Surface landmarks to locate the thenar branch of the median nerve: an anatomical study.

The thenar branch of the median nerve can be injured during carpal tunnel release. The purpose of this study was to identify surface landmarks to consistently predict the location of the thenar branch of the median nerve. Surface landmarks were marked and incised in 28 cadaveric hands. The incisions were made along the longitudinal line of the third web space and the horizontal cardinal line from the hamate hook to the ulnar border of the thumb. The origin of the thenar branch was determined in relation to these longitudinal and horizontal vectors. The origin of the thenar nerve branch was consistently observed in the radial proximal quadrant formed by the aforementioned longitudinal and horizontal vectors. The thenar branch origin was observed to be an average of 8.6 +/- 1.9 mm radial to the longitudinal axis along the third web space. The origin of the thenar branch was observed to be an average of 6.3 +/- 2.0 mm proximal to the horizontal axis between the hamate hook and the ulnar border of the thumb. The thenar branch was observed precisely at the intersection of the longitudinal vector from the second web space to the scaphoid tubercle and the horizontal vector from the hamate hook to the radial edge of the proximal metacarpophalangeal crease in all 28 cadaveric hands. On the basis of these 28 cadaveric dissections, the location of the thenar branch of the median nerve can be predicted by the intersection of the longitudinal vector from the second web space to the scaphoid tubercle and the horizontal vector from the hamate hook to the radial aspect of the metacarpophalangeal crease.