Introduction
Compression neuropathy of the radial nerve is much less common than in the ulna or median nerves. Five distinct clinical syndromes have been described.
- Proximal Radial Nerve Palsy
- Posterior Interosseous Nerve Syndrome (PINS)
- Radial Tunnel Syndrome (RTS)
- Wartenberg's Syndrome (Cheilalgia Paresthetica)
- Terminal PIN Entrapment
Anatomy
The radial nerve originates from the posterior cord of the brachial plexus and contains fibers from C5, C6, C7 and C8. The nerve continues on the anterior surface of the subscapularis, teres major and latissimus dorsi. It can be seen through the triangular interval (borders: superior -- teres major; lateral -- humerus shaft; medial -- long head of the triceps). It is accompanied by the profunda brachii artery and its venae comitantes, and anastomosing branches from the posterior circumflex humeral artery.
It passes into the spiral groove behind the middle third of the humeral shaft where it lies between the lateral and medial heads of the triceps muscle. It pierces the lateral intermuscular septum 10 cm to 12 cm proximal to the elbow joint to enter into the anterior compartment. It lies between the brachialis and brachioradialis muscle bellies. It divides into its terminal branches 3 cm to 5 cm distal to the lateral epicondyle: the superficial radial and deep radial (posterior interosseous).
The radial nerve gives off its branches in a predictable fashion (from proximal to distal):
- Posterior brachial cutaneous nerve
- Motor branches to the triceps muscle
- Motor branch to the anconeus
- Inferior lateral brachial cutaneous nerve
- Posterior antebrachial cutaneous nerve
- Motor branch to brachioradialis
- Motor branch to extensor carpi radialis longus
- Motor branch to extensor carpi radialis brevis
- Terminal branches:
- Superficial radial nerve
- Deep radial nerve
Proximal Radial Nerve Palsy
Etiology
There are many causes of proximal radial nerve palsy; nearly all reflect acute neuropraxia and not chronic compression. The most common causes include humeral shaft fracture (Holstein-Lewis), tourniquet palsy and continuous pressure from a drunken stupor "Saturday night palsy."
Clinical Features
All branches of the radial nerve distal to the lesion would be affected, but clinically, they can be affected to varying degrees. Characteristically, there is weakness or absence of wrist extension. There may be absence of the elbow extension, depending upon the level of the lesion. Supination is maintained by the biceps. Finger extension can be maintained by the intrinsic muscles. Sensory loss usually includes the dorsum of the first web space and posterior/lateral aspect of the forearm and arm.
Diagnosis
The diagnosis is made clinically. EMG/NCV may be useful, but is more often used to follow the recovery.
Treatment
Since nearly all of these lesions are from neuropraxia, most will recover spontaneously and all should initially be treated nonoperatively. Conservative treatment consists of observation and maintenance of elbow, wrist and finger motion.
Failure of return of function by four months is an indication for operative exploration. Neurolysis is all that is generally needed. If there is a defected, then nerve grafting can be performed.
For the closed humeral shaft fracture with a radial nerve palsy, initial treatment is conservative. If the radial nerve palsy develops following manipulation of the fracture, then radial nerve entrapment must be suspected, and should be surgically explored.
If more than 1 year has elapsed since the loss of function, recovery is unlikely and tendon transfers are recommended. High radial nerve deficit tendon transfers were popularized by Jones:
- Pronator teres to ECRB
- Palmaris longus to EPL
- FCR to EDC
Posterior Interosseous Nerve Syndrome /
Radial
Tunnel Syndrome
Etiology
Compression of the posterior interosseous nerve is can occur at five sites about the elbow:
- Fascial bands connecting the brachialis and brachioradialis ó rare
- Leash of Henry -- a fan of vessels arising from the radial recurrent artery
- Leading edge of the proximal portion of the ECRB
- Arcade of Frohse -- fibrous proximal portion of the superficial head of the supinator - most common site of compression
- Fibrous bands between the superficial and deep heads of the supinator
Compression of the posterior interosseous branch of the radial nerve can cause a spectrum of clinical scenarios. Depending on the central complaint, the symptom complex is referred to as either posterior interosseous nerve syndrome (PINS) or radial tunnel syndrome (RTS). PINS is characterized by weakness without pain, while RTS is characterized by pain and no weakness, but there is frequent overlap.
For unknown reasons, certain compressing structure are more likely associated with either RTS or PINS. Fibrous bands in the distal supinator are reported primarily in association with RTS, while space occupying lesions at the elbow are commonly reported in PINS.
Clinical Features
RTS usually has an insidious onset and affects manual workers whose job requires strenuous, repetitive motion of the upper extremity. Patients typically are in the fourth to sixth decade. The pain is dull, poorly localized in the radial proximal forearm. It is aggravated by use, but may be present at rest.
On physical examination, the characteristic tenderness is maximal in the mobile wad, about 5 cm distal to the lateral epicondyle. Because 5% to 10% of patients who present with lateral epicondylitis have RTS, two provocative tests have been described to help differentiate these two syndromes:
- Middle finger extension test: Extending middle finger against resistance with elbow extended and wrist neutral will tense the ECRB over the nerve and may provoke aching pain. Because lateral epicondylitis will also worsen with this test, it must be compared with the passive stretch of the entire extensor mass, which is worse with lateral epicondylitis.
- Resisted supination: Resisted supination with the elbow extended (to neutralize the biceps supination strength) will tense the supinator and cause exacerbation of symptoms.
Diagnosis
Differentiation from lateral epicondylitis and C7 radiculopathy is crucial, as both are more common than radial tunnel syndrome. Diagnostic radial tunnel block is crucial to the diagnosis.
EMG/NCV usually do not give abnormal results. However measurements obtained during resisted supination may have a higher diagnostic yield.
Treatment
Conservative treatment should consist of 3 to 6 months of anti-inflammatory medications; limited splinting; avoidance of repetitive forceful supination; and hand therapy, including ultrasound and radial tunnel slide exercises. Surgical treatment consists of release of the entire radial nerve in the proximal forearm. Results are mixed, with good and excellent results ranging from 51% to 80%.
Posterior Interosseous Nerve Syndrome
Clinical Features
Men are affected more often than women. A history of repeated or strenuous effort is common. The onset of weakness is usually preceded by pain in the elbow or forearm.
On physical examination, the classic finding is inability to extend the MCP joints of the fingers with the wrist in neutral position. (Tenodesis and intrinsic function allow full finger extension with wrist flexion). In addition, there will be lack of thumb IP extension, and lack of thumb abduction. Often there is radial deviation of the wrist because of weakness of the ECU, with sparing of the ECRL and possibly the ECRB.
Diagnosis
Because of the characteristic clinical picture, the diagnosis is rarely in doubt. EMG/NCV is often abnormal, and may be useful in localizing the exact area of compression. Further diagnostic imaging is necessary to rule out a space occupying lesion.
Treatment
Initial treatment should consist of finger extension splinting, and range-of-motion exercise. Failure to spontaneously recover within 3 months in an indication for operative release. Operative treatment consists of complete release of all five potential sites of compression through one of three approaches:
- Anterior (Henry) approach -- extensile approach between the brachialis and brachioradialis then between the ECRB and pronator teres.
- Posterior (Thompson) approach -- approach between the ECRB and EDC.
- RTS approach -- approach between the brachioradialis and ECRL.
Wartenberg's Syndrome (Cheilalgia Paresthetica)
Etiology
Compression of the superficial branch of the radial nerve is usually external: from handcuffs, tight cast, watchband or direct blow. The superficial branch of the radial nerve pierces the antebrachial fascia between the brachioradialis and extensor carpi radialis tendons which "scissor" with pronation (converge) and supination (diverge), and can cause fascial entrapment.
Clinical Features
Patients complain of local tenderness over the area where the nerve pierces the fascia, and position-related dysesthesia in the dorsum of the first web space.
Diagnosis
Symptoms often overlap with the more common DeQuervain's tenosynovitis, but can be differentiated by more proximal pain, Tinel's sign over the fascial entrapment area, and false Finkelstein's test (pain with hyperpronation, wrist flexion, ulna deviation and clenched fist, but independent of thumb motion). Diagnosis can be confirmed by local nerve block.
Treatment
Conservative treatment consists of wrist splinting, anti-inflammatory medication, restriction of activity and therapy.
Operative treatment involves decompressing the nerve by widening the fascial exit between the brachioradialis and ECRL. If necessary, part or all of the brachioradialis tendon may be resected. Up to 86% of patients report good or excellent pain relief.
Terminal PIN Syndrome
Etiology
Entrapment of the PIN at the wrist is rare. Chronic entrapment is reported and usually aggravated by rapid repeated wrist dorsiflexion. Post-surgical scarring is more common than chronic entrapment. Iatrogenic injury, such as from the harvesting of PIN for nerve graft can result in a painful neuroma.
Clinical Features
Classically, patients complain of dull aching pain on the dorsum of the wrist along the axis of the fourth dorsal compartment. Since there is no cutaneous innervation of the PIN, there is no detectable sensory loss.
Diagnosis
Diagnosis can be established by anaesthetic block of the PIN several centimeters proximal to the distal radioulnar joint in the fourth extensor compartment. This injection is critical to differential Terminal PIN syndrome from other more common causes of dorsal wrist pain: dorsal ganglions, carpal ligament injuries and DRUJ pathology.
Treatment
Conservative treatment consists of anti-inflammatory medications, wrist splinting, hand therapy and modification of activities.
Operative PIN neurectomy is via exposure of the radial aspect of the fourth dorsal extensor compartments. The PIN branches extensively at the distal radioulnar joint, and is more easily identified proximal to the DRUJ. Results are good in patients with good response to preoperative nerve block.
Bibliography
- Barnum M, Mastey RD, Weiss APC, Akelman E. Radial tunnel syndrome. Hand Clinics. 1996;12(4):679-689.
- Eaton CJ, Lister GD. Radial nerve compression. Hand Clinics. 1992;8(2):345-357.
- Kleinert JM, Mehta S. Radial nerve entrapment. Orthop Clin North Am. 1996;27(2):305-315.