THE EFFECTS OF LOW MEDIAN NERVE BLOCK ON THUMB ABDUCTION STRENGTH

The relative contributions of the abductor pollicis longus (APL) and a bductor pollicis brevis (APE) to thumb abduction strength (TAS) were d etermined after a selective nerve block in 21 normal volunteers. The m edian nerve was anaesthetized (Mocked) at the wrist. Needle electromyo graphy verified paralysis of the APE and usually the opponens pollicis ; in 6 study subjects, the superficial head of the flexor pollicis bre vis (FPB) was also paralyzed. The APL, innervated by a branch of the p osterior interosseous nerve, remained functionally intact. TAS was mea sured by a mechanical device before and after median nerve block. Medi an nerve block at the wrist resulted in a dramatic decrease in TAS in all volunteers. The mean loss of TAS was 70.3% in men and 74.3% in wom en. Postblock TAS tended to be greater in those subjects with retained function of the FPB. This study verifies that TAS is primarily a func tion of the APB.