The clinical features of radial nerve compression and irritation at the wrist require careful examination to rule out the more common conditions of tennis elbow and de Quervain’s tenosynovitis at the wrist.
Proximal median nerve compression is less common than carpal tunnel syndrome (CTS), rarely requires surgical intervention, and can be differentiated from CTS as it is not likely to cause nocturnal pain.
Surgical decompression of the ulnar tunnel is the most common treatment since the primary cause is space-occupying lesions.
The clinical features of these nerve compressions correlate well with sensory and motor changes common to the involved nerve. Electrodiagnosis is less helpful with the radial tunnel and pronator syndrome conditions than for the more common nerve compressions such as carpal and cubital tunnel syndromes.
Radial Tunnel Syndrome
Radial tunnel syndrome was first described as a distinct clinical entity in 1956 when Michele and Krueger described the “radial pronator syndrome.” They presented a pain syndrome distinct from lateral epicondylitis and proposed an anatomic basis for compression of the posterior interosseous nerve (PIN) that could cause refractory lateral elbow pain. In a summary of the 1960 Annual Meeting of the British Medical Association, Capener became the first to report operative release of the supinator for refractory tennis elbow. In 1972, Roles and Maudsley coined the term radial tunnel syndrome and proposed that entrapment of the PIN could cause lateral elbow and forearm pain.
The anatomy of the radial nerve and its branches about the elbow is variable. A theoretical space, the radial tunnel originates near the level of the radiocapitellar joint where the nerve lies on the capsule of the radiocapitellar joint. The medial border of the tunnel is formed by the brachialis muscle proximally and the biceps tendon more distally. The roof and lateral border of the tunnel begin as the brachioradialis and extensor carpi radialis longus (ECRL) muscles, and more distally are represented by the deep surface of the extensor carpi radialis brevis (ECRB). The radial tunnel was originally described as terminating at the entrance of the nerve into the proximal border of the supinator; other investigators have suggested that the radial tunnel continues to the distal border of the supinator. Five potential areas of entrapment have been described ( Box 51-1 and Fig. 51-1 ).
Thickened fascial tissue superficial to radiocapitellar joint
Fibrous origin of ECRB or fibrous bands within the ECRB
Radial recurrent vessels–leash of Henry
Proximal border of supinator—arcade of Frohse
Disal edge of supinator
ECRB, extensor carpi radialis brevis.
At the level of the elbow, the nerve is covered by fibrofatty connective tissue. Thickened bands of fascia from the capsule course around the nerve and anchor the surrounding musculature to the elbow capsule. The first potential area of compression of the radial nerve or its branches can occur here. , The roof of the tunnel begins as a collection of fascial interconnections between the brachialis and the brachioradialis. The structures of the roof continue distally, the biceps tendon becomes the medial border of the tunnel, and the proximal portion of the ECRB becomes the lateral border of the tunnel. At this level, the deep surface of the ECRB may contain thickened fibrous bands from its tendinous origin and contribute to the second possible area of compression of the nerve.
The third potential area of compression is a group of vessels with an intimate association with the radial nerve and its branches. These vessels have been referred to as leash of Henry and usually are branches of the proximal radial artery. They course laterally across the biceps tendon and proximally into the radial tunnel. These branches may impinge on the nerve throughout the proximal portion of the radial tunnel.
At the proximal border of the supinator, the radial nerve has divided into its superficial branch and its deep branch, the PIN. The PIN continues, penetrating the supinator muscle on the proximal radius. As it penetrates, a fibrous band on the leading edge of the supinator, the arcade of Frohse, may impinge on the nerve. This represents the most common region where the PIN is compressed. In a series of 90 patients, 83 had distinct compression at this site. The arcade arises as a semicircular structure from the tip of the lateral epicondyle and the medial aspect of the lateral epicondyle. Anatomic variations in the composition of these origins have been reported by Spinner. The lateral origin of the arcade is always firm and tendinous in nature, whereas the medial half of the arcade is firm and tendinous in 30% of specimens. In his 1979 report, Werner described the arcade as fibrous in 78 of 90 cases. In addition, Prasartritha reported that the arcade was tendinous in 57% of dissections performed on 30 Thai cadavers. The nerve then continues distally within the supinator muscle and emerges as its distal aspect, giving branches to the superficial extensors. The final potential area of compression of the PIN is the distal border of the supinator muscle. , Fibrous or tendinous bands present in this region of the supinator were reported to occur in 65% of dissections performed on 30 Thai cadavers.
The patient with radial tunnel syndrome usually complains of pain in the dorsal forearm. It is localized to the mobile wad musculature: the ECRL, ECRB, and brachioradialis (BR), and over the course of the radial nerve in the proximal forearm. The pain is usually 4 to 5 cm distal to the lateral epicondyle and may radiate proximally and distally over the forearm. The pain is characterized as a deep burning or aching, worse after activity involving forearm pronation and wrist flexion. Rest pain and night pain are also features of radial tunnel syndrome. Sensory complaints and muscular weakness have been reported but are not characteristic of the syndrome. ,
Characteristic physical examination findings have been described. The first is resisted extension of the long finger with the elbow in full extension, forearm in pronation, and the wrist in neutral ( Fig. 51-2 ). The test is positive when pain is produced in the ECRB or BR over the course of the radial nerve. The second provocative maneuver is resisted supination of the forearm, with the elbow in extension ( Fig. 51-3 ). This maneuver is painful when patients with radial tunnel syndrome have compression of the PIN at the arcade of Frohse. A third characteristic finding with palpation is a point of maximal tenderness within the extensor musculature 4 to 5 cm distal to the lateral epicondyle ( Fig. 51-4 ). ,
The differential diagnosis of radial tunnel syndrome includes intra-articular elbow pathology, PIN compression, cervical radiculopathy, lateral epicondylitis, and other entities ( Box 51-2 ). An important distinction is between radial tunnel syndrome and lateral epicondylitis. These two entities have been reported to coexist in 5% of patients. Differentiation between the two syndromes can be difficult because of the overlap in symptoms and difficulty with physical examination. The areas of maximal tenderness are separated by several centimeters at best. Classically, the pain in lateral epicondylitis occurs at or just distal to the lateral epicondyle over the ECRB portion of the common extensor origin ( Fig. 51-5 ). The pain in radial tunnel syndrome is located between 4 and 5 cm distal to the epicondyle within the extensor musculature, either laterally between the BR and ECRB muscles or medially between the mobile wad and the brachialis muscle ( Fig. 51-4 ). Provocative tests for radial tunnel syndrome as listed earlier can be, but usually are not, positive in lateral epicondylitis. Passive stretch of the ECRB muscle and common extensor muscle origin are more likely to be painful in lateral epicondylitis. Passive stretch of the common extensor origin can be performed by extending the elbow and flexing the wrist and fingers. Also, lateral elbow pain is increased with resisted wrist extension in patients with lateral epicondylitis, but not for radial tunnel syndrome.
Chronic extensor compartment syndrome
Chronic anconeus compartment syndrome
Lateral antebrachial neuritis
Posterior interosseous nerve syndrome
Radiocapitellar articular pathology
Diagnostic injection can also be performed to help in the diagnosis of radial tunnel syndrome and to differentiate it from lateral epicondylitis. An injection between the brachialis and BR within the radial tunnel has been reported to help confirm the diagnosis of radial tunnel syndrome. To help confirm the diagnosis, the injection should produce some degree of motor block and transient relief of symptoms. In patients with possible coexistent radial tunnel and lateral epicondylitis, an injection over the lateral epicondyle common extensor origin that results in incomplete relief of pain favors the diagnosis of radial tunnel syndrome.
PIN compression is differentiated from radial tunnel syndrome by the presence of motor abnormalities. These abnormalities can range from partial weakness to complete loss of function and may be preceded by pain over the course of the radial and posterior interosseous nerves. Radiocapitellar pathology can be differentiated from radial tunnel syndrome with a history of antecedent trauma or chronic overuse syndrome, MRI or plain radiography, and mechanical abnormalities on physical examination.
The presence of abnormalities on electrophysiologic examination of patients with a clinical diagnosis of radial tunnel syndrome remains controversial. Many believe that radial tunnel syndrome may be present despite normal electrophysiologic studies. Abnormalities have been reported by multiple investigators, but there is no consensus on what abnormalities are uniformly present or diagnostic. In their initial report, Roles and Maudsley reported increased motor latencies in 8 of 10 patients. Electromyographic (EMG) abnormalities have been reported in the presence of normal nerve conduction velocities (NCVs) by Jebsen and Engber. Lister and Ritts and their associates have also reported EMG abnormalities.
In 1980, Rosen and Werner reported on 28 patients with a clinical diagnosis of radial tunnel syndrome. They performed preoperative and postoperative testing, which included motor conduction velocity at rest, motor conduction velocity with active supination, and EMGs. They found no differences in motor conduction velocity at rest between controls and study subjects, nor did they find any differences between sides on subjects. They did demonstrate significant differences in NCV with active supination, as well as EMG differences between controls and subjects. They concluded that a dynamic compression of the PIN at the level of the supinator can produce lateral elbow pain and local tenderness where the nerve passes through the supinator.
In 1991, Verhaar and Spaans concluded that the signs and symptoms present in patients with radial tunnel syndrome are not caused by compression of the PIN. They based their report on 16 patients with radial tunnel syndrome who underwent EMGs and NCVs, as well as NCV testing while performing resisted supination. They reported no EMG abnormality in any of the patients. They reported one patient with an increased motor latency, which returned to normal on follow-up examination without operative treatment.
In 1998, Kupfer and colleagues reported a series of 25 patients who underwent preoperative and postoperative electrodiagnostic examination. They recorded radial nerve motor latency with the forearm in neutral, passive supination, and passive pronation. They demonstrated that an increased latency can occur in all three positions. Statistically significant increases in latency were demonstrated with respect to the control group. They also demonstrated a statistically significant decrease in motor latency postoperatively. They concluded that the differential motor latency of the radial nerve was a sensitive diagnostic factor in patients with radial tunnel syndrome.
Operative treatment of radial tunnel syndrome is indicated after failure of nonoperative management (see Chapter 52 ). Before surgery is considered, all other potential causes for pain should be ruled out. Coexistent lateral epicondylitis and intra-articular pathology of the radiocapitellar joint should be identified and treated if possible. There are four common approaches to surgical decompression of the radial nerve and its branches. Pertinent features of each approach are presented.
Anterior (Modified) Henry Approach
In the anterior (modified) Henry approach, a curvilinear incision is made beginning approximately 5 cm proximal to the lateral epicondyle and extending distally along the anterior portion of the brachioradialis muscle. The incision is then carried obliquely across the elbow flexion crease near the medial border of the BR muscle. Proximally, the fascia is divided between the biceps/brachialis and the BR. Distally, the fascia is opened medial to the BR.
Next, the interval between the brachialis and BR is developed, and the radial nerve is identified. The BR is retracted gently with the radial nerve, and the interval with radial nerve is developed distally. At the level of the lateral epicondyle, the superficial branch of the radial nerve is identified and protected. Moving from proximal to distal, the nerve is mobilized by freeing it from the capsule of the radiocapitellar joint and any constricting fascial bands. The ECRB is then lifted off the nerve, and its deep origin divided if it contains any potentially compressing fibrous bands. Next, the branches of the recurrent radial artery are identified and ligated. The PIN is dissected free, and the proximal border of the supinator muscle, the arcade of Frohse, is identified and carefully divided. Moving distally, the supinator muscle is divided, and the PIN is dissected out as it proceeds through the supinator. Care is taken to preserve any branches of the nerve to the supinator. At the distal border of the supinator, branches of the nerve may take acute angles to innervate the superficial extensor muscles, and caution is warranted. The PIN should be freed from any fibrous bands in the distal portion of the supinator.
Posterior Approach of Thompson
In Thompson’s posterior approach, a curvilinear incision is made from several centimeters proximal to the lateral epicondyle on the supracondylar ridge, anterior to the lateral epicondyle, and distally to the ulnar side of Lister’s tubercle. The interval between ECRB and the extensor digitorum communis (EDC) is identified, and the fascia is incised. If difficulty is encountered in entering this interval, distal palpation of the abductor pollicis longus (APL) and extensor pollicis brevis can be used to identify the plane between the ECRB and the EDC, and the dissection is carried from distal to proximal, mobilizing the ECRB and EDC to reveal the supinator muscle covering the proximal radius.
At this point, the PIN can be identified proximally or distally in the supinator muscle. From proximal to distal, the origin of the ECRB and ECRL are detached from the lateral epicondyle and retracted. The PIN is identified at the proximal border of the supinator, and the arcade of Frohse is identified. The dissection of the PIN and release from potential sites of compression proceed as previously described.
Another approach is to identify the PIN distally and trace it proximally through the supinator muscle. The dissection is then carried proximally, the leash of Henry is identified, and muscular branches are ligated. The PIN or the proper radial nerve is dissected free from fascial and muscular adhesions on the joint capsule up to the level of the lateral epicondyle.
Transmuscular Brachioradialis-Splitting Approach
Multiple skin incisions have been described for the transmuscular brachioradialis-splitting approach. Straight longitudinal, S -shaped curvilinear, and transverse incisions have been recommended. The subcutaneous tissue is divided, and the lateral antebrachial cutaneous nerve identified and protected if present. The BR is identified by palpation, and the fascia covering it is split longitudinally. With use of blunt dissection, the BR is divided by the surgeon while two retractors are used to maintain the interval created. The dissection proceeds until a layer of fat is visualized. The dorsal sensory branch of the radial nerve is identified in the fat, and beneath that the PIN and the proximal border of the supinator muscle are identified. After the branches of the radial nerve are identified, the exposure is extended by further distal and proximal splitting of the BR. Potential compressing structures can now be identified and released from proximal to distal within the window of the BR muscle.
Approach Through the Brachioradialis/Extensor Carpi Radialis Longus Interval
A lazy S -shaped incision is made over the BR-ECRL interval. The subcutaneous tissues are divided, and the interval between the BR and ECRL is identified. Care is taken to identify and protect the lateral antebrachial cutaneous nerve. The interval between the BR and ECRL is developed from their origins on the lateral epicondyle to the middle of the supinator. The dorsal sensory branch of the radial nerve is identified and traced proximally. The PIN is identified. Proximal dissection also reveals motor branches from the radial or PIN to the ECRB. Retraction of the ECRL and ECRB laterally allows for exposure of the distal border of the supinator muscle and release of the remainder of the supinator muscle.
Surgical Decision Making
The operative approach used should be individualized and depends on the expected location of pathology and the surgeon’s experience. Advantages and disadvantages for each procedure are summarized in Table 51-1 (online).
|Anterior (modified) Henry approach||Allows easy access to the proximal portion of the radial tunnel; distally, can be used to expose the entire radius; main disadvantage with the anterior approach is the potential for extensive scarring.|
|Posterior approach of Thompson||Provides excellent exposure distally, but identifying the muscular interval and proximal exposure can be difficult. Can be used in combination with an anterior approach or BR-ECRL interval exposure to visualize the proximal portion of the radial tunnel. Main disadvantages are the possibility of a second incision to expose the proximal portion of the radial tunnel and the potential for traction injury to nerve branches during exposure.|
|Transmuscular brachioradialis-splitting approach||Provides direct access to the arcade of Frohse. The scar produced using a transverse incision is more aesthetically appealing than for the other approaches. Major disadvantage of this approach is that it is not extensile and is limited by the length of the brachioradialis muscle. Both proximal and distal exposure can be difficult.|
|Approach through the BR-ECRL interval||Provides similar access to the radial tunnel as the brachioradialis-splitting approach, provides better proximal exposure, and does not result in damage to the brachioradialis muscle.|
Results of Surgical Treatment
Initial reports of operative treatment for radial tunnel syndrome were favorable, but recent reports have been less favorable. See Table 51-2 (online) for a summary of relevant reported studies.