Can a total knee replacement (TKR) be performed after a patellectomy?

Total Knee Replacement After Patellectomy

Yes, total knee replacement (TKR) can be performed after patellectomy, but a posterior stabilized implant should be used rather than a minimally stabilized design to reduce the risk of instability and early revision. 1

Implant Selection

The critical decision in post-patellectomy TKR is choosing a posterior stabilized prosthesis over minimally stabilized designs. 1 This recommendation is based on evidence showing:

• Posterior stabilized implants had zero revisions in post-patellectomy patients, while minimally stabilized designs had a 33% revision rate (5 of 15 patients), with 3 requiring early revision due to instability. 1
• The absence of the patella creates mechanical disadvantage in the extensor mechanism, requiring additional constraint from the prosthesis itself. 2, 1
• Semi-constrained or constrained components have been suggested as treatment strategies to compensate for extensor mechanism dysfunction. 2

Expected Functional Outcomes

Post-patellectomy TKR provides reasonable pain relief but compromised functional results compared to standard TKR:

• Pain scores remain comparable to standard TKR (IKS knee score improving from 41 to 78 points), but function scores are consistently lower. 3
• Range of motion is generally preserved (averaging 0-104° pre-patellectomy TKR and 2-106° post-procedure). 4
• Extensor lag occurs in approximately 50% of patients, though typically mild (<10°). 4
• Active extension deficits are common, occurring in the majority of patients without patellar reconstruction. 3

Patellar Reconstruction Considerations

Patellar reconstruction with autograft or allograft during TKR can be attempted but has significant limitations:

• Autologous bone grafts from the tibial plateau or homologous grafts from bone bank femoral heads can improve active extension, but fixation failure is common (4 of 7 grafts removed in one series). 3
• When grafts remain in place, they can improve IKS function scores from 35 to 72 points and restore active extension. 3
• Graft viability at 2 years has been demonstrated on microradiography, but long-term success requires improved fixation techniques using transosseous transverse sutures. 3

Critical Pitfalls to Avoid

• Never use minimally stabilized implants in post-patellectomy knees—the instability risk is unacceptably high. 1
• Component malposition is particularly problematic in these patients, as patellofemoral instability already occurs in 1-12% of standard TKA cases and is exacerbated without a patella. 5, 6
• Postoperative quadriceps strengthening is essential to compensate for the absent patella and maximize functional outcomes. 7
• Expect functional limitations including difficulty with stairs in approximately 25% of patients. 4

Postoperative Monitoring

Standard radiographic surveillance applies:

• Weight-bearing anteroposterior and lateral radiographs are the initial imaging modality for evaluating alignment and component positioning. 6
• CT is the preferred modality for measuring component rotation if instability or malalignment is suspected. 5, 6
• Annual weight-bearing radiographs are recommended for detecting progressive malalignment. 6