Which specific nerve is most commonly at risk of injury in a completely displaced, extension-type pediatric supracondylar humerus fracture that exhibits posteromedial displacement of the distal fragment?
A
Anterior interosseous nerve
B
Musculocutaneous nerve
C
Ulnar nerve
D
Radial nerve
Explanation
Posteromedial displacement of the distal fragment drives the sharp proximal fracture spike anterolaterally, endangering the radial nerve.
Clinical Context: Pediatric supracondylar humerus fractures are predominantly extension-type (95%). The direction of displacement of the distal fragment dictates the neurovascular structures at risk, based on where the proximal spike protrudes.
- Posterolateral displacement (most common): The proximal spike goes anteromedial, putting the median nerve (specifically the anterior interosseous nerve, AIN) and the brachial artery at greatest risk. AIN palsy presents as the inability to make an 'A-OK' sign (weakness of FPL and FDP to the index finger).
- Posteromedial displacement: The proximal spike goes anterolateral, piercing the brachialis muscle and tenting or injuring the radial nerve.
- Flexion-type fractures: Endanger the ulnar nerve.
- Iatrogenic ulnar nerve injury occurs most frequently during the placement of the medial pin in cross-pinning constructs.
References:
1. Skaggs DL, et al. 'Operative treatment of supracondylar fractures of the humerus in children.' J Bone Joint Surg Am. 2001.
2. Omid R, et al. 'Supracondylar humeral fractures in children.' J Bone Joint Surg Am. 2008.