Pisi-Palmaris Muscle: An Anatomical Study of a Novel Hypothenar Muscle Variant

The presence of anomalous muscles in the hand are present in around 22-35% of individuals, leading to potential clinical implications. During a routine cadaveric dissection of a 72 year old male, a unique hypothenar muscle variant was identified: the pisi-palmaris muscle. Detailed dissection and literature review determined the origin, insertion, and relationships of the muscle. The pisi-palmaris originated from the pisiform bone, deep to the tendon of the flexor carpi ulnaris and the volar carpal ligament, and inserted onto the transverse carpal ligament, merging with fibers of the abductor and flexor digiti minimi muscles. Based on its distinguishing anatomical features, we believe this muscle represents a previously unreported anatomical variant. Given its proximity to the ulnar nerve within Guyon's canal, this variant may contribute to ulnar nerve compression. Recognizing its presence may decrease the risk of diagnostic error or iatrogenic injury during nonoperative interventions or surgical decompression and improve patient outcomes and guide treatment. LEVEL OF EVIDENCE: V.