Posterior Interosseous Nerve Syndrome

Original Editor - David Adamson

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Clinically Relevant Anatomy

File:PIN.jpg

poterior interosseous nerve

The posterior interosseous nerve is a continuation of the radial nerve as it passes down the posterior side of the forearm. The radial nerve wraps around the posterior aspect of the arm to the anterior side of the lateral epicondyle of the humerus. As it passes below the lateral epicondyle the radial nerve begins back on a posterior course and then it splits into the superficial and deep radial nerves. The continuation of the deep radial nerve passes through the supinator muscle to become the posterior interosseous nerve. The posterior interosseous nerve can become entrapped with this course through the supinator muscle in the arcade or canal of Froshe in approximately 30% of the population. The role of the posterior interosseous nerve is motor only to the wrist and finger extensors as well as the supinator.    

Mechanism of Injury / Pathological Process

Compression of the posterior interosseus nerve may arise from activities that promote repetitive gripping combined with supinatory movements. This diagnosis may be associated with lateral epicondylitis.

Clinical Presentation

A patient who presents with this diagnosis of posterior interosseus syndrome may have a history of vague proximal posterior forearm pain with no weakness in more mild cases. In more severe cases, the patient may present with weakness in the wrist and finger extensors. Because the extensor carpi radialis longus and in some cases the extensor carpi radialis brevis are innervated before the radial nerve passes into the supinator, there is usually some sparring of wrist extension. Also because of lack of extensor carpi ulnaris, there may some radial deviation of the wrist with extension with the remaining innervated ECRL and ECRB. There will be no sensory loss as this nerve carries motor fibers only. In mild cases posterior interosseus syndrome may be difficult to delineate from lateral epicondylitis and may be considered only after a failed resolution of lateral epicondylitis. There will be no changes with electro diagnostic studies with lateral epicondylitis.

Diagnostic Procedures

Diagnosis of posterior interosseus syndrome can be identified with EMG studies of the nerve. Differentiation of the lateral aspect of the nerve can be made with delays with the laterally innervated musculature. This includes involvement of the abductor pollicis longer, extensor pollicis longus, extensor pollicis brevis, and extensor indicis. The medial aspect of the nerve will have involvement of all the other extensors. Differentiation of posterior interosseus syndrome from lateral epicondylitis may be achieved with lidocaine injection at the lateral epicondyle. This should relieve lateral epicondyle pain however it will not change compression pain distally at the supinator.Recently there is evidence for the use of ultrasound for  identification of peripheral nerve compression syndromes. 

Management / Interventions

Initial conservative management of radial nerve entrapments includes rest and modification of activities.  Activity modification includes educating the patient on limiting repetitive forced supinatory activities,  repetitive pronation activities, repetitive forceful gripping,  or resisted end range elbow extension activities.  To help control the inflammation that may be contributing to the syndrome, the use of anti-inflammatory medications may be prescribed.  The use of a static forearm based functional position splint may be used to rest the extensor muscles of the wrist and fingers.  The splint may also include the elbow to limit elbow extension and forearm pronation/supination.  In cases with more significant weakness,  an  extension  assist outrigger component may be added to aid in passive finger extension for improved hand function. 

For cases that worsen or fail to resolve with conservative care after 3-6 months,  surgical decompression may be indicated  to prevent further nerve damage. Recovery and outcome will depend on the extent of the nerve damage with the vast majority of neuropraxic  problems resolving.   Treatment of a patient after they have had a decompression includes a gradual return to activities over a 6 week period.       

Differential Diagnosis

The primary diagnosis that may cause difficulty with differential diagnosis is lateral epicondylitis. In early stages, both diagnoses may present with similar presentations with dorsal forearm pain and pain with resisted wrist extension. The patient who presents with posterior interosseus syndrome may have subtle finger extension and thumb extension weakness. The use of a lidocaine injection may aid in the diagnosis of lateral epicondylitis as it should significantly decrease pain in this diagnosis for a temporary period of time.
Compression or injury of the radial nerve may occur along its course on the posterior side of the humerus in the radial groove from humeral shaft fractures or as it winds to the anterior side of the lateral epicondyle from epicondylar fractures. It may also become compressed from the fibrous bands of the radiocapitellar joint. In cases with high radial nerve injury, only the triceps would be spared so there would be complete absence of the wrist, finger, and thumb extensors. The superficial branch of the radial nerve may become entrapped as it runs under the tendon of the brachioradialis. This diagnosis is known as Wartenberg's disease and is sensory only.  

Key Evidence

Interventions for treating the posterior interosseus nerve syndrome: a systematic review of observational studies.

Ultrasonographic evaluation of the iatrogenic peripheral nerve injuries in upper extremity.

edian and radial nerve compression about the elbow.  A unified approach to radial tunnel syndrome and lateral tendinosis.

Recent Related Research (from Pubmed)

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References

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