5. Prosthetic Design
• Constraint
– Ability of prosthesis to provide varus – valgus and
flexion –extension stability in presence of
ligamentous laxity / bone loss
8. Prosthetic Design
Cruciate stabilized
• Cam and post mechanism
• Insert more congruent / dished
Advantages
Easier to balance knee
More range of motion
Disadvantages
Cam jump
Post wear
Patellar clunk syndrome
Additional cut from distal femur
ABSOLUTE INDICATION
•Previous patellectomy
•Inflammatory arthritis
•Deficient PCL
9. Cruciate sacrifice / retain - Evidence
• PS increased ROM –
No functional improvement
• No difference in ROM
between PS and CR
• PCL does not work in CR knees
• Increased wear Ps knee – cam
& post
Cochrane review – No difference in
function whether cruciate retained
or sacrificed
10. Prosthetic Design
Semiconstrained design
• No axle connecting tibia
and femur
• Large tibial post and deep
femoral box
• Varus / valgus stability
• Rotational stability
More femoral resection
Early loosening – increased
constrained
INDICATIONS
MCL/ LCL attenuation
Flexion gap instability
11. Prosthetic Design
Constrained Hinged design
• Linked femoral and
tibial components
• Tibial bearing rotates
around yoke
Aseptic loosening
Large amount bone
resection
INDICATION
Global ligamentous
deficiency
Hyperextension instability
13. Fixed Bearing or mobile bearing -
Evidence
• No advantage of mobile bearing over fixed
bearing
• Increased wear in undersurface of mobile
bearing
14. Prosthetic Design
Hi flex design
• Cultural / pt
expectation
• Cut more posterior
condyle
Preop flexion - most significant - Gatha etal 2008
No difference in ROM - Mehin JBJS 2010
No difference in ROM Sumino Int Ortho 2010
15. Radiographs
• Standing Ap & Lateral
• Sunrise – Merchant view
• Hip to ankle x- rays
– Bony deformity
– Short stature ( < 150 cm)
– Very tall ( > 190 cm)
16. Radiographs
• Femoral and tibial cut
• Position of femoral canal entry
• Bone defects
• Joint subluxation
• Ligament stretch out – Varus Thrust
• Ligament release
• Constraint needed
23. Technical Goals
• Restore mechanical
alignment
• Restore joint line
• Balanced ligaments
• Normal Q angle
24. Femoral Cut
• Valgus cut angle
• AAF – MAF
• Between 5 – 7 deg
• Intramedullary guide
25. Tibial Cut
• Angle between AAT –
MAT
• Tibial cut angle- Zero
• Tibial deformity – cut
perpendicular to MAT
• Intra or extramedullary
guide
26. Joint line preservation
• Inserting prosthesis prosthesis same size as removed
bone and cartilage
• Elevate joint line –
mid flexion instability
Abnormal patellofemoral tracking
Equivalent to Patella Baja
• Lowering joint line
Lack of full extension
27. Knee Balancing
• Balance in Coronal and
saggital plane
• Concave side –
ligaments contracted –
release
• Convex side – ligaments
stretched – Fill gap
38. Sagital plane balancing
• Mc Pherson’s rule
Symmetric gap – address tibia
Asymmetric gap – address femur
39. Tight in Extension
Tight in flexion
Symmetric gap Cut more tibia
Loose in
Extension
Loose in Flexion
Symmetric gap
•Thicker poly
•Tibial Metal
augmentation
40. Extension good
Loose in flexion
Asymmetric gap
1. Increase size
femoral
component
2. Translate
femoral
component
posterior
3. Use thicker
poly and
readdress as
tight
extension gap
48. Patellar component
• Centre or medialized
• Avoid lateralizing
• Increases Q angle and
cause patella
maltracking
49. Patella Baja
• Patellar component
superior
• Lower joint line
• Transfer tibial tubercle
cephalad
• Patellectomy
50. Patella resurfacing vs non resurfacing
• Resurfacing
– Component loosening
– Clunk
– Fracture
– AVN
• Non resurfacing
– Anterior knee pain
– May require second
resurfacing
51. Patellar resurfacing Vs non resurfacing
- Evidence
• Metal backed patella higher complications
• Patellar replacement does not gurantee
painless Patellofemoral joint
• No significant benefit of patellar replacement
52. Complication
• Femoral notch
Saw cuts into anterior femoral cortex
Increases chance of periprosthetic fracture
Femoral stem extension
53. Complication
• Peroneal Nerve palsy ( .3 to 2 %)
Pre op Flexion and Valgus def
Tourniquete time > 120 min.
Epidural anaesthesia post op
Aberrant retractor placement
EMG & NCV at 3 months
Nerve decompression at 3 months
58. Summary
• Choose correct pt
• Plan properly
• Adequate exposure
• Follow principles to align and balance knee
• Meticulous closure
Hope for the best
because 20 % of pt.
with well performed
TKR are not happy !!
