CT-scanning study of cross-sectional area of the carpal tunnel in cases of carpal tunnel syndrome.

The cross-sectional area, transverse and anteroposterior diameter of the carpal tunnel were investigated by CT scanning in 68 cases of carpal tunnel syndrome (CTS) and in 100 normal controls of both sexes. The cross-sectional areas of the carpal tunnel in idiopathic CTS of both sexes were significantly smaller, whereas those in secondary CTS were larger than in normal controls. In female wrists with idiopathic CTS narrowing of distal carpal tunnel was attributed to short transverse diameter in wrists with normally shaped hook of the hamate, or to decreased anteroposterior diameter in wrists with abnormally short hook of the hamate. The smallest cross-sectional area in both types of CTS and in normal controls is located at the proximal border of distal carpal tunnel (D 1 level). This coincides with the thickest portion of the flexor retinaculum and, together with our operative findings, supports the conclusion that the essential compression on the median nerve takes place at the D 1 level in idiopathic CTS.