Effects of Selective Activation of the First Dorsal Interosseous and Opponens Pollicis on Thumb CMC Kinematics

Abstract

Objective: Symptomatic thumb carpometacarpal (CMC) joint osteoarthritis is common. Early data support selective strengthening of the first dorsal interosseous (FDI) and opponens pollicis (OP) muscles for conservative management with improvement in pain and functional outcomes scores. There are limited biomechanical studies to support such strengthening programs. The purpose of these studies was to quantify the kinematics and joint kinetics at the thumb CMC joint during simulated pinch with selective activation of the FDI and OP muscles. The first study was completed with all ligamentous attachments of the CMC joint intact. The second study was completed with all CMC ligaments released. Hypothesis: Our hypothesis was that increased loads in the FDI and OP result in effects to the joint kinematics and reduce subluxation. Results: Our results from both studies show the OP and FDI act synergistically to center the first metacarpal on the trapezium and reduce subluxation during simulated pinch. The OP is the predominant corrective force but tends to overcorrect if unopposed. The FDI tempers the action of OP and contributes to improved CMC congruency. Conclusion: Our conclusion is these biomechanical data support selective thenar muscle re-education and strengthening programs for conservative management of thumb CMC joint osteoarthritis and pain.