Review Question - QID 213115

This patient has sustained a displaced extension-type supracondylar humerus fracture. The most common neuropraxia in this setting is the anterior interosseous nerve (AIN), which would result in weakness in the flexor pollicis longus (FPL) muscle.

AIN palsy is the most common neuropraxia after pediatric extension-type supracondylar humerus fractures. The AIN innervates the FPL, the pronator quadratus, and the flexor digitorum profundus (FDP) of the index and long fingers. Most of these neuropraxias resolve with observation without significant long term sequelae. The ulnar nerve is most commonly implicated with flexion-type supracondylar humerus fractures.

Shore et al. performed a study to investigate the outcome of motor nerve injuries associated with extension-type supracondylar humerus fractures. They reported that the median time to nerve recovery was 2.3 months; 60% of injuries had nerve recovery by 3 months and over 90% of patients had complete nerve recovery at final follow-up. They concluded that the majority of nerve injuries associated with pediatric extension-type supracondylar humerus fractures recover within 6 months without acute nerve decompression.

Babal et al. performed a meta-analysis of nerve injuries associated with pediatric supracondylar humeral fractures. They reported that AIN injury predominated in extension-type fractures, while ulnar neuropathy occurred most frequently in flexion-type injuries. They concluded that medial elbow pinning carries a greater overall risk of nerve injury as compared with lateral-only pinning and that the ulnar nerve is at risk of injury in medially pinned patients, while the median nerve is at risk in laterally pinned patients.

Figures A and B demonstrate a displaced extension-type pediatric supracondylar humerus fracture.

Illustration A demonstrates upper extremity motor and sensory innervation.

Incorrect Answers:
Answers 1 & 5: Dorsal and palmar interossei muscles are innervated by the ulnar nerve, which is more commonly injured in flexion-type injuries.
Answers 2 & 3: Extensor digitorium communis and extensor pollicis longus are innervated by the posterior interroseous nerve, a deep branch of the radial nerve that is not as commonly injured as the AIN.