Knee extensor mechanism

Question 1

Describe the dynamic stability of the patella?

Answer 1

• Vastus medialis- medial restraint to lateral translation
• vastus lateralis- lateral restraint to medial translation

Question 2

Describe the static stability to patella?

Answer 2

• Medial patellofemoral ligament (MPFL)
  
  • femoral insertion between medial epicondyle and adductor tubercle
  • primary restraint in first 20^o of knee flexion
  • patellotibial ligament
  • retinaculum
• Lateral retinaculum
  
  • ​10% of total restraint
• medial patellomeniscal ligament
  
  • ​13% of total restraint

Question 3

What is the blood supply to the patella?

Answer 3

• Superior, medial and lateral geniculate arteries
• inferior, medial and lateral geniculate arteries
• anterior geniculate artery
• descending geniculate artery

Question 4

What is the function of the patella?

Answer 4

• Transmits tensile forces generated by quads to patellar tendon
• increases lever arm of extensor mechanism
• **patellectomy decreases extension force by 30%

Question 5

What is the Qangle?

Answer 5

Quads vs patella tendon

• the angular difference between the quads tendon and patella tendon insertion => Q angle
  creates a lateral force across the patellofemoral joint
• A line drawn from the anterior superior iliac spine to middle of patella to tibial tuberosity
• Normal is males 13 degrees, females 18 degrees

Question 6

What measurements can be made on an xray for patella?

Answer 6

• patellar height- install-salvati ratio
• lateral patellofemoral angle- normal angle that opens up laterally
• congruence angle normal -6 degrees

Question 7

What is CT and MRI useful for in patella disease?

Answer 7

• CT
  
  • better visualisation of patellofemoral alignment/fx
  • trochlear geometry
• MRI
  
  • best modality to assess articular cartilage ( T2)

Question 8

Describe patellar instability?

Answer 8

• classified into
• Acute traumatic
  
  • M=F
  • May occur from direct blow
• Chronic patholaxity
  
  • >F
  • Recurrent subluxation episodes
  • assoc w maligament
• Most commonly occurs in 2-3 rd decade

Question 9

What are the risk factors for patellar instability?

Answer 9

• Ligament laxity= ehler’s danlos syndrome
• Dysplastic vastus medialis oblique
• lateral displacement of patella
• patella alta
  
  • patella doesn’t articulate with sulcus, losing its constraint effects
• Trochlear dysplasia
• excess lateral patellar tilt ( measured in extension)
• Increased Q angle
• Previous patellar instability event
• ‘miserable malalignment syndrome’
  
  • 3 things that -> increase q angle
  • femoral anteversion
  • genu valgum
  • external tibial torsion/pronated feet

Question 10

What is the pathophysiology of patellar instability?

Answer 10

• Usually non contact twisting injury with knee extended & foot externally rotated
  
  • pts usually reflexively contract quads therby reducing patella
  • osteochondral fx often occur as patella relocates
• Direc blow- less common

Question 11

What is the usual site of avulsion of the MPFL?

Answer 11

• At origin
• Between femoral medial epicondyle and adductor tubercle

Question 12

What is the presentation of patellar instability?

Answer 12

• complaints of instablity
• anterior knee pain
• 0/E
  
  • acute dislocation= haemarthrosis
  • medial sided tenderness - over MPFL
  • increase in patellar translation - in quadrant of 3- midline 0
    
    • normal is <2 quadrants of translation
  • increased Q angle
  • patellar apprehension
    
    • passive lateral translation-> guarding & sense of apprehension
  • J sign
    
    • excessive lateral translation in extension which pops into groove as patella engages the trochlea early in flexion
    • assoc with patella alta

Question 13

What is seen on xrays of patellar instability?

Answer 13

• Medial patellar facet fx - most common
• Lateral femoral condyle fx
• lateral xray
  
  • patellar height
  • blumenstat’s line extended to inferior pole of patella in 30 degrees if flexion
  • Install-salvatti index normal (0.8-1.2)
  • Sunrise/merchant’s view
    
    • best for patella tilt
    • lateral patellofemoral angle
    • congruency angle

Question 14

What can be measure on CT for patellar instability?

Answer 14

• The tibial tubercle- trochlear groove distance
• if >20 mm need tibial tubercle medialisation osteotomy
• (A) first drawing a line from the trough of the trochlea perpendicular to the line connecting the posterior condyles. These lines are superimposed onto an image through the tibial tubercle (B), and the TT-TG distance is measured as that between the above-described line and the tibial tubercle (distance AB).
  *

Question 15

What is the tx of adult patellar instability?

Answer 15

• Adult instability
  
  • NSAIDS, activity modification, physio
  • mainstay
  • short term immobilisation then 6 wks of controlled motion
  • emphasis on
    
    • closed chain short arc quads exercises
    • quads strengthening
    • core & hip strengthening to imporve limb position & balance
    • consider aspiration for tense effusion

​​Operative

• Arthrosopic debridement vs repair of osteochondral fragment
• MPFL repair
  
  • acute 1st time w bony fragment
  • direct repair done in first few days
• MPFL reconstruction w autograft/allograft
  
  • for recurrent instability
  • gracilis or semitendinous used
  • femoral origin can be found on xray- schottle point
• Fulkerson- type osteotomy ( ant & medial tibial tubercle transfer)
  
  • anteromedial displacement of osteotomy and fixation. if tibail tubercle trochlear groove distance is >20mm on CT.correct TT-TG to 10-15mm
• Tibial tubercle distalization
  
  • for patella alta
• Lateral release
  
  • if excessive lateral tilt ot tightness after medialisation
• Trochleoplasty

Question 16

What is the tx of paeds patellar instability?

Answer 16

• same principles as adult but
• must preserve the physis
• DON’T do a tibial tubercle osteotomy ( will harm the growth plate of prox tibia)

Question 17

What are the complications of patellar instability?

Answer 17

• Recurrent dislocation
  
  • ​redislocation rates w non op tx maybe high at 2-5yrs
• medial patellar dislocation and medial patellofemoral arthritis
  
  • almost exclusively iatrogenic as result of prior patellar stabilisation surgery

Question 18

What is lateral patellar compression syndrome?

Answer 18

• Improper traking of the patella in trochlear groove
• caused by tight lateral retinaculum
  
  • leads to excessive lateral tilt without excessive patellar mobility

Question 19

What is the miserable triad?

Answer 19

• A term coined for anatomical characteristics that leads to an increase in Q angle adn exacerbation of patellofemoral dysplasia
• include
  
  • femoral anteversion
  • genu valgum
  • external tibial torsion/promated feet

Question 20

What is the presentation of lateral patellar compression syndrome?

Answer 20

• Pain on climbing the stairs
• theatre sign - pain w sitting for long periods of time

O/E

• Pain w compression of patella & moderate lateral facet tenderness
• inability to evert the lateral edge of patella

Question 21

what is seen on xray of lateral patellar compression syndrome?

Answer 21

• Patellar tilt in lateral direction

Question 22

What is the tx of lateral patellar compression syndrome?

Answer 22

Non operative

• NSAIDS, activity modification, physio
  
  • mainstay of tx
  • vastus medialis strengthening
  • closed chain short arc quads exercises

​​Operative

• Arthroscopic lateral release
  
  • objective evidence of lateral tiliting
• Patellar realignment surgery
  
  • Maquet ( tubercle anteriorization)
    
    • only for distal pole lesions
    • only elevate 1cm or risk skin necrosis
  • Elmslie-Trillat ( medialisation)
    
    • instability in lateral direction
  • Fulkerson alignement surgery
    
    • tubercle anterioisation and medialisation
    • CI superior medial arthrosis

Question 23

Describe the technique of arthroscopic lateral release?

Answer 23

• Use superior portal to show medial facet doen’t articuate w trochlea at 40^o of knee flexion
• ensure adeqyate Haemostasis
• post op the patella should be passively tilted to 80^o
• complications
  
  • perisistent / worse night pain
  • patellar instability w medial translation

Question 24

What is idiopathic chondromalacia patellae?

Answer 24

• Condition characterised by idiopathic articular changes of the patella
• aka anterior knee pain/patellofemoral syndrome
• occur in adolescents/ young adults
• F>M
• pathophysiology
  
  • poorly understood
  • maybe roughening or damage to the undersurface cartilage of patella
    
    • limb malalignment
    • muscle weakness
    • chondral lesions
    • patella maltracking

Question 25

Name any associated conditions of idiopthic chondromalacia patellae?

Answer 25

• Miserable malalignment syndrome
  
  • femoral anteversion
  • External tibial torsion/pronated feet
  • genu valgum

Question 26

Describe the pain receptors of the knee?

Answer 26

• Subchondral bone has weak potential to generate pain signals
• Anterior fat pad & joint capsule have highest potential for pain signals

Question 27

Describe the classification of idiopthic chondromalacia patellae?

Answer 27

• Outerbridge
• Type 1 = Softening
• Type 2 =Fissures
• Type 3= Crabmeat changes
• Type 4= exposed subchondral bone

Question 28

What is the presentation of idiopthic chondromalacia patellae?

Answer 28

• Diffuse pain in peripatellar/retropatellar area
• worse on climbing/descending the stairs
• worse w prolonged sitting w knees bent
• squatting/kneeling

O/E

• Quads muscle atrophy
• signs of patella maltracking
  
  • increased femoral anteversion or tibial ext rotation
  • lateral subluxation of patella or loss medial patellar mobility
  • positive patella apprehension tx
  • pain w compression of patella

Question 29

What imaging is best for idiopthic chondromalacia patellae?

Answer 29

• Xray
  
  • chondrosis
  • shallow sulcus, patella alta/baja, lateral patella tilt
• CT
  
  • trochlear geometry
  • TT-TG distance
  • torsion of limb
• MRI
  
  • best modality to assess articular cartilage

Question 30

What is the tx for idiopthic chondromalacia patellae?

Answer 30

Non operatively

• Rest , rehab and nsaids
  
  • done for minimum of 1 year
  • rehab on VMO strengthening
  • core strengthening
  • closed chain short arc quads exercises

Operative

• Arthroscopic Debridement
  
  • Outbrigde 2-3 chondromalacia
  • mechanical debridement/radiofrequency debridement
• Lateral retinacular release
  
  • Tight lateral retinacular capsule
  • open vs arthroscopic
• Patellar realignment surgery
  
  • MPFL reconstruction
  • Maquet ( anterior tubercle elevation)
  • Fulkerson ( anterior -medialisation)
  • Elmsie- Trillat osteotomy

Question 31

Describe the epidemiology of quadriceps tendon rupture?

Answer 31

• Rupture of quads tendon -> disruption in the extensor mechanism
• more common than patellar tendon rupture
• pts >40 yrs

M>F 8:1

• Occurs in nondominnat limb >2 as often
• location
  
  • usually at insertion of patella
• Risk factors
  
  • diabetes
  • renal failure
  • rheumatoid arthritis
  • Hyperparathyroidism
  • connective tissue disorders
  • steriod use

Question 32

What is the classification of quads tendon ruptures?

Answer 32

• Partial
• Complete

Question 33

What is the presentation of quadriceps tendon rupture?

Answer 33

• Tenderness at site
• papable defect within 2cm of superior pole
• unable to SLR= complete
• unable to SLR against resistance

Question 34

What is seen on xrays with quadriceps tendon rupture?

Answer 34

• Patella baja

Question 35

Describe the tx of quadriceps tendon rupture?

Answer 35

Nonoperatve

• Knee brace
  
  • partial tear w intact quads mechanism

Operative

• Primary repair w reattachment to patella
  
  • complete rupture w loss of extensor mechanism

Question 36

Describe teh surgical repair of quads tendon?

Answer 36

• Midline incision
• longitudinal 3 drill holes in patella
• non absorable 5.0 ethibond sutures in running locking fashion then thru drill hole in patella
• retinaculum repair with heavy absorbable sutures
• ideally knee should be able to flex to 90o post repair
• post op
  
  • inital immobilistion in brace
  • eventual flexibility and strengthening exercises

Question 37

Describe the tehnique for chronic rupture repair?

Answer 37

• Midline approach
• often the tendon retracts 5cm if >2 wks
• repair with similar technique to acute but a tendon lengthening proceedure may be necessary
• Codivilla V to Y lengthning
• auto or allograft tissue may be needed to secure quads tendon to patella

Question 38

What are the complications of quads tendon rupture?

Answer 38

• Strength deficit
  
  • 33-50%
• Stiffness
• Functional impairment
  
  • 50% pts are unable to return to prior level of activity/sports

Question 39

Describe the epidemiology of patellar tendon rupture?

Answer 39

• Incidence
• common 3-4th decade
• M>F
• location
  
  • quads>patella
• Risk factors
  
  • weakening collagen
    
    • SLE
    • Rheumatoid arthritis
    • chronic renal disease
    • diabetes mellitius
  • Local
    
    • patellar degeneration- most common
    • previous injury
    • patellar tendinopathy

Question 40

What is the pathophysiology of patellar tendon rupture?

Answer 40

• Mechanism
  
  • tensile overload of extensor mechanism
  • most ruptures occue w knee in flexed position
  • greatest forces on tendon when knee >60o
• 3 patterns of injury
  
  • avulsion w or without bone from inferior pole- most common
  • midsubstance
  • distal avulsion from tibial tubercle
• ***rupture is usually the result of end stage or long standing chronic tendon degeneration***

Question 41

What is the presentation of patellar tendon rupture?

Answer 41

• Sudden quads contraction w knee in lfexed position

symptoms

• infrapatella pain
• popping sensation
• difficulty WB

O/E

• Elevation of patella height
• large haemarthrosis/ecchymosis
• unable to active SLR or maintain extended knee

Question 42

What is seen on imaging of patellar tendon rupture?

Answer 42

Xray

• patella alta
• install- salvati ratio >1.2

USS

• effective at detecting /localising rupture

MRI

• most senstive to detect

Question 43

What is the tx of patellar tendon rupture?

Answer 43

Nonoperative

• immobilisation in full extension w progressive wb exercise programme
  
  • partial tears w intact extensor mechanism

Operative

• Primary repair
  
  • complete patella tendon ruptures
  • end to end repair
  • tranosseous tendon repair- can be protected by cerclage wre between patella & tibial tuberosity
  • suture anchor repair
• Tendon reconstruction
  
  • severely disrupted or degenerative patella tendon
  • semitendinous or gracilis tendon harvesting
  • free tendon ends are passed thru transosseous hole of patella, thru thru transosseous hole of tibial tubercle to make a circular graft
  • post op
    
    • passive extension & active close chain flexion ( heel slides)
    • prone open chain knee flexion