Phasic relationships of the intrinsic and extrinsic thumb musculature.

Dynamic electromyography has proven to be useful in testing patients with spastic disorders who are candidates for tendon transfer or lengthening operations. The purpose of this investigation was to define the normal phasic activity of the thumb muscles during simple, reproducible activities. Fine wire electrode pairs were inserted into the extensors pollicis longus and brevis, abductors pollicis longus and brevis, flexors pollicis longus and brevis, opponens pollicis, adductor pollicis, and first dorsal interosseus of 5 normal subjects. Motions of the carpometacarpal joint and the interphalangeal joint of the thumb were recorded by electrogoniometer. Proximal joint positions were controlled by the subject at the elbow, forearm, and wrist. Normal timing was described for each muscle during hand opening and closing, key pinch with and without force, and opposition pinch with and without force. The data support the concept of individual motor strategies: normal persons often select different combinations of muscles to accomplish a functional goal.