Colour difference of subcutaneous fat and palmar fat pad in open carpal tunnel release

Carpal tunnel syndrome is the most common compression neuropathy of the extremity. The most frequent occurring post-operative complication of open carpal tunnel release is the incomplete release of the transverse carpal ligament. A constant pad of palmar fat pad has been found to provide a reliable indicator of the distal extent of the surgical decompression of the transverse carpal ligament. We investigated the colour difference between subcutaneous fat and palmar fat pad.

This is a prospective case series of 15 patients undergoing open carpal tunnel release. Digital images of the patients' subcutaneous and palmar fat were taken. The colour of each type of fat was described in a device independent, objective manner using the CIELab colour space. The colour difference was measured using ΔE, the Euclidean distance between the CIELab coordinates of the colours. Wilcoxon signed-rank test was used to compare colour character differences between subcutaneous and palmar fat. The colour difference, ΔE, was assessed and reported with 95% confidence intervals (CI).

There is a visually detectable colour difference between subcutaneous and palmar fat. The minimum ΔE was 4.45. The mean ΔE was 13.03 (95% CI 9.79-16.27). The palmar fat pad is more yellow than the subcutaneous fat (P = 0.002).

Our findings can assist in the identification of the palmar fat pad to ensure safer and a complete release of the transverse carpal ligament in carpal tunnel release.