337 - A Real Knuckle Dragger: Snowboarder with Elbow Dislocation Resulting in Proximal Median Neuropathy

Case Diagnosis: Proximal median neuropathy at the elbow

Case Description: 28 year old female with remote history of left elbow terrible triad injury s/p repair presented 2 months after a fall while snowboarding, with repeat dislocation of the elbow. Patient noted weakness with flexion of thumb and digits 2 & 3, which later resolved. However, loss of two point discrimination at digits 1-3 persisted. Sensory conduction studies of left median nerve showed amplitude was significantly reduced (45%) compared to right, while motor responses were preserved. Electromyography showed abnormal insertional and spontaneous activity, as well as rapidly firing motor units with reduced recruitment in the pronator teres (PT) and abductor pollicis brevis (APB). There were high amplitude, long duration, polyphasic units in the PT, and units of normal morphology in the APB. In total, there was electrophysiologic evidence for a median neuropathy proximal to the branch to the PT, involving both the median and anterior interosseus nerve (AIN).

Discussions: In this patient, the proximal injury to the median nerve resulted in a transient AIN deficit (manifested by benedictine sign and inability to make pinch grip into an "O" shape due to involvement of the flexor pollicis longus and flexor digitorum profundus at digits 2 & 3). Electrodiagnostically, the relative sparing of distal median sensory and motor conductions in the presence of a moderate proximal median neuropathy illustrates the fascicular nature of traumatic nerve injury. Overall, the preserved distal conductions portends a good prognosis. Indeed at follow-up 4 months later, the patient’s numbness had resolved.

Conclusions: A fall while snowboarding can result in posterior elbow dislocation. While injury to the ulnar nerve is most common, injury to the median nerve is also possible. This patient’s prior elbow trauma may have predisposed to fascicular type nerve injury on repeat dislocation. Electrodiagnosis in this case allowed for localization and prognostication.