The Relationship Between Arm Abduction Position and the Risk of Iatrogenic Anterior Branch of the Axillary Nerve Injuries: A Cadaveric Study

BACKGROUND: The axillary nerve is at risk for iatrogenic injuries in surgical procedures involving the lateral aspect of the shoulder joint. To date and to our knowledge, there have been no studies that have compared the relevant distances in the common arm abduction positions used in these types of surgery as well as the relative risks of each position. PURPOSE: To evaluate the effect of arm abduction position on the distance from the acromion process to the axillary nerve in the common abducted arm positions. STUDY DESIGN: Descriptive laboratory study. METHODS: The shoulders of 10 fresh-frozen, full-body cadaveric specimens were used. A saber incision was made at the anterolateral edge of the acromion, and the anterior branch of the axillary nerve was identified. The distance between the anterolateral edge of the acromion process and the axillary nerve was measured 3 times in each of 4 positions: with the arm at the side as well as at 30°, 60°, and 90° of abduction. Then, the same procedure was performed from the midlateral and the posterolateral edges of the acromion process. The distances of the acromion process to the axillary nerve in the 4 positions were compared using 2-way analysis of variance. RESULTS: The mean distances from the anterolateral edge of the acromion process to the anterior branch of the axillary nerve were 52.76 ± 4.64 mm with the arm at the side, 49.48 ± 4.77 mm at 30° of abduction, 46.00 ± 4.75 mm at 60° of abduction, and 42.88 ± 4.59 mm at 90° of abduction. There was a significant decrease in the distance from the anterolateral edge of the acromion process to the axillary nerve as the abduction angle of the arm increased from 0° to 60°, 0° to 90°, and 30° to 90° (P < .05). CONCLUSION: The distances from the acromion process to the axillary nerve were shorter in all abducted arm positions than with the arm at the side. CLINICAL RELEVANCE: To avoid iatrogenic axillary nerve injuries, surgeons should be aware of the safe zone based on the shortest distance from the acromion process to the axillary nerve to ensure no accidental damage to this structure instead of using the mean distance of 5 cm.