Background: Operative fixation has become increasingly more common for treatment of hand fractures. The dorsal cutaneous branch of the ulnar nerve (DCBUN) is a distal sensory branch of the ulnar nerve. Iatrogenic injuries during surgery were reported in previous study. Although many authors have described the DCBUN anatomy at the wrist, our review of the literature did not reveal any reports that define the relationship between DCBUN and the fifth metacarpal bone.

Objective: To investigate the anatomical relationship between the DCBUN and the fifth metacarpal bone.

Materials and Methods: Thirty-one fresh cadavers were dissected. The number and distribution of DCBUN branches relative to the ulnar styloid and imaginary point of the fifth metacarpal bone were recorded.

Result: In 29 specimens, the DCBUN had 2 branches while the rest had 3 branches. The mean distance from the origin of DCBUN to the ulnar-most base of the bone in dorsal view (point A) was 7.41 cm. The mean distance from the DCBUN branching point to point A was 2.83 cm. The most ulnar branch of DCBUN innervated to subcutaneous border along the most ulnar and palmar side of the bone. The mean proportion of the length between point G, where the most radial branch crosses over the most radial side of the bone and the radial-most base of the bone in dorsal view (point B) (GB), and the length of the most radial side of the bone between base (point B) and head (point D) (BD) was 0.15 (range: 0.0-0.45).

Conclusion: The results of this study suggest the safe area for making a skin incision to be at the mid-axial ulnar side of the fifth metacarpal bone to prevent ulnar branch injury. A dorsal skin incision over the proximal half of the fifth metacarpal bone may injure the radial branch.

Keywords: Ulnar nerve, dorsal cutaneous branch of the ulnar nerve, fifth metacarpal bone, ulnar styloid, DCBUN