Posterior Interosseous Nerve Syndrome

Original Editors - Lyn Bruyndonckx

Top Contributors - David Adamson, Kim Jackson, Alan Jit Ho Mak, Anas Mohamed and Evan Thomas  

Definition/Description

Posterior interosseous nerve syndrome is a neuropathic compression of the posterior interosseous nerve where it passes through the radial tunnel.[1] This may result in paresis or paralysis of the digital and thumb extensor muscles, resulting in an inability to extend the thumb and fingers at their metacarpophalangeal joints. The only movement patients may be able to do is the dorsoradial direction.[2]

Radial nerve.jpg

Clinically relevant anatomy

The posterior interosseous nerve is located close to shaft of the humerus and the elbow. This nerve is the deep motor branch of the radial nerve. Proximal to the supinator arch, the radial nerve is divided into a superficial branch and posterior interosseous branch. The radial nerve supplies the majority of the forearm and hand extensors. Damage to this branch of the radial nerve results in posterior interosseous nerve syndrome.


The radial tunnel is a space that extends 5cm from the radial head to the distal margin of the supinator. This tunnel is attached laterally to the brachioradialis, extensor carpi radialis longus and extensor carpi radialis brevis and medially to the biceps tendon and brachialis. The floor is formed by the deep head of the supinator and the capsule of the radiocapitellar joint, while the roof is formed by the superficial head of the supinator and the radial recurrent vessels.[3]


At the level of the lateral epicondyle, between the brachioradialis and brachialis muscles, the radial nerve, which has its origin in the brachial plexus, divides into its 2 terminal branches: the superficial radial nerve and the posterior interosseous nerve.[4] The superficial radial nerve ends proximal to the radial tunnel. The posterior interosseous nerve is much longer and enters the radial tunnel underneath a musculotendinous arch, the arcade of Frohse. The arcade of Frohse, which is the most common point of compression, is a connection between the deep and superficial heads of the supinator and is fibrotendinous in 30% of the population. The posterior interosseous nerve continues in the radial tunnel through the supinator, as it goes from the anterior to the posterior surface of the forearm.

The posterior interosseous nerve is a motor nerve and sequentially innervates supinator, extensor carpi radialis brevis, extensor digitorum communis, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis, extensor pollicis brevis, extensor pollicis longus, and extensor indicis.[3][5]

Epidemiology/Etiology

Epidemiology

Posterior interosseous nerve syndrome is more common in males, manual laborours and bodybuilders, with an incidence of 3 per 100 000.[6] With a humeral shaft fracture, there is a 12% chance of associated with radial nerve paralysis.[7]

Etiology

Posterior interosseous nerve syndrome can be caused by a traumatic injury, tumors, inflammation and an anatomic injury. With repeated pronation and supination a dynamic compression of the nerve in the proximal part of the forearm can be created.[8]

Posterior interosseous nerve syndrome usually develops spontaneously[1] and is caused by compression injuries to the upper extremity, mostly in the arcade of Frohse[9]. It is the area where the nerve enters the supinator muscle[10] and is the most common place for a compression of the nerve. However, it can also occur following trauma, such as a blow to the proximal dorsal region of the forearm. Impingement of the radial nerve results in posterior interosseous nerve syndrome.[7] Compression of the posterior interosseous nerve is associated with repetitive activities that involve gripping, wrist supination and pronation, with a component of wrist extension.[11]This diagnosis may be associated with lateral epicondylitis.[12]

Posterior interosseous nerve syndrome can be iatrogenic following reduction of radial fracture, transposition of the ulnar nerve or release of the extensor origin for lateral epicondylitis.[1] The causes of posterior interosseous nerve syndrome include intrinsic nerve abnormalities and extrinsic compression.[2]

Characteristics/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 innvervated before the radial nerve passes into the supinator, there is usually some sparring of wrist extension. Also, because of the lack of extensor carpi ulnaris, there maybe some readial deviation of the wrist withe extension with the remaining innvervated ECRL and ECRB.[13][14]

Most nerve entrapments occurs due to an osseoligamentous tunnel narrowing. In the case of a posterior interosseous nerve entrapment, the compression occurs within the musculo-tendinous radial tunnel. In 69.4%, the nerve is compressed by the fibrous arcade of Frohse.[15]


There is a very slow development of the symptoms. The duration of symptoms averaged 2-3 years before a definitive diagnosis could be made.[8] Symptoms of nerve entrapment syndromes are generally involving pain, sensory and motor changes, sensations of popping, paresthesias, and paresis. There will be no sensory loss as this nerve carries motor fibers only.


Posterior interosseous nerve syndrome is characterized by motor deficits in the distribution of the posterior interosseous nerve.[15] While the posterior interosseous nerve does have afferent fibres that transmit pain signals from the wrist, it does not carry any cutaneous sensory information that can help distinguish a posterior interosseous nerve palsy from cervical radiculopathy. The clinical presentation of posterior interosseous nerve syndrome is characterized by the loss of function due to variable degrees of weakness involving ulnar deviation.

Differential diagnosis

Posterior interosseous nerve syndrome is one of the pathologies that can cause lateral elbow pain (lateral epicondylitis). In early stages, both diagnosis 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.[16][17]

The other pathologies that are associated with lateral elbow pain are:

Diagnostic procedures

Careful clinical and electrophysiological examination is important and essential for a reliable diagnosis.[10]

Physical examination

  • History
  • Functional limitations or deficits
  • Palpation: Abnormal tenderness is expected over the arcade of Frohse and eventually over the lateral epicondyle
  • Neural tension test
  • Muscle testing (with resistance):[3][20] There a partial or complete paralysis of the wrist extensors:
    • The patient is unable to extend the thumb and other fingers of the affected side at the metacarpophalangeal joints
    • Wrist extension is possible, but only with a dorso-radial direction, due to the weakened extensor carpi ulnaris
    • Resisted supination and pronation of the forearm can produce pain, as well as resisted extension of the middle finger
    • The brachioradialis, extensor carpi radialis longus and extensor capri radialis brevis are innervated by more proximal branches of the radial nerve, so may be spared

Special investigations

The following special investigations are used to assist in making the diagnosis.[1] It further aids to establish the topography of the lesion and the severity of the muscular denervation.[10]

  • Electromyography: Identify level of compression
  • Nerve conduction velocity
  • MRI: Not commonly used:
    • To determine specific area of compression
    • Assist in surgical planning

Outcome measures

Medical management

There are several medical ways to treat the posterior interosseous nerve syndrome.

Conservative management

  • Reduction of local inflammation and swelling around the nerve:[21]
    • Wrist and/or elbow splints
      • The arm can be put in an above-elbow cast for ten days with the elbow flexed at 90°, the forearm supinated and the wrist in neutral position[22]
      • In cases with more significant weakness, extension assist outrigger component maybe added to aid in passive finger extension for improved hand function.
    • NSAID’s
    • Activity modification to reduce local inflammation and swelling around the nerve
  • Corticosteroid injections[22]
  • Therapeutic ultrasound[22]
  • Physiotherapy[22]
  • Reduction of synovitis:[23]
    • Heat
    • Rest
    • Mild range of motion

Surgery

  • Indication:
    • No improvement with conservative management after 3-6 months
    • Pain present after 12 weeks
    • Surgical decompression may be indicated to prevent further nerve damage.
  • Aim: To obtain full recovery
  • Recovery and outcomes: Will depend on the extent of nerve damage with the vast majority of neuropraxic problems resolving. Treatment of a patient after they have a decompression includes a gradual return to activities over a 6 weeks period.
  • Surgery: Depends on how and where impingement is present[23][24]
    • Arcade of Frohse release
    • Resection of lesions
    • Posterior interosseous nerve release
    • Release of superficial radial nerve
    • Lengthening of supinator
    • Synovectomy

Physiotherapy management

Conservative management

3-6 months of physiotherapy with regular re-assessment of signs and symptoms is recommended. If there is no response to therapy, evidence of denervation, or persistent paralysis, surgical decompression should be considered.[15]

Physiotherapy should include a multimodal approach. The following can be considered based on the patient presentation:

Post-surgical rehabilitation

  • Commence active range of motion from day 3-5
    • Incorporate stretching of extensors
  • Commence strengthening from week 3-4

Patients can return to light duty work between week 2 and 3 post-operatively, while return to baseline function can take between 6 and 12 weeks.

[26]

Clinical bottom line

The posterior interosseous nerve is the deep branch stemming off the radial nerve. Compression can be caused by trauma, repetitive strain and inflammation. This is then known as posterior interosseous nerve syndrome, which may result in paresis or paralysis of the digital and thumb extensor muscles, resulting in an inability to extend the thumb and fingers at their metacarpophalangeal joints. Conservative management includes splinting, NSAID's and physiotherapy, and symptoms normally resolve within 3-6 months. Failed conservative management is an indication for surgery, where nerve releases are the most common surgical intervention. Physiotherapy also plays a big part in the post-operative management, and rehabilitation generally lasts between 6 and 12 weeks.

Key Evidence

References

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