**8. Radial nerve**

#### **8.1. Anatomy**

The radial nerve receives innervation form C5-C8 and T1 roots, being the terminal branch of the posterior cord. It enters the arm behind the brachial artery, medial to the humerus and anterior to the long head of the triceps muscle running through the radial groove at the humerus, giving off branches for both heads of the triceps muscle. It descends distally along the border of the brachialis muscle and approximately 2cm distal to the elbow, the radial nerve divides into the posterior interosseous nerve and the superficial sensory divisions. The posterior interosseous nerve passes beneath the fibrous proximal margin of the supinator muscle, known as the arcade of Frohse, and bifurcates to innervate the extensor carpi ulnaris muscle and the digital extensor muscles. The radial nerve does not innervate any hand muscle [26] (Figure 8).

**Figure 8.** Radial nerve anatomy showing its divisions at the forearm.

#### **8.2. Radial nerve entrapment**

Lister et al, in 1979, suggested 4 possible sites of radial nerve compression: the fibrous bands anterior to the radial head, the "radial recurrent fan" of vessels described by Henry, the tendinous margin of the extensor carpi radialis brevis, and the arcade of Frohse. A fifth site of possible compression of this nerve is at the radial tunnel, which represents the fascia at the superficial portion of the supinator muscle that may compress the deep branch of the radial nerve. Nevertheless, the compression of the posterior interosseous branch is the most impor‐ tant entity in this matter (Figure 9).

*8.3.3. Treatment*

*8.4.1. Etiology*

*8.4.2. Diagnosis*

*8.4.3. Treatment*

neous tissues distally.

*8.5.1. Etiology*

the midforearm.

**8.5. Wartenburg's syndrome**

indicated with a dorsoradial surgical approach [28].

proximal radioulnar joint or radioocapitellar joint.

help; the diagnosis is basically from careful and serial evaluations.

**8.4. Posterior interosseous syndrome**

In case of pressure palsy, observation is indicated as most of the symptoms may recover in hours, several weeks or even months. If the patient only presents with moderate symptoms limited to the sensory division of the nerve, a trial of systemic steroids and rest of the arm usually is considered. In severe and progressive cases a surgical decompression may be

Compression Neuropathies http://dx.doi.org/10.5772/55316 121

Brachial neuritis, fibrous bands anterior to the radial head, fibrous proximal edge of extensor carpi radialis brevis, arcade of Frohse, distal edge of supinator, lipomas and synovitis from

The patient will present with weakness of the hand and wrist often with rapid onset. The wrist extension is preserved but it will move radialwards because of failure of extensor carpi radialis brevis and extensor carpi ulnaris. There will be no elevation of the metacarpophalangeal joints with no retroposition of the thumb. The majority of cases have no sensory disturbance in the distribution of the superficial branch of the radial nerve. Electrophysiologyc studies are of little

The management can be divided in operative and non-operative options. Observation is initially indicated if no space-occupying lesion is suspected up to 12 months. It is accompanied by splinting of the wrist in extension or by the use of a dynamic extension splint. Severe or progressive cases need surgical decompression, which has little risk, very low morbidity, and is typically followed by prompt relief from the pain. The surgery consists in a total external neurolysis of the nerve, starting 2cm distal to the elbow crease carried through the subcuta‐

This syndrome originates from compression of superficial radial nerve as it emerges from beneath brachioradialis muscle to reach the subcutaneous plane over the radial border of the distal forearm. At the point of exit from beneath the muscle, a compression of the nerve can develop. It does not develop spontaneously, but is an infrequent complication of trauma to

**Figure 9.** Posterior interosseous branch and its relation with the supinator muscle.

#### **8.3. Proximal radial nerve compression**

#### *8.3.1. Etiology*

There are many possible causes of proximal radial nerve compression, being the most common by direct pressure in the axilla, traumatic division, iatrogenic injury or by traction. At the elbow, it may be caused by a fibrous band from the shaft of the humerus that crosses the nerve to the lateral epicondyle [27].

#### *8.3.2. Diagnosis*

The patient will present with slight weakness of elbow flexion, marked weakness of elbow and wrist extension, finger elevation, thumb retroposition and numbness over the dorsal aspect of thumb base. If the compression is at the elbow, the patient will not have disturbance of the radial wrist extensor muscles as their motor nerves separate from the radial nerve proximal to the elbow, but the sensory branch will be affected as the motor division to the digital extensor muscles. Electrophysiologic studies are not diagnostic unless there is significant denervation.

#### *8.3.3. Treatment*

**8.2. Radial nerve entrapment**

tant entity in this matter (Figure 9).

**Figure 9.** Posterior interosseous branch and its relation with the supinator muscle.

There are many possible causes of proximal radial nerve compression, being the most common by direct pressure in the axilla, traumatic division, iatrogenic injury or by traction. At the elbow, it may be caused by a fibrous band from the shaft of the humerus that crosses the nerve

The patient will present with slight weakness of elbow flexion, marked weakness of elbow and wrist extension, finger elevation, thumb retroposition and numbness over the dorsal aspect of thumb base. If the compression is at the elbow, the patient will not have disturbance of the radial wrist extensor muscles as their motor nerves separate from the radial nerve proximal to the elbow, but the sensory branch will be affected as the motor division to the digital extensor muscles. Electrophysiologic studies are not diagnostic unless there is significant denervation.

**8.3. Proximal radial nerve compression**

to the lateral epicondyle [27].

*8.3.1. Etiology*

*8.3.2. Diagnosis*

Lister et al, in 1979, suggested 4 possible sites of radial nerve compression: the fibrous bands anterior to the radial head, the "radial recurrent fan" of vessels described by Henry, the tendinous margin of the extensor carpi radialis brevis, and the arcade of Frohse. A fifth site of possible compression of this nerve is at the radial tunnel, which represents the fascia at the superficial portion of the supinator muscle that may compress the deep branch of the radial nerve. Nevertheless, the compression of the posterior interosseous branch is the most impor‐

120 Peripheral Neuropathy - A New Insight into the Mechanism, Evaluation and Management of a Complex Disorder

In case of pressure palsy, observation is indicated as most of the symptoms may recover in hours, several weeks or even months. If the patient only presents with moderate symptoms limited to the sensory division of the nerve, a trial of systemic steroids and rest of the arm usually is considered. In severe and progressive cases a surgical decompression may be indicated with a dorsoradial surgical approach [28].

#### **8.4. Posterior interosseous syndrome**

#### *8.4.1. Etiology*

Brachial neuritis, fibrous bands anterior to the radial head, fibrous proximal edge of extensor carpi radialis brevis, arcade of Frohse, distal edge of supinator, lipomas and synovitis from proximal radioulnar joint or radioocapitellar joint.

#### *8.4.2. Diagnosis*

The patient will present with weakness of the hand and wrist often with rapid onset. The wrist extension is preserved but it will move radialwards because of failure of extensor carpi radialis brevis and extensor carpi ulnaris. There will be no elevation of the metacarpophalangeal joints with no retroposition of the thumb. The majority of cases have no sensory disturbance in the distribution of the superficial branch of the radial nerve. Electrophysiologyc studies are of little help; the diagnosis is basically from careful and serial evaluations.

#### *8.4.3. Treatment*

The management can be divided in operative and non-operative options. Observation is initially indicated if no space-occupying lesion is suspected up to 12 months. It is accompanied by splinting of the wrist in extension or by the use of a dynamic extension splint. Severe or progressive cases need surgical decompression, which has little risk, very low morbidity, and is typically followed by prompt relief from the pain. The surgery consists in a total external neurolysis of the nerve, starting 2cm distal to the elbow crease carried through the subcuta‐ neous tissues distally.

#### **8.5. Wartenburg's syndrome**

#### *8.5.1. Etiology*

This syndrome originates from compression of superficial radial nerve as it emerges from beneath brachioradialis muscle to reach the subcutaneous plane over the radial border of the distal forearm. At the point of exit from beneath the muscle, a compression of the nerve can develop. It does not develop spontaneously, but is an infrequent complication of trauma to the midforearm.

#### *8.5.2. Diagnosis*

The patient will present local pain and sensory disturbance to the dorsal-lateral skin of the hand, with tingling over back of thumb base, with a positive Tinel's sign at the point of exit of the nerve from beneath the braquiradialis muscle. As this muscle is a supinator muscle pain is accentuated by attempting this motion while the forearm is passively pronated. Electrophi‐ siologic tests reveal reduced conductions and are generally not necessary for diagnosis.

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#### *8.5.3. Treatment*

Surgical decompression using a dorsoradial approach. The superficial radial nerve is identified and released at it emerges beneath the brachioradialis tendon. The prognosis is excellent.
