Radial Nerve Entrapment

The radial nerve is the largest branch of the brachial plexus and is the continuation of the posterior cord, with nerve fibers from C6, C7, C8, and occasionally T1. It innervates the extensor and supinator musculature located in the arm and forearm and provides distal sensation.

The course of the radial nerve carries it across the latissimus dorsi deep to the axillary artery. It passes the inferior border of the teres major, winds around the medial side of the humerus, and enters the triceps muscle between the long and medial heads. It follows the spiral groove of the humerus, piercing the lateral intermuscular septum (10 cm proximal to the lateral epicondyle) from posterior to anterior, and runs between the brachialis and brachioradialis to lie anterior to the lateral condyle of the humerus.[5]

Branches to the brachioradialis and the extensor carpi radialis longus are given off just proximal to the elbow. The anconeus receives a branch from the radial nerve as well. The nerve then divides into a superficial branch and a deep branch. The extensor carpi radialis brevis may receive its innervation either from the radial nerve proper or from the posterior interosseous nerve.

The superficial branch, which is purely sensory, runs under cover of the brachioradialis in the forearm. Eight centimeters proximal to the tip of the radial styloid, the nerve pierces the fascia medial to the brachioradialis to lie dorsal to the extensor tendons. It divides into a medial branch and a lateral branch to innervate the radial wrist (with some variable overlap from the lateral antebrachial cutaneous nerve), dorsal radial hand, and dorsum of the radial three-and-a-half digits (to approximately the middle phalanx level).

The deep branch of the radial nerve, the posterior interosseous nerve, winds to the dorsum of the forearm, around the lateral side of the radius, and through the muscle fibers of the supinator. It then divides into medial and lateral branches, each of which supplies different extensor muscles.[10]

Clavert et al dissected 30 cadaveric upper limbs to define the radial nerve anatomic landmarks and to determine the relationship of the radial nerve main trunk and branches to the peripheral osseous and muscular structures in the anterior aspect of the elbow joint, so as to identify likely causes of compressive neuropathy.[11] No radial compressive neuropathy was found at the level of the supinator arch, and no adhesions were identified between the radial nerve and the joint capsule.

In four cases, Clavert et al noted dense fibrous tissue surrounding the radial nerve supply to the extensor carpi radialis brevis.[11] Neither fibrous structures nor adhesions of the deep branch of the radial nerve were observed along its course through the supinator. The fibrous arch of the supinator arose in a semicircular manner and was tendinous in 87% of extremities and membranous in 13%. The average length of the Frohse arcade was 25.9 mm, and the angle formed by the radial shaft and supinator arch was 23 degrees.

Nerve injury secondary to compression or traction depends on intensity and duration.[4]

Seddon classified nerve injuries into the following three categories[12] :

• Neurapraxia - This is a transient episode of motor paralysis with little or no sensory or autonomic dysfunction; no disruption of the nerve or its sheath occurs; with removal of the compressing force, recovery should be complete
• Axonotmesis - This is a more severe nerve injury, in which the axon is disrupted but the Schwann sheath is maintained; motor, sensory, and autonomic paralysis results; recovery can occur if the compressing force is removed in a timely fashion and if the axon regenerates
• Neurotmesis - This is the most serious injury, in which both the nerve and its sheath are disrupted; although recovery may occur, it is always incomplete, secondary to loss of nerve continuity

Sunderland classified nerve injury into five categories, as follows[4] :

• The first is similar to neurapraxia
• The second is similar to axonotmesis
• The third, fourth, and fifth degrees correspond to varying degrees of neurotmesis

Radial nerve palsy

Radial nerve palsy in the arm most commonly is caused by fracture of the humerus, especially in the middle third (Holstein-Lewis fracture) or at the junction of the middle and distal thirds. The nerve may be compressed by the lateral intermuscular septum. This palsy may occur acutely at the time of the injury, secondary to fracture manipulation, or from a healing callus.

Other, less common causes of radial nerve palsy in the arm include compression at the fibrous arch of the lateral head of the triceps and compression by an accessory subscapularis-teres-latissimus muscle.[13, 14, 15, 16, 17]

Radial tunnel syndrome

This diagnosis is highly controversial and is thought to be a result of overuse. Some authors believe that radial tunnel syndrome may represent an early posterior interosseous nerve syndrome.[3] Sites of compression include the fibrous bands attached to the radiocapitellar joint, radial recurrent vessels, the tendinous origin of the extensor carpi radialis brevis, the tendinous origin of the supinator (ie, arcade of Frohse), and fibrous thickenings within and at the distal margin of the supinator.[18, 19, 20]

Posterior interosseous nerve syndrome

The etiology of posterior interosseous nerve syndrome is similar to that of radial tunnel syndrome. Compression is thought to occur after takeoff of the branches to the radial wrist extensors and the RSN. After emerging from the supinator, the nerve may be compressed before it bifurcates into medial and lateral branches, causing a complete paralysis of the digital extensors and dorsoradial deviation of the wrist secondary to paralysis of the extensor carpi ulnaris.

If compression occurs after the nerve bifurcates, selective paralysis of muscles occurs, depending on which branch is involved. Compression of the medial branch causes paralysis of the extensor carpi ulnaris, extensor digiti quinti, and extensor digitorum communis. Compression of the lateral branch causes paralysis of the abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis proprius. Most commonly, entrapment occurs at the proximal edge of the supinator.

Other possible etiologies for posterior interosseous nerve dysfunction include trauma (Monteggia fractures[21] ), synovitis (rheumatoid), tumors, and iatrogenic injuries.

Wartenberg syndrome, described in 1932, is essentially entrapment of the superficial sensory branch of the radial nerve. Many factors may contribute to the development of Wartenberg syndrome. In patients with de Quervain tenosynovitis, secondary irritation of the RSN is frequent. Other common causes include postoperative injury, external compression, and trauma.

The anatomic site of compression corresponds to the transit of the nerve from its submuscular position beneath the brachioradialis to its subcutaneous position on the extensor carpi radialis longus. Especially with pronation, these two muscles can create a scissorlike effect, compressing the RSN.

Among the problems associated with the three major nerves in the upper extremity, radial nerve entrapment is the least common. Carpal tunnel syndrome (median nerve compression at the wrist) and cubital tunnel syndrome (ulnar nerve compression at the elbow) are much more frequent.[22, 23]

Outcome and prognosis depend on the type of injury to the affected nerve, as follows:

• With a neurapraxic lesion, whether it is in the arm, elbow, or wrist, return to normal function is rapid and complete in at least 90% of cases
• With axonotmesis, the results after early release are not as good, and complete return of function is less reliable; recovery will probably be complete, but it will take longer, depending on the distance the nerve must travel to reach the denervated muscle
• Neurotmesis rarely occurs in an entrapment syndrome, but if the nerve continuity has been completely disrupted, complete recovery will not occur, and the degree of recovery can only be estimated; the results of treating neurotmesis, even with surgical repair, are generally unsatisfactory

Noaman et el studied 36 patients who underwent early surgical exploration of radial nerve injury associated with fracture of the shaft of the humerus.[24] A narrow dynamic compression plate was generally used for fixation. Compression at the lateral intermuscular septum was present in 19 cases, entrapment in the fracture site in nine, and loss of continuity in eight.

In this study, neurolysis was required in 20 cases, epineurorrhaphy in nine, interfascicular nerve grafts in five, and first-intention tendon transfer in two.[24] Mean follow-up was 8.2 years. Outcome was rated good to excellent in 28 patients, fair in one, and poor (failure) in three. First-intention tendon transfers were performed in two patients, and two patients were lost to follow-up. Mean delay to recovery was 7 months after neurolysis and nerve repair and 15 months after nerve grafts. Fracture was united in all cases, and the mean time of union was 5 months.

Radial nerve palsy

Radial nerve palsy in the middle third of the arm is characterized by palsy or paralysis of all extensors of the wrist and digits, as well as the forearm supinators. Very proximal lesions also may affect the triceps. Numbness occurs on the dorsoradial aspect of the hand and the dorsal aspect of the radial three-and-a-half digits. Sensation over the distal and lateral forearm is supplied by the lateral antebrachial cutaneous nerve and therefore is preserved.[13, 14, 15, 16, 17]

Radial tunnel syndrome

Radial tunnel syndrome is characterized by pain over the anterolateral proximal forearm in the region of the radial neck. This syndrome often appears in individuals whose work requires repetitive elbow extension or forearm rotation. The maximum tenderness is located four fingerbreadths distal to the lateral epicondyle. (By way of comparison, with lateral epicondylitis, maximum tenderness is usually directly over the epicondyle.) Symptoms are intensified by extending the elbow and pronating the forearm. In addition, resisted active supination and extension of the long finger cause pain. Weakness and numbness usually are not demonstrated.[18, 19, 20]

Posterior interosseous nerve syndrome

Patients with posterior interosseous nerve syndrome present with weakness or paralysis of the wrist and digital extensors. Pain may be present, but it usually is not a primary symptom. Attempts at active wrist extension often result in weak dorsoradial deviation as a consequence of preservation of the radial wrist extensors but involvement of the extensor carpi ulnaris and extensor digitorum communis. These patients do not have a sensory deficit.

Rarely, compression of the posterior interosseous nerve may occur after bifurcation into medial and lateral branches. Selective medial branch involvement causes paralysis of the extensor carpi ulnaris, extensor digiti quinti, and extensor digitorum communis. With compression of the lateral branch, paralysis of the abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis proprius is noted.

Wartenberg syndrome

Patients with the diagnosis of Wartenberg syndrome complain of pain over the distal radial forearm associated with paresthesias over the dorsal radial hand. They frequently report symptom magnification with wrist movement or with tight pinching of the thumb and index digit. These individuals demonstrate a positive Tinel sign over the radial sensory nerve and local tenderness. Hyperpronation of the forearm can cause a positive Tinel sign. A high percentage of these patients reveal physical examination findings consistent with de Quervain tenosynovitis.

Radiography

In a suspected entrapment of the radial nerve in the arm, radiography should be performed to detect or rule out a fracture, healing callus, or tumor as the cause of entrapment. In radial tunnel syndrome and posterior interosseous nerve syndrome, radiographs should be obtained to detect or rule out elbow or forearm fractures, dislocations or instabilities, tumors, and arthrosis.

Magnetic resonance imaging

Magnetic resonance imaging (MRI) is useful in detecting tumors such as lipomas and ganglions, as well as aneurysms and rheumatoid synovitis.

A study by Jengojan et al found that magnetic resonance neurography based on diffusion tensor imaging was capable of detecting nerve changes during acute entrapment of the radial nerve at the spiral groove.[25] Compression of the nerve resulted in a transient increase in local radial nerve fractional anisotropy values.

Ultrasonography

Ultrasonography (US) is capable of providing useful information in the evaluation of the upper-extremity nerves, including the radial nerve; in addition to entrapment neuropathies, it can demonstrate pathologies such as nerve tumors and traumatic nerve injuries.[26]  

Toros et al, in a study of 26 patients with sensory or motor deficiency of a peripheral nerve from trauma or entrapment, confirmed that high-resolution US could show the exact location, extent, and type of lesion, yielding important information that might not be obtained by other modalities.[27]  US provided reliable visualization of injured nerves in all 26 patients. Axonal swelling and hypoechogenicity of the nerve was diagnosed in 15 cases, loss of continuity of a nerve bundle in 17, formation of a neuroma of a stump in 6, and partial laceration of a nerve with loss of the normal fascicular pattern in 5. US findings were confirmed at operation in the 19 patients who underwent surgery.[27]

Lo et al compared US with electrophysiologic testing in the diagnosis of entrapment neuropathy of the radial nerve at the spiral groove, which is relatively common but technically challenging to localize. The study included 32 normal controls, to obtain ultrasound parameters of the radial nerve, and 10 patients with suspected radial neuropathy, in whom US and electrophysiologic techniques were used. US correctly identified all six patients with radial neuropathy; the four patients with other diagnoses did not show ultrasound abnormalities. US also required significantly less time than electrophysiologic testing did.[28]

Electromyography (EMG) and nerve conduction studies yield abnormal results in radial nerve injuries in the middle and distal third of the humerus. EMG helps locate the site of injury and helps the clinician monitor the nerve recovery over time. EMG may not be positive for 3-6 weeks following injury. By 4 months after the injury, nerve recovery should be demonstrable. EMG may be performed initially to provide a baseline, but unless the nerve is severed, no changes will be observed for 3-6 weeks.

All electrodiagnostic test results are within normal limits in radial tunnel syndrome.

In posterior interosseous nerve syndrome, nerve conduction studies and EMG usually yield abnormal results and help determine the site of compression. These findings may not become abnormal for 3-6 weeks after injury. Serial EMG usually is not necessary once the diagnosis is established but can be used to document improved or worsening nerve function.

If the medial branch of the posterior interosseous nerve is compressed, EMG and conduction studies reveal abnormal function of the extensor carpi ulnaris, the extensor digitorum communis, and the extensor digiti quinti. If only the lateral branch is compressed, then abnormal function of the abductor pollicis longus, the extensor pollicis longus and brevis, and the extensor indicis proprius is revealed. The site of compression is localized by all function proximal to the compression being normal and all function distal to the compression being abnormal.

To help differentiate lateral epicondylitis from radial tunnel syndrome, injection of cortisone and lidocaine injection may be performed. An injection into the area of the lateral epicondyle should resolve almost all of the symptoms of lateral epicondylitis, at least temporarily. Injection of cortisone and lidocaine into the area of the radial tunnel usually fails to relieve the discomfort or relieves it only incompletely.

In de Quervain disease, injection of cortisone and lidocaine into the tendon sheath of the extensor pollicis brevis and the abductor pollicis longus relieves the symptoms immediately and sometimes permanently. An injection of cortisone and lidocaine into the area of compression of the superficial radial nerve causes the symptoms to subside; however, numbness in the nerve distribution follows, and when the injection wears off, the symptoms return.

A Tinel sign is present in patients with Wartenberg syndrome but usually not in those with de Quervain disease. The two conditions may be related. The inflammation from de Quervain disease causes an inflammation of the nerve. With resolution of one condition, the other may subside or may be adequately treated with an injection.[29]

Immediate exploration of a palsied nerve after a closed fracture of the humerus is contraindicated. A 6- to 12-week period of expectancy is indicated to allow the swelling and palsy to subside. With a palsy developing after a closed manipulation, a further gentle remanipulation is carried out. Open exploration is indicated if there is no relief of the palsy or if it is felt that the nerve may be entrapped between the fracture fragments.

In an open fracture or with a gunshot wound to the humerus with an associated palsy, exploration of the nerve at the time of debridement, as well as possible fixation, is the treatment of choice.[13, 14, 15, 16, 17]  Nerve injuries in continuity to an open fracture are gently explored and followed for 6-12 weeks before any further treatment is initiated.

In radial tunnel syndrome, prolonged conservative treatment is indicated if the only symptom is pain. If pain does not resolve after 12 weeks, surgery may be indicated.[3, 18, 19, 20]

In posterior interosseous nerve syndrome, institute conservative treatment for 6-12 weeks. Surgery is indicated if no improvement occurs or paralysis increases.

Wartenberg syndrome is best treated nonoperatively. Local application of steroids or iontophoresis is used. Nerve decompression is indicated only in resistant cases.

Conservative treatment varies according to the level and the cause of radial nerve neuropathy.[30] A period of immobilization and anti-inflammatory pharmacologic therapy may diminish swelling and improve symptoms. In addition, functional splints help prevent contracture and improve function as signs of nerve healing follow. For example, an appropriate functional splint for a high palsy includes a static extension splint for the wrist and a dynamic extension apparatus for the proximal phalanges.

The initial treatments for radial tunnel syndrome and posterior interosseous nerve syndrome are similar. Splints and activity modification help limit repetitive elbow extension, forearm pronation, and wrist flexion. Anti-inflammatory drugs and a single cortisone shot in the affected area are administered for both conditions, but in posterior interosseous nerve syndrome, weakened muscles are protected with a cock-up splint.

Compression of the superficial radial sensory nerve (RSN) in the distal forearm is best treated conservatively by eliminating any possible external compression, decreasing inflammation by utilizing a thumb spica forearm-based splint (allowing interphalangeal motion), and administering anti-inflammatory medications and cortisone injections. Injections for de Quervain disease should fill the first extensor compartment, whereas those for Wartenberg syndrome are placed in the subcutaneous tissues just dorsal to the compartment. If symptoms continue unabated after 4-6 months and the diagnosis is clear, consider neurolysis or neuroma excision, followed by burying of the nerve ends in bone.

Choice of surgical approach

Surgical treatment of the radial nerve in the arm is carried out through either the anterolateral approach or the posterior approach. The anterolateral approach offers excellent nerve exposure over the distal half of the humerus. For more proximal exposure, the posterior approach is recommended. If needed, both approaches can be employed together for wide exposure.[23, 16, 18, 20, 12]

Preparation for operation

Appropriate preoperative blood work, a chest radiograph (if indicated), and a careful physical examination are warranted preoperatively. Standard preoperative laboratory studies are required. The patient is positioned supine with the arm on an arm board. A tourniquet is essential. For proximal nerve lesions, a sterile tourniquet may be needed, and the lateral decubitus position is preferred. Prophylactic antibiotics are used. General anesthesia without complete paralysis is preferred for proximal lesions so that intraoperative nerve stimulation may be utilized.

Procedure

The favored approach begins posterolaterally in the interval between the deltoid and the lateral head of the triceps. It proceeds distally between the biceps and the lateral head of the triceps, crossing the lateral intermuscular septum 10 cm proximal to the lateral epicondyle. The incision continues in the biceps-brachialis interval. At this point, the incision joins the anterolateral approach recommended for exposure of the radial nerve at the elbow.

The superficial fascia is incised, and the lateral antebrachial cutaneous nerve is isolated and protected as it emerges between the biceps and brachialis. The deep fascia is incised in line with the skin incision and the radial nerve located deep within the intermuscular interval between the brachialis and brachioradialis. The nerve is traced proximally and distally, releasing any possible points of compression.

Proximally, compression of the radial nerve at the lateral intermuscular septum must be suspected, especially in cases associated with humerus fractures. In these cases, the nerve may be encased in scar, buried in the fracture, or surrounded by callus. Meticulous dissection and a complete neurolysis are required.

To explore and release the nerve in the supinator and surrounding area, the incision is started 20-25 cm above the elbow and is continued to the dorsum of the forearm. Care must be taken during the dissection because 5-6 cm above the elbow, branches are given off to the brachioradialis and the extensor carpi radialis longus and brevis. The nerve is followed distally beneath the brachioradialis and into the supinator. The distal margin of the supinator is identified, and the fascia is incised between the extensor carpi radialis longus and brevis and the extensor digitorum communis. Once the nerve is exposed, it is followed proximally to the distal margin of the supinator, where numerous branches are given off.

Once these branches have been protected, the superficial layer of the supinator is incised at right angles to the direction of its fibers, and the fibrous arcade of Frohse is incised to complete exposure of the posterior interosseous nerve. In this exposure, all the potential sites of compression of the posterior interosseous nerve (ie, arcade of Frohse, supinator muscle, and distal fascia) are released.

Great care must be exercised in exposing the posterior interosseous nerve. The following should be kept in mind:

• Proximally, watch for the branches to the brachioradialis and the extensor carpi radialis longus and brevis, as well as the superficial branch of the radial nerve
• Release the supinator along its entire course
• Remember that compression may be present not only at the arcade of Frohse but also where the nerve exits the muscle
• Incise the superficial layer of the supinator very carefully to avoid injuring the enclosed nerve
• Protect the numerous muscular branches given off distal to the supinator
• Distally, protect branches of the RSN and lateral antebrachial cutaneous nerve

In exposing the superficial radial nerve at the wrist for relief of a chronic Wartenberg syndrome that is not responsive to conservative treatment, the incision is made over the suspected area of compression; however, it must be transverse rather then longitudinal in order to prevent further scarring in this area. The incision is very superficial, and any area of compression is released. If a neuroma is present, it is resected and the ends buried in healthy tissue.

Immediately after release of the radial nerve in the arm, a splint is used to put the arm, forearm, and wrist at rest, with the elbow flexed to 90° and the forearm in neutral pronosupination. Motion is initiated quickly with graduation to the appropriate functional splint. Rehabilitation emphasizes motor and sensory reeducation and must be tailored to the individual patient.

After posterior interosseous nerve exploration and release, a similar long arm splint is used for a short duration postoperatively. A range of motion (ROM) exercise program is started at 1 week and is continued throughout treatment. Protective splints may be utilized along with graduated muscle stretching and then strengthening. The patient may not be able to return to normal activities for 3-4 months.

RSN decompression or neuroma excision is followed by a short-arm thumb spica splint. Again, ROM is initiated quickly. Protective splints are frequently needed, and sensory reeducation and desensitization are the mainstays of treatment in the postoperative phase.

A major complication of radial nerve entrapment is injury to the nerve during surgical exploration. Severing or stretching the nerve is not uncommon while attempting to extricate the nerve in the middle and distal thirds of the arm from a bony spicule or healing callus. Counsel the patient about this risk. In exploring the posterior interosseous nerve, a large ganglion or lipoma may be seen encompassing the nerve, and during dissection, the nerve may be severed or severely stretched.

Another complication is failure of the patient to seek medical help until the affected muscles have atrophied or fibrosed. Although nerve decompression should still be strongly considered, the possibility of a satisfactory outcome from neurolysis alone is slim, and tendon transfers may need to be performed at the same time.

Other complications are those that can occur with any form of surgery, including infection, wound dehiscence, keloid formation, and incomplete recovery of function for no apparent reason.

If nerve entrapment has caused only mild damage to the nerve (neurapraxia), recovery should be rapid and complete in a short period of time—approximately 2-8 weeks. If the injury is more severe (axonotmesis), recovery will take longer, and the timetable is determined by how far the regenerating axon must grow to reinnervate the paralyzed muscles. Nerves typically heal at a rate of 1 mm/day. The most severe form of nerve injury (neurotmesis) rarely results from nerve entrapment. If there is discontinuity of the axon and sheath, there is no chance for a full recovery.

The result of any surgery is dependent on the damage to the nerve preoperatively. With neurapraxia—whether it is in the arm, elbow, or wrist—following early release, the result should be a return to normal function in 80-90% of cases. With axonotmesis, the results, even after early release, will not be as favorable as those with neurapraxia; complete return of function is rare. With neurotmesis, the results are unsatisfactory even with surgical repair.