

• flexion contracture 10-15 degrees
• flexion < 90 degrees

2. Incidence = 1.3%-12%

3. Risk factors

• preoperative factors
  
  • poor preoperative ROM = most important factor
  • patella baja
  • increased medical comorbidities
  • low pain tolerance
• technical factors
  
  • overstuffing patellofemoral joint
  • malrotation
  • tight flexion and/or extension gaps
  • joint line elevation
  • excessive tightening of extensor mechanism during closure
    
    • closure in flexion (as opposed to extension) may limit this complication
  • tight PCL in cruciate-retaining prosthesis
• postoperative factors
  
  • delayed rehabilitation
  • infection
  • HO
  • hamstring spasms
  • usually resolves within 6 months

Question 177

TKA Stiffness

Treatment

1. Nonoperative

• indications
• Contraindications

2. Operative
   * indications

Answer 177

1. Nonoperative : manipulation under anesthesia

• indications
  
  • flexion <90 degrees within first 12 weeks of operation (timing is controversial)
    
    • over aggressive manipulation
      
      • fracture
      • extensor mechanism disruption
• Contraindications
  
  • stiffness >3 months postoperatively
  • manipulation associated with greater risk and lower benefit

2. Operative

• arthroscopic lysis of adhesions with manipulation under anesthesia
  
  • indications
    
    • persistent late stiffness
• revision total knee arthroplasty
  
  • indications
    
    • identifiable technical cause for stiffness

Question 178

High Tibial Osteotomy

Angular deformity in the knee leads to abnormal distribution of weight bearing stresses:

• can accelerate wear in medial or lateral compartments of the knee and lead to degeneration
• HTO is commonly combined with cartilage restoration procedures to provide better mechanical environment for biologic repair

1. Predominately done for _____ deformities
2. Prognosis

• varus-producing high tibial osteotomy
  
  • success rate is ____% in 10 years
• valgus-producing high tibial osteotomy
  
  • success rate is __to__% in 10 years

Answer 178

1. predominately done for varus deformities [less common for valgus deformities]

2. Prognosis

• varus-producing high tibial osteotomy
  
  • success rate is 87% in 10 years
• valgus-producing high tibial osteotomy
  
  • success rate is 50-85% in 10 years

Question 179

High Tibial Osteotomy

indications

Contraindications

Answer 179

1. Indications

• young, active patient (<50 years) in whom an arthroplasty would fail due to excessive wear
• healthy patient with good vascular status
• non-obese patients
• pain and disability interfering with daily life
• only one knee compartment is affected
• compliant patient that will be able to follow postop protocol

2. General contraindications

• inflammatory arthritis
• obese patient BMI>35
• flexion contracture >15 degrees
• knee flexion <90 degrees
• procedure will need >20 degrees of correction
• patellofemoral arthritis
• ligament instability
• varus thrust during gait

Question 180

High Tibial Osteotomy

Varus-producing tibial osteotomy

1. Surgical goals
2. Indications & specific contraindications

Answer 180

Varus-producing tibial osteotomy

• Surgical goals
  
  • unload the involved joint compartment by correcting tibial malalignment
  • maintain the joint line perpendicular to mechanical axis of the leg
• Indications
  
  • can be done for valgus knee with lateral compartment degeneration
    
    • deformity should be <12 degrees or else the joint line will become oblique
  • specific contraindications
    
    • medial compartment arthritis
    • loss of medial meniscus
    • distal femoral osteotomy better if lateral femoral condyle hypoplasia present

Question 181

High Tibial Osteotomy

Complications [6]

Answer 181

• Recurrence of deformity
  
  • 60% failure rate after 3 years when
    
    • failure to overcorrect
    • patients are overweight
• Loss of posterior slope
• Patella baja
  
  • refers to a shortened patellar tendon which decreases the distance of the patellar tendon from the inferior joint line
    
    • can be caused by raising tibiofemoral joint line in opening wedge osteotomies
    • can be caused by retropatellar scarring and tendon contracture
    • can cause bony impingement of patella on tibia
• Compartment syndrome
• Peroneal nerve palsy
  
  • more common in lateral opening wedge osteotomy and lateral closing wedge osteotomy
  • minimal risk in medial opening wedge osteotomy
• Malunion or nonunion

Question 182

TKA Instability

1. Incidence
2. Types [5]

Answer 182

1. incidence

• common cause of early failure following total knee arthroplasty
• accounts for 10-20% of revisions

2. Types

• extension (varus-valgus) instability
• flexion (anteroposterior) instability
• mid-flexion instability
• genu recurvatum
• global, multiply-operated instability

Question 183

TKA Instability

Extension (varus-valgus) Instability

1. definition
2. types [2]
3. Treatment

Answer 183

1. Extension (varus-valgus) Instability

• Definition
  
  • varus/valgus instability
  • types
    
    • symmetrical
      
      • caused by excessive distal femoral resection, causing flexion/extension gap mismatch
    • asymmetrical
      
      • more common
      • ligamentous asymmetry caused by failure to correct deformity in the coronal plane
• Treatment
  
  • symmetrical instability
    
    • distal femoral augments to tighten extension gap
    • upsizing poly will fail as it affects both flexion and extension gaps
  • asymmetrical instability
    
    • balance ligaments accordingly
      
      • controlled release of soft tissue on contracted side
      • if ligamentously insufficient, varus/valgus constrained device needed
  • if caused by, intraoperative MCL transection/deficiency
    
    • suture repair or suture anchor reattachment, use of either CR or PS implant, hinged knee brace for 6 weeks postoperatively
    • use of unlinked constrained prosthesis

Question 184

TKA Instability

1. Mid-flexion instability
2. Genu recurvatum

Answer 184

Mid-flexion instability - Controversial topic, poorly understood

• Causes
  
  • associated with modification of the joint line
  • involves malrotation when the knee is flexed between 45 and 90 degrees
  • potential contributing factors
    
    • femoral component design in sagittal plane
    • attenuation of anterior MCL
    • overall geometry of the tibiofemoral joint
• Treatment
  
  • typically, full revision is required
  • goals
    
    • restoration of joint line
    • equalize flexion and extension gaps

2. Genu recurvatum: Definition = fixed valgus deformity and iliotibial band contracture

• Causes: associated with poliomyelitis, rheumatoid arthritis, or Charcot arthropathy
  
  • poliomyelitis - patient walks with knee locked in hyperextension, ankle in equinus due to quadriceps weakness
• Treatment:
  
  • typically long-stemmed posterior stabilized, or varus/valgus constrained implant
  • rotating-hinge reserved for salvage as residual hyperextension may occur, leading to early failure