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convert to semi-constrained design
8%
77/952
downsize femoral component and increase tibial insert thickness
60%
568/952
resect more proximal tibia
3%
30/952
anteriorize femoral component
13%
123/952
increase posterior tibial slope
15%
146/952
Select Answer to see Preferred Response
This patient has a gap imbalance resulting in the knee being loose in extension and tight in flexion. This can best be addressed by downsizing the femoral component and increasing the tibial insert thickness. Achieving a well-balanced total knee arthroplasty is critical for implant survival. Sagittal balancing involves ensuring the flexion and extension gaps are symmetric. As a general rule, when there is a symmetric gap imbalance (i.e. both flexion and extension gaps are tight/loose), adjustments should be made on the tibia. For asymmetric gap issues, adjustments should be made on the femur. Stambough et al reviewed flexion instability after TKA. Nonsurgical treatment focus on quadriceps strengthening and bracing. Revision for flexion instability can be addressed by increasing posterior condylar offset, decreasing tibial slope, raising the joint line plus adding a large polyethylene insert, and addressing any malrotation. Outcomes following revision for TKA instability are generally worse than for other causes. Sriphirom et al assess the effect of downsizing the femoral component size on flexion and extension gaps intraoperatively in PS TKA. The authors found that both the medial and lateral flexion and extension gaps were larger than their initial size. They concluded that downsizing the femoral component may alter the extension gap as well. Illustration A demonstrates a treatment strategy for achieving sagittal balance based on different combinations of tight, balanced, and loose flexion and extensions gaps. Incorrect answers: Answer 1: Converting to a PS-TKA may improve flexion instability but would not address the extension gap. Answer 3: Cutting the proximal tibia would improve the flexion tightness but also increase the extension gap. Answer 4: Anteriorizing the femoral component would improve the tight flexion gap but would not address the extension gap. Answer 5: Increasing the posterior tibial slope only could improve the tight flexion gap but would not address the loose extension gap.
3.3
(7)
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