Surgical anatomy of median nerve at the carpal tunnel in adult black Kenyan population: A cadaveric study

Abstract

Background: The median nerve, a branch of brachial plexus in the upper limb, is at risk of injury at the carpal tunnel during wrist surgeries. Several studies have been conducted on the variations of median nerve in the carpal tunnel but there is no regional or local published data. Knowledge of anatomical variations of the median nerve at the wrist is important in repair of traumatic injuries and treatment of carpal tunnel syndrome as these situations require precise dissection of the nerve and such variations and injuries are not uncommon. Objective: To describe the variations in the course and distribution of the median nerve and its branches in the carpal tunnel in an adult black Kenyan population. Methods: The study conducted at the Human Anatomy Laboratory of Moi University School of Medicine, Eldoret using anatomical cross sectional design. A census of fifty six left upper limbs that met the inclusion criteria were dissected according to the techniques described by The Cunningham’s Manual of Practical Anatomy 16th Edition. The course and distribution of the median nerve and its branches in the carpal tunnel were described and photographs taken. The distal wrist crease and longitudinal axis of hand were taken as reference points. Data was recorded in data collection sheets and fed into electronic database with restricted access. Data analysis done using STATA version 13SE. Results were presented using tables and box plots. Results: Median nerve passed deep to the flexor retinaculum (FR) in all the specimens. Its location was mostly on the radial side (78.57%) of the carpal tunnel. The level of division was distal to FR in 76.79%, within in 14.28% and proximal in 8.93%. Persistent median artery was present in 3.57%. The thenar motor branch (TMB) arose from the lateral branch in 76.79% of the cases. The course of the TMB was extraligamentous in 76.79% and subligamentous in 23.21%. The TMB supplied all the 3 thenar muscles in 82.14% and only the Abductor Pollicis Brevis and Opponens Pollicis in 17.86%. Accessory thenar branches distal to FR were present in 12.5% of cases. The TMB was located 32.46 ± 4.03mm from the distal wrist crease (DWC). The TMB terminated 8.85 ± 1.59mm to the radial side of the longitudinal axis of the hand. Conclusion: The course and distribution of the median nerve at the carpal tunnel is variable and was found to be similar to the findings in most of the previous studies. There was radial sided dominance of median nerve course. The TMB was located in an area defined by 32.46 ± 4.03 mm from the DWC and 8.85 ± 1.59 mm to the radial side of the longitudinal axis of the hand. Recommendations: Surgeons should be aware of the variations in the course and distribution of median nerve at carpal tunnel and take extra care in high risk areas where TMB is located. Ulnar sided incisions of the transverse carpal ligament is upheld.