Comparison between patella cartilage volume and radiological assessment of the patellofemoral joint.

OBJECTIVES There is no information on how patella cartilage relates to the radiological grade of individual features of patellofemoral osteoarthritis (osteophytes or joint space narrowing) which have been used in most epidemiological and clinical studies. In this study we compared patella cartilage volume as measured by magnetic resonance imaging (MRI) with radiological assessment of the patellofemoral joint. METHODS 157 subjects with specific features of patellofemoral osteoarthritis (osteophytes and joint space narrowing) ranging from grade 0-3 were examined (age 62 +/- 10 years, 62% female). Each subject had skyline and lateral patellofemoral radiographs performed. Patella cartilage volume was determined by processing images acquired in the sagittal plane using T1-weighted fat saturated MRI at an independent work station. RESULTS Grade of joint space narrowing (JSN) as measured on skyline and lateral patellofemoral radiographs was inversely associated with patella cartilage volume. After adjusting for age, gender and body mass index, for every increase in grade of skyline JSN (0-3), the patella cartilage volume was reduced by 411 mm3. For every increase in lateral patellofemoral JSN grade (0-3), the adjusted patella cartilage volume was reduced by 125 mm3. The relationship was stronger for patella cartilage volume and skyline JSN (r = -0.54, p < 0.001) than for lateral patellofemoral JSN (r = -0.16, p = 0.015). There was no significant association between patella cartilage volume and osteophytes measured on skyline or lateral radiographs. CONCLUSIONS There is a significant negative association between patella cartilage volume and JSN, but not osteophytes. This association was strongest for the skyline rather than lateral radiographs. Longitudinal studies will be needed to determine the role of patella cartilage measurement in assessing progression of patellofemoral osteoarthritis.