This board review post will go over the basics of Radial Nerve Palsy.
How does one get a radial nerve palsy?
Contrary to what I previously thought, “Saturday-night palsy” rarely results from prolonged axilla compression. The classic story of an intoxicated person falling asleep with their arm draped over the back of a park bench is misleading. Prolonged axillary compression would cause brachial plexus compression and would likely damage multiple nerves, not just the radial nerve.
The most common site of compression to cause radial nerve palsy is actually at the humeral shaft where there is little soft tissue protection of the nerve. Any prolonged compressive force on the humerus from a hard surface will cause a radial nerve palsy, which means the classic story is more like an intoxicated person falling asleep on a hard floor. Of note, radial nerve palsy is also called Bridegroom’s Palsy – referring to the bride’s head resting on the groom’s arm with the groom too scared to say anything about his progressive neurologic deterioration.
How do you diagnose radial nerve palsy?
After taking a good history, the primary goal in your physical exam for wrist drop is to make sure this is an isolated peripheral neuropathy only and not a plexopathy involving multiple nerves or a central lesion, like a stroke.
The radial nerve controls extension of the wrist, fingers and thumb, with dysfunction resulting in wrist and finger drop.
The physical exam should focus on testing for median and ulnar nerve function. The median nerve can be tested through flexion of the thumb, pointer and middle fingers. Testing for ulnar nerve function, particularly finger adduction, can be limited when the patient’s fingers and wrist are flexed and this will lead to a misdiagnosis of multiple nerve palsy. The examiner should lay the patient’s hand on a flat surface with the fingers slightly extended in order to give them the best chance at testing success. A simple test is placing a piece of paper between their fingers and seeing if they can hold it while you attempt to pull away.
What tests should I order?
With a good physical exam showing peripheral radial neuropathy only, no other tests are required.
What is the treatment?
Radial nerve palsy will typically resolve on its own, with regain of function over weeks to months. The patient should be splinted with the wrist at 60 degrees dorsiflexion for the wrist drop. It is also recommended that the individual fingers be dorsiflexed with a specialized splint to prevent contractures and improve function.
This is an example of the individual finger splints. As mentioned, the wrist should be in 60 degrees dorsiflexion which is not shown here.
This is primarily a board review post and is not based upon an up-to-date literature review.
References
Snow, David and E. Bradshaw Bunney. Peripheral Nerve Disorders. In: Walls R, Hockberger R, Gausche-Hill M. Rosen’s Emergency Medicine: Concepts and Clinical Practice, Ninth Edition Philadelphia, PA: Elsevier Inc; 2018.
Morton DA, Foreman K, Albertine KH. eds. The Big Picture: Gross Anatomy New York, NY: McGraw-Hill; 2011. http://accessmedicine.mhmedical.com/content.aspx?bookid=381§ionid=40140002. Accessed March 14, 2018
Wrist drop image from: http://neuromuscular.wustl.edu/nanatomy/radial.htm
Charles Murchison
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