A Clinical Application Study on Ultrasonographic Cross-Sectional Area of Median nerve at the Wrist in Patients with Carpal Tunnel Syndrome

The carpal tunnel is an important anatomical structure well known to hand and wrist surgeons due to the prevalence of carpal tunnel syndrome and frequency of carpal tunnel release surgery. The carpal tunnel is formed by the flexor retinaculum, a fibrous band spanning across the concave carpus which attaches radially to the tubercle of the scaphoid and the trapezium and ulnarly to the pisiform and hook of hamate. Through this tunnel travel the flexor pollicis longus and four flexor digitorum profundus tendons on the deep surface, and the flexor carpi radialis and four flexor digitorum superficialis tendons more superficially. The median nerve passes radial to the flexor digitorum superficialis tendons, just deep to the flexor retinaculum. The median nerve most commonly divides into palmar common digital branches distal to the carpal tunnel, however numerous anatomical variations have been described. These include a bifid median nerve with proximal bifurcation above the carpal tunnel, as well as variations in the palmar cutaneous branch and motor branch to thenar muscles. There are also reported anomalous communications between the median and ulnar nerve, of both motor and sensory branches. A comprehensive understanding of the normal and variant anatomy in this region is essential to preventing iatrogenic injury during carpal tunnel release. The aim of this presentation is to review the relevant literature and summarise the anatomical variations of the median nerve in the carpal tunnel.