Isolated musculocutaneous nerve injury following a pedestrian-automobile collision: A case report

Abstract

Isolated musculocutaneous nerve (MCN) lesion is rare and usually associated with direct trauma. Along with the rarity of this condition, other muscles involved in elbow flexion, such as brachioradialis and pronator teres, can mask the weakness induced by the MCN injury and make it difficult to identify it. Here, we report a 17-year-old patient with isolated MCN palsy following a single episode of anterior shoulder contusion. A lack of suspicion for this rare condition delayed diagnosis until 7 months post injury, when atrophy of muscles in the left upper arm became prominent and weakness of the elbow flexors persisted. After 6 months of rehabilitation therapy rather than undergoing surgical exploration, elbow flexor strength was nearly fully recovered but sensory symptoms remained. The mechanism of injury is speculated to be a sudden overloading of the anterior shoulder with extension and external rotation, which overstretched and compressed the MCN within the coracobrachialis muscle where the nerve is relatively fixed. Although isolated peripheral nerve injury is rare, it can be caused by a single episode of vigorous impact. Therefore, even in patients without any external wounds, careful physical examination with suspicion of peripheral nerve injury as one of the differential diagnoses is needed.