The anatomy of the dorsal cutaneous branch of the ulnar nerve - a safe zone for positioning of the 6R portal in wrist arthroscopy.

The dorsal branch of the ulnar nerve passes close to the 6 Radial portal used in wrist arthroscopy. We examined 20 cadaveric limbs to establish the course of this nerve. We found it consistently crossed a line between the ulnar styloid and the fourth web space at an average of 2.4 cm from the ulnar styloid (range 1.8-2.8 cm). This represented 23% (+/- 2.5 STD range 19-27%) of the distance from the styloid process to the fourth web space. Recommendations are made to help avoid iatrogenic injury to the nerve during arthroscopy. The literature on the anatomy of this nerve and its variations and the clinical relevance of this knowledge are discussed.