Distance between the median nerve and ulnar neurovascular bundle: clinical significance with ultrasonographically assisted carpal tunnel release.

In ultrasonographically assisted carpal tunnel release, the zone of the transverse carpal ligament between the median nerve and ulnar neurovascular bundle is of significance because proximity of the cutting device to these structures depends on its width. In this study, we measured the width of the zone at 5 levels in 60 wrists from 54 patients with surgery-indicated idiopathic carpal tunnel syndrome. The width of the 5 levels ranged from 2.8 to 11.2 mm (mean, 7.1 mm) at the hook of the hamate, 3.0 to 12.5 mm (mean, 7.9 mm) at the distal one fourth of the carpal tunnel, 2.8 to 12.4 mm (mean, 8.0 mm) at the midsection of the tunnel, 1.5 to 13.0 mm (mean, 7.4 mm) at the proximal one fourth of the tunnel, and 5.3 to 17.2 mm (mean, 10.2 mm) at the wrist crease. These widths were not significantly correlated with radiographic measurements of the hand (cord of the radiocarpal joint arc, carpal height, third metacarpal, and hand length). We conclude that there is considerable variation of the width among individuals. Based on our clinical experience (3 wrists of 3 patients in this study), patients with a width of < or =3 mm at any level should be screened out preoperatively by wrist imaging. Our findings also may be of use to surgeons performing endoscopic carpal tunnel release.