Review Question - QID 215761

Following radial nerve neuropraxia, motor function predictably returns in a proximal to distal fashion, with the extensor indices proprius being the last muscle to regain function.

Radial nerve neuropraxia is unfortunately one of the complications following ORIF of humerus fractures through a posterior approach. The radial nerve crosses the humerus from medial to lateral and can be identified 14 cm proximal to the lateral epicondyle of the humerus as it pierces the lateral intermuscular septum. The radial nerve provides sensation to the posterior arm and dorsal of the hand. It's terminal branch, the posterior interosseous nerve (PIN) supplies motor innervation to the ECRB, extensor digitorum, EDM, ECU, supinator, APL, EPB, EPL and EIP. Of these, the EIP receives the most distal innervation, and thus, is the last muscle to regain function following a radial nerve neuropraxia. Typical motor recover occurs in a proximal to distal direction (Illustration A).

Claessen et al review the factors associated with radial nerve palsy after operative treatment of diaphyseal humeral shaft fractures. They report that an iatrogenic radial nerve palsy occurred in 18 of 259 diaphyseal humeral fractures (7%), and was related to the chosen approach. They conclude that lateral and posterior exposures of the humerus most commonly result in iatrogenic radial nerve palsy and this complication should be discussed with patients preoperatively.

Carroll et al review management of humeral shaft fractures. They report that while closed treatment with a functional brace remains the standard of care, operative stabilization is sometimes required. They conclude that with operative treatment of humeral shaft fractures comes the risk of iatrogenic radial nerve palsy.

Illustration A demonstrates the location of innervation of the muscles supplied by the PIN with the EIP being most distal.

Incorrect Answers:
Answer 1: The brachioradialis is the first muscle to regain function following radial nerve neuropraxia as it is innervated the most proximally.
Answer 2 and 4: EDM and ECRL are more proximally innervated than the EIP.
Answer 5: The triceps is not typically denervated in the setting of radial nerve neuropraxia following humeral shaft ORIF.