Abstract
Aim
The aim of the study was to assess the impact of a self aligning unidirectional mobile tibial bearing and the use of a patella button on lateral patella release rates within a knee system using a common femoral component for both the fixed and mobile variants.
Methods and results
A total of 347 patients undergoing TKR were included in the study and randomly allocated to receive either a Mobile Bearing (171 knees) or a Fixed Bearing (176 knees) PS PFC Sigma TKR. Further sub-randomisation into patella resurfacing or retention was performed for both designs. The need for lateral patella release was assessed during surgery using the ‘no thumbs’ technique.
The lateral release rate was similar for fixed bearing (9.65%) and mobile bearing (9.94%) implants (p=0.963).
Patella resurfacing resulted in lower lateral release rates when compared to patella retention (5.8% vs 13.8%; p=0.0131). This difference was most marked in the mobile bearing group where the lateral release rate was 16.3% with patella retention compared to 3.5% with patella resurfacing (p=0.005).
Conclusion
The addition of a rotating platform tibial component had no impact on the lateral release rate in this study. Optimising patella geometry by patella resurfacing appears more important than tibial bearing deisgn per se. The combination of a mobile bearing design and patella resurfacing appears to optimise the lateral release rate and patello-femoral tracking in the PS PFC Sigma design which has a deeply radiused trochlea on the femoral component. The results with a patella resurfacing confirm the results with this prosthesis reported by Pagnano et al in Clin Orthop 428 pp221-227.
