Radial Tunnel Syndrome – Causes, Symptoms, Treatment

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Radial Tunnel Syndrome refers to a rare compressive neuropathy of the posterior interosseous nerve (PIN) as it passes through the radial tunnel resulting in pain without motor or sensory dysfunction. This pain-only phenomenon is contrasted with PIN compression syndrome, which describes a more severe PIN compressive neuropathy, ultimately causing injury to the large myelin fibers of the PIN resulting in wrist extensor weakness as well as pain. The PIN is a branch of the radial nerve at the elbow and supplies motor innervation to the dorsal extensor compartment of the forearm and sensory fibers to the dorsal wrist capsule. The PIN courses between the two-headed origin of the supinator and around the radial neck posteriorly. It crosses above the abductor pollicis longus (APL) and passes just posterior to the interosseous membrane down the forearm. Its sensory supply to the dorsal wrist capsule is located in the fourth dorsal wrist compartment. The PIN does not provide cutaneous innervation. Of note, radial tunnel syndrome is an entity with much debate with some experts in the field, even questioning its existence.

Radial tunnel syndrome (RTS) is caused by increased pressure on the radial nerve as it travels from the upper arm (the brachial plexus) to the hand and wrist.

Anatomy of Radial Tunnel Syndrome

The radial nerve originates from the posterior cord of the brachial plexus to innervate the triceps muscle, extensors of the wrist, and the extensors of the fingers and thumb (). The nerve divides into the superficial and deep branches immediately proximal to the superior border of the superficial layer of supinator muscle (the arcade of Froese). PIN also carries unmyelinated (group IV) afferent fibers from the wrist capsule and small myelinated (group IIA) afferent fibers from muscle along with its distribution. Group IV unmyelinated fibers from muscles have been associated with nociception and pain which may explain the patient sensory complaints in pure PIN engagement.

The anatomic radial tunnel extends from the radial head to the inferior border of the supinator muscle (). the boundaries is formed by the supinator, extensor carpi radialis longus, extensor carpi radialis brevis, and brachioradialis muscles (). Demonstrate the potential compression sites of the radial nerve.

Possible areas of compression of the PIN in the radial tunnel include (from proximal to distal) fibrous bands anterior to the radiocapitellar joint, the leash of Henry (radial recurrent artery anastomosis), medial edge of ECRB, the arcade of Frohse (proximal edge of the supinator), and distal edge the supinator. The most common site of compression is the arcade of Frohse. A risk factor for the development of radial tunnel syndrome is repetitive prono-supination with the elbow at 0 to 45 degrees of flexion. This type of repetitive motion increases pressure in the radial tunnel, causing irritation of the nerve.

Causes of Radial Tunnel Syndrome

The radial nerve originates from the posterior cord of the brachial plexus (C5-T1) immediately posterior to the axillary artery. It passes along the posterior aspect of the axilla. It gives off three distinct branches, the posterior cutaneous nerve of the arm and two branches that provide innervation to the long and short head of the triceps. It then passes through the rotator interval along with the profunda brachii artery. The nerve then courses between the humerus and the long head of the triceps in the posterior compartment of the arm. Next, it crosses the posterior border of the humerus in the spiral groove in a medial to the lateral direction. There, it gives off the inferior lateral cutaneous nerve of the arm, posterior cutaneous nerve of the forearm, and branches to the lateral head of the triceps, medial head of the triceps, and anconeus muscles. Next, the radial nerve pierces the lateral intermuscular septum and courses anterior to the lateral condyle of the elbow between the brachioradialis and brachialis muscles. There, it innervates extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), brachioradialis, and brachialis. At the level of the elbow, it divides into its terminal branches, the superficial sensory branch, PIN, branch to ECRB.

The radial tunnel is defined as a five centimeter (cm) potential space in the dorsal aspect of the forearm extending from the level of the radiocapitellar joint to the proximal edge of the supinator. It is bordered laterally by the brachioradialis, ECRL, and ECRB muscles. The medial border consists of the biceps tendon and brachialis muscle. The floor of the radial tunnel is the capsule of the radiocapitellar joint.

Although the radial artery proper is not found within the radial tunnel, its first branch (radial recurrent artery) is. The radial recurrent artery courses proximally on the supinator and forms an anastomosis with the anterior branch (radial collateral artery) of the profound brachii (deep brachial) artery. The radial recurrent artery, along with its venae comitantes, is a site of PIN compression known as the leash of Henry. The radial artery continues distally in the forearm between the brachioradialis and flexor carpi radialis (FCR). It passes between FCR and the first dorsal extensor compartment at the level of the carpus and gives off the superficial palmar branch. Finally, it courses between the two heads of the first dorsal interosseous muscle and forms the deep palmar arch as it joins the deep branch of the ulnar artery.

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Symptoms of Radial Tunnel Syndrome

Radial tunnel syndrome causes posterolateral elbow pain that is similar to tennis elbow and may sometimes occur in conjunction with that condition. Patients may typically have weakness of extension at the wrist and third digit. The pain is often reproduced upon resisted supination of the forearm, and pain at the radial tunnel on resisted hyperextension of the wrist.

Radial Tunnel Syndrome is characterized by pain in the forearm that generally centers a few inches below the elbow. Some of the symptoms of Radial Tunnel Syndrome include:

  • Pain that worsens when rotating the wrist
  • Outer elbow tenderness
  • Decreased ability to grip
  • Loss of strength in the forearm, wrist, and hand
  • Difficulty extending wrist

Diagnosis of Radial Tunnel Syndrome

History and Physical

Radial tunnel syndrome manifests as dorsal and radial proximal forearm aching pain. Discomfort is exacerbated with movements requiring prono-supination of the forearm or resisted elbow flexion (lifting heavyweight). Although the PIN does not provide cutaneous innervation, paresthesias over the dorsal thumb-index webspace have been reported. Patients are tender to direct palpation over the mobile wad of the forearm with the point of maximum tenderness 2 to 5 cm distal to the lateral epicondyle of the humerus. This area of point tenderness is the primary finding in radial tunnel syndrome on physical examination. Radial tunnel syndrome is often difficult to distinguish from lateral epicondylitis or tennis elbow and represents concomitant pathology in 5% of cases. Classically, patients with lateral epicondylitis are point tender over the lateral epicondyle and not the dorsal forearm. Provocative physical examination maneuvers include resisted supination and long finger extension. Both should reproduce pain without weakness, although it is possible that any perceived weakness may be due to pain. Additionally, wrist flexion and passive pronation can reproduce the dorsomedial proximal forearm pain by increasing the pressure in the radial tunnel to 250 mm Hg. Notably, patients with radial tunnel syndrome should not have a weakness. This is contrasted with PIN compression syndrome, where the weakness of the wrist extensors is a significant examination finding secondary to damage of the myelin of the PIN.

The rule of nine, as described by Loh et al., can be used to help evaluate patients with a diffuse, ill-defined elbow, or forearm pain. Using this test, nine circular areas are marked out on the patient’s volar elbow in a 3×3 grid. The numbering starts on the proximal lateral side with 1 and moves distally so that number 4 is the proximal circle in the middle row, number 7 is the proximal circle in the medial row, and number 9 is the distal circle in the medial row. Each zone is palpated, and patients are given the option of responding with “painful,” “uncomfortable,” or “nothing.” Areas 1 and 2 correspond to the course of the radial nerve and will be painful in cases of radial tunnel syndrome. Areas 5 and 6 correspond to the median nerve, and the medial row serves as controls. Tenderness to palpation in areas 7 to 9 suggests that the correct diagnosis may lie elsewhere.

Evaluation

Advanced imaging, including magnetic resonance imaging (MRI), has a limited role in the diagnosis of radial tunnel syndrome as it is often negative. MRI is useful; however, to evaluate common locations of PIN entrapment and to identify other causes of compression such as tumors, ganglion cysts, or heterotopic ossification. Electrodiagnostic studies are also negative as the large myelinated fibers of the PIN are not affected. Again, these studies can be used to rule out other causes of neuropathy such as foraminal stenosis in the cervical spine. An injection of local anesthetic into the radial tunnel can be a helpful diagnostic tool, but care must be taken to ensure that the anesthetic does not travel to the lateral epicondyle, which would relieve pain from lateral epicondylitis.

Treatment of Radial Tunnel Syndrome

Conservative Treatments

  • Rest – The most important way to treat Radial Tunnel Syndrome is to avoid repetitive motion that caused the condition in the first place. Depending on your occupation, this may involve modifying your work duties or taking more frequent breaks. In some cases, immobilization with a splint or cushioning of the nerve with an elbow pad are used to facilitate healing.
  • Physical Therapy – A physical therapist can provide soft tissue massage, which can help to improve circulation to the area. They might also recommend gentle stretching and strengthening exercises.
  • Hot / Cold Treatment – Hot/cold treatment involves applying cold (ice) to your injury for 10-15 minutes every 2 or 3 hours. Heat treatment is sometimes used before stretching or physical therapy to help make your muscles more flexible.
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Medication

  • Anti-inflammatory medication –  and removable splints. Activity modification includes avoiding activities that require a persistent extension of the elbow with wrist flexion and forearm pronation. Radial tunnel steroid injections can be attempted with good reported results. Surgery is reserved for severe, recalcitrant cases and consists of radial tunnel release typically through a dorsal approach.
  • Medications – Pain medications or anti-inflammatory medication can help with the inflammation and pain, although this is usually a temporary measure to alleviate symptoms.
  • Corticosteroid Injections – Corticosteroid injections can help reduce the pressure that is put on the radial nerve, and help reduce inflammation.

If surgery is indicated, the PIN should be carefully explored, and all possible sources of compression released. Studies comparing the results of conservative versus surgical intervention in radial tunnel syndrome are lacking, making the duration of appropriate nonoperative management and the natural history of untreated radial tunnel syndrome unknown.

Surgical Technique

Numerous surgical techniques have been described for surgical exploration and surgical determination of the site of radial nerve compression. Of those described, the brachioradialis splitting approach is typically the most utilized.

In this author’s practice:

  • The patient is positioned supine, with the operative arm/forearm on a narrow arm board.
  • A tourniquet is placed on the most proximal part of the arm, dependent upon the patient’s habitus. The arm is elevated for 60 seconds without using an exsanguination sleeve/wrap, and the tourniquet is inflated to 250 mmHg (minimum 100 mmHg above the patient’s systolic blood pressure).
  • The arm is placed in a neutral rotation position, with the thumb pointing in the same plane as the humerus.
  • A line is marked on the forearm, with a surgical marking pen, connecting the apex of the lateral epicondyle to the radial styloid process. An incision is then made with a center point equivalent to 80% of the transepicondylar distance, and extended 2 cm proximally and distally along the line drawn (Figure 2).
  • Following the full thickness skin incision, the antebrachial fascia is incised and the muscle fibers of the brachioradialis muscle are split using blunt dissection.
  • Once the brachioradialis split dissection is completed, the superficial fibers of the supinator will become visible, as noted by their different fiber direction. The surgeon will now be able to palpate the PIN moving, with a digit placed gently on the supinator, while pronating-supinating the forearm. The nerve will be felt to be moving beneath the palpating digit.
  • Once the precise location of the PIN has been identified, the superficial leaf of the supinator can be carefully incised, in line with the nerve course, and elevated away from the nerve beneath. The nerve can then be traced proximally and distally, with a combination of sharp and blunt dissection methods to release any compressive sites. (Figure 3)
  • Fibrous bands such as the aponeurotic proximal edge of the supinator can simply be incised, but arterial and venous sites of compression may need to be tied off or cauterized with a bipolar radiofrequency probe.
  • Once all sites of compression have been removed, the tourniquet should be deflated, in order to identify any potential bleeding vessels and prevent any potential post-operative bleeding. Local anesthetic is infiltrated into the incision, and the patient is pre-warned that a wrist drop will be experienced until the local anesthetic effect subsides, between 2-6 hours.
  • Post-operative instructions include full active and passive range of motion, analgesia as required, and cryotherapy to help reduce swelling and improve pain control.

Surgical treatment

The dorsal approach between the mobile wad and finger extensors (Thompson):

The forearm is positioned in pronation and the incision is made one inch distal to the lateral epicondyle and extended along the midpoint of the wrist. The posterior cutaneous nerve of the forearm, usually located anterior to the incision, should be identified and protected. Then, the mobile wad, formed by the muscle bellies of the brachioradialis, extensor carpi radialis longus and brevis, is identified and dissected from the rest of the extensor muscles. A well-defined yellowish fascial which is more prominent at the distal is the landmark that separates extensor carpi radialis berberis and extensor digitorom common muscles from each other. After separating the two muscles bluntly, the underlying supinator muscle, with its characteristic shiny oblique fibers, is identified. The arcade of Frohse is identified as a tendinous band at the proximal side of the supinator muscle. Initially, the radial recurrent blood vessels (leash of Henry) should be ligated just proximal to the arcade of Froese. The arcade of Frohse is released, and the superficial head of the supinator muscle is divided totally to ensure that the inferior margin of the supinator is completely released. If surgical treatment of associated lateral epicondylitis is desired, the incision can be extended proximally.

The dorsal approach between brachioradialis and wrist extensors:

The skin incision is similar to the dorsal (Thompson) approach. Unlike the previous approach, the interval between the brachioradialis and extensor carpi radialis longus is selected. The posterior cutaneous nerve of the forearm should be identified and protected. After identification of the fascial interval between the two muscles, there belies divided from each other and the supinator muscle is exposed. The rest of the dissection can be continued bluntly to expose the arcade of Froese. Some investigators advocate the release of the extensor carpi radialis brevis tendon at the lateral epicondyle from its origin to treat any associated lateral epicondylitis as well.

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Anterior approach

While the forearm is in supination, a curvilinear incision is chosen; beginning before the lateral epicondyle and extending distally along the groove between the brachioradialis muscle and the biceps. The incision is extended between the mobile wad and Brachioradialis where the radial nerve exists. After identification of the radial nerve, the nerve is followed distally as it bifurcates into the superficial radial nerve and the posterior interosseous nerve (PIN). The arcade of Frohse is released and the radial recurrent blood vessels are ligated. The entire length of the supinator muscle is visualized and completely released.

Since an anterior approach has the capability of exposure of the radial nerve both proximal and distal to the elbow, it is more useful in cases with probable compression of the radial nerve proximal to the elbow.

Transmuscular brachioradialis-splitting approach

In this approach, the incision is slightly anterior to the previous incision described with Thompson. After skin incision, the Brachioradialis fascia is released longitudinally and the muscle fibers are split along the muscle fibers bluntly until the radial nerve is exposed. The arcade of Frohse and the superficial head of the supinator muscle are divided completely.

Three planes have been described to approach the PIN dorsally, ECRB and EDC, ECRL and brachioradialis, and brachioradialis muscle splitting. The plane between the brachioradialis and the biceps tendon insertion can be utilized if an anterior approach is required. The decision regarding which approach to use should be made based on the surgeon’s comfort level as well as the need to address other pathology. The dorsal (Henry) approach can be extended distally in the forearm while the anterior approach can be used when there is concern regarding nerve compression proximal to the elbow.

The dorsal (Henry) approach utilizes the plane between ECRB and EDC. The incision is made in the palpable groove between the mobile wad (brachioradialis, ECRL, and ECRB) and remaining wrist extensors (i.e., EDC). Immediately anterior to this incision is the posterior cutaneous nerve of the forearm, which should be identified and protected. An easily identifiable fascial plane marks the interval between ECRB and EDC. Upon entering the interval, it is often easier if blunt dissection progresses in a distal to proximal direction. The supinator is then identified with its characteristic oblique muscle fibers at the base of the ECRB/EDC interval. At this point, the arcade of Frohse can be visualized as a tendinous band on the proximal edge of the supinator. Immediately proximal to this is an area of fatty tissue containing the PIN. The area if fatty tissue should be carefully explored to identify the radial recurrent blood vessels (leash of Henry). The arcade of Frohse, the leash of Henry, and the entire supinator muscle should be divided to relieve PIN compression.

The incision for the brachioradialis-splitting approach is slightly more anterior over the mobile wad. The brachioradialis fascia is divided, and muscle fibers split bluntly, gaining access to the supinator and PIN.

To gain access to the interval between brachioradialis and ECRL, the same incision described for the brachioradialis-splitting approach is utilized. Instead of going directly through brachioradialis, the fascial plane between brachioradialis and ECRL is identified and dissected.

The anterior approach to the radial tunnel is helpful when concomitant radial nerve compression proximal to the elbow is identified or suspected. An MRI can help further evaluate if this clinical scenario is suspected. A curvilinear or lazy-S incision is performed, starting just proximal to the lateral epicondyle of the elbow with an extension along the interval between brachioradialis and biceps distally. The incision is carried along the ulnar border of brachioradialis and the mobile wad. In the interval between brachialis and brachioradialis, the radial nerve proper should be identified. The radial nerve is then followed distally until it branches into the PIN and superficial radial nerve with any sites of compression released. The radial tunnel can then be accessed using the distal aspect of the incision.

Complications

Complications following surgical radial tunnel release include recurrent symptoms of nerve entrapment, bleeding, infection, and iatrogenic nerve injury.

REferences

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