Unusual bilateral muscular variation in the medial forearm: separate humeral and ulnar bellies of flexor carpi ulnaris and anomalous muscle addition

Abstract

We report herein an unusual bilateral variation in musculature of the medial forearm discovered during routine anatomical dissection. On the left side there was complete separation of humeral and ulnar bellies of the flexor carpi ulnaris, while on the right there was an anomalous muscle addition from the medial epicondyle extending to the hamate. In the left forearm, tendons of both humeral and ulnar bellies remained separate until insertion on the pisiform and an extratendinous slip passed laterally from the humeral head to insert on the hamate. On the right, the flexor carpi ulnaris only had minor connection to the medial epicondyle and was essentially ulnar in origin. The anomalous muscle originated entirely from the medial epicondyle and was innervated predominantly by the median nerve. Before insertion on the hamate, an extratendinous slip passed medially to insert on the tendon of flexor carpi ulnaris. Additional variations associated with the flexor carpi ulnaris are discussed and importance of these muscular variants evaluated.