Mark N. Awantang, Joseph M. Sherrill, Christopher J. Thomson, and Thomas R. Hunt III
DEFINITION
Radial tunnel syndrome was first described by Michele and Krueger7 in 1956 as radial pronator syndrome.
It was described as a compression neuropathy involving primarily the posterior interosseous nerve (PIN), associated with a predominant symptom of pain.
ANATOMY
The radial nerve pierces the lateral intermuscular septum 10 to 12 cm above the lateral epicondlye. It travels along the lateral border of the brachialis muscle and is covered laterally and anteriorly by the brachioradialis (BR), extensor carpi radialis longus (ECRL), and extensor carpi radialis brevis (ECRB) muscles (see Fig.1B, Chap.76).
It divides into the PIN and the superficial radial sensory nerve 3 to 5 cm distal to the lateral epicondyle.
The PIN then enters the “radial tunnel.”
The floor of the tunnel begins at the anterior capsule of the radiocapitellar joint and continues as the deep head of the supinator.
The roof begins as inconstant fibrous bands between the brachialis and BR and then continues as the medial border of the ECRB. Distally, the roof of the tunnel consists of the superficial or oblique head of the supinator.
The radial tunnel ends with the distal edge of the supinator.
Proximal to the supinator, the nerve often is crossed superficially by branches of the radial recurrent artery known as the vascular leash of Henry.
PATHOGENESIS
Roles and Maudsley11 described the concept of radial nerve compression in 1972, suggesting that it could result in a wide spectrum of symptoms. Radial tunnel syndrome, defined as localized pain over the mobile wad, is thought to be a result of compression of the PIN.
If the primary complaint is of weakness, the symptom complex is referred to as posterior interosseous syndrome, even though the pathogenesis in both conditions is thought to be due to a compression neuropathy.
The compression may rarely be due to space-occupying lesions such as ganglion, neoplasm, or florid synovitis of the proximal radioulnar, radiocapitellar, or ulnotrochlear joints.
The sites of compression of the PIN most often cited are the fibrous proximal border of the supinator (arcade of Frohse), the medial border of the ECRB, fibrous bands passing volar to the radial head, and the vascular leash of Henry.
The arcade of Frohse and the medial border of the ECRB are thought to be the most common sites of compression.
Werner17 recorded pressures from 40–50 mm Hg exerted on the nerve with passive stretch of the supinator muscle. Pressures exceeding 250 mm of Hg have been recorded on the nerve with stimulated tetanic contraction of the supinator muscle. Ischemia of the nerve has been demonstrated at 60–80 mm of Hg, and blockade of axonal transport at 50 mm of Hg.
The documented changes in pressure due to positioning of the forearm in conjunction with the observation that symptoms often are associated with repetitive pronation and supination have led to the theory that the clinical syndrome may be provoked by dynamic and intermittent compression on the radial nerve.
Although the PIN is considered a motor nerve, it has been well documented that afferent sensory fibers run within the nerve. The muscles innervated by the PIN contain nerve endings corresponding to group IIA fibers. These fibers are commonly thought to be responsible for the pain from muscle cramps, and, therefore, could likely be mediators of pain in radial tunnel syndrome.
Because of the common association with (or difficulty in distinguishing it from) lateral epicondylitis, some authors have suggested that referred pain from lateral epicondylitis or intraarticular pathology may contribute to radial tunnel syndrome.
In 1984, Heyse-Moore3 suggested that radial tunnel syndrome may be an analogue of a musculotendinous lesion of the common extensor tendon, causing lateral epicondylitis in the supinator.
PATIENT HISTORY AND PHYSICAL FINDINGS
The diagnosis of radial tunnel syndrome is based on clinical findings. Historically, it was described as a cause of treatmentresistant lateral epicondylitis. The two disorders may have similar and overlapping symptoms.
Symptoms can be variable, but the classic history described by the patient with radial tunnel syndrome is of pain over the lateral forearm musculature distal to the lateral epicondyle (along the course of the radial nerve) that is exacerbated by activity.
The pain is often described as a constant “aching” that is aggravated by or prevents activities.
Pain is most pronounced with active supination, and less severe with activities involving extension of the fingers.
Lesser symptoms of weakness of the finger and wrist extensors also may be present, as may dysesthesias over the distal lateral forearm and wrist.
Other symptoms include writer's cramp, paresthesias, night cramps, and radiation of pain proximally and distally in the arm and forearm. Some patients complain of a “popping” sensation over the elbow during pronation.
The most specific finding on physical examination is pain with digital pressure placed over the course of the radial nerve at the radial neck, or the proximal edge of the supinator.
Two other pathognomonic signs (described by Lister et al6) are pain in the lateral forearm with resisted extension of the middle finger, and pain with resisted supination.
These signs differ from those associated with lateral epicondylitis, which are tenderness over the lateral epicondyle and lateral epicondylar pain elicited by resisted wrist extension with the elbow in extension.
The most sensitive examination for radial tunnel syndrome involves application of firm constant pressure over the mobile wad on to the radial neck to locate the point of maximum tenderness.
The middle finger test—extension of the middle finger against resistance with the elbow extended—transmits pressure to the third metacarpal, indirectly tensioning the ERCB and causing increased pressure on the PIN.
If pain is reproduced at the point of maximal tenderness with supination of the forearm against resistance, the supinator is implicated as the culprit in intermittently increasing pressure on PIN.
IMAGING AND OTHER DIAGNOSTIC STUDIES
If the patient's clinical examination is suggestive of elbow arthritis or cervical radiculopathy, radiographs of the elbow and a cervical spine series may be helpful in elucidating associated pathology that may contribute to a neuropathy of the radial nerve caused by an anterior osteophyte of the elbow or degenerative disc disease of the cervical spine.
MRI can be helpful in identifying possible cervical degenerative disc disease or elbow ganglia.
Injection of lidocaine into the radial tunnel has been described as a diagnostic tool for radial tunnel syndrome.
Because it is difficult to reliably contain the anesthetic within the radial tunnel, the main criticism of this technique is the lack of specificity in differentiating pathology of the radial nerve from other sources of pain.
Multiple studies using electromyography (EMG) and nerve conduction velocity have shown no consistent relation between symptoms of radial tunnel syndrome and the findings of either electromyographic or nerve conduction studies.
In 1980, Rosen and Werner12 demonstrated that static motor nerve conduction at rest was not significantly different between symptomatic patients and a nonsymptomatic control group. They did find, however, that active supination of the forearm produced an increase in the conduction time of the PIN across the supinator muscle more often in patients with radial tunnel than in control subjects.
Verhaar and Spaans16 tested patients while holding the forearm in active supination and found that 14 of 16 patients with radial tunnel syndrome had no abnormal latency on nerve conduction studies or abnormality of the EMG.
Kupfer et al4 found that differential latency (ie, different latency measurements recorded in the same nerve in different positions) may be more significant in identifying “pathologic” latency than comparing a measured latency to a standard “normal “ latency measurement. Differential latencies were higher in patients with radial tunnel syndrome than in the control group and improved after surgical decompression, correlating with clinical results.
DIFFERENTIAL DIAGNOSIS
Lateral epicondylitis
Posterior interosseous nerve palsy
Cervical radiculopathy C5–6
Neuritis of the lateral antebrachial cutaneous nerve
Waardenburg syndrome
Myofascial pain syndrome
NONOPERATIVE MANAGEMENT
A course of nonoperative treatment should always be attempted.
Activity modification may be helpful, particularly in patients whose vocation or avocation involves frequent repetitive supination and pronation of the forearm.
The patient should attempt stretching exercises of the supinator and the ECRB, with pronation of the forearm and wrist flexion with the elbow in extension. Gentle strengthening exercise also may be helpful in improving symptoms.
An injection of local anesthetic and corticosteroid in the radial tunnel may provide relief in some patients.
SURGICAL MANAGEMENT
Surgical management should be considered in the patient who has failed nonoperative treatment. A 4-to 6-week trial of nonoperative treatment should be sufficient to determine whether there is any improvement.
There is no consensus as to which anatomic structures should be released at the time of surgery. It is agreed, however, that this is typically a clinical decision. Electrodiagnostic studies have not been shown to locate the area of pathology reliably.
Most authors recommend releasing the PIN as it passes under the superficial head of the supinator by dividing the fibrous arcade of Frohse and the tendinous border of the ECRB, as needed.
Lister6 and others emphasize release of the fibrous bands of the radial tunnel anterior to the radial head.
Sponseller15 has reported cases where the PIN is compressed by the distal aspect of the supinator muscle.
Some surgeons advocate the release of the common extensors as well as structures compressing the PIN to address all potential causes of pain. Ritts et al10 stated that the pathology of radial tunnel syndrome and that of lateral epicondylitis appear to be interrelated.
Little literature has been published supporting release of the superficial sensory branch of the radial nerve. It has been associated with neurapraxia and complex regional pain syndrome.8
The surgeon should remain mindful of less common causes of pain over the radial tunnel, including radial nerve compression proximal to the supinator.
When the diagnosis is not clear on physical examination, and the patient has symptoms and examination findings suggestive of lateral epicondylitis, surgical treatment of lateral epicondylitis can be done concomitantly.
Preoperative Planning
A tourniquet should be placed on the arm to facilitate visualization. If it is thought that more proximal release or exploration of the radial nerve into the arm may be necessary, a sterile tourniquet is used.
Positioning
The patient is placed in the supine position, with the arm and forearm rotated as needed to facilitate the preferred approach.
Approach
The most direct dissection path to the radial nerve may be established by palpating the radial nerve through the mobile wad and rolling the PIN under a thumb with enough force to cause an extension flicker of the digits.
Multiple surgical approaches are possible. Determination of which structures require decompression may influence the approach chosen.
Anterior approach
Advantages: it can easily be extended proximally to decompress the radial nerve in the arm if indicated. This exposure may be of benefit in cases of compression on the nerve by rarer causes such as elbow synovitis or ganglia.
Disadvantages: in muscular patients it can be difficult to retract the BR radially well enough to obtain adequate visualization of the radial tunnel. Distal compression sites often are difficult to release.
Transbrachioradialis approach
Advantage: provides a more direct approach to the radial tunnel, improving exposure
Disadvantage: some surgeons find the intramuscular dissection unappealing given the relative paucity of definable landmarks.
Posterior and posterolateral approaches (the author's favored approaches)
Advantage: dissection between the ECRB and the extensor digitorum communis (EDC), or between the BR and ECRL, allows direct exposure to the entire radial tunnel with relatively less dissection and a bloodless field.
Disadvantage: the ECRB–EDC interval is limited in that it does not allow easy extension of the incision to expose the radial nerve more proximally.
TECHNIQUS
POSTERIOR APPROACH AND NERVE DECOMPRESSION (EDC–ERCB INTERVAL)
Exposure
The forearm is held in pronation. The radial nerve is palpated just posterior to the mobile wad (TECH FIG 1A).
A 5-cm longitudinal incision is made over the proximal lateral forearm along Thompson's cardinal line from Lister's tubercle to the lateral epicondyle (TECH FIG 1B).
The posterior cutaneous nerve of the forearm is identified and protected (TECH FIG 1C).
The interval between the EDC and ERCB is located. The overlying fascia is first incised, beginning distally where the structures are better identified. The incision is extended proximally to the lateral epicondyle.
The EDC and ECRB muscles are separated bluntly, using finger dissection, or with scissors, as required (TECH FIG 1D).
Opening of this interval will reveal the superficial fascia of the ERCB, to which the fibers of the EDC often are securely attached and from which they must be carefully released.
TECH FIG 1 • A. The points of maximal tenderness help delineate the course of the nerve and isolate areas of compression. B. Standard positioning, use of a sterile tourniquet, and placement of the 5-cm posterior proximal forearm incision. C. The posterior cutaneous nerve of the forearm is consistently seen crossing the proximal incision, superficial to the fascia. It must be protected. D. The fascia between the EDC and ECRB has been divided, and the supinator is exposed.
TECH FIG 2 • A. The thick ECRB fascia is readily visualized once the EDC is separated and retracted posteriorly. Here the ECRB is fractionally lengthened. B. The proximal tendon of the ECRB is visualized and retracted superiorly, revealing the proximal fat (hemostat) covering the PIN and the superficial fascia of the supinator more distally. C. The supinator fascia has been incised and the muscle dissected, leaving only the tight arcade of Frohse proximally. D. Before release of the arcade, the ECRB motor branches are isolated and protected. E. The PIN is now completely released.
Releasing the Compression
The leading edge of the ECRB often is thickened and taut (TECH FIG 2A). This potential site of nerve compression is incised.
Release of the origin of the ECRB simultaneously treats coexisting lateral epicondylitis.
Further blunt dissection in the EDC–ECRB interval reveals fibers of the superficial head of the supinator distally and fat more proximally over the radial neck (TECH FIG 2B).
The PIN will be found within this fat.
Gentle dissection of the nerve is performed through this proximal fat as necessary for complete visualization of the nerve.
Proximally, the leash of Henry usually is seen running transversely, superficial to the nerve.
Typically the vessels are not large or obviously constricting.
If any of the vessels of the leash are substantial enough to appear to cause compression, or if they impede full decompression of the supinator, they are separated and coagulated with bipolar cautery.
Once the nerve is well visualized proximally, the superficial fascia of the supinator is released in a proximal-todistal direction to the most distal border of the supinator.
A white crescent-shaped band of fibers represents the proximal border of the superficial head of the supinator; this is termed the arcade of Frohse (TECH FIG 2C).
This arcade can be observed to tighten over the PIN as the forearm is pronated.
These fibers of the superficial head of the supinator are then carefully released. Protect the small motor branches to the ECRB (TECH FIG 2D).
This release generally results in significant stretching of the remaining underlying supinator muscle fibers and appears to reduce tension over the nerve.
The nerve is inspected and palpated along its entire course for any other sites of compression.
During palpation, special attention is paid to the proximal nerve in the interval between the brachialis and BR.
A thin fascial layer occasionally is present. This layer is confluent with the fascia of the superficial supinator that extends proximally, causing compression of the nerve. If this is present, it is carefully released.
Before completion, visualize and palpate the nerve over its entire course to make sure there are no further sites of compression, especially proximally (TECH FIG 2E).
The fascial layer between the ECRB and the EDC is closed with absorbable suture, the skin is closed in the usual manner, and an above-elbow splint is applied with the elbow at 90 degrees and the wrist extended 20 to 30 degrees.
POSTEROLATERAL APPROACH AND NERVE DECOMPRESSION (ERCL–BR INTERVAL)
A 5-to 7-cm incision is made starting at the lateral epicondyle and heading distally along the posterior border of the BR with protection of the sensory nerve branches.
The fascial interval between the BR and the ECRL is defined.
The BR is a deeper red compared with the ECRL due to its thinner overlying fascia.
The interval is further developed using blunt finger dissection
Difficulty in dissection usually indicates that the muscular interval is not correct.
The remainder of the procedure mirrors that detailed for the EDC–ERCB interval.
BRACHIORADIALIS MUSCLE-SPLITTING APPROACH AND NERVE DECOMPRESSION
A 4-to 6-cm longitudinal incision is made over the proximal, anterolateral surface of the forearm, starting distal to the elbow flexion crease and 3 cm radial to the biceps tendon and extending over the radial head.
A 4-cm transverse incision just distal to the radial head also may be used.
The deep fascia is divided in the line of the skin incision, and the BR is exposed. Its fibers are parted by blunt dissection.
Immediately deep to this muscle, the vivid white of the superficial branch of the radial nerve is seen. Inspection at the level of the radial head reveals the fat overlying the PIN.
The transverse branches of the radial recurrent artery and accompanying veins are divided as they pass between the PIN and radial sensory nerve.
The radial nerve and its branches are now more fully exposed by dividing adhesions and fibrous bands overlying the nerve as well as the proximal fibrous edge of the ECRB.
The superficial branch is followed distally anterior to the extensor carpi radialis brevis.
The PIN is traced as it disappears beneath the fibrous edge of the superficial proximal border of the supinator, easily distinguished by its prominent oblique striations.
This fibrous edge and the muscle are divided longitudinally.
The nerve is carefully inspected for untreated sites of compression before closure and splinting.
MODIFIED ANTERIOR APPROACH OF HENRY AND NERVE DECOMPRESSION
A 5-cm longitudinal incision is made beginning at the antecubital flexion crease and proceeding distally along the medial border of the BR.
More proximal and extensile exposure may be obtained by extending the incision obliquely across the elbow flexion crease in the interval between the brachialis and the BR.
The deep fascia is incised, and the BR is retracted radially. The proximal radial tunnel can be visualized over the capitellum.
Any constricting vessels are ligated and divided.
The superficial sensory branch of the radial nerve and the PIN are identified.
The PIN is traced distally.
Significant retraction of the BR is required for adequate exposure.
The medial border of the ERCB is released to aid in exposure and to eliminate a potential site of compression.
The arcade of Frohse is visualized, and the supinator muscle is divided to its distal border.
The arm is supinated and pronated to identify constricting structures, and the course of the PIN is carefully inspected.
Despite closure and splinting, as detailed previously, the scar often is conspicuous.
POSTOPERATIVE CARE
Patients are splinted for 7 to 10 days.
Gentle active range of motion exercises are initiated and progressively advanced. Nerve gliding exercises are emphasized.
Patients are allowed to resume normal activities in a progressive and graded fashion over the next few weeks.
OUTCOMES
The efficacy of surgical treatment for radial tunnel syndrome is widely variable.
This variability in results may be due to heterogeneous patient populations and varying diagnostic criteria.
Lister et al,6 Roles and Maudsley,11 and Ritts et al10 all reported high cure rates after release of the PIN.
Sotereanos et al14 reported more modest results (11 of 38 good or excellent), although their population did have a high proportion of worker's compensation patients.
Verhaar and Spaans16 reported even more modest results (1 of 10 patients had good results; 3 of 10 had fair results). Their diagnostic criterion was limited to tenderness over the radial nerve where it passes under the arcade of Frohse.
COMPLICATIONS
The incidence of PIN palsy following the procedure is reported to be low.
Sotereanos et al14 reported a 31% incidence of paresthesias of the superficial radial nerve.
Paresthesias of the lateral cutaneous nerve of the arm have also been reported.
REFERENCES
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