BIOMETRY OF THE MOTOR BRANCHES OF THE MEDIAN AND ULNAR NERVES: TWENTY DISSECTIONS (APPLICATION TO HYPONEUROTISATION OF THE SPASTIC HAND)

Abstract

Purpose: The purpose of this study was to establish the map of the motor branches of the median and ulnar nerves of the forearm and to count the Martin-Gruber anastomoses. Knowledge of anatomic variability would be useful for hyponeurotisation surgery of the spastic hand. Variations in the antebrachial emergence of the six motor branches of the medial nerve and the three motor branches of the ulnar nerve were studied.

Material and methods: This study was conducted on twenty anatomic specimens obtained from five men and five women. We measured the length of the forearm and identified the origin of each motor branch of the medial and ulnar nerves using a horizontal line between the meidal and lateral epicondyles as the reference line.

Results: Mean length of the forearm was 26.93±2.6 cm. Unlike the origin of the superior and inferior pronator teres nerves, and the palmaris longus, flexor carpi radialis, and flexor digitorum superficialis nerves which were very variable (coefficient of variation 49%–113%), the origin of the anterior interosseous nerve of the forearm (CV=39%) and its branches, and the flexor pollicis longus nerve and the flexor digitorum profondus nerves (CV =23% and 29% respectively) were much more regular. The superior and inferior origins of the flexor carpi ulnaris nerve were variable (CV = 157 and 22%) while the origin of the nerves for the deep flexor of the IV and V fingers showed a better coefficient of variation (13%). We observed four Martin-Gruber anastomoses (20%).

Conclusion: This study demonstrated the wide anatomic variability of the medial and ulnar nerves both interin-dividually and intraindividually. Emergence of certain nerve branches appeared to be more regular, particularly the lower group of the median nerve and the anterior interosseous nerve of the forearm. It was however impossible to identify two groups exhibiting a statistically significantly greater frequency for the median nerve. The anatomic variations of the ulnar nerve were less pronounced. The inconsistency of the inferior flexor carpi ulnaris is noteworthy.