The position of the median nerve in relation to the palmaris longus tendon at the wrist: a study of 784 MR images.

Iatrogenic injury of the median nerve has been reported after endoscopic carpal tunnel release and corticoid injection. In 784 MR images of the wrist, the position of the median nerve in relation to the palmaris longus tendon was analysed. The ulnar edge of the median nerve was found medial to the palmaris longus tendon in 14% and 36% of patients at the proximal wrist crease and entrance of the carpal tunnel, respectively, compared with 23% and 40% of patients with carpal tunnel syndrome (88 patients). The position of the median nerve in relation to the palmaris longus tendon varies widely. It is suggested that the palmaris longus tendon may not be considered a safe landmark to locate the position of the median nerve and care should be taken when introducing an endoscopic instrument or during steroid injection for carpal tunnel syndrome.Level of evidence: IV.