High baseline pain is associated with treatment adherence in persons diagnosed with thumb base osteoarthritis: an observational study

Background: Thumb osteoarthritis (OA) is a common and disabling condition. Adherence to prescribed conservative interventions may affect outcomes of thumb OA trials. Purpose: The aim of the study was to determine whether baseline pain and hand function is associated with treatment adherence over 12 weeks in participants with thumb base OA. Study design: Observational cohort study nested within a randomized-controlled trial. Methods: Ninety-four participants from the intervention group were included in the analysis. Baseline pain and function were assessed using a 100 mm Visual Analogue Scale and the Functional Index for Hand Osteoarthritis questionnaire (0-30), respectively. Participants received a combination of treatments including education, orthosis, hand exercises, and topical anti–inflammatory gel. Adherence was measured using a daily self-reported diary. Participants were classified as non–adherent, partially adherent or fully adherent if they completed none, 1 and/or 2 or all 3 of the interventions as prescribed. Ordinal logistic regression modelling was performed. Results: At 12-week follow-up, half of the participants were fully adherent to the treatments (n = 46, 48.9%), 30.9% of participants were partially adherent (n = 29) and 20.2% were non–adherent (n = 19, 20.2%). High baseline pain was a significantly associated with better adherence in the unadjusted model [OR = 3.15, 95% CI (1.18, 8.42)] and adjusted model [OR = 3.20, 95% CI (1.13, 8.20)]. Baseline function was not associated with adherence [OR = 1.03, 95% CI (0.47, 2.23)]. Conclusion: High baseline pain was associated with better adherence in participants with thumb base OA. Higher baseline functional impairment was not associated with better adherence.