Review Question - QID 219250

Extension-type supracondylar humerus (SCH) fractures most commonly injure the anterior interosseous nerve (AIN), a neuropraxia that causes weakness of the flexor pollicis longus (FPL) with attempted flexion of the thumb interphalangeal joint.

Supracondylar humerus (SCH) fractures are the most common type of elbow fractures in children, accounting for 50% to 70% of all fractures around the elbow. Extension-type SCH fractures account for the vast majority (approximately 96% to 98%) of all pediatric supracondylar fractures of the humerus, whereas flexion types occur in only approximately 2% to 4% of patients (Illustrations A and B, respectively). The standard operative treatment for displaced extension-type and flexion-type SCH fractures alike is reduction followed by percutaneous pin fixation. Though some disagreement does exist regarding optimal pin placement, with some advocating that the use of a medial pin may unnecessarily risk ulnar neurapraxia, whereas the use of lateral pins alone may demonstrate less biomechanical strength, it is commonly accepted that of all complications associated with supracondylar humeral fractures, nerve injury ranks highest. In extension-type SCH fractures, the most commonly affected nerve is the anterior interosseous nerve (AIN), which is reflected by weakness of the flexor pollicis longus muscle and resultant thumb interphalangeal joint flexion. In flexion-type SCH fractures, on the other hand, though still occurring more rarely, ulnar nerve neuropraxia is more commonly seen.

Babal et al. provide a meta-analysis of nerve injuries associated with pediatric supracondylar humerus fractures. The authors identified data from 5148 patients and found that traumatic neuropraxia occurred at a weighted event rate of 11.3%. Anterior interosseous nerve injury predominated in extension-type fractures, representing 34.1% of associated neuropraxias, while ulnar neuropathy occurred most frequently in flexion-type injuries, representing 91.3% of associated neuropraxias. They also found that nerve injury induced by lateral-only pinning occurred at a weighted event rate of 3.4%, while the introduction of a medial pin elicited neuropraxia at a weighted event rate of 4.1%, leading them to conclude that lateral pinning carried an increased risk of median neuropathy, whereas the use of a medial pin significantly increased the risk of ulnar nerve injury.

Dormans et al. reviewed acute neurovascular complications with supracondylar humerus fractures in children. The authors retrospectively reviewed 200 pediatric patients with acute Type III supracondylar humerus fractures and found a 9.5% incidence of associated neurologic injury. They concluded that anterior interosseus nerve injury was the most common nerve injury seen and that diagnosis may be subtle and cause delayed diagnosis. Regardless, return of function occurred in all patients at 6 to 16 weeks after the injury without surgical intervention.

Illustration A demonstrates a radiograph of an extension-type SCH fracture. Illustration B demonstrates a radiograph of a flexion-type SCH fracture.

Incorrect Answers:
Answer 1: Finger abduction occurs via the interossei which are innervated by the deep branch of the ulnar nerve, not the AIN.
Answer 2: Thumb extension at the IPJ occurs via the extensor pollicis longus (EPL), which is innervated by the posterior interosseous nerve (PIN) branch of the radial nerve.
Answer 4: Thumb opposition occurs via the opponens pollicis, which is innervated by the recurrent branch of the median nerve.
Answer 5: Wrist extension occurs via radial nerve-innervated musculature. Though the radial nerve is the second-most-commonly affected nerve in the setting of extension-type SCH fractures, the AIN remains the most commonly injured.