Topographic anatomy of structures liable to compress the median nerve at the elbow and proximal forearm.

Introduction: Several structures liable to compress the median nerve have been described around the elbow and proximal forearm. Signs of deficit justify surgical exploration and decompression by exoneurolysis. Better knowledge of the locations of these structures would ensure reliable and effective exploration.

Hypothesis: The study hypothesis was that compressive structures show precise topography, with few variations in distance along the median nerve course.

Material And Methods: The study was performed on 36 upper-limb cadaver specimens. The measurement reference level was the humeral bi-epicondylar line. Proximal-to-distal dissection located: (1) Struthers' ligament, (2) the pronator teres bellies (PT) with their anatomic particularities of structure and insertion, (3) the lacertus fibrosus, (4) the fibrous arcade of the flexor digitorum superficialis (FDS), (5) the accessory muscles, (6) the origin of the anterior interosseous nerve (AIN), (7) and the vascular arches.

Results: Struthers' ligament was not located, but 1 case of medial bicipital fibrous arcade was found. The lacertus fibrosus crossed the median nerve at +1.5±0.6cm. PT insertion was high in 19 cases (53%). The humeral PT belly was thin in 21 cases (58%), crossing the median nerve more distally (+1.8±0.8cm) than the thicker muscles (+1±1.1cm) (p=0.016). The ulnar PT belly was fibrous in 14 cases (39%). A fibrous arcade was found between the 2 PT bellies in 23 cases (64%). The FDS arcade was located at 4.5-7cm from the bi-epicondylar line. An accessory flexor pollicis longus belly was found in 11% of cases. The AIN origin was at +4±1.6cm from the reference. A vascular pedicle crossed the median nerve in 3 cases.

Discussion: The present study inventoried and mapped 6 potentially compressive structures neighboring or crossing the median nerve. Except for the FDS arcade, they showed very precise proximal-to-distal location, with variations of 0.5 to 1.5cm.

Level Of Evidence: IV; case series.