Comorbid interphalangeal joint pain and erosive osteoarthritis are associated with worse hand function in individuals with symptomatic thumb base OA

OBJECTIVE: Hand osteoarthritis (OA) trials often target exclusively the thumb base joint, although concomitant widespread interphalangeal (IP) joint involvement is frequent. We aimed to compare hand strength and function between individuals with isolated thumb base OA and those with coexistent IP joint pain and erosive OA. METHODS: Baseline data from a thumb base OA trial were analyzed (n = 204). Participants were age >/=40 years with symptomatic and radiographic thumb base OA. Only the index hand was included. Self-reported IP joint pain (in any proximal, distal, or thumb IP joint), hand function score (Functional Index for Hand Osteoarthritis questionnaire [range 0-30]), and hand grip and tip-pinch strength test results were obtained at baseline. Radiographs were scored for OA severity at each joint (Kellgren/Lawrence grade) and for the presence of erosive OA at the thumb base or IP joints. Multiple linear regression was used adjusting for age, sex, body mass index, and radiographic thumb base OA severity. RESULTS: Compared to individuals with isolated thumb base OA (62%), those with concomitant IP joint pain (17%) and erosive OA (21%) had significantly worse hand function (beta = 1.82 [95% confidence interval (95% CI) 0.36, 3.28] and beta = 1.47 [95% CI 0.74, 2.88], respectively). In addition, coexistence of erosive OA was independently associated with lower grip and tip-pinch strength (beta = -5.14 [95% CI -7.58, -2.70] and beta = -0.61 [95% CI -1.05, -0.17], respectively). CONCLUSION: Concomitant IP joint pain and erosive OA are associated with worse hand function in individuals with thumb base OA. Patient stratification based on these characteristics may improve the design of future thumb base OA trials.