Immobilisation versus early active motion following primary flexor pollicis longus tendon zones 1-2 repair: protocol for a registry-based multicentre randomised controlled trial in Sweden.

INTRODUCTION: Flexor pollicis longus (FPL) tendon injuries in the thumb are surgically challenging and require careful postoperative rehabilitation to avoid complications such as tendon rupture, stiffness and impaired hand function. Rupture rates after FPL repairs are substantially higher than those reported for finger flexor tendons. Although controlled early active motion (EAM) is widely used following FPL repairs, rehabilitation protocols developed for finger flexor tendons may not be directly transferable to the thumb because of differences in anatomy, biomechanics and functional demands. This study investigates whether immobilisation for 4 weeks postoperatively can reduce rupture rates without compromising functional outcomes after FPL injuries.

METHODS AND ANALYSIS: This registry-based randomised controlled unblinded superiority trial will be conducted across five academic hand surgery centres. Patients aged 15 years or older with a complete FPL injury in zone 1 or 2 will be included. Participants will be randomised 1:1 to either the EAM group, in which training starts 2–5 days postoperatively with protection by a dorsal cast and a volar removable splint or the casted immobilisation group for 4 weeks. After 4 weeks, the same rehabilitation protocol will be introduced for both groups. The primary outcome is the frequency of tendon rupture over 12 months. The secondary outcomes include patient-reported outcome measurements and patient-reported satisfaction, active range of motion of metacarpophalangeal and interphalangeal joints, grip and key pinch strength at 3 and 12 months postoperatively. All data are collected within the Swedish National Quality Registry for Hand Surgery. The primary outcome will be analysed on an intention-to-treat basis using a stratified analysis (stratified by centre), with the absolute risk difference and relative risk reported with 95% CIs. Secondary outcomes will be analysed using generalised estimating equations and standard tests for continuous and ordinal data, with results presented as effect estimates with 95% CI.

ETHICS AND DISSEMINATION: The trial was approved by the Swedish Ethical Review Authority (2025-00730-02). All participants are asked to provide written informed consent. The results will be disseminated as published articles in peer-reviewed journals.

TRIAL REGISTRATION NUMBER: NCT06836349.