VARIATIONS IN THE TENDONS OF THE INSERTION OF THE ABDUCTOR POLLICIS LONGUS AND EXTENSOR POLLICIS BREVIS

Among 150 Chinese forearms dissected, an accessory tendon or tendons in the abductor pollieis longus muscle were found in 140 sides (93.3%), while in the rest (6.7%) the anomaly did not exist. In these 140 forearms, one accessory tendon was found in 97 (64.7%)and in the remaining 43 (28.7%) two accessory tendons were present. As regards the extensor pol- licis brevis muscle, one accessory tendon was found in only two cases (1.3%) in the whole series. It was noted that the two tendons of the abductor pollicis longus and extensor pollicis brevis pass through the same osteofibrous canal in 59 (39.4%), through two completely separated osteofibrous canals in 12 (8%), and in 79 out of the 150 forearms dissected. The two osteofibrous canals were partially separated as follows: in 32 (21.3%), the distal half only was separated by a thick fibrous band while in the other 47 (31.3%) only the distal third or even less was separated. The insertions of the main tendon and accessory tendons of the abductor pollicis longus muscle was even more extensive and complicated. Only in 3 cases the insertion could be regarded as normal, in the other 147 (98%), the insertion was either into the base of the 1st metacarpal bone, the abductor pollicis brevis muscle, the capsule of the 1st carpo-metacarpal joint, the greater multangular bone, the opponens pollicis muscle, the fascia over the thenar eminence or the navicular bone. The implications of the variations were discussed.