Multiple tendons of the additional belly of flexor pollicis longus in the carpal tunnel: Embryological perspective and their clinical significance

Abstract

Although the flexor pollicis longus is known to show the additional head of the origin, the occurrence of its additional tendons in the carpal tunnel are seldom reported. The presence of such additional tendons in the carpal tunnel cannot be overlooked during the radiological and surgical procedures in this region. Herein, we report a rare case of additional muscle belly of flexor pollicis longus. The additional muscle belly after a short course divided into three tendons. All three tendons entered the carpal tunnel along with flexor pollicis longus, passing deep to the flexor retinaculum. Within the carpal tunnel, two of these tendons fused and terminated by merging with the undersurface of the flexor retinaculum. The third tendon terminated by joining the flexor digitorum superficialis tendon for the index finger, in the palm. An additional slip of the first lumbrical muscle took origin from the third tendon of the additional muscle belly of flexor pollicis longus. Further, the embryological basis and clinical significance of current case is discussed.