Distribution pattern of the deep branch of the ulnar nerve in the hypothenar eminence

The deep branch of the ulnar nerve (DBUN) was carefully dissected, using gross and microtechniques, in 21 fresh frozen cadaver upper extremities. This study emphasized branching patterns of the DBUN to the hypothenar muscles and the interrelationship of variations in hypothenar muscle anatomy and DBUN branching patterns. The DBUN generally passed between the abductor digiti minimi and the flexor digiti minimi, and then through the interval between superficial and deep layers of the opponens digiti minimi on its course to the deep palm. Innervation of the hypothenar muscles was by one to four branches of the DBUN. The most common distribution pattern was two major branches, which occurred in 14 (66%) of the specimens. Of these 14 specimens, nine exhibited normal hypothenar muscle anatomy, suggesting a prevalent relationship between three normal muscles and two nerve branches. One main branch occurred in four (19%) specimens, three branches occurred in two (9%) specimens, and four branches occurred in one (4%) specimen. Anatomic variations in the hypothenar muscles were significant, the most notable being the absence of flexor digiti minimi in eight (38%) of the specimens.