Background: The axillary nerve may be injured during percutaneous fixation of proximal humerus fractures. This study investigated the kinematic behavior of the superior and inferior borders of the axillary nerve under varying shoulder positions. This information may reduce iatrogenic neurologic injury during fracture reduction and hardware placement.
Methods: The lateral deltoid approach was performed on 7 fresh frozen shoulders. The inferior and superior borders of the axillary nerve were tagged. Screws were placed in the anterior, middle, and posterior acromion as landmarks. Three-dimensional distances of the inferior and superior border of the nerve were measured to the mid-acromion while the shoulder was placed in combinations of forward flexion, vertical abduction, and humeral rotation. The distances were compared by repeated measures ANOVA statistical analysis.
Results: The distance from the mid-acromion to the superior border of the axillary nerve was 66.6 mm (+/-5.7), and to the inferior axillary nerve was 75.7 mm (+/-5.8) with the shoulder in neutral position. Vertical abduction to 60 degrees significantly moved the superior and inferior borders of the axillary nerve to a distance of 53.9 (+/-7.7) and 61.6 mm (+/-8.1), respectively (P < 0.005). Forward flexion had no significant effect on the position of the axillary nerve (P > 0.5). The longest distance from the mid-acromion to the inferior border of the axillary nerve was 86 mm with the arm forward flexed.
Conclusions: The main determinant of axillary nerve position with respect to the acromion is vertical abduction. Axillary nerve position is essentially unaffected by varying degrees of humeral rotation and forward flexion. Vertical glenohumeral abduction to 60 degrees is required to move the nerve significantly closer to the acromion.