ANATOMICAL BASIS OF THE VARIABLE ASPECTS OF INJURIES OF THE AXILLARY NERVE (EXCLUDING THE TERMINAL BRANCHES IN THE DELTOID MUSCLE)

The course of the axillary n. is complex with three points of angulati on that may be used to delineate four segments and a fifth segment tha t corresponds to the intramuscular ending of the nerve in the deltoid m. The purpose of this study was to determine the precise anatomy of t he nerve and of its branches, and some morphologic features for each s egment. Thirty-two shoulders from embalmed adult cadavers have been st udied. The axillary n. was divided in five segments: 1) from its origi n to the inferior border of the subscapularis m., 2) from the subscapu laris m. to the anterolateral border of the tendon of the long head of the triceps brachii m., 3) from the triceps to the posteromedial part of the surgical neck of the humerus, 4) from the humerus to the entry into the deltoid m., 5) the intramuscular distribution of the nerve i n the deltoid m. In each segment from 1 to 4 were noted the origins of the branches to the subscapularis and teres minor mm. and to the scap ulohumeral joint, and the origins of the lateral cutaneous brachial n. and of the terminal motor branches to the deltoid m. The length and t he diameter of the nerve in the segments and the distance from the seg ment S1 to the musculotendinous junction of the sub-scapularis m. were measured. The results showed that the mean diameters were about 4.1 m m in segment 1, 4.1 mm in segment 2 and 3.4 mm in segment 3, The mean distance to the musculotendinous junction was 7.7 mm. Many variations in the levels of origin of the different muscular, articular or cutane ous branches were found without symmetry between the right and left si des, The lateral cutaneous brachial n. was absent in four cases. The r esults are compared with those in the literature. The division into fi ve segments is proposed to radiologists and surgeons for evaluation or operative procedures on the axillary n., and to provide a hypothesis about the variable aspects of injuries of the nerve.