Bilateral reversed Palmaris longus muscle with trifid insertion – A rare variation

The palmaris longus muscle (PL) is described as probably the most variable muscle in the human body, being variable both in number and form. 1 It can be absent in about 11% of bodies and this absence is more often in females and on the left side. 1,2 Bilateral absence is more common than unilateral absence. 1 Concerning the kind of muscle, it may be fleshy throughout its entire length or may be digastric. The muscle may have a proximal tendon or a distal one. It may be fleshy distally and tendinous proximally (Palmaris longus inversus), being known as the reversed palmaris longus muscle (RPL). The insertion is also highly variable and the muscle may be attached to the fascia of the forearm, the tendon of flexor carpi ulnaris, the flexor retinaculum, the pisiform or the scaphoid bones, the abductor pollicis brevis muscle, the fascia or muscles of the hypothenar eminence, one of the flexor tendons, or near the metacarpophalangeal joints. 1 The distal end of the PL is of clinical interest because of its possible relationships with the median and ulnar nerves. Usually the anatomical variations of the PL are not symptomatic. Nevertheless, a RPL can cause median nerve compression, 2,3 and less frequently ulnar nerve compression. 4