The Association of Index-to-Ring Finger Ratio With Trapeziometacarpal Joint Osteoarthritis in an Elderly Korean Population

Objective Index-to-ring finger ratio (IRFR) has been reported to be associated with joint osteoarthritis (OA). We aimed to evaluate the association between IRFR and trapeziometacarpal joint (TMCJ) OA in an elderly Korean population. Methods A population-based sample included 604 participants with a mean age of 74.8 years. IRFR was radiographically measured by the ratio of the length of the right second to fourth phalangeal bones (“phalangeal IRFR”) and metacarpal bones (“metacarpal IRFR”), and was visually classified as either type 1 (index finger longer than or equal to ring finger) or type 2 (index finger shorter than ring finger). Odds ratios (ORs) for the presence of OA (Kellgren-Lawrence [KL] grade > 1) and for severe OA (KL grade > 2) were analyzed using logistic regression. Results The phalangeal IRFR averaged 91.3%, the metacarpal IRFR 116.7%, and 304 out of 604 participants (50.3%) had type 2 IRFR. We found TMCJ OA in 112 participants (18.5%), and severe TMCJ OA in 33 participants (5.5%). Presence of TMCJ OA was significantly associated with age (OR 1.04; 95% CI 1.01-1.06) and metacarpal IRFR (OR 0.94; 95% CI 0.88-0.99), and severe TMCJ OA with age (OR 1.08; 95% CI 1.03-1.12) and type 2 IRFR (OR 3.07; 95% CI 1.13-8.33). Conclusion Radiographic IRFR, specifically metacarpal IRFR, was associated with the presence of TMCJ OA, and visual IRFR with severe TMCJ OA in both elderly Korean men and women. The results of this study suggest that IRFR might serve as an easily measurable biomarker to identify patients vulnerable to TMCJ OA.