PHASIC RELATIONSHIPS OF THE INTRINSIC AND EXTRINSIC THUMB MUSCULATURE

Dynamic electromyography has proven to be useful in testing patients w ith spastic disorders who are candidates for tendon transfer or length ening operations. The purpose of this investigation was to define the normal phasic activity of the thumb muscles during simple, reproducibl e activities. Fine wire electrode pairs were inserted into the extenso rs pollicis longus and brevis, abductors pollicis longus and brevis, f lexors pollicis longus and brevis, opponens pollicis, adductor pollici s, and first dorsal interosseus of 5 normal subjects. Motions of the c arpometacarpal joint and the interphalangeal joint of the thumb were r ecorded by electrogoniometer. Proximal joint positions were controlled by the subject at the elbow, forearm, and wrist. Normal timing was de scribed for each muscle during hand opening and closing, key pinch wit h and without force, and opposition pinch with and without force. The data support the concept of individual motor strategies: normal person s often select different combinations of muscles to accomplish a funct ional goal.