Determinants of change in patella cartilage volume in healthy subjects.

OBJECTIVE: To examine whether the amount of patella cartilage in healthy, middle-aged subjects is stable or changes over time, and what factors may influence the changes. METHODS: Eighty-five subjects (28 men and 57 women, mean age 55.5 yrs) had magnetic resonance imaging of their dominant knee at baseline and 2 years later. Patella and tibial cartilage volume was measured at baseline and followup. Risk factors assessed at baseline were tested for their association with change in patella cartilage volume over time. RESULTS: Mean annual percentage loss of patella cartilage was 2.1 (95% confidence interval: 1.1-3.2; p < 0.001). Age, gender, body mass index, and initial cartilage volume did not affect rate of change of patellar cartilage volume. There was a weak association between change in patellar cartilage volume and change in lateral tibial cartilage volume (R = 0.23, p = 0.03) but not medial tibial cartilage volume (R = 0.09, p = 0.43). CONCLUSION: In healthy subjects, a significant amount of patella cartilage is lost annually. The poor correlation between patella and tibial cartilage loss suggests that pathogenetic mechanisms for osteoarthritis in the patellofemoral and tibiofemoral joint may differ. Further work will be required to determine whether the rate of patella cartilage loss in healthy subjects is steady or phasic, and to determine which factors can be modified to reduce cartilage loss.