Radial Tunnel Syndrome

Farhad Pirouzmand and Rajiv Midha

Case Presentation

A 48-year-old, right-handed treasury manager had been experiencing aching discomfort deep in her right posterolateral forearm for 14 months prior to her initial presentation. Her pain came on spontaneously with no specific physical activity or trauma. An episode of “lateral epicondylitis” had been successfully treated in the past. The pain had been radiating down her forearm to the wrist with exacerbation while squeezing objects, lifting, or even shaking hands. She had been a semiprofessional bowler for about 40 years who was now unable to lift the ball due to the pain. She could also no longer play golf. She denied any numbness or muscle weakness in her hand. Examination revealed normal muscle power and reflexes. Sensory exam revealed slightly altered sensation in the radial nerve distribution. There was a tender spot deep to the brachioradialis muscle ˜3 to 4 cm distal to the lateral epicondyle (which was not tender itself) (Fig. 32–1). The middle finger resisted extension, and resisted supination of the forearm reproduced her pain. Initially, she was managed conservatively with anti-inflammatory drugs, short periods of rest, and modified sports activity, with transient symptomatic relief. However, symptoms returned 1 year later when she tried to pick up a 3.5 lb bowling bowl. Her neurological examination remained completely normal. Due to the intractable symptoms and her wishes to pursue her professional bowling career, she opted for exploration and operative release of her radial nerve and posterior interosseous nerve (PIN) via an intermuscular approach between the brachioradialis and extensor carpi radialis longus muscles (Fig. 32–2). The nerve appeared grossly normal, and intraoperative electrophysiological studies were also normal. Follow-up over 1 year has confirmed relief of her symptoms even with previously provocative activities, and she has resumed bowling.

Figure 32–1 Photo showing the forearm of the patient with radial tunnel syndrome and focal tender spot (X) deep to the brachioradialis (BR) and extensor carpi radialis longus (ECRL) muscles.

Diagnosis

Radial tunnel syndrome (RTS)

Anatomy

At the level of the elbow, the radial nerve lies in an invariant intermuscular plane between the brachioradialis and brachialis muscles. Shortly thereafter, in the proximal forearm, the nerve divides into the smaller-diameter superficial sensory radial nerve (which lies deep to the brachioradialis as it courses down the forearm) and the larger motor branch, the PIN. The latter dives obliquely and deeply toward the posterior interosseous membrane, passing through a series of fibromuscular tunnels. The underlying pathology for RTS is assumed to be compression of the PIN at the following anatomical sites:

Arcade of Frohse, a fibrotendinous band at the proximal portion of the superficial head of the supinator. This band is thickened in 30% of dissected adult specimens. In addition to this more common compression level, another potential entrapment point has been described at the distal portion of the superficial part of the supinator over the PIN exit point.
Extensor carpi radialis brevis (ECRB) tendinous origin. This tough free border can compress the PIN dynamically during wrist flexion or pronation, especially with the elbow extended. Occasionally, ECRB has an extra origin from the fascia of the forearm flexor muscle group, which can act as a thin fibrous band compressing the PIN.
Radial recurrent vessels. These vessels, which supply the extensor muscle group, can be engorged with exertion and provide potential dynamic compression of the PIN.

The RTS is thought to be due to PIN entrapment, and among the conditions described here, the arcade of Frohse has been mostly implicated as the offending compressive pathology. It seems that the majority of published cases are idiopathic. The compression is due to a combination of both static and dynamic factors in the proximal forearm as described. The PIN has no cutaneous sensory component, so the pain presumably arises from compression of small myelinated afferent fibers or from supramaximal stimulation of large afferent fibers from muscle spindles. In the more widely accepted syndrome of PIN entrapment (syndrome), the resulting compression results in a pure motor neuropathy, with finger drop and radial deviation of the dropped wrist, and not a pain syndrome.

Figure 32–2 (A) The incision between the brachioradialis and extensor carpi radialis longus muscles is outlined, as is the more classical incision for the more proximal and elbow-level radial nerve. (B) With adequate retraction of the extensor muscles, the radial nerve branching into the superficial sensory radial (with forceps underneath) and the larger and (seen to be) subdividing posterior interosseous nerve are exposed. The more superficial supinator muscle edge has already been divided to obtain the decompression and exposure seen.

Characteristic Clinical Presentation

RTS is a pain syndrome characterized by pain over the lateral aspect of the proximal forearm, presumably related to entrapment of the PIN. This syndrome is often confused with tennis elbow, although patients can have both problems simultaneously. The diagnosis of RTS remains a clinical one, with no reliable objective criteria to differentiate among different pain syndromes in this region. Because of lack of objective criteria, the syndrome remains a controversial diagnostic entity.

RTS is most frequently seen in workers who perform repetitive tasks requiring frequent forearm pronation-supination and elbow flexion-extension. The patient usually complains of lateral elbow pain. It may develop insidiously or more acutely after strenuous exercise of the elbow or forearm. The pain is typically dull and aching in nature, deep in the proximal forearm extensor muscle group with radiation usually down in the forearm. Night pain is a common complaint. Due to the resemblance of pain in tennis elbow, initial treatment is usually directed toward treatment of the latter. This treatment obviously fails, hence the term resistant tennis elbow, which is so commonly employed for RTS. The three important clinical characteristics of RTS are as follows:

Maximal tenderness and pain overlying the area of PIN passage under the proximal supinator edge. This is just distal to the radial head through the mobile proximal extensor muscle group. In lateral epicondylitis (i.e., tennis elbow) the most tender point is over the lateral epicondyle at the region of the extensor muscle group attachment. In ˜5% of patients, both of these areas are tender. In a considerable number of these patients, symptomatic PIN compression is due to extensor muscle group spasm around the inflamed epicondyle. This will resolve after treatment of the underlying epicondylitis.
Increased pain with active supination with wrist dorsiflexion or passive forearm pronation with the wrist in flexion. Both of these situations produce tension in the supinator and ECRB with an increase in PIN compression.
Middle finger test. The patient is asked to extend the elbow, wrist, and middle finger against constant pressure applied on the dorsum of the third proximal phalanx. Due to insertion of the ECRB on the base of the third metacarpal bone this provokes contraction of the ECRB with reproduction of pain at the elbow and proximal lateral forearm.

Differential Diagnosis

There are many causes of forearm pain, the vast majority of these being related to musculoskeletal conditions in and around the elbow joint. Pain following injury is usually a result of damage to soft tissue structures (muscles, ligaments, and tendons), joints, or bones and should not be diagnosed as RTS. Spontaneous onset of pain or pain following repetitive activity in the proximal lateral forearm is usually secondary to lateral epicondylitis or tennis elbow. This and similar inflammatory conditions must be entertained and treated, or excluded before the diagnosis of RTS is considered. Finally, there are patients with intrinsic pathology, such as a ganglion cyst or nerve sheath tumor, affecting the radial nerve in the proximal forearm that may present with pain in the lateral forearm and a paucity of neurological findings in the nerve distribution. Patients with these structural lesions may be diagnosed with appropriate imaging preoperatively or occasionally intraoperatively at nerve exploration.

Diagnostic Tests

Electrophysiological Studies

The role of electrophysiological study in the diagnosis of RTS is not clear. Part of the problem arises from a lack of uniform objective diagnostic criteria for the patient population. Most reports have found no abnormalities, although Rosen and Werner have demonstrated slowing of the motor conduction during forced supination of the forearm. Diagnosis is therefore based purely on the characteristic symptoms of pain and provocative findings, without neurological deficit.

Management Options

Considering the difficulty in diagnosing RTS with certainty, the initial step in treatment is an adequate period of conservative treatment for several months. This includes rest with a wrist dorsiflexion splint, nonsteroidal anti-inflammatory agents, and changes in activity, including avoidance of repetitive elbow extension, forearm supination/pronation with forceful wrist dorsiflexion. The occupations or hobbies involving the troublesome activities should be modified. If symptoms persist after conservative treatment, and other treatable causes including tennis elbow have been ruled out or appropriately managed, surgical release of the compressive pathologies may be considered. Ritts et al have advocated the use of local lidocaine block into the radial tunnel as a diagnostic confirmatory test for RTS. Although this may be useful, one concern is that an intraneural injection may result in an injection nerve injury.

The goal of operation is wide and complete exposure with release of all the possible compressing structures as follows:

Proximal arcade of Frohse with or without complete superficial supinator head division
ECRB tendinous origin with volar forearm fibrous bridge in its origin if present
The radial recurrent vessels at the radial tunnel

There are three different approaches for exposure of the PIN at the proximal forearm. These include the proximal anterior at the elbow (between the brachioradialis and brachialis), proximal posterior intermuscular [longitudinal incision between the brachioradialis and extensor carpi radialis longus (ECRL)] muscle fibers, as shown in Fig. 32–2, and distal posterior (between ECRB and extensor digitorum) approaches. The differences lie in the approach to the PIN through the mobile muscle group in the radial forearm, which consists of the brachioradialis, ECRL, and ECRB. The authors prefer the intermuscular approach for most cases (Figs. 32–1 and 32–2). This provides access to the nerve where it is most likely to be compressed and with the least noticeable scar. The distal posterior approach between ECRB and extensor digitorum is preserved for cases with atypical tenderness at the distal edge of the supinator over PIN exit point or when initial proximal supinator division has failed to relieve the symptoms. In these cases pain and tenderness usually occur at the junction of the proximal and middle third of the forearm over the emerging PIN. This approach displays the distal two thirds of the supinator muscle and allows distal decompression of the PIN.

Outcome and Prognosis

Due to the difficulty in confirming the presumptive diagnosis of RTS in many patients, the treatment result remains variable. Patients typically present with prolonged duration of symptoms, usually due to delay in the diagnosis. However, the result can still be satisfactory. Good results have been reported in 65 to 70% of patients. It is of paramount importance to consider RTS when dealing with patients with forearm pain that has not responded to conventional therapies. Obviously, further objective criteria are required to reliably diagnose and subsequently treat the patients.

Pearls

RTS typically presents with forearm pain and no motor or sensory loss.
Diagnosis is mainly based on the typical clinical presentation. No conclusive supportive tests are available.
Surgical treatment is generally successful if all the possible compressive pathologies are released.

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