An independent extensor of the ring finger muscle coexisting with extensor indicis duplicated tendons: embryological considerations and clinical implications

The posterior compartment of the forearm contains muscles that enable independent and group extension of the digits. The ring finger is known to be extended by the extensor digitorum communis only. This case report provides evidence of an independent extensor of the ring finger (ERF) muscle, which co-existed with the duplicated tendons of the extensor indicis (EI) muscle unilaterally. An incidental finding during the routine dissections of the posterior compartments of the forearm and the dorsum of the hand is presented. An independent ERF muscle originated from the intermuscular fascia between the muscle bellies of the EI and extensor carpi ulnaris and inserted onto the dorsal expansion of the ring finger. The EI muscle had duplicated tendons that inserted onto the dorsal expansion of the index finger. Both ERF and EI muscles were innervated by the deep branch of the radial nerve and were supplied by muscular branches of the posterior interosseous artery. This report provides photographic evidence of an independent ERF muscle that can enable independent extension of the ring finger. The ERF muscle could be a result of embryological developmental errors of the posterior compartment of the forearm muscles. Clinically, knowledge of these rare variations may be important for the appropriate evaluation and management of the conditions affecting the posterior aspect of the wrist and hand. • An independent extensor of the ring finger was discovered unilaterally. • Extensor indicis duplicated tendons were discovered unilaterally. • Neurovasculature of the extensor of the ring finger and extensor indicis. • Embryological considerations of the extensor ring finger and extensor indicis. • Extensor of the ring finger and extensor indicis clinical implications.