Radial nerve entrapment is an uncommon diagnosis that is prone to under-recognition. Compression or entrapment can occur at any location within the course of the nerve distribution, but the most frequent location of entrapment occurs in the proximal forearm. This most common location is typically in proximity to the supinator and often will involve the posterior interosseous nerve branch.
The radial nerve arises from C5 to C8 and provides a motor function to the extensors of the forearm, wrist, fingers, and thumb. The superficial radial nerve provides a sensory function to the posterior forearm. Depending on the location of entrapment, a patient may experience pain, numbness, weakness, and overall dysfunction or any combination of these.
Radial nerve entrapment is often thought to be a result of overuse but can certainly occur secondary to other causes such as direct trauma, fractures, lacerations, compressive devices, or post-surgical changes. The radial nerve divides into the superficial radial and posterior interosseous nerves at the level of the radiocapitellar joint. The posterior interosseous nerve runs along the radial neck before piercing the supinator muscle, a common site of entrapment. The nerve further divides into four terminal branches that can typically be compressed at one of four other sites as well. These four sites are the fibrous bands around the radial head, the recurrent radial vessels, the arcade of Frohse, and/or the tendinous margin of the extensor carpi radialis brevis. Overuse actions and exercises that can lead to this condition are often repetitive pronation and supination of the wrist and forearm and commonly occur in the locations discussed previously.
This condition is typically a result of nerve injury secondary to compression, traction, or direct trauma, causing a process of local swelling, edema, or even partial or complete laceration. The compression and/or traction often occur secondary to repetitive motions causing inflammation or architectural changes to the surrounding tissue. There are varying degrees of nerve damage severity. In mild cases, the compression of the nerve causes no permanent damage to the nerve and nerve sheath fully recover. More severe cases can cause permanent damage to the nerve and/or nerve sheath, causing persistent deficits.
Multiple classification systems exist to categorize nerve injury grading. A popular one is the Sunderland Classification which is detailed as follows:
Correlating Sunderland and Seddon's classification systems with one another:
The presentation can certainly vary given multiple areas of possible entrapment. Symptoms usually develop very slowly. The duration of symptoms often averages multiple years before a definitive diagnosis is made. As mentioned previously, symptoms of this type of nerve entrapment are pain, sensory and motor changes, paresthesias, and/or paralysis. Physical exam and/or history often reveal symptoms limited to the dorsoradial aspect of the distal forearm and hand. Findings of decreased sensation over the dorsoradial aspect of the forearm or hand are helpful in establishing the diagnosis. A positive Tinel sign along the radial aspect of the mid-forearm is suggestive of this process. Wrist flexion, ulnar deviation, and pronation place strain on the nerve and will often reproduce or exacerbate symptoms. Resisted extension of the middle finger with the elbow extended is another sign of nerve entrapment. This sign is often used to aid in the diagnosis of lateral epicondylitis, but it also often positive in cases of radial nerve entrapment.
First and Second Degree Nerve Injuries
Third Degree Nerve Injuries (Neurotmesis)
Most complications are related to surgery and include:
Consider a differential diagnosis of De Quervain tenosynovitis, intersection syndrome, lateral antebrachial cutaneous neuropathy, thumb carpometacarpal arthritis, C6 radiculopathy, lateral epicondylitis, or elbow bursitis.
Motor deficits indicate an entrapment or injury to the posterior interosseous nerve branch of the radial nerve. It does not carry any cutaneous sensory information, though. These clinical findings can help distinguish an entrapment of this branch versus a compression more proximal or even cervical radiculopathy.
The clinical presentation of posterior interosseous nerve entrapment is characterized by the loss of motor function due to variable degrees of weakness involving ulnar deviation.
If splinting is warranted, the splint will usually need to be worn for at least two to four weeks, or until symptoms have dissipated. Consider the addition of protective padding if the patient is an athlete and involved with sports that cause repetitive forearm trauma.
The acute management of radial nerve entrapment is surgical. However, once the surgery is completed, the patient needs to be followed by a neurologist, hand surgeon, specialty trained nurses, physical, and occupational therapist. After the healing is complete, most patients require extensive rehabilitation to recover motor and sensory function. In addition, the patient must wear protective splints to protect the hand. Orthopedic nurses monitor patients and provide education. Recovery often takes months, and compliance with the exercise program is key.  [Level 5]
The outcomes after radial nerve entrapment depend on the severity of the injury. For those with neuropraxic injury, the outcome is good in most cases. For those with axonotmesis, recovery depends on the completeness of release. Unfortunately, many patients have residual deficits. Following neurotmesis, recovery is usually limited even with surgical repair. All patients need extended physical and occupational therapy, and recovery can take months or even years. [Level 5]
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