Objective: Cartilage loss is a key pathological feature of OA and can be assessed indirectly using radiography or directly through MRI. A number of cross-sectional studies have suggested that primary generalized osteoarthritis (PGOA) may be a distinct disease, but despite the high frequency of involvement of the hip and the knee joints in OA, very few studies have looked at the radiographic association between these two joints, and none has done so using MRI. The aim of this study was to examine the association of hip and knee cartilage measured by both radiography and MRI.

Methods: We studied 151 participants from the Tasmanian Older Adult Cohort (TASOAC) study, who were selected randomly from the southern Tasmanian electoral rolls. MRI was used to assess hip and knee cartilage volume and radiography was used to assess joint space narrowing (JSN). Correlation analyses were used to compare cartilage volume measurements and JSN.

Results: In adjusted analysis, there was a consistent, positive association between knee and hip cartilage volume that was best for total knee cartilage volume (r = 0.16-0.40, all P < 0.05). In contrast, there was at best a weak correlation, depending on the site, between hip and knee JSN (r = -0.01 to 0.21).

Conclusion: Hip and knee cartilage volume are more strongly associated than hip and knee JSN, suggesting a commonality of cartilage volume at different anatomic sites. The weaker radiographic association may reflect less measurement error with MRI or the contribution of multiple structures to joint space in the knee.