Functional relevance of patellofemoral thickness before and after unicompartmental patellofemoral replacement

The aim of this study was to assess the increase in the anterior height of the knee after unicompartmental patellofemoral replacement and the impact of this increase on the range of motion and function of the knee. Twenty-eight patients (34 knees) who underwent patellofemoral replacement with FPV(TM) prosthesis between 2005 and 2009 were identified and retrospectively analyzed using chart and radiological review. Trochlear height and patellar thickness were measured combined and compared pre and postoperatively. The range of movement and functional outcome scores after 6-12 months follow-up were noted. The effect of increased postoperative anterior-posterior height of the knee on the range of motion was studied. Postoperative mean range of flexion of the knee joint was 116°. The mean Oxford knee score was 21 points. The mean American Knee Society Knee Score was 80 points for pain and 61 points for function. The trochlear height and patellar thickness were increased by 3.5 and 2.5 mms respectively, resulting in average total increase of 6mm in the anterior-posterior height of the knee. We found no relationship between range of motion and function of the knee and the increase in the anterior-posterior height. We found a negative correlation between increase in the anterior-posterior height and preoperative anterior-posterior height. FPV patellofemoral replacement results in correct anatomical reconstruction of the trochlear height rather than 'overstuffing' of the patellofemoral joint. There is an increase in anterior-posterior height of the knee but this does not affect range of movement or clinical outcome.