Recon 1 (TKA) Flashcards
What natural mechanics of the knee contribute to OA
Increased adductor moment
- Bc ankle center is medial to knee
- Walking = adduction moment at knee
- Increased if varus leg = ankle center MORE medial because knee is more lateral
- Medial compartment overload
Late : varus thrust
Which injections are backed by the AAOS recs for knee OA
Steroids = short term relief
PRP may help
No support for hyaluronic acid
What supplements are mentioned in the knee OA AAOS recs
Tumeric, ginger extract, glucoasamine, chondroitin, vit D
Indications for osteotomy for OA
1 compartment disease (medial > lateral)
<45yo
Too active (job) so worried will wear through a TKA
If a knee is in varus, where do you do your osteotomy
HTO - produce valgus
Most likely prox tib vara
If knee is in valgus, where do you do your osteotomy
DFP - produce varus
Most likely hypoplastic lateral femoral condyle
CI to HTO
- Inflammatory arthritis
- Min 90deg flexion
- Flexion contracture >10deg
- Lig instab (ie varus thrust)
- Coronal subluxation >1cm (indicates fixed deformity)
- Medial compartment bone loss
- Lateral compartment narrowing (stress XR)
Complications HTO opening wedge
HTO - open wedge medial to create valgus
Patella baja
Collapse - lose correction
Nonunion
Autograft site harvest pain
Complications HTO closing wedge
HTO - close lateral to create valgus
Patella baja (loss flexion)
Lose posterior slope
Peroneal nerve
Does history of HTO change your TKA?
YES
Longer OR time
More frequent use of revision implants
Who is the best candidate for a DFO?
Valgus >12deg
Lateral OA
OK for some mild patellofem disease (reduce the Q angle so will improve patellofem mechanics)
CI to DFO
Inflammatory arthritis
Flexion <90deg
Flexion contracture >10deg
Lig instab (valgus thrust)
Coronal subluxation
Prior medial meniscectomy
Medial compartment narrowing (stress XR)
Complications DFO
Nonunion
Lose correction (think osteoporosis)
Residual patello-fem maltracking
If need an osteotomy at the time of TKA, which one are you doing?
Crescentic dome
The osteotomy overlaps so allows for the IM guides for TKA
CI UKA
Inflam arthritis
Fixed deformity (flexion contracture >10deg)
Previous meniscectomy in opposite compartment
ACL def (esp mobile bearing unis)
NOT patellofem OA - does not affect outcomes of a fixed bearing UKA… although if severe patellofem OA a uni wont help them
Presentation & treat of stress fracture after UKA
TIBIAL
Pain free -> spontaneous onset pain
Aspiration = blood
Treat
- Stable tibial comp = limited WB
- Compromised tibial comp = TKA
Causes of tibial bearing extrusion in UKA
Mobile bearing
- loose flexion gap = revise to thicker poly
Cemented tibia (all poly)
- tibia fracture
- tight flexion gap = implant lift off anterior = loosens -> spits out
What happens if you over or under correct with your UKA
Over = ds progression opposite compartment
Under = implant overload
- Accelerated poly wear
- Osteolysis
Where will you get implant subsidence with UKA? 3 reasons why
TIBIAL
Reasons = weak bone
1. Deep cut (aka no subchondral to support)
2. Undercoverage (no cortical rim support)
3. Osteoporosis
What is the best treatment for isolated patellofem arthritis
TKA, esp older patients
What time frame of a pre op CSI for TKA has an infection association
2 weeks
Which DMARDs can you continue through TKA/THA
MTX
Sulfasalazine
Hydroxychloroquine
Leflunomide
Doxycycline
Daily dose steroids (no stress dose)
When stop biologics before TKA/THA? What is the exception?
Plan OR at end of dosing cycle (aka half life of drug)
IE: dosing cycle = q2wk, OR on week 3
EXCEPT Tofacitinib bc dosing interval very short (stop 7d pre op)
When to restart biologics post op
2 wks as long as incisions look ok
Why continue some SLE medications through op period? Otherwise, when dc and restart?
Cont if organ involvement
Organ damage from disease > infx risk
MMF
Tacro
Cyclosporine
Azothioprine
Dc 1 wk before OR
Restart 3-5d post op
When stop AC pre op
1 wk:
- antiplatelet (ASA)
- factor 10 inhib
- warfarin
- NSAIDs
What do you do if a patient says they have a penicillin allergy pre op TKA/THA?
Test dose - most aren’t actually allergic
Bc non-cephalosporin meds have increased infx rates (vanco, clinda)
What is the relation of the TKA femoral cut to the mechanical axis?
Perpendicular
Allows even mechanical loading of implant with WB
What does the valgus cut angle measure? What variable can change valgus cut angle?
Angle between anatomic (IM guide) and mechanical (cut perpendicular to this) axis of the femur
Femoral length can change the cut angle - measure in tall and short pts XRs
Taller <4
Shorter >8
What is the tibial cut angle zero?
Mechanical = anatomic axis in the tibia
Why just as easy to use extramed guide
Unless some weird tibial deformity
What is the max amt joint line change TKA
8mm
Otherwise change lig tension
What are the main 2 TKA techniques
- Measured resection
- Ligament balancing
- Coronal balance: varus/valgus
- Sag balance: flex/ext
Order of medial releases for varus knee
Osteophytes
Capsule (include dMCL) - release 1.5cm below jt on tibia
Post med corner - corrects fixed IR
sMCL
- Tight in ext: release post oblique (not POL) - posterior closer to joint line
- Tight in flex: release ant - anterior, more distal
Order of releases valgus knee
Osteophytes
Lateral capsule (ALL)
Popliteus - tight in flex
IT band - tight in ext
LCL - affects both flex + ext
What is the ALL
Attaches mid tibia, behind Gerdys
Xs IR tibia
What happens if you cut popliteus when you didn’t mean to
Does NOT sig affect stability 0-90deg
Can put in a PS knee (don’t have to go straight to constrained implant)
What is McPherson’s rule of 1/4s for extra-articular coronal deformity?
If coronal def is within distal 1/4 femur or prox 1/4 tibia + deformity >20deg
- Concomitant osteotomy w/ TKA via closed wedge
- Diaphyseal press fit stem for rotational stability
Try to avoid huge bone cuts bc change the ligament length - pushes you to highly constrained implants
Releases for a flexion contracture in order
Always do w/ knee flexed to let pop art fall away
Pop art behind capsule at tibial PCL insertion
- Osteophytes
- Post capsule
- GR
What 3 variables control the flexion gap
- Posterior femur cut (2mm resection = 10deg flexion correction)
- Tibial cut (both flex + ext)
- PCL
If you have a symmetric gap problem, where do you cut first?
If you have an Asymmetric gap problem, where do you cut first?
Symm: tibia
Asymm: femur
Solve: loose ext, loose flex
Add to tibia : thicker poly vs augments
Solve: tight ext, normal flexion
Cut distal femur
If contracture, release post capsule
Solve: normal ext, tight flexion
- CHECK post slope (normal 6-10) - too flat (ant slope) = no flexion
Remove post femur
Partial release of PCL (if doing a CR knee)
Use smaller femur
What happens with trials in a CR knee that is tight in flexion?
Tibial trial lifts off in flexion
Think tight PCL
Solve: normal ext, loose flexion
FEMUR
Add post fem augments (or cement)
Increase fem comp size A to P
OR
Add to tibia -> now ext gap will be tight (2 step solution)
Solve: loose ext, normal flex
Think slack post capsule
Add distal fem / bring femoral comp more distal
OR add tibia -> now tight flexion gap (2 step solution)
Con to quad sparing approaches TKA
Malalignment higher in quad sparing
Muscle block jigs
Periop recs TKA AAOS
TXA decrease EBL (TXA CI color blindness for toxicity)
Peripheral nerve block and periarticular local decrease opioid use
Rehab day of TKA reduces hospital stay
Evidence AGAINST (1) intraop nav, (2) PSI, (3) drains, (4) CPM because no diff in outcomes
What is the AAOS rec for tibial comp designs
NO DIFF
- PS vs CR
- All poly vs modular tibias
- Patellar resurfacing (always resurface inflam arthritis) - higher risk if you selectively resurface - go all in or all out
- Cemented vs cementless tibias
Mechanism TXA, CI
Lysine analogue
Reversible bind lysine receptor on plasminogen (blocks plasminogen -> plasmin)
Reduces clot breakdown
T1/2 = 3hrs, renal excretion
CI : seizure, decreases seizure threshold (so just give it topical instead!)
AAOS rec for gabapentinoids vs pregabalin
Against gabapentinoids - no reduction post op pain
Pro pre-gabalin (2-4x more potent)
Pro/con adductor vs femoral nerve block
Femoral - motor + sensory, need KI, doesn’t cover posterior knee
Adductor - sensory only to med + ant knee, equiv pain relief, doesn’t cover post knee, earlier ambulation bc motor intact
- Saphenous then branches to infrapat br
NONE get posterior knee why do periarticular local
Contents of adductor canal
Fem a + v, saph n
AAOS recs for DVT after TKA
No ROUTINE post op duplex - don’t go looking for something w/o clinical concern
Pharmacologic - no superior agent, ASA as effective
Mechanical
Use of pharm and mech - MODERATE rec
What change do you make for AC for factor 5 leiden mutation after THA and TKA
No change in dosage or length AC
Why do you care about femoral notching
Decreases load to failure
In BENDING, you will have a short oblique frx starting at the notch
Higher frk risk if notch >3mm below ant fem cortex
- Consider bypass stem
What pre op deformity is most likely to cause peroneal nerve palsy w/ TKA? When do you go explore if does not recover?
Valgus + flexion
Abt 3mo
What vessel at risk with a lateral retinacular release? Sequelae?
Lat sup genicular art
You care because 1ary BS patella is inf-med, but you cut this on approach
This would be the 2nd hit to BS
Increased risk AVN patella - can fragment post op
What is min patella thickness to avoid frx
13mm
Treat patella frx with TKA w/ sufficient bone stock
- Min lag, implant well fixed = non op
- Prevent retinacular disruption that would cause ext lag - > 10deg lag, TKA stable = open ORIF/ext repair
- > 10deg lag, TKA unstable = revision TKA + address patella
If going to revise patella, need at least 13mm for the pegs
Treat patella frx TKA with inadequate bone stock
Implant resection - suture bone/ST together
Patellectomy - extensor imbrication
If you break a femoral condyle in TKA, which one is more likely? Treat?
Medial > lat femoral condyle
PS knee +/- ORIF
Treat intra op MCL injury
Primary repair OK - post op brace 6wks
Convert to a high post for varus/valgus support (NOT PS)
Treat intra op extensor mechanism disruption
Comes off at the tib tub
MUST do ext recon
1. Allograft - bulky so if you have bad coverage, can lead to infection
2. Marlex mesh - no patella so persistent lag, also have to cast in extension so will lose flexion, must have good bone on tibia (can’t use with endoprostheses)
Trt TKA arthrofibrosis
Manipulate 6-8wks post op
Do not manipulate late = supra cond fem frx
Later - open lysis (but high failure rate so sometimes requires revision)
What metal allergy is most common? What is the cell process?
Nickel > Co > Cr
T cell - T4 HST
Skin patch testing doesn’t work
Get a lymphocyte T cell proliferation test
What are the 2 forms of PCL resection (CS) knees?
Cam post
Extended ant poly lip (ultra congruent, ant stabilized) - lip is as high as post
2 main functions of PCL in CR knees
Flexion stability - more consistent joint line restoration
Controls rollback
If PCL is too tight in a CR knee, can cause excess posterior poly wear
What happens if PCL loosens late in CR knee
Late flexion instab
Pain/effusion, inability to get up from low chair, stairs
What is paradoxical roll forward in CR knees
ACL is gone, PCL is intact
COR should move back as you flex knee
But kinematics are very different because ACL gone
Get sliding wear on the poly - COR moves forward through flexion
What happens if the flexion gap is too lose in a PS knee? What are 3 common causes of this?
Cam jump aka femur in front of post
1. Cut popliteus - flexion gap loose in figure 4
2. Over release ant sMCL
3. Ant translation femur
- Femur slides up when cementing
- Or press fix, if between 2 sizes and you go with the smaller femur leaving flexion gap loose
What is patellar clunk? What type of TKA does this happen in?
PS only
- High and wide boxes = BAD
Suprapatellar scar gets caught in box in 30-45deg flexion
Prevent at time of OR by synovectomy
Treat after with scope or open scar removal
What are causes of anterior wear on the post in PS knees?
Knee hyper ext
Flex femoral comp
Too much posterior tib slope = femur slides post
Ant translation tib comp
What are 2 patients who cannot get a CR knee (at least a PS)?
Patellectomy
Inflam disease (don’t trust the ligaments)
Pros/cons ultracongruent knees?
PRO
Bone conserving
If you cut PCL, can switch to this without going to a pull PS system
CON
More poly = more wear surface
Minimal rollback - you need to add more posterior slope
Flexion gap laxity
Why do you get bearing spinout in a rotating platform tibia?
Loose flexion gap
XR see AP of the poly, lateral of femur
What are 2 cons to modular tibias (vs all poly)
1 con to all poly
Modular
1. Poly dislocation
2. Backside wear
All poly
If you cement wrong, you’re boned
What is the failure mechanism of all poly tibia
Peripheral bending - does NOT fracture
Cement then cracks -> loosens
Most common site for osteolysis TKA + cause
Posterior femur
Submicron shedding microparticular poly debris
MACROPHAGE
- Upreg RANKL
- Rank increases osteoclasts
- Bone resoprtion
TNFa, IL 1b, IL 6
Indications for a hinge TKA
Global instab
Hyperext instab (post polio)
Endo resection
Relative:
- MCL def
- Charcot
What is the con with hinge TKA
Bucking
Any ext mech deficit causes buckling
Infection markers TKA
> 3K WBC
70% neutrophils
How to improve exposure for revision TKA
Take most lateral incision possible since revasc comes from the medial side
ER tibia to release post med corner
Lateral knee release
Quad snip - no more than 1cm, must do transverse
TTO - stiff knee w/ baja
What is go to for metaphyseal defects revision TKA
Cones - cement implant into cone
RF TKA infection
Smoking - stop 30d prior
DM
Malnutrition, albumin <3.5
Hx surg, esp w/ decreased ROM
BMI>35
Age>70
Autoimmune / immune sx disorders
Blood transfusion - indep risk factor
How do biofilms resist abx - 2 mechanism
EPS matrix - limits [abx] in the film
Persister cells - enter dormancy when abx levels high, then resumes growth with removal of stress agents, need radical debridement to remove
Major criteria PJI
+aspiration
Draining sinus
What is alpha defensin
Peptide released by neutrophils
High PPV and NPV
<3wks treat acute PJI
Poly exchange
Any post op wound drainage after 5 days, minimum a washout - likely a poly exchange
What are the best qualities of abx spacer
Increased surface area: beads > block
More porous cement - adding abx increases porosity
Higher [abx]
No more than 1gm of abx per 40gm cement powder - more than this reduces the mechanical properties by 10%
What do you do if you get a positive intraop culture during a presumed aseptic revision
Do single stage revision
IV abx 6wks
BS for medial GR flap
Medial sural art
Hallmarks for fungal PJI + treat
Most common candida
XR: marginal erosions
MRI: erosions at ligament insertions sites
Sometimes
Can have normal serum markers
Trt: 2 stage always, long term abx bc spores can lay dormant
Antifungals disrupt the cell wall
How does patellar component shape effect Q angle
More V shaped = less restrained
Increased “effective” Q angle
What fem/tib component mistakes will cause patellar maltracking?
IR + medialization
What is are 2 anatomic risk factor for IR femoral component
If you use a posterior referencing system with:
1. Lat fem cond hypoplasia
2. Valgus wear
How should you resurface the patella if concerned about tracking?
Medialize patella component (on the patella bone available)
Don’t overstuff
3 conditions associated with patella baja
Low riding patella after:
- HTO
- Tib tub transfer
- Trauma
How does patella baja present with TKA? How fix?
Lose knee flexion
Pain 2/2 impingement
Clunk
Trt: lower the joint line (revision knee system) or place patellar component high
Intraop troubleshooting for maltracking during TKA
Tourniquet down
What is catastrophic wear for TKA
Premature TKA failure 2/2 macroscopic poly failure
Untreated -> metalosis
NOT osteolysis
RF for catastrophic wear
Poly too thin (<8mm)
Flat poly - high contact loads bc low contact area (want congruent poly)
What is a major argument against CR knees?
Take ACL out, leave PCL - changes linked kinematics of the knee
Instead of normal femoral rollback (screw home mechanism) - get sliding
Sliding = bad for poly
Best method of poly fabrication
Direct compression molding!
NO ram bar
Best method poly sterilization
No oxygen = cross linking = improved wear
BAD = O2 -> free radicals, wear
Worst method of machining poly
NOT cutting tools -> causes stretch effect, white band of oxidation in the poly
3 types of knee AVN
- Spontaneous = most common
F, >50 - sudden onset pain 6-8wks
Single - med fem cond
Rare in other knee - Secondary (steroids, EtOH)
F, <50
Diffuse - lat fem cond
Common opposite knee, hip, etc - Post arthroscopy
Med fem cond
M=F
Sudden pain 6-8wks post op
What is the pathomechanics of spont AVN
Some mechan overload (increased adductor, osteoporosis, etc)
Subchondral microfracture
Increase intra oss pressure -> edema
Disrupt BS -> necrosis
Remodel -> collapse
Trt spont AVN
No collapse: non-op limited WB
- Scope if mech sx
- HTO (<45yo, valgus to start aka something to correct)
Collapse: UKA vs TKA
- UKA > TKA
- TKA for spont AVN does worse than for OA - higher pain, loosening
Lesions >50% width likely to progress, more likely arthroplasty
TREAT post scope AVN SAME PATHWAY
Presentation/imaging secondary AVN
Gradual onset
Positive condyle squeeze test - increase intraoss pressure
Imaging will involved both condyles and both sides of the joint (why not tumor)
Ddx infection
Treat secondary AVN
Non-op
No collapse: core decompression, scope (mech sx)
- Relieve intra-oss pressure
Collapse: TKA
- Inferior to OA TKA
