Ulnar Nerve Injury during Treatment of Fourth and Fifth Metacarpal Fractures: A Case Report and Anatomical Review.

The deep branch of the ulnar nerve (DBUN) is a pure motor nerve. It passes through a hypothenar fibromuscular tunnel and courses radially on the interossei surface. The DBUN is not frequently considered during hand fracture surgery, despite the anatomical course of the nerve in close relation to the carpal and metacarpal bones, which makes it vulnerable to penetrating injury and being injured during hand surgery fixations. In this article, we describe a case of DBUN injury after percutaneous pinning of the fourth and fifth metacarpal bone fractures complicated by intrinsic muscle wasting of the hand that was treated with neuroma excision and sural nerve graft. We present the case of a 36-year-old man, who had a fracture of the base of the fourth and fifth metacarpal bones, which was treated with multiple K-wires. A few months later, the patient presented with weak abduction/adduction of the three ulnar fingers and prominent wasting in the intrinsic muscles of the hand. On hand exploration, a 2-cm neuroma was found along the course of the DBUN distal to the hypothenar fibromuscular tunnel, which was treated by neuroma excision and nerve grafting. Fractures of the fourth and fifth metacarpals and carpometacarpal dislocations are very common and are often treated surgically. To fix these fractures, awareness of the DBUN course in the hand and its proximity to the carpal and metacarpal bones is important. High caution should be taken during percutaneous pinning by inserting K-wires under radiological guidance, minimizing pining attempts and limiting pin tip protrusion to 1-2 mm.