Study protocol for a multicenter non-inferiority randomized controlled trial to assess functional outcomes and cost-effectiveness of a primarily non-operative treatment strategy with cast immobilization versus immediate operative treatment followed by cast immobilization for patients with complete ulnar collateral ligament ruptures, including Stener lesions: MUSCAT study.

Background: Guidelines recommend operative treatment followed by cast immobilization for acute complete ulnar collateral ligament (UCL) ruptures, including Stener lesions. This recommendation is based on expert opinion, anatomic theories, and low-quality observational case series. High-quality studies comparing non-operative treatment to operative treatment are lacking. We hypothesize that primarily non-operative treatment with cast immobilization (cast immobilization) is non-inferior regarding functional outcome and carries concomitant lower costs compared with immediate operative treatment followed by cast immobilization (operative treatment) for complete UCL ruptures, including Stener lesions.

Methods: This is a multicenter randomized controlled non-inferiority trial (RCT) including patients of 18 years and above, requiring treatment for an acute complete UCL rupture, including Stener lesions. Patients are randomized to cast immobilization or operative treatment followed by cast immobilization. Immobilization consists of 4 weeks of a non-removable cast around the metacarpophalangeal (MCP) and carpometacarpal (CMC) joint of the thumb in a neutral position, followed by a removable cast for 4 weeks for both groups. Patients in the cast immobilization group are re-evaluated 2 to 3 weeks after the start of cast immobilization to examine thumb stability and determine if secondary surgery is required. In case of persistent laxity, secondary surgery is required. The primary outcome is hand function expressed as the Michigan Hand outcome Questionnaire (MHQ) at 6 months (from injury to 6 months after).

Discussion: If cast immobilization is non-inferior to operative treatment, the proposed treatment strategy will reduce patient burden by preventing surgery. It is expected that about one in ten patients who started with cast immobilization will need secondary surgery during re-evaluation. As a result, completion of the treatment will take longer for these patients compared to patients who received immediate operative treatment.

Trial registration: Central Committee on Research Involving Human Subjects (CCMO), NL78886.100.21; registered on 4 October 2021. Medical Research Ethics Committees United (MEC-U), R21.006; registered on 09 December 2021. Clinical Trial register, identifier: NCT05291260; retrospectively registered on 22 March 2022.