The radial nerve is the most commonly injured nerve in mid- or distal humeral shaft fractures. This association arises from the nerve’s anatomical course along the posterior aspect of the humerus, where it traverses the spiral groove in the mid-shaft region before descending laterally toward the distal arm. Fractures in these regions often displace bone fragments or cause soft tissue swelling, directly compressing, stretching, or lacerating the radial nerve. Understanding this relationship is critical for clinicians to diagnose, manage, and prevent long-term functional deficits in patients with humeral injuries.
(what nerve is most commonly injured in a mid- or distal humeral shaft fracture?)
Anatomically, the radial nerve originates from the posterior cord of the brachial plexus (C5–T1) and wraps around the humerus posteriorly in the spiral groove, approximately 10–15 cm distal to the acromion. As it courses distally, it pierces the lateral intermuscular septum near the junction of the middle and distal thirds of the humerus, transitioning from the posterior to the anterior compartment. This path renders the nerve vulnerable to injury, particularly in fractures involving the middle third of the humeral shaft or the distal third, such as the Holstein-Lewis fracture, a spiral fracture of the distal shaft historically linked to radial nerve palsy.
The mechanism of injury varies. Primary radial nerve injuries occur at the time of fracture due to direct trauma, bone fragment displacement, or traction. Secondary injuries may arise during closed reduction, surgical fixation, or callus formation during healing. Approximately 10–15% of humeral shaft fractures result in radial nerve dysfunction, with higher rates reported in open fractures or those with significant displacement. Neuropraxia—a transient conduction block without axonal disruption—is the most common injury type, followed by axonotmesis (axonal injury with intact connective tissue) and neurotmesis (complete nerve severance).
Clinically, radial nerve injury presents with motor deficits, including weakness or paralysis of wrist and finger extensors, leading to wrist drop. Sensory loss may occur over the dorsal aspect of the hand, first dorsal web space, and lateral three-and-a-half digits. Diagnosis involves a thorough neurological examination, supplemented by electromyography (EMG) and nerve conduction studies (NCS) after three weeks to assess injury severity and localization. Imaging modalities like X-rays and CT scans help evaluate fracture patterns, while MRI or ultrasound may visualize nerve continuity in complex cases.
Management hinges on injury type and fracture stability. In closed fractures with neuropraxia or early axonotmesis, conservative management with fracture immobilization and serial neurological assessments is preferred, as spontaneous recovery typically occurs within three to four months. Surgical exploration is indicated in open fractures, worsening deficits, or absence of recovery after three to six months. Nerve repair, grafting, or tendon transfers may be necessary for neurotmesis or irreversible injuries. Fracture fixation via plates, intramedullary nails, or external fixation should prioritize anatomical alignment to mitigate nerve compression.
Prognosis varies. Over 70% of radial nerve injuries associated with closed fractures resolve spontaneously, with recovery beginning within weeks. Delayed or incomplete recovery warrants further investigation. Complications include chronic pain, muscle atrophy, and joint contractures, emphasizing the need for early physical therapy to maintain range of motion and strength.
(what nerve is most commonly injured in a mid- or distal humeral shaft fracture?)
In conclusion, the radial nerve’s anatomical proximity to the humeral shaft makes it susceptible to injury in mid- or distal fractures. Prompt recognition through clinical and diagnostic evaluation, coupled with tailored conservative or surgical management, optimizes functional outcomes. Clinicians must remain vigilant for radial nerve involvement in these fractures to mitigate long-term disability and enhance patient recovery.