Abstract
The relative contributions of the abductor pollicis longus (APL) and abductor pollicis brevis (APB) to thumb abduction strength (TAS) were determined after a selective nerve block in 21 normal volunteers. The median nerve was anesthetized (blocked) at the wrist. Needle electromyography verified paralysis of the APB and usually the opponens pollicis; in 6 study subjects, the superficial head of the flexor pollicis brevis (FPB) was also paralyzed. The APL, innervated by a branch of the posterior interosseous nerve, remained functionally intact. TAS was measured by a mechanical device before and after median nerve block. Median 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 women. Postblock TAS tended to be greater in those subjects with retained function of the FPB. This study verifies that TAS is primarily a function of the APB.
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