Sebileau's muscle is an anatomical variant, an accessory muscle slip found in the forearm. It is not a consistently present, major named muscle but rather an additional component observed in a percentage of individuals.
Anatomy and Location Typically, Sebileau's muscle originates from the anterior surface of the ulna or radius, often close to the interosseous membrane or the pronator quadratus muscle. Its fibers then course distally to insert into the tendon of the flexor pollicis longus muscle (FPL), which is responsible for flexing the thumb. Due to its position and insertion, it is considered an accessory head or slip of the flexor pollicis longus.
Function When present, Sebileau's muscle contributes to the action of the flexor pollicis longus, assisting in the flexion of the interphalangeal joint of the thumb. Its functional significance is generally minor given its variant nature and integration with the primary thumb flexor.
Clinical Significance As an anatomical variation, Sebileau's muscle is primarily of interest to anatomists and surgeons. While often asymptomatic, accessory muscles in the forearm can occasionally contribute to compression syndromes or be encountered unexpectedly during surgical procedures in the wrist and hand. Its presence may be noted during dissection or advanced imaging studies.
Etymology The muscle is named after Pierre Sebileau (1860-1953), a French anatomist and surgeon, who described this anatomical variation.