Conservative Treatment With Relative Motion Flexion Orthosis for Boutonniere Injuries in Fingers

Boutonnière injuries involve disruption of the central slip of the extensor tendon over the proximal interphalangeal (PIP) joint (zone III) of the finger. This leads to imbalance in the extensor mechanism, with volar displacement of the lateral bands and progressive development of Boutonnière deformity, characterized by PIP flexion and compensatory DIP hyperextension. Due to the often gradual onset and closed injury mechanism, diagnosis is frequently delayed. If untreated, the condition may result in stiffness, joint contractures, pain, reduced range of motion (ROM), and long-term functional impairment.

Current conservative treatment typically consists of prolonged immobilization of the PIP joint in extension, followed by dynamic orthotic management. Although widely used, evidence supporting existing treatment strategies is limited and outcomes are variable. Treatment is often demanding for patients due to prolonged splinting and restricted hand function during rehabilitation.

The Relative Motion Flexion (RMF) orthosis has been introduced as an alternative treatment strategy aimed at restoring balance within the extensor mechanism while allowing greater functional use of the hand during rehabilitation. However, current evidence is limited to small case series, heterogeneous cohorts, and studies with methodological limitations. Further prospective evaluation is therefore needed.

This study is designed as a prospective longitudinal pilot cohort study with repeated within-subject measurements. The primary purpose is to evaluate feasibility and to generate parameters required for planning a future randomized controlled trial, including estimates of variability in range of motion outcomes and within-subject correlations over time.

The study will also explore preliminary effects of RMF orthosis treatment on finger range of motion, as well as secondary outcomes including pain, grip strength, functional hand limitations, and patient-reported tolerability and adherence.

A total of 25 adult patients with acute or subacute closed central slip injuries (zone III) will be recruited consecutively at the Hand Surgery Rehabilitation Unit, Skåne University Hospital, Malmö, Sweden.

Participants will be treated with an RMF orthosis according to a structured rehabilitation protocol consisting of 6 weeks of continuous use followed by 6 weeks of intermittent use during daytime and nighttime. Treatment is delivered as part of routine rehabilitation follow-up, with adjustments made as clinically indicated.

Outcomes will be assessed at baseline, 3 months, and 12 months after treatment initiation. Primary outcome is range of motion (ROM) measured at the MCP, PIP, and DIP joints using a goniometer. Secondary outcomes include pain intensity (Numeric Rating Scale), grip strength (Jamar dynamometer), hand function (QuickDASH), and a study-specific questionnaire assessing adherence and tolerability. Recruitment rate will be recorded as number of eligible patients included per month.

As a pilot study, no control group is included. Analyses will focus on within-subject changes over time and estimation of parameters needed for sample size calculation in a future randomized controlled trial. Data will be analyzed using descriptive statistics and nonparametric longitudinal methods, including Friedman tests and Wilcoxon signed-rank tests for paired comparisons across time points.

The study will be conducted in accordance with the Declaration of Helsinki. Ethical approval will be sought from the Swedish Ethical Review Authority (Etikprövningsmyndigheten). Written informed consent will be obtained from all participants. All data will be pseudonymized and handled in accordance with applicable data protection regulations (GDPR). The study involves minimal risk, and participants will be monitored throughout the rehabilitation period.

This pilot study will provide essential feasibility data and preliminary clinical outcomes for RMF orthosis treatment. The results will inform the design of a future randomized controlled trial and may contribute to improved evidence-based management of Boutonnière injuries, with the potential to enhance functional recovery and optimize rehabilitation strategies.