Review Question - QID 218105

This patient has a radial nerve palsy secondary to likely neuropraxia from a distal one-third humeral shaft fracture. Of the answers provided, the brachioradialis and/or the extensor carpi radialis longus (ECRL) would be expected to recover first.

The incidence of radial nerve palsy after a humeral shaft fracture has been estimated as being between 7% and 22%. In patients with open fractures and radial nerve palsies, the radial nerve should be identified and evaluated for disruption. If using the anterolateral approach, the radial nerve is identified between the brachialis and brachioradialis distally. If using the posterior approach, the radial nerve is found medial to the long and lateral heads and 2cm proximal to the deep head of the triceps. The radial nerve exits the posterior compartment through the lateral intramuscular septum ~10 cm proximal to the radiocapitellar joint, and the lateral brachial cutaneous/posterior antebrachial cutaneous nerve can be used as an anatomic landmark leading to the radial nerve during a paratricipital approach. Controversy remains regarding the need for early exploration in a patient presenting with a closed humerus fracture and concurrent radial nerve palsy, because approximately 77% of patients treated without exploration have spontaneous recovery of radial nerve function. Anatomic studies have demonstrated a relatively consistent order of the radial nerve motor branches in the forearm (proximal to distal): BR, ECRL, supinator, ECRB, extensor digitorum communis, ECU, extensor digit quinti, abductor pollicis longus, extensor pollicis longus, extensor pollicis brevis, and EIP. Note that because the EIP is the last motor branch from the radial nerve, it is likely to be the last to recover following a high radial nerve palsy.

Ilyas et al. provide an updated systematic review on radial nerve palsy recovery in the setting of humeral shaft fractures. They reported the overall prevalence of radial nerve palsy was 12.3% and that patients with radial nerve palsy treated nonsurgically had a rate of spontaneous radial nerve recovery of 77.2%. They further reported that patients who failed nonsurgical management and underwent nerve exploration more than 8 weeks after their injury had a rate of recovery of 68.1%, and those treated with early (within 3 weeks of the injury) surgical exploration and fracture repair had a rate of recovery of 89.8%.

Ljungquist et al. provide a review on the etiology, workup, diagnosis, management, and outcomes of radial nerve injuries. They report that radial nerve injuries continue to challenge hand surgeons, and the course of the nerve and its intimate relationship to the humerus place it at high risk for injury with humerus fractures.

Abrams et al. performed a cadaveric study evaluating the anatomy of the radial nerve motor branches in the forearm. They report the innervation order from proximal to distal (based on mean shortest branch lengths) was brachioradialis, extensor carpi radialis longus, supinator, extensor carpi radialis brevis, extensor digitorum communis, extensor carpi ulnaris, extensor digiti quinti, abductor policis longus, extensor policis longus, extensor policis brevis, and extensor indicis proprius.

Figure A demonstrates a spiral fracture of the distal one-third of the humeral shaft, otherwise known as a Holstein-Lewis fracture. Note that these fractures are commonly associated with neuropraxia of the radial nerve (22% incidence).

Incorrect Answers:
Answer 1: This patient’s radial nerve was likely injured around distal third of the arm near the fracture site, and therefore the innervation to the medial and long head of the triceps is far proximal to the zone of injury. Note: shortly after passing through the triangular interval, the radial nerve gives a motor branch to the lateral head of the triceps brachii followed by two sensory branches: the inferior lateral cutaneous nerve of the arm and the posterior cutaneous nerve of the forearm.
Answers 2, 3 and 5: The radial nerve branches to ECRB, EPL, and EIP occur more distal than those to the BR and ECRL and therefore reinnervation will occur later, and reinnervation moves proximal to distal.