Extensor carpi ulnaris: bilateral accessory tendons to the fifth metacarpal

Introduction Awareness of potential variations in muscular organization and routing of tendinous insertions is essential for those in medical education, practice, and research. In the upper limb the extensor carpi ulnaris muscle originates from the lateral epicondyle of the humerus by the common extensor tendon and from the posterior aspect of the proximal half of the ulna to insert on the base of the 5th metacarpal [1]. Several interesting reports of accessory tendon slips arising from extensor carpi ulnaris have been documented, most of which describe variants that arise at the level of the wrist or dorsum of the hand [2–5]. As indicated recently [6], additional studies of accessory tendon slips associated with extensor carpi ulnaris in different populations are needed to ascertain potential extent of variation that may occur in this important muscle of the extensor compartment. We describe an unusual case in which bilateral accessory tendons of extensor carpi ulnaris occurred; the left accessory tendon was of short length similar to aforementioned variants, but on the right it originated from the muscle belly in the mid-forearm. Both variants passed across the dorsum of the hand to insert on the head of the 5th metacarpal medial to and separate from extensor digiti minimi. Case Report Bilateral occurrence of variant tendons arising from extensor carpi ulnaris was observed in an elderly Caucasian female cadaver during routine dissection and preparation of specimens for nursing and allied health anatomy laboratories. In the left upper limb, the tendon variant was identified as it crossed the dorsum of the hand, medial and parallel to the tendon of extensor digiti minimi (Figure 1a). Upon reflection of the extensor retinaculum it was noted that this 8.5 cm slip arose directly from the dorsal aspect of the extensor carpi ulnaris tendon, shared the 6th extensor compartment, and in its course crossed over the insertion of extensor carpi ulnaris (Figure 1b). The accessory tendon was 1 mm in width, consistent in this dimension, and inserted on the head of the 5th metacarpal medial to and separate from extensor digiti minimi. Some terminal fibers blended with the proximal extensor expansion along its medial aspect. As shown in Figure 2a, the right tendon variant arose from a small muscle slip located on the lateral aspect of extensor carpi ulnaris 14 cm distal to its origin from the lateral epicondyle. This 2 cm muscular slip was located near the origin of the muscle’s primary tendon. The tendon variant was 2 mm wide and closely accompanied the tendon of extensor carpi ulnaris on its lateral side, consistent in width throughout Zailene D. FLOOD Dustin J. HAWLEY Mia C. MARSHALL Anthony A. CAPEHART