Radial Mononeuropathy 

Updated: Jun 14, 2018
Author: Wayne E Anderson, DO, FAHS, FAAN; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE 

Overview

Background

Radial neuropathies result from injury due to penetrating wounds or fractures of the arm, compression, or ischemia. Most commonly, they present with a wrist drop. The pattern of clinical involvement is dependent on the level of injury.[1]

Radial neuropathies can occur from surgical procedures such as humeral nailing performed to stabilize an acute humeral fracture.[2]

The terms Saturday night palsy and honeymooner's palsy refer to the concept of placing one's arm over another chair, with the resultant pressure causing injury to the radial nerve.

Pathophysiology

An introduction to radial nerve anatomy is essential for understanding the common mechanisms and location of its injury. The radial nerve branches from the posterior cord of the brachial plexus. It receives root innervation from C5-T1 spinal roots. In the upper arm, the radial nerve gives off a branch to the triceps muscle before it wraps around the humerus at the spiral groove. Three sensory branches, which supply the skin over the triceps and posterior forearm, also are given off at this level. Here, its proximity to the humerus makes it susceptible to compression and/or trauma.

After exiting the spiral groove, the radial nerve supplies the brachioradialis muscle before dividing into the posterior interosseous branch and a sensory branch. The posterior interosseous branch is a pure motor nerve that supplies the supinator. It then dives into the supinator through the fascia to supply the muscles of the wrist and finger extension. This fascia is another common site for nerve damage to occur. The sensory branch that arises approximately at the elbow travels down the forearm, becoming superficial at the wrist before it supplies the lateral aspect of the dorsum of the hand. See the image below.

The Radial Nerve from Gray's Anatomy (published 19 The Radial Nerve from Gray's Anatomy (published 1918, public domain, copyright expired).

Epidemiology

Frequency

United States

Radial neuropathy is the fourth most common mononeuropathy.

Race

No racial preponderance is known.

Sex

No gender predilection has been observed.

Age

Radial neuropathy is reported in all age groups.

 

Presentation

History

Symptoms are dependent on the site of the lesion.

  • The most common reported symptom is wrist drop.

  • If the lesion is high above the elbow, then numbness of the forearm and hand may be an additional symptom.

  • If the lesion is in the forearm, sensation typically is spared despite the wrist drop.

    • Pain in the forearm resembling tennis elbow may be prominent.

    • This presentation is initially acute for several days to weeks.

  • If the lesion is at the wrist, patients report isolated sensory changes and paresthesias over the back of the hand without motor weakness.

Physical

Radial neuropathy typically presents with weakness of wrist dorsiflexion (ie, wrist drop) and finger extension.

  • If the lesion is in the axilla, all radial-innervated muscles are involved.

    • The triceps and brachioradialis reflexes are decreased.

    • Sensation is decreased occur over the triceps, the posterior part of the forearm, and dorsum of the hand.

  • Acute compression of the radial nerve commonly occurs at the spiral groove. If the lesion is at this level, all radial-innervated muscles distal to the triceps are weak.

    • Triceps reflex is preserved, but brachioradialis is decreased.

    • Sensory loss is over the radial dorsal part of the hand and the posterior part of the forearm.

    • Numbness over the triceps area is variable.

  • In isolated posterior interosseous lesions, sensation is spared and motor involvement occurs in radial muscles distal to the supinator.

    • Brachioradialis reflex is intact.

    • The extensor carpi radialis sometimes is also spared, resulting in radial deviation with wrist extension.

    • Pain may occur with palpation at the proximal forearm and with forceful supination.

  • In distal radial sensory lesions at the wrist, no motor weakness occurs. Numbness of the dorsal hand is noted, sparing the fifth digit.

Causes

See the list below:

  • Penetrating trauma can cause injury anywhere along the nerve.

  • Compressive lesions high in the axilla can occur from improper use of crutches.

  • Compression injuries at the humeral spiral groove occur in patients with sustained compression of this area over a period of several hours.[3]

    • This is reported in patients who fall asleep in a drunken or drug-induced stupor with the arm over a chair. It also can occur in honeymooners.

    • Fracture of the humerus is a common cause of radial neuropathy due to compression or secondary laceration of the nerve as it wraps around the humerus near the spiral groove.[4]

    • Radial neuropathy has also been reported in wheelchair users, when the spiral groove of the humerus is compressed on a hard wheelchair surface.[5]

  • Subluxation of the radius can produce radial nerve injury in the proximal forearm.

  • The posterior interosseous syndrome typically occurs from compression of this division of the radial nerve as penetrates the supinator muscle within the proximal forearm.[6]

    • It is associated with repetitive supination of the forearm and hypertrophy of the supinator muscle.

    • It also can occur secondary to elbow synovitis, ganglion cysts[7] , enlarged bursa from the elbow, or tumors (especially lipomas at the entry of the radial nerve into the supinator muscle).

  • Isolated distal sensory radial neuropathy is associated with compression from handcuffs and tight bracelets.

  • Bilateral radial palsies suggest lead intoxication. Lead exposure may be occupational.[8]

 

DDx

 

Workup

Imaging Studies

See the list below:

  • A recent study showed that ultrasound examination can localize radial neuropathy more rapidly than standard electrophysiological testing.[9, 10] Visualization of the superficial radial nerve with high-resolution sonography has recently been reported.[11, 12]

  • Occasionally, imaging of the elbow region or the humeral area is indicated to determine if any mass or bony lesions are compressing the nerve. Plain radiographs may show bony causes of compression, such as fractures, dislocations, callus formations, or osteophytes. MRI is particularly helpful for soft tissue evaluation and more direct imaging of the nerve.[6]

Other Tests

Nerve conduction studies and needle electromyography (EMG) are essential for specific localization and to rule out a more generalized process.

 

Treatment

Medical Care

Therapy is dependent on the site and cause of the lesion.

  • When the lesion is due to external compression at the spiral groove, removing the source of the compression and conservative management is indicated.

  • Physical therapy and wrist splinting helps in reestablishing functional use of the hand.

  • If the lesion is due to a humeral fracture, the fracture must be carefully reduced and set to avoid further injury. This may require external fixation.

  • If no recovery is noted within several months, then exploration for the site of compression or transection with possible surgical re-anastomosis may be indicated.[13]

  • With posterior interosseous neuropathies, repetitive supination of the forearm should be avoided.

  • In distal radial sensory nerve lesions, management is typically conservative.

Surgical Care

Surgical exploration may be considered for a chronic compressive lesion or transection.

  • Surgical exploration frequently is indicated for release of the nerve from tethered points in the forearm.

  • Localizing the lesion prior to surgery via EMG is important to assist the surgeon in identifying which section of the nerve is most likely involved.

  • When transection is suspected as the mechanism of injury, conservative management for several months is indicated to assure that no nerve regrowth has occurred either clinically or by electrodiagnostic measures.

  • If no regeneration or inadequate regeneration is confirmed, surgical exploration with possible re-anastomosis may be indicated.

  • Selective tendon transfer may allow for finger extension and thumb extension in cases of long-standing, irreparable radial nerve lesions.[14, 15]

  • Consensus has not been reached regarding the need for and timing of surgical therapy to treat radial nerve palsy with accompanying humeral fracture.[16, 17, 18, 19]

Consultations

Electrodiagnostic consultation is important in radial mononeuropathy in order to:

  • Localize the lesion

  • Provide useful prognostic information in traumatic radial neuropathy

 

Medication

Medication Summary

Although no medications are specifically designed for radial mononeuropathy, in cases of neuropathic pain related to the neuropathy, various agents that may help reduce neuropathic pain should be considered.

 

Follow-up

Further Outpatient Care

Physical therapy may accelerate improvement after tendon transfer for irreversible radial nerve injury.

Prognosis

See the list below:

  • Prognosis depends on the degree and type of radial nerve injury. In most cases of mild injury, recovery after several months is expected.

  • In cases where recovery fails, tendon transfer surgery may provide adequate hand function.

  • Electromyographic testing may help not only to localize the lesion but also to provide prognostic information.

Patient Education

In patients with posterior interosseous lesions, discuss avoidance of repetitive supination of the forearm.

 

Questions & Answers