[Extensor indicis muscle as a replacement for the abductor pollicis longus muscle. A case report].

The abductor pollicis longus muscle is very important for the function of the thumb. Its deficit hinders grasping bigger objects. Therefore, the reconstruction of the APL tendon is important in chronic injuries. The interposition of a tendon graft is considered the best method. However, the muscle loses its contractility very quickly because of its small gliding amplitude. Consequently, this procedure is only usable in the first six to eight weeks after injury. Later the function of the abductor pollicis longus muscle can only be recovered by a tendon transposition. The described tendon transposition methods the palmaris longus tendon, the flexor carpi radialis tendon and the radial half of the extensor carpi radialis longus tendon--do not fulfill the requirements of a good tendon transposition. Functional considerations may make the extensor indicis muscle the best substitution for the abductor pollicis longus. There is no disturbance of the function of the index finger by loss of the extensor indicis muscle. Both the extensor indicis and the abductor pollicis longus are functional synergists and are under voluntary control of the brain. By mobilization of the extensor indicis, abductor pollicis longus strength can be approached. A difference exists in the gliding amplitude of both muscles. The gliding amplitude of the extensor indicis is 55 mm while that of the abductor pollicis longus is 28 mm. If the extensor indicis muscle is placed under moderate tension the gliding amplitudes are identical. The strength of the abductor pollicis longus is 0.092 kp/m. The strength of the extensor indicis is unknown.(ABSTRACT TRUNCATED AT 250 WORDS)