The risk of neurovascular injury with distal locking screws of humeral intramedullary nails.

The upper extremities of two elderly cadavers were amputated at the fore-quarter level and underwent placement of the Biomet uniflex humeral nail in the left extremities and the Richards Russell-Taylor humeral nail in the right extremities. Distal locking screws were placed lateral to medial in the Biomet nails and in the anterior to posterior plane in the Richards nails. Dissection was performed about the distal humerus to identify the neurovascular structures at risk from screw placement. The radial nerve was at direct risk with lateral to medial screw placement and the ulnar nerve and median nerve/brachial artery bundle was at risk if significant overpenetration of the medial cortex occurred. The musculocutaneous nerve was at direct risk with placement of a distal screw from anterior to posterior. Sections of the distal humerus demonstrated the medullary canal to begin narrowing at 3 cm and fill with dense bone 1.5 cm superior to the proximal edge of the olecranon fossa. This may interfere with distal placement of the humeral nail, altering the position of the distal fixation holes, and also may contribute to distraction at the fracture site.