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Radial Nerve Entrapment

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Radial Nerve Entrapment

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A number of radial nerve entrapments are recognized and are named according to the location at which they occur.

The radial nerve is the most commonly injured peripheral nerve and, because of its spiral course across the back of the mid-shaft of the humerus, and its relatively fixed position in the distal arm as it penetrates the lateral intermuscular septum, it is the most frequently injured nerve associated with fractures of the humerus.

Radial Nerve Entrapment Types

Four radial nerve entrapments are commonly cited:

  1. high radial nerve palsy,
  2. posterior interosseous nerve syndrome (PINS),
  3. radial tunnel syndrome (RTS),
  4. superficial radial nerve palsy.

There is motor and sensory involvement with the high radial nerve palsy, motor involvement with the PINS, pain with the RTS, and sensory disturbances with the superficial radial nerve palsy. Symptoms of pain, cramping, and tenderness in the proximal posterior (dorsal) forearm, without muscle weakness, are associated with RTS, whereas PINS involves the loss of motor function of some or all of the muscles innervated by the PIN and is thus characterized by weakness.

See Also: Radial Nerve Palsy Test
Radial Nerve anatomy
Radial Nerve Anatomy

High Radial Nerve Compression

A spontaneous nerve compression may occur in the mid-arm at the level of the lateral head of the triceps due to strenuous muscular exercise. A mid-shaft humerus fracture can result in a radial nerve entrapment at the spiral groove of the humerus in 14% of humeral fractures.

Regardless of the cause, a high radial nerve palsy will result in the following:

  1. a loss of wrist extension (dropped hand),
  2. an inability to extend the fingers and thumb,
  3. a decrease in sensibility of the first posterior (dorsal) web space.
  4. Involvement of the triceps muscle is dependent on the level of compression.

A cervical radiculopathy and thoracic outlet syndrome must be considered in the differential diagnosis.

High Radial Nerve Compression
High Radial Nerve Compression

Posterior Interosseous Nerve Syndrome (PINS)

There are five potential sites of compression of the Posterior Interosseous Nerve as it traverses through the radial tunnel:

  • the fibrous bands that connect the brachialis to the brachioradialis;
  • the vascular leash of Henry, a fan of blood vessels that cross the nerve at the level of the radial neck;
  • medial proximal portion (leading edge) of the ECRB;
  • Between fibrous bands at the proximal and distal edge of the supinator. The proximal border of the supinator, through
    which the radial nerve passes, is referred to as the arcade of Frohse.

Symptoms of Posterior Interosseous Nerve entrapment include:

  1. lateral elbow pain that radiates into the distal forearm and is aggravated by repetitive pronation and supination, most specifically resisted supination.
  2. Tenderness is noted 3–4 cm distal to the lateral epicondyles where the radial nerve crosses the radial head and penetrates the supinator muscle.
  3. PIN palsy produces an inability to extend the MCP joints of the thumb, index, long, ring, or small fingers either individually or in combination.
  4. Additionally, there is a loss of thumb IP extension and radial abduction of the thumb.

Since the PIN can innervate the ECRB prior to the nerve’s entrance into the radial tunnel, this muscle may not be involved in the PIN palsy. Thus, when compression within the radial tunnel is sufficient to cause paralysis but there is no palsy, the condition is termed PINS.

Initial conservative intervention includes”

  1. rest,
  2. activity modification,
  3. the use of a cock-up splint.
  4. Regular gentle stretching of the wrist extensor muscles, with the elbow held in full extension is begun after a spontaneous recovery.
Posterior Interosseous Nerve Syndrome
Posterior Interosseous Nerve Syndrome

Radial Tunnel Syndrome RTS

Radial Tunnel Syndrome involves compression of the deep branch of the radial nerve. The term RTS was introduced by Roles and Maudsley, who suggested that RTS was the cause of resistant tennis-elbow pain.

The same structures implicated in PIN compression syndrome can cause RTS, although RTS is often thought of as a
dynamic compression syndrome. This is because compression of the nerve occurs during elbow extension, forearm pronation, and wrist flexion, which causes the ECRB and the fibrous edge of the superficial part of the supinator to tighten around the nerve.

Men and women are equally affected, and the compression appears to be common in the fourth to sixth decades of life.

The symptoms from this compression can mimic those of tennis elbow:

  1. tenderness over the lateral aspect of the elbow,
  2. pain on passive stretching of the extensor muscles,
  3. pain on resisted extension of the wrist and fingers.

Pain, which is poorly localized over the radial aspect of the proximal forearm, is the most common primary presenting symptom in RTS. In fact, it is the only nerve compression syndrome in which the signs and symptoms are not based on the nerve distribution.

Radial Tunnel release
Radial Tunnel Syndrome

Physical examination include:

  1. Upon palpation, maximal tenderness is usually elicited over the radial tunnel, some 5 cm distal to the lateral epicondyle, anterior to the radial neck.
  2. Resisted middle finger extension, which tightens the fascial origin of the ECRB, and resisted supination of the forearm with the elbow fully extended should reproduce the pain at the point of maximal tenderness.
  3. Positioning the arm in elbow extension, forearm pronation, and wrist flexion produces significant compression of the radial nerve.

Conservative treatment include:

  1. Focus on education to avoid the provocative positioning of the arm into forceful extension and supination of the wrist and forearm
  2. Rest,
  3. Stretching,
  4. Splinting: If a wrist immobilization splint is used, it is fitted in 45 degrees of extension for continual wear.

Surgical treatment is reserved for patients whose symptoms are not relieved by conservative intervention.

Radial Tunnel release
Radial Tunnel Release

Radial Sensory Nerve Entrapment

The term Wartenberg’s syndrome or cheiralgia paresthetica is used to describe a mononeuritis of the superficial radial nerve, which can become entrapped where it pierces the fascia between the brachioradialis and Extensor carpi radialis longus tendons.

Symptoms include shooting or burning pain along the posterior-radial forearm, wrist, and thumb, associated with wrist flexion and ulnar deviation. These symptoms can lead the clinician to believe that the first carpometacarpal joint and/or tendons of the anatomic snuffbox are involved and that de Quervain’s disease is present.

See Also: De Quervain Tenosynovitis
Wartenberg's syndrome


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