Density mapping of nerve endings in the skin of the palm and flexor retinaculum of the hand. Application to open carpal tunnel release.

ABSTRACT

In order to re-evaluate the safest area to incise skin and the flexor retinaculum (FR) when performing a carpal tunnel release (CTR), we carried out a mapping study of the nerve endings in the skin and FR on cadaver specimens, which, unlike previous studies for the first time, includes histomorphometry and image digital analysis. After dividing the skin and FR into 20 and 12 sections, respectively, we carried out a histomorphological analysis of nerve endings. The analysis was performed by two neutral observers on 4-µm histological sections stained with hematoxylin-eosin (H-E), and Klüver-Barrera with picrosirius red (KB + PR) methods. A semi-automatic image digital analysis was also used to estimate the percentage of area occupied per nerve. We observed a lower quantity of nerve endings in the skin of the palm of the hand in line with the ulnar aspect of the 4th finger. The ulnar aspect of the FR was the most densely innervated. However, there are no statistically significant differences between sections in the percentage of area occupied per nerve both in the skin and in the FR. We concluded that there is not a safe area to incise when performing carpal tunnel surgery, but taking into account the quantity of nerve endings present in skin and FR, we recommend an incision on the axis of the ulnar aspect of 4th finger when incising skin and on the middle third of the FR for CTR.