Cross-Sectional Area of the Carpal Canal Proximal and Distal to the Wrist Flexion Crease

The purposes of this study were as follows: (1) to locate the position of the distal wrist flexion crease with respect to the carpal bones, specifically the proximal pole of the capitate, and (2) to determine the cross-sectional area of the carpal canal proximal and distal to the wrist flexion crease to enable us to determine whether or not there is a focal area of narrowing that would provide an anatomic basis for the proximal extent of carpal tunnel release. This study had 2 parts. The first part was a plain radiographic study of 21 uninjured wrists in 12 volunteers that defined the position of the distal wrist flexion crease with respect to the carpus. The second part was a magnetic resonance imaging study of 13 wrists in asymptomatic volunteers that measured the cross-sectional area of the carpal canal proximal and distal to the wrist flexion crease. In 19 of 21 wrists the distal wrist flexion crease was within 2 mm of the proximal pole of the capitate. We noted a gradual increase in the area of the carpal canal moving proximal from its narrowest point. There was no significant increase in area until approximately 23 mm proximal to the narrowest point. We noted no focal area of narrowing in the cross-sectional area of the carpal canal either proximal or distal to the wrist flexion crease.