Musculus lumbricalis pollicis.

Abstract

In six cases of thumb hypoplasia, a muscle arose from the anomalous flexor pollicis longus tendon in the region of the metacarpophalangeal joint, passed across the narrowed first web space, joined the lumbrical belly of the index, and inserted into the extensor hood of that digit. Traction on the muscle at its origin in the thumb produced extension of the interphalangeal joints of the index finger. Because of its attachments and action, this muscle has been given the name musculus lumbricalis pollicis. Not previously described in this form, the muscle is significant in hypoplasia because its contraction will act to narrow the already deficient first web space. In all instances where it was present, the musculus lumbricalis pollicis was excised.