Effect of first dorsal interosseous strengthening on clinical outcomes in patients with thumb osteoarthritis: a study protocol for a randomized controlled clinical trial

BACKGROUND: Thumb carpometacarpal osteoarthritis (CMC OA) is characterized by chronic progressive degeneration of the joint cartilage, with high prevalence. Patients present with pain at the base of the thumb, morning stiffness, and muscle weakness, symptoms that affect hand function and therefore interfere in activities and social participation. Movements that involve grip or lateral pinch are the most affected and directly impact independence, self-care, and leisure activities. In the literature consulted, several protocols with exercises for these patients were found. However, most do not compare the same intervention modality and only provide basic methodological information, with no consistent information on training load and load progression. In addition, most protocols only address the strengthening of the abductor and extensor thumb muscles and pinching or grasping exercises. However, some biomechanical and electromyographic studies have demonstrated the important role of the first dorsal interosseous muscles as stabilizers of the thumb carpometacarpal joint. METHODS: This is a randomized, controlled, double-blind, and parallel clinical trial that will include 56 participants, over 40 years old, with radiographic evidence of thumb base osteoarthritis. Participants will be randomly allocated into two groups: control and intervention. The following evaluations will be conducted: the Australian/Canadian Hand Osteoarthritis Index, Canadian Occupational Performance Measure, Nine-Hole Peg Test, grip and pinch strength associated with muscle activation assessment, and Bilateral Upper Limb Function Test at four different times: baseline, session 13, session 18, and follow-up. Treatment will take place over 6 weeks, with reassessments in the fourth and sixth weeks and 3 months after the end of the intervention (follow-up). Qualitative variables will be expressed as frequency and percentage, and quantitative variables as mean and standard deviation. Intergroup comparison of the intervention will be performed by repeated measures ANOVA, considering the effect of the two groups and four assessments, and interactions between them. DISCUSSION: This study will demonstrate whether the specific strengthening of the first dorsal interosseous muscle has a superior and positive effect on the clinical picture of patients with CMC OA. Additionally, if specific strengthening of the muscle is not superior to the traditional protocol in the literature, it will also be determined whether the two protocols are equivalent in terms of the best clinical picture. TRIAL REGISTRATION: Brazilian Registry of Clinical Trials (ReBEC) RBR-8kgqk4. Prospectively registered on 15 January 2020