The change in position of the axillary nerve with rotation of the arm.

The axillary nerve is the most commonly injured nerve around the arm. In the deltopectoral approach, classical teaching states that lateral rotation of the humerus increases the distance between the subscapularis and the axillary nerve. This is the first anatomical study to quantify the distance change between the axillary nerve and subscapularis produced by arm rotation. Eight arms were placed in the supine position and a classical deltopectoral approach was performed. With digital calipers, measurements were made from the closest identifiable margin of the nerve to the inferior extent of the tenotomy. All measurements were made with the arm in 0° abduction and elbow in 90° of flexion, and repeated with the arm in 45° of medial rotation, 0° lateral rotation and 45° of lateral rotation. The mean d Axillary Nerve to subscapularis was recorded as 30.9 mm (95% CI:25.3-36.3), 39.4 mm(95% CI:34.1-44.8), and 46.1 mm (95% CI:41.1-51.2) for 45° MR, 0°, and 45° LR, respectively. Using paired-samples T-testing, the mean change in distance when moving from 45° MR to 0° was +8.5 mm (P < 0.0001), and from 0° to LR 45°, +6.7 mm (P < 0.0001). There is a significant difference in the distance between the subscapularis tenotomy and the axillary nerve with medial and lateral rotation. Laterally rotating the arm increased the distance by 6.7 mm, reaffirming that positioning the glenohumeral joint in a position of LR during subscapular tenotomy is protective against iatrogenic injury of the axillary nerve. Clin. Anat. 32:268-271, 2019.