Background: We have observed that patients with restricted thumb opposition sometimes develop dysfunction of the intrinsic muscles around the metacarpal joint of the middle finger. Therefore, we developed a middle finger abduction exercise program which focuses on improvement of intrinsic muscle function during post-operative rehabilitation after thumb carpometacarpal arthroplasty. We report on the efficacy of the program herein.

Methods: Three patients with Eaton stage III-IV thumb carpometacarpal arthritis were included in the study. The effects of the exercise program were recorded. Ultrasonography and surface electromyography were used to evaluate the effects of the exercise in two healthy volunteers.

Results: Five minutes of exercise resulted in a 1- to 2-point improvement in the Kapandji opposition score, and a 1- to 3-cm improvement in thumb opposition to the base of the small finger. Ultrasonography and electromyography revealed that adductor pollicis, abductor pollicis brevis, opponens pollicis, and abductor digiti minimi contractions became more synchronous.

Conclusion: Our middle finger abduction exercise program improves thumb opposition significantly. The program may be particularly useful for post-operative rehabilitation after thumb surgeries: thumb opposition can be improved without thumb motion, which can be painful in the early post-operative period.