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.