Supernumerary tendons of the abductor pollicis.

During a study of variants of the tendon of the abductor pollicis longus (APL) muscle, in 1 of 110 upper extremities prepared, we recorded the rare finding of a division of the APL muscle tendon into 7 sections in the first tunnel. Whereas the actual main tendon inserted at the base of the first metacarpal bone, as depicted in the textbooks, the supernumerary tendons attached to the fascia of the opponens pollicis muscle to the radial edge of the abductor pollicis brevis muscle and to the dorsoradial third of the base of the first metacarpal bone. All accessory tendons were arranged in a radial formation around the main tendon within the same synovial sheath, but the main tendon occupied a separate compartment. In 80% of the upper extremities prepared for this study, the classical description of the abductor tendon did not apply. The classical representation of a single abductor tendon applied to only 20% of the upper extremities examined. In about one third of the wrists prepared, the first tunnel was clearly divided by a septum, so that 2 or more osteofibrous tunnels were present within the main tunnel. The number, thickness and length of such accessory tendons have a functional significance in the development of de Quervain's stenosing tendovaginitis and possibly also have a practical significance, as they may be regarded as a source of transplant material for plastic reconstructions.