Clustering of hand osteoarthritis progression and its relationship to progression of osteoarthritis at the knee.

OBJECTIVE To investigate patterns of osteoarthritis (OA) progression within hand joints and the relationship between hand OA progression and progression of OA at the knee. METHODS Radiographic progression over 6 years, defined as change in osteophytes or joint space narrowing above the smallest detectable change, was assessed on hand and knee radiographs of 236 hand OA patients participating in the Genetics, Arthrosis and Progression (GARP) sibling pair cohort study using OARSI atlas. Clustering of radiographic progression between hand joint groups (DIP, PIP, IP-1 and CMC-1) was assessed using χ(2) test. Symmetry, clustering by row and ray and familial aggregation in sibling pairs were also evaluated. The association between hand OA progression and progression of OA at the knee was assessed using generalised estimating equation analysis. RESULTS There was clustering of OA progression between hand joint groups, the strongest relationship among DIP, PIP and IP-1 joints. Other patterns were symmetry (OR 4.7 (95% CI 3.3 to 6.5)) and clustering by row (OR 2.9 (95% CI 1.9 to 4.6)) but not by ray (OR 1.3 (95% CI 0.7 to 2.4)). There was familial aggregation of hand OA progression. Patients with progression of hand OA had a higher risk for radiographic change at the knee than those without hand OA progression (OR 2.3 (95% CI 1.3 to 4.0)). CONCLUSIONS Progression of hand OA clusters between hand joint groups, especially between IP joints, and within sibling pairs. It is associated with OA change at the knee. These findings contribute to defining hand OA subsets and suggest a role for systemic factors.