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A 25-year-old woman presents with a 3-week history of being unable to extend her right wrist. She remembers noticing wrist numbness and weakness after waking up on the couch following a night out drinking. She denies any known injury. She says the sensation to her wrist has returned but the ability to extend her wrist has not. On examination, full sensation of the right hand and wrist is noted, but she is unable to extend the wrist and metacarpophalangeal joints.
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The presentation is consistent with a drop wrist or radial nerve palsy. The radial nerve forms at the posterior cord of the brachial plexus and arises in the axilla. Branches of the nerve innervate the triceps muscle as it exits the axilla. The nerve then descends distally down the radial groove of the posterior lateral humerus. Distally it wraps around the humerus laterally and moves anteriorly around the lateral epicondyle. The nerve then travels through the cubital fossa, where it divides within the forearm into 2 branches: the deep branch, which controls movement to the posterior compartment of the forearm, and the superficial branch, which supplies sensation to the hands and fingers. The deep branch of the radial nerve forms the posterior interosseous nerve approximately 8 cm from the elbow. The posterior interosseous nerve further divides into branches that innervate the wrist and finger extensors.
Injury to the radial nerve can occur from prolonged compression of the nerve (“Saturday night palsy”), as a result of compression from a tumor or other masses or as a result of fracture of the humerus. Radial nerve injury occurs in up to 18% of all humeral shaft fractures. Saturday night palsy is associated with sleeping with the arm over a chair, which causes prolonged compression to the radial nerve. A high level of intoxication is usually involved, and the person fails to notice the pain and paresthesia associated with the nerve being compressed during sleep.
It is important to differentiate injury of the actual radial nerve from posterior interosseous nerve injury as the cause of radial nerve palsy or wrist drop. Motor function of the extensor carpi radialis longus (wrist extension with radial deviation) usually remains intact with a posterior interosseous nerve injury but not with radial nerve injury. Proximal radial nerve injuries from compression in the axilla, most commonly from crutches, can cause weakness to the triceps and wrist extensors.
Electromyography and nerve conduction studies can determine the level of nerve injury and help track nerve recovery. Nerve regeneration can be seen on electromyography by 3 to 4 weeks but it may take up to 4 months to see recovery.
Most radial nerve palsies will resolve spontaneously over time as the nerve regenerates slowly. The wrist and metacarpophalangeal joints should be splinted in extension, and the patient should begin physical therapy. Physical therapy continues full passive range of motion as the nerve recovers. The patient must understand that motor recovery can be slow, and physical therapy is essential to preserve motion.
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopedics for Physician Assistants (JOPA).
References
- Hammert WC. Radial nerve palsy. Orthopaedic Knowledge Online Journal. 2009;7(10). http://orthoportal.aaos.org/oko/article.aspx?article=OKO_HAN026#abstract. Accessed December 1, 2015.
- Taylor B. Radial nerve. Orthobullets Web site. Updated September 30, 2014. http://www.orthobullets.com/anatomy/10103/radial-nerve. Accessed December 1, 2015.
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