Abstract
Introduction
The Bristol Knee Group has prospectively followed the results of over 500 isolated patellofemoral arthroplasties. Initial experience with the Lubinus prosthesis was disappointing. The main causes of failure were mal-tracking and instability leading to excessive polythene button wear and disease progression in the tibio femoral joint.
This experience resulted in the design of a new prosthesis to correct the tracking problems and improve the wear. We have now performed over 425 Avon arthroplasties with a maximum follow-up of 9 years.
Results
Survivorship at 5 years and the functional outcome have been reported with 95.8% survivorship, and improved function with Oxford score from 18 to 39 points out of 48. There have been 14 cases with mal-tracking (3%). Several of these cases have required proximal or distal realignment with the Elmslie or Insall procedures. Two knees with patella alta required distalisation of the tibial tubercle. Symptomatic progression of the arthritic disease in the medial or lateral tibio-femoral compartments has occurred in 28 cases (7%) causing recurrent joint pain. Radiographic follow-up has shown a higher rate of disease progression emphasising the importance of careful assessment of patients prior to operation.
We have investigated 8 cases of persistent unexplained pain. Analysis of these cases suggests 3 possible causes. An extended anterior cut leading to overstuffing, insufficient external rotation and over sizing of the femoral component leading to medial or lateral retinacular impingement. Six of these cases have been successfully treated by revision of the femoral component leading to dramatic resolution of the symptoms.
Conclusion
Minor misplacement of the femoral component can lead to retinacular impingement causing persistent pain. Attention to detail in the performance of the operation will prevent these problems. Disease progression remains a risk in any compartmental arthroplasty and may be inevitable, thus strict pre-operative criteria are essential.
