Cushioned Insoles for First Metatarsophalangeal Joint Osteoarthritis: Protocol for the SOLE Randomised Controlled Trial

INTRODUCTION: First metatarsophalangeal (MTP) joint osteoarthritis (OA) is a common and disabling condition that causes substantial pain and impairs quality of life. Cushioned insoles have the potential to lower plantar pressures beneath the hallux and possibly reduce pain, but their clinical effectiveness has not been investigated. This study describes the protocol for a randomised controlled trial (RCT) assessing whether daily use of cushioned insoles produces greater reductions in first MTP joint walking pain, and other symptoms, over 12 weeks than sham insoles. METHODS AND ANALYSIS: This two-arm, parallel group, superiority RCT will recruit 108 community-dwelling adults aged 45 years and older with symptomatic radiographic first MTP joint OA. Participants will be randomised to receive three pairs of either cushioned insoles (6 mm low-density ethyl vinyl acetate (EVA)) or visually similar thin sham insoles (2 mm high-density EVA), to be worn for 12 weeks. The primary outcome is the 12-week change in first MTP joint pain during walking, assessed using an 11-point numerical rating scale (0-10, higher scores worse pain). Secondary outcomes include 12-week changes in physical function, other measures of first MTP joint pain, health-related quality of life, physical activity, and fear of movement. Global ratings of change in pain and function will also be assessed at 12 weeks. Other measures will also be collected. Analyses will include all participants as randomised using linear and log-binomial regression adjusted for baseline values. Prespecified sensitivity and moderator analyses will also be conducted. ETHICS AND DISSEMINATION: This study has been approved by the University of Melbourne Greater than Low Risk Human Research Ethics Committee. Findings will provide the first evidence regarding the efficacy of cushioned insoles for the management of first metatarsophalangeal joint OA. Results will be disseminated via peer-reviewed journals, scientific conferences, information on our website and lay summaries for participants. TRIAL REGISTRATION: Prospectively registered on the 14 of December 2023 with the Australian New Zealand Clinical Trials Registry, reference ACTRN12623001304628.