Radial Tunnel Syndrome (RTS) is a condition characterized by pain near the elbow and forearm, resulting from the compression of the radial nerve. This nerve becomes irritated as it passes through the radial tunnel, a narrow, muscular space in the forearm. While relatively rare, RTS often presents with symptoms similar to Lateral Epicondylitis, or “Tennis Elbow.” The key difference is the source of the pain: RTS involves nerve irritation, while Tennis Elbow is related to tendon inflammation.
The Anatomical Location of the Radial Tunnel
The radial tunnel is located on the outside, or lateral, aspect of the elbow and extends down into the forearm. This anatomical corridor is roughly five centimeters long, transmitting a branch of the radial nerve. The tunnel begins near the radiocapitellar joint, the articulation between the head of the radius bone and the humerus.
This pathway houses the deep branch of the radial nerve, which primarily carries motor signals to the muscles. The boundaries of the tunnel are formed by muscle groups and connective tissues, including the brachioradialis and the extensor carpi radialis longus and brevis muscles on the lateral side. The floor is formed by the elbow joint capsule and underlying bone. As the deep branch travels through this area, it passes between the two heads of the supinator muscle, continuing as the posterior interosseous nerve that supplies the extensor muscles of the forearm.
How Nerve Compression Causes Pain
The pain associated with Radial Tunnel Syndrome results from compression of the radial nerve’s deep branch within this confined space. The nerve is vulnerable at several points of entrapment within the tunnel. These sites include fibrous bands near the elbow joint, a network of blood vessels known as the leash of Henry, and the sharp edge of the extensor carpi radialis brevis muscle.
The most frequent site of compression is the Arcade of Frohse, a band of tissue at the entrance of the supinator muscle that acts like a sling over the nerve. When the forearm is involved in dynamic activities, especially those requiring repetitive rotation, gripping, or wrist extension, the pressure within the tunnel increases.
Normal pressure is approximately 50 mmHg, but this can spike to 250 mmHg when the supinator muscle is stretched during movements like forced wrist flexion. This high, sustained pressure restricts blood flow to the nerve, causing a localized lack of oxygen called ischemia. The resulting irritation and inflammation of the nerve fibers create the characteristic pain signals of the syndrome.
Symptoms and Distinguishing Features
The typical presentation of Radial Tunnel Syndrome is a deep, aching pain felt in the forearm, often radiating from the outside of the elbow down the arm. Unlike many nerve entrapments, RTS usually presents with pain as the primary symptom, and often without the tingling or numbness sensations seen in other nerve conditions. The pain frequently worsens with activities that involve twisting or forceful extension of the wrist and fingers, and it may become more noticeable at night.
Diagnosing RTS is challenging due to its similarity to Lateral Epicondylitis, which is an inflammation of the common extensor tendon at the elbow. A key differentiator is the location of maximum tenderness upon physical examination. In Lateral Epicondylitis, the pain is focused directly at the bony prominence on the outside of the elbow, known as the lateral epicondyle.
With Radial Tunnel Syndrome, the point of maximum tenderness is typically located a few centimeters further down the forearm, approximately 3 to 5 cm distal to the lateral epicondyle, over the supinator muscle. Furthermore, pain from RTS is often reproduced by resisted middle finger extension or forearm supination, which stretches the nerve. Unlike Posterior Interosseous Nerve (PIN) syndrome, RTS is defined by the absence of significant motor weakness.
Options for Relief and Recovery
Initial management for Radial Tunnel Syndrome focuses on reducing inflammation and pressure on the nerve. Activity modification involves avoiding repetitive motions that exacerbate nerve compression, such as forceful gripping or forearm rotation. Rest and the use of nonsteroidal anti-inflammatory drugs (NSAIDs) can help to alleviate the pain and swelling around the nerve.
Physical therapy can be beneficial, incorporating techniques like nerve gliding exercises to promote the smooth movement of the nerve within the tunnel. Splinting or bracing the wrist and elbow may also be used to limit movement and reduce irritation. For cases that are resistant to these measures, a corticosteroid injection into the radial tunnel area may be considered to further reduce localized inflammation.
If conservative management fails to provide significant symptom relief after several months, surgical decompression may be considered. The goal of the operation is to release the pressure on the nerve by cutting the entrapping structures, such as the Arcade of Frohse. Surgery is reserved for severe, persistent cases that have not responded to non-operative treatment.