A unique case of mid-tendon palmaris longus muscle – dissection presentation and literature review

The palmaris longus (PL) muscle is one of five muscles that originates from the common flexor tendon, which attaches at the medial epicondyle of the humerus, and has its own insertion distally into the palmar aponeurosis. Although the PL contributes minimal biomechanical function, its wide anatomic variation can produce pathologies in the forearm and wrist such as median nerve entrapment. The present work describes a unique case of a PL distally migrated muscle belly with wide tendon both proximal and distal not noted in other anatomical or surgical reference materials. Herein, the current case is compared to previously reported PL variations and their documented frequencies by region and ethnicity. Key findings include several studies showing Caucasian populations with greater than 25% frequencies of absent PL, compared to 4-6% in African regions. Potential explanations for this finding include evolutionary adaptations associated with manual labor and need for increased grip strength. In addition, the considerations of abnormal PL in surgical procedures inclusive of challenges in graft procedures that might present with such anatomic variations of the PL are examined.