ANATOMIC DELINEATION OF THE ULNAR NERVE AND ULNAR ARTERY IN RELATION TO THE CARPAL-TUNNEL BY AXIAL MAGNETIC-RESONANCE-IMAGING SCANNING

In a number of publications the distal branches of both the ulnar arte ry and ulnar nerve have been identified as being positioned ulnar to t he hook of the hamate. We undertook a magnetic resonance imaging proje ct in patients who presented for carpal tunnel release to determine ho w far radially vital structures of Guyon's canal may be located and if they may overlap the carpal tunnel al the hook of the hamate. Cross-s ectional magnetic resonance imaging scans of 20 patients were performe d prior to carpal tunnel release with the wrist positioned in neutral, flexed, and extended positions. Linear measurements were made either radial or ulnar to the hook of the hamate taken as the reference point . In the neutral position, the ulnar nerve was found to be, on average , 3.6 mm ulnar to the hook of the hamate (range of 5.8 mm radial to 7. 5 mm ulnar). The ulnar artery averaged 0.7 mm to the radial side of th e hook of the hamate (range 7.8 mm radial to 2.8 mm ulnar). Guyon's ca nal extended 28% of the way across the carpal ligament (range 9 to 63% ). With the wrist in flexion and extension, there was an ulnar displac ement and a radial displacement, respectively, of these structures rel ative to the hook of the hamate.