Bitendinous Palmaris Longus Muscle: A Case Report
Journal of Clinical and Diagnostic Research
During routine dissection, a bitendinous PLM was encountered on the left extremity in a female cadaver. Right PLM was normal. Vernier caliper and scale were used to perform the morphometry of the muscle. With a tendinous origin of 6 cm (length) from the medial epicondyle of the humerus to the proximal muscle belly (measuring 7.2 cm in length), the Palmaris longus tendon bifurcated on its course towards insertion. The point of bifurcation of the tendon of insertion was at 6.7 cm from the distal
... cm from the distal end of the muscle belly. From the point of bifurcation, the medial division merged with the distal margin of the Flexor retinaculum and the Palmar aponeurosis, normally. The lateral division inserted into the base of the Thenar eminence [Table/ Fig-1 ]. The length of the lateral and medial divisions of the tendon from the point of bifurcation till insertion was 7 cm and 6 cm, respectively. The length of the tendons of insertion, therefore, was 13.7 cm (with the lateral division) and 12.7 cm (with the medial division). Hence, the total length of the PLM with the lateral and medial divisions was 26.9 cm and 25.9 cm, respectively. The tendon of insertion narrowed in width towards the insertion; the width of the tendon at the distal end of the muscle belly was 0.9 cm, 0.7 cm at the point of bifurcation and both lateral and medial divisions measured 0.5 cm from bifurcation till insertion. exhibited a tendinous origin followed by a short muscle belly and a bifid tendon of insertion with the medial tendon following normal insertion and the lateral one inserting into the base of the thenar eminence. PLM, a weak flexor of the wrist, exhibits interesting variants being the most variable muscle in the body  recording an agenesis of 10%. Among vertebrates, it is restricted to mammals (ruminants, pachyderms, rodents and carnivores) and its absence among higher apes (primates) [2,3], but, its presence in lower groups suggests retrogression due to gradual development of prehension [4,5]. It is best developed when the forelimb performs a weightbearing role. The variations of PLM were classified as: Complete agenesis; Variation in location, Form of the fleshy portion; Aberrancy in attachment at either extremity; Duplication or triplication; Accessory slips; Replacing elements of similar form or position .