Posterior interosseous nerve syndrome is a chronic neuromuscular compressive or nerve compression neuropathy of the posterior interosseous nerve which innervates the extensor compartment of the forearm. It usually has an insidious onset, sudden often presenting with weakness in finger and thumb extension.

Posterior interosseous nerve syndrome may be a neuropathic compression of the posterior interosseous nerve where it passes through the radial tunnel this might end in paresis or paralysis of the digital and thumb extensor muscles, leading to an inability to increase the thumb and fingers at their metacarpophalangeal joints. Wrist extension is preserved thanks to the action of the extensor carpi radialis longus innervated by the nervus radialis.

Anatomy

The posterior interosseous nerve may be a branch of the nervus radialis, which comes off the posterior cord of the plexus brachialis. With nerve roots C5 to T1, the nervus radialis travels down the arm and divides into superficial and deep branches within the proximal forearm. Normally the deep branch of the nervus radialis dives into the posterior forearm through the heads of the supinator to emerge because of the posterior interosseous nerve. Anatomical variants include the deep nervus radialis passing through the Arcade of Frohse to become the posterior interosseous nerve. This variant can increase susceptibility to impingement. The posterior interosseous nerve supplies motor innervation to the posterior forearm. The terminal branch of the posterior interosseous nerve travels distally into the ground of the 4th dorsal compartment of the wrist to innervate the dorsal wrist capsule.

Compression neuropathies of the nervus radialis distal to the elbow include radial tunnel syndrome, posterior interosseous nerve syndrome, and Wartenberg syndrome. Each of those has distinct symptoms, which may help with identifying the right diagnosis. Posterior interosseous nerve syndrome may be a compressive neuropathy of the posterior interosseous nerve which innervates the extensor compartment of the forearm it always has an insidious onset, often presenting with weakness in finger and thumb extension. However, there should be preservation in wrist extension thanks to the nervus radialis innervated extensor carpi radialis longus its often self-limiting and resolves with conservative measures. However, symptoms that are refractory to nonoperative treatment may require surgical decompression.

Causes

• Posterior interosseous nerve syndrome can result from trauma, gunshot wound, sudden fall, space-occupying lesions like
• Rheumatoid arthritis,
• Muscle weakness
• Motorbike driving, mechanical work such as range use to tight or loose any pars
• Brachial neuritis, and injury
• Spontaneous compression.[rx]
• The most common site of compression is at the arcade of Frohse (the proximal edge of the supinator).
• Repetitive pronation supination activities in your daily life activity can also can posterior interosseous nerve syndrome.[rx][rx][rx]

Symptoms

• Pain
• Paresthesia, numbness, itching in the affected area,
• Sensory disturbances are present
• Muscle spasm, weakness
• It usually has a sudden onset, often presenting with weakness in finger and thumb extension. However, there should be preservation in wrist extension movement due to the radial nerve innervated extensor carpi radialis longus.[rx]
• Insidious onset of weakness, numbness in finger extension at the MCP joint.
• Weakness in extension and abduction of the thumb joint.
• Deep ache in the proximal forearm may develop.
• It may often be associated with lateral elbow pain that is exacerbated by pronation and supination.
• Wrist drop is not a symptom as the extensor carpi radialis brevis and longus remain intact.
• When asked to make a fist, the wrist may deviate radially due to extensor carpi ulnaris weakness.
• Positive Tinel’s sign in severe injuries may be found
• A possible positive radial nerve tensioning test may be positive.

Diagnosis

Physical examination

• History
• Functional limitations of movement or deficits
• Palpation: muscle weakness, motor function weakness. Abnormal tenderness is expected over the area of Frohse and eventually over the lateral epicondyle
• Neural tension test
• Muscle testing (with resistance): There is partial or complete paralysis, weakness of the wrist extensors
  • The patient is unable to extend the thumb and other fingers of the affected side metacarpophalangeal joints
  • Wrist extension is possible, typically in a radially deviated direction, due to the preservation of the extensor carpi radialis longus the weakened extensor carpi ulnaris muscle
  • Resisted supination and pronation of the forearm can cause pain, as well as the resisted extension of the middle finger
  • The brachioradialis and the extensor carpi radialis longus are innervated by the most proximal branches of the radial nerve, so may be spared

Plain radiograph

Radiography can assist in including underlying fractures, dislocations, dislocated problems, instability, or arthrosis as an underlying cause of the compression.

Ultrasound

Ultrasound can be useful in both localizing and quantifying the degree of constriction. The most commonly seen finding is posterior interosseous nerve enlargement problem or swelling, discolor at the proximal aspect of the compression site.

MRI

Imaging diagnosis based primarily on muscle denervation pattern; nerve injury abnormal signal intensity or atrophy in muscles innervated by the posterior interosseous nerve. MRI can also be used to identify any extrinsically compressive lesions, evaluate potential compression sites, and ultimately for surgical planning if intervention is appropriately done.

Electromyography (EMG)

The evaluation may include an electromyography (EMG) and nerve conduction study (NCS).[10] This study may show denervation changes within the muscles innervated by the posterior interosseous nerve. there’ll be sparing of muscles innervated by the nervus radialis, including triceps, anconeus, brachioradialis, and extensor carpi radialis longus (ECRL). there’ll even be normal nerve nerve impulse of the superficial nervus radialis.

Treatment

Treatment of posterior interosseous nerve syndrome starts with non-surgical management, which may include splinting, physiotherapy, activity modification, and surgery is reserved for those refractory to conservative management for a minimum of 3 months.

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

Conservative management

• Reduction of local inflammation and swelling around the nerve
  • 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
    • 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
• Therapeutic ultrasound
• Physiotherapy
• Reduction of synovitis:
  • Heat
  • Rest
  • Mild range of motion

Surgery

Surgical decompression focuses on releasing areas of compression. Areas that will be decompressed include releasing fibrous bands superficial to the radiocapitellar joint, the fibrous fringe of extensor carpi radialis brevis (ECRB), ligating the leash of Henry (radial recurrent artery), releasing the arcade of Frohse, and therefore the distal fringe of the supinator.

• 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
  • 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.

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

• Cryotherapy: Increase extensibility and reduce tone of local muscles
• Ultrasound
• TENS
• Deep tissue massage and stretching exercises: Improve extensibility of the muscles who surround the brachial plexus and radial nerve
  • Focus on:^[30]
    • Thoracic outlet
    • Pectoralis minor
    • Triceps
    • Brachioradialis
    • Supinator
    • Extensor carpi radialis longus and brevis
• Dry needling: Increase extensibility and reduce tone of local muscles
• Neural mobilizations:^[30]
  • Reduce mechanical extra- and intra-neural adhesion
  • Assist the neuromodulation of symptoms
• Manual therapy^[9]: Regain elbow mobility
• Strengthening^[20] and range of motion exercises
• Stretching exercises:
  • Focus on supinator
  • Passive wrist extensions stretches:
    • Place hand on table and move upper body over wrist
    • Prayer stretch

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.

References

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