The association of radiographic foot osteoarthritis and radiographic osteoarthritis at other sites.

OBJECTIVE: To quantify the association between radiographic foot osteoarthritis (OA) and radiographic OA at four joints: second distal interphalangeal (DIP), third proximal interphalangeal (PIP), first carpometacarpal (CMC), and the knee.
METHODS: Data collected for the Clearwater Osteoarthritis Study (COS) were analyzed (N=3436). The study outcome was first metatarso-phalangeal joint (first MTP) OA status. The predictor variables were second DIP, third PIP, first CMC, and knee OA. The Kellgren and Lawrence scale determined OA status. The strength of the association between foot OA and other sites was further explored by unilateral and bilateral categories.
RESULTS: For both genders, we found a significant, positive relationship between grade 2+ foot OA and second DIP, third PIP, first CMC, and knee OA. This relationship maintained its significance after adjustment for age, body mass index, and occupational history. Adjusted odds ratios ranged from 3.2 for the second DIP joint (P<0.0001) to 3.7 for the knee joint (P<0.0001). Relative to unilateral joint disease, co-existing bilateral disease yielded a significantly elevated risk for foot OA for all joints examined. While other studies have not specifically examined co-occurrence with foot OA, our findings are consistent with results from related studies.
CONCLUSIONS: There is a dearth of studies exploring foot OA. Our findings support the theory of a systemic etiology involved in the development of OA. Future epidemiological studies that further distinguish the relationship between OA at differing sites will provide an enhanced ability to describe the respective influences of mechanical and systemic factors in the development of this disease.