A Bitendinous Palmaris Longus: Aberrant Insertions and Its Clinical Impact - A Case Report

Abstract

During routine anatomical dissection, we encountered a unilateral variation in the insertion of Palmaris longus tendon on the right upper limb of an 82-year-old formalin embalmed, male cadaver. The fusiform muscle belly of Palmaris longus with dimensions 17.5×1.5×0.95 cm, proximally originated from medial epicondyle of the humerus, along with the other superficial flexor muscles of forearm. The muscle belly prolonged downwards into two separate well-formed flattened tendons at the middle of the forearm, 9 cm proximal from wrist, ran towards the wrist covering flexor digitorum superficialis and median nerve, on the medial side of flexor carpi radialis tendon [Table/ Fig-1a]. The superficial tendon was thicker, size 10.5×0.75 cm, passed over the flexor retinaculum, and at the distal half of the retinaculum, it is divided into three slips. The central slip, thick, broad and shiny, appeared to be the main continuation, merged with apex of the flattened palmar aponeurosis. The lateral collateral slip, thicker and stronger, was fused with the deep fascia covering abductor and flexor pollicis brevis muscles and contained few muscle fibres of origin of these muscles. The medial collateral slip, relatively small and thin, merged with deep fascia covering abductor and flexor digiti minimi [Table /Fig-1b]. The deep tendon was relatively thin, size 9.5×0.5 cm, passed deep to flexor retinaculum and faned out to merge with transverse tendinous fibres of flexor retinaculum [Table /Fig-1c].The Palmaris longus tendon on the left side of forearm was normal as in textbook morphology. DisCussionPalmaris longus, a superficial flexor of the forearm, arises from medial epicondyle of humerus by the common flexor origin, from adjacent intermuscular septum, and also from antebrachial fascia. The slender, fusiform belly converges into a long flattened tendon in the middle of the forearm, runs on the medial side of flexor carpi radialis, crosses the wrist superficial to flexor retinaculum, and terminates into a flat palmar aponeurosis. A few fibres interweave with the transverse fibres of the flexor retinaculum. It is supplied by median nerve of brachial plexus through C7 and C8 segments of spinal cord.It is a week flexor of metacarpo-phalangeal and carpometacarpal joints, but mainly anchor the skin and fascia of the hand and in resisting the horizontal shearing forces in distal direction, as in holding a golf club [1]. The most frequent variations include complete absence in one or both sides; anomalies in the form and location of

Clinical Application of Anomalous Muscles for Tendon Transfer in the Upper Limb: A Systematic Review of the Literature

“…Anomalies of flexor and extensor tendons are relatively common in the upper extremity. They have been widely reported in the literature with various terms such as anomalous muscle, supernumerary muscle, or accessory muscle [3,4,6,21,22]. It is not uncommon to encounter such a muscle incidentally during a routine tendon transfer surgery, which presents a challenging situation for the surgeon to decide on how to proceed.…”

“…Numerous authors have recognized various muscular anomalies and incidence and respective patterns in the upper extremity. Most of the studies were either about anatomical findings in cadavers or those found incidentally in the operating field [2][3][4][5][6][7][8][9][10][11]. Although the majority of anomalous muscles are asymptomatic, they may occasionally produce persistent pain, unexplained mass, or compression neuropathy necessitating surgical excision [7,8,[11][12][13][14][15][16][17].…”

Hypertrophied reverse palmaris longus muscle: a rare cause of carpal tunnel syndrome

“…The PL is characterized by high-morphological variability including presence of an accessory muscle belly, occurrence of the reversed muscle, fusion with other muscles, the presence of an atypical tendon course, and inserts or bifurcated/multiple tendinous insertions. 19,[24][25][26][27][28][29][30]…”

A Cadaveric Study on Variations of Palmaris Longus and Its Clinical Significance

“…As the forelimbs became prehensile, the functions of Palmaris longus has been taken over by intrinsic muscles of hand. 3 In humans, it is a weak flexor of metacarpophalangeal and carpometacarpal joints, cupping of the palm, tensor of palmar aponeurosis. However, its absence does not significantly affect the strength or grip of the hands.…”