Radial and axillary nerves. Anatomic considerations for humeral fixation.

Because the axillary and radial nerves can be injured during operative exposure and fixation of the humerus, accurate delineation of their location is vital to avoid complications. The authors investigated the relationship of the radial and axillary nerves for radiographically and surgically identifiable bony landmarks. Fifty fresh human cadaveric upper extremities were dissected to identify the nerves as they crossed the lateral intermuscular septum and the humeral surgical neck, respectively. Longitudinal distances between the nerves and the superior aspect of the humeral head, the surgical neck, the superior extent of the olecranon fossa, and the distal aspect of the trochlea were measured with calipers. The average distance from the axillary nerve to the proximal humerus was 6.1 +/- 0.7 cm (range, 4.5-6.9 cm) and 1.7 +/- 0.8 cm (range, 0.7-4.0 cm) from the surgical neck. The radial nerve traversed the lateral intermuscular septum 17 +/- 2.3 cm (range, 13-22 cm) from the proximal humerus, 12 +/- 2.3 cm (range, 7.4-16.6 cm) from the olecranon fossa, and 16 +/- 0.4 cm (range, 9.0-20.5 cm) from the distal humerus, representing the approximate midpoint of the bone. Anteroposterior locking screws placed into the proximal humerus endanger the axillary nerve because it lies directly over the posterior cortex as little as 0.7 cm from the surgical neck. As the radial nerve crosses the lateral intermuscular septum more proximal than generally was thought, it is at risk during implant insertion in the distal half of the humerus. Using measurements calculated from preoperative and intraoperative imaging, the approximate position of the nerve could be determined to better plan fixation method and implant location.