The radial nerve is a peripheral nerve, originating from the posterior cord of the brachial plexus, at nerve roots C7, C8, and T1. It provides the medial and lateral heads of triceps brachii with motor innervation, as well as the extensors of the wrist, brachioradialis, and the overlying skin and articulation with sensory information.
A lesion to this nerve describes any pathological process capable of negatively affecting this nerveâ€™s function.
There are numerous possible causes for radial nerve lesions:
- The nerve may become entrapped between the heads of the triceps brachii muscle.
- Within the axilla, the radial nerve is vulnerable to humeral fractures and dislocations.
- â€œSaturday night palsyâ€ can be acquired by sleeping with the arm over the back of a chair, or having someoneâ€™s head compress the arm. This palsy is the result of compression of the lower portion of the brachial plexus, and may also involve other brachial nerves. This lesion is usually temporary.
- The radial nerve may also be compressed at the level of the axilla due to inadequately adjusted crutches. This lesion is also usually temporary.
- As the nerve passes down in the spiral groove of the humerus, it may be injured by a fracture of the shaft of the humerus.
- At the level of the elbow, the radial nerve can be entrapped at a number of sites, most commonly at the proximal border of the tendon of the supinator muscle called the arcade of Frohse.
- Another possible lesion to the radial nerve at the level of the elbow is a ruptured synovium, with its effusion compressing the nerve.
- At the wrist, the radial nerve is vulnerable to lesions from plaster casts, wristbands, handcuffs, surgery, injections, ganglions and neuromas.
- Another rare cause of radial nerve lesion is lead poisoning.
The clinical picture of a patient suffering from an ulnar lesion will vary in accordance with the level at which the nerve has been damaged. The more cephalad the lesion, the more extensive the signs and symptoms.
Common signs include: wrist drop, or weakness in active wrist and finger extension, weakness of the triceps brachii, and absent or diminished triceps tendon, and brachioradialis reflexes.
Check for tenderness over the radial tunnel. There may be pain when the fingers are extended against resistance.
Sensory examination may also reveal some abnormalities in the skin supplied by the radial nerve.
Chronic lesions to the radial nerve may show evidence of wasting in the muscles it supplies, as well as flaccidity of these muscles