K wiring of the fifth metacarpal - is the dorsal cutaneous branch of the ulnar nerve at risk?

Introduction Antegrade K wiring of the fifth metacarpal for treatment of displaced metacarpal neck fractures is a well recognized surgical procedure. However it is not without complication and injury to the dorsal cutaneous branch of the ulnar nerve has been reported in up to 15% of cases. Methods We performed a cadaver study to determine the proximity of this nerve to the K wire insertion point at the base of the fifth metacarpal. K wires were percutaneously inserted under image intensification in sixteen cadaver hands and advanced into the head of the metacarpal. Wires were then cut and bent outside the skin. This was then followed by meticulous dissection of the ulnar nerve from proximal to distal. A number of measurements were taken to identify the distance from the insertion point of the K wire to each branch of this nerve. Results The distance from the insertion point at the base of the fifth metacarpal to the dorsal component of the nerve averaged 5.6 mm (range 1mm–12mm) and from the volar component was 6 mm (range 1mm–10mm). The heel of the wire was touching the nerve in five cases. Conclusion Our findings highlight the importance of making a small incision and bluntly dissecting to bone at the base of the fifth metacarpal to protect the nerve. In addition, use of a tissue protector is vital when drilling the 2mm hole at the base of the fifth metacarpal. We have confirmed that the dorsal cutaneous branch of the ulnar nerve is vulnerable during insertion of an antegrade intramedullary K wire for treatment of neck of fifth metacarpal fractures.