Axillary nerve injury is a risk of the deltopectoral approach to the proximal humerus. The anterior motor branch is potentially vulnerable during subdeltoid dissection. Insertion of the pectoralis major tendon is an easily identifiable landmark on the humerus. This anatomical study explored whether the superior aspect of the pectoralis major tendon is a useful landmark for localizing the anterior motor branch of the axillary nerve as it travels under the lateral and anterior deltoid muscle. A total of 30 fresh-frozen human bilateral cadaveric upper extremities were examined. A deltopectoral approach was used to expose the pectoralis major tendon insertion and the anterior motor branch of the nerve under the deltoid muscle. The distance between the nerve as it crossed the posterolateral humerus and superior border of the pectoralis major tendon was measured. The axillary nerve was a mean 3.2 mm (range, 0-8 mm) distal to the superior border of the pectoralis major tendon insertion. No significant differences were observed in this anatomical relationship with the shoulder in abduction or external rotation. The nerve was not proximal to the superior border of the pectoralis major tendon in any specimen. The superior border of the pectoralis major tendon insertion represents a reliable landmark for the anterior motor branch of the axillary nerve as it travels under the deltoid muscle. The nerve is located at the level of the proximal centimeter of the pectoralis major tendon. Appreciation of this relationship may decrease risk of injury to the nerve when using a deltopectoral approach. [Orthopedics. 2017; 40(3):e460-e464.].
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