Materials and Methods: The institution’s prospective database of unicompartmental knee replacements was reviewed for all Oxford Phase III Unicompartmental Knee Replacement (Biomet, UK) undertaken from January 2004 to July 2007. This identified a total of 645 procedures undertaken. We included all cases where there was pre-operative skyline radiographs and American Knee Scores, Oxford Knee Score and SF-12 data, in addition to skyline radiographs, OKS and SF-12 data with a minimum of 2 years follow-up. All patients without this baseline and follow-up data were excluded. This provided a total of 196 knees (162 patients)

Using Altman’s nomogram, the sample size was calculated to be 85 for a power of 90%, with an α significance level of 0.05.

Using this database, digital radiographs were assessed using the institution’s PACS system. Pre-operative and follow-up skyline radiographs following Jones et al’s (1993) patellofemoral scoring system were examined by four assessors utilising Jones’ patellofemoral scoring system. In addition, in cases where patellofemoral joint changes were evident, each assessor acknowledged whether this involved the medial, lateral or bilateral aspects of the patellofemoral joint.

Intra-observer reliability was made comparing the four assessors.

Statistical analysis was performed, using the Statistical Package for the Social Sciences (SPSS) 16.0 for Windows (SPSS Inc, Chicago, Illinois).

In order to determine whether changes in patellofemoral joint status related to patients function or quality of life, the difference in OKS and SF-12 from pre-operative to the follow-up period was assessed.

Results: There was a statistically significant progression of patellofemoral osteoarthritis as found on the preoperative and postoperative radiographs (p< 0.01, Mann Whitney), there was a correlation between a low OKS and Jones patellofemoral score (P< 0.05, Mann-Whitney). However, there was no correlation between the site of patellofemoral involvement and outcome scores.

Conclusion: Due consideration should be taken when offering medial unicompartmental knee replacement to patients with patellofemoral involvement and this is independent of the site of patellofemoral involvement.