Aims: To investigate the heterogeneous effects of a combination of conservative therapies compared with usual care for thumb base osteoarthritis (OA) according to clinically relevant characteristics.
Methods: Pre-planned subgroup analysis from 204 participants included in a randomized clinical trial which compared a combination of education for joint protection and OA, a splint for the base of the thumb, hand exercises, and topical diclofenac sodium 1% gel, with education for joint protection and OA alone for individuals with radiographic and symptomatic thumb base OA. The primary outcomes were changes in pain (visual analogue scale [VAS], 0-100 mm) and hand function (Functional Index for Hand Osteoarthritis questionnaire, 0-30) from baseline to 6 weeks. Other outcomes were changes in grip and pinch strength, and patient’s global assessment (PGA) (VAS, 0-100mm). Subgroups of interest were the presence of interphalangeal joint pain, erosive hand OA, first CMC joint subluxation assessed on radiograph (mm; > vs. ≤ mean), and baseline radiographic OA severity (Kellgren Lawrence grade). Linear regression models were fitted, adding interaction terms for each subgroup.
Results: Mean age was 65 ± 10 years and 76% were female. The treatment effect of the combined intervention was greater in participants with lower joint subluxation compared with those with higher subluxation (mean between-group difference in pain -11.98 [95%CI -21.03, -2.93] versus 2.06 [-6.32, 10.45], respectively, interaction p-value 0.026; and PGA -10.26 [-20.27, -0.25] versus 4.23 [-5.04, 13.51), respectively, interaction p-value 0.037). There was no statistically significant heterogeneity for the other subgroups or outcomes.
Conclusion: A combination of conservative therapies provided greater benefits over 6 weeks in individuals with lower joint subluxation, although the magnitude of the treatment effect was small. Treatment strategies may need to be customized for those with greater joint subluxation. These results are hypothesis-generating only as the trial was not powered for subgroup analyses.