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.
Highlights
The flexor pollicis longus muscle (FPL) is one of the deep muscles of the forearm
Macalister [8] and Wood [2] have noted the unusual origin of first lumbrical muscle from the additional tendinous slip of FPL
Kumar et al have reported the cases of presence of an additional muscle belly from the FPL [10]
Summary
The flexor pollicis longus muscle (FPL) is one of the deep muscles of the forearm. It originates from the grooved anterior surface of the radius and from the adjacent interosseous membrane and gets inserted to the base of the distal phalanx of the thumb [1]. The occurrence of accessory head of the FPL has been reported frequently [2,3,4,5,6,7]. Though FPL is known to present the accessory head frequently, the occurrence of its additional muscle bellies and tendons is very rare. We report an additional muscle belly of FPL having unique mode of insertion. The embryological basis and clinical significance of variant additional belly of FPL are discussed
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