Anatomical Factors Contributing to Radial Nerve Excursion at the Brachium: A Cadaveric Study

Abstract

Purpose: The radial nerve appears to be more vulnerable to injury in the brachium than the median and ulnar nerves. The underlying mechanism for this increased vulnerability is not well explained. We hypothesize that the radial nerve has less excursion than the median and ulnar nerves because it is anatomically tethered by the lateral intermuscular septum (LIS) and that elbow positioning and LIS release will improve its excursion.

Methods: Eight paired fresh-frozen cadaveric upper extremity specimens were used. The radial, median, and ulnar nerves were transected at the level of the spiral groove. Nerve excursion was determined at a constant tension of 100 g from 0° to 90° of elbow flexion and repeated for the radial nerve after releasing the LIS. The cross-sectional areas of nervous and connective tissue were then determined histologically.

Results: Radial and median nerve excursion correlated positively with increased elbow flexion, and ulnar nerve excursion correlated negatively with increased elbow flexion. Release of the LIS significantly improved radial nerve excursion at 0°, 60°, and 90° of elbow flexion. Release of the LIS with 90° of elbow flexion increased radial nerve excursion by approximately 3 times. Histological analysis demonstrated similar mean composition of nonnervous connective tissue among the 3 nerves.

Conclusions: The radial nerve is anatomically tethered in the brachium by the LIS and has limited excursion compared with the median and ulnar nerves. Radial nerve excursion improves with elbow flexion and LIS release. Flexing the elbow to 90° doubles radial nerve excursion. Releasing the LIS as well triples the excursion of the radial nerve. Histological composition was similar among the three nerves at the brachium.

Clinical relevance: Releasing the LIS and flexing the elbow improve radial nerve excursion. These steps may be useful during humeral fracture fixation.

Keywords: Brachium; humeral fracture; lateral intermuscular septum; nerve excursion; radial nerve.