Abstract
Background
The cemented mobile bearing metal backed low contact stress patellofemoral arthroplasty (LCS PFA) is a newer design belonging to the second generation of inlay type implant, based on the more successful knee arthroplasty model. The advantage is the patella can articulate with the trochlear implant as well as the femoral component of a total knee replacement (TKR).
Patients
This series is a cohort of 21 patients who underwent 24 (3 bilateral) unicompartmental PFA replacements for isolated patellofemoral osteoarthritis. We have used the mobile bearing LCS PFA in all of them. There were 3 males and 18 females. Average age was 51(40-58) years. The Oxford Knee score was used to assess the results.
Results
At the latest follow-up averaging 2.7 (0.5 to 4) years, 9 patients showed excellent improvement in their knee scores, 5 patients showed fair improvement and 7 patients very little. There were 9 revisions in 7 patients either due to mechanical problems or with persistent symptoms. We had 4 patients with mechanical complications who underwent revision and 4 patients had a conversion to TKR. The revision rate at 2 years was 33%. There were no infections or loosening of trochlear implants.
Conclusion
The revision rate for this implant seems to be very high and mainly with the patellar implant (at the metal polyethylene interface). The Australian Orthopaedic association annual joint registry report 2008 reported a higher revision rate for the same implant at 5% from a pool of 1057 patients. The young active patient having a patellofemoral replacement may put extreme force on their patellar implant. We strongly advocate patellofemoral arthroplasties to be analysed separately from the unicompartmental knees in the National Joint Registries to highlight any persistent issues with this implant.
