Radial Tunnel Syndrome (RTS) is a relatively uncommon compressive neuropathy involving the radial nerve or one of its deep branches in the forearm. This condition occurs when the nerve is physically squeezed or irritated as it passes through a narrow anatomical corridor near the elbow, leading to pain. RTS is primarily characterized by pain, often without the typical motor weakness or sensory loss (numbness or tingling) associated with more severe nerve entrapments.
Understanding the Radial Nerve Pathway
The radial nerve originates from the brachial plexus and travels down the arm, providing motor and sensory function. Near the elbow, the main nerve trunk divides into two branches: the superficial sensory branch and the deep motor branch, known as the posterior interosseous nerve (PIN).
The radial tunnel is a potential space, approximately five centimeters long, beginning near the radiocapitellar joint. The PIN passes through this tunnel, making it vulnerable to compression from surrounding muscles and fibrous tissues. The most frequent site of entrapment is the Arcade of Frohse, a fibrous arch forming the proximal edge of the supinator muscle.
Compression can also occur at other points, including fibrous bands at the radiocapitellar joint and where the radial recurrent vessels cross the nerve. Repetitive movements, especially those involving forearm rotation and wrist extension, can cause friction and swelling, intermittently compressing the nerve.
Symptoms of Nerve Compression
RTS is characterized by pain in the proximal forearm, often described as a deep, nagging ache or a burning sensation. This discomfort is typically felt on the top or outer side of the forearm, radiating several centimeters below the elbow. Symptoms often worsen with activities requiring forceful twisting of the forearm, such as using a screwdriver or turning a doorknob, and may be more noticeable at night. RTS typically causes pain without resulting in significant muscle weakness because the compression is often dynamic or intermittent.
Differentiating Radial Tunnel Syndrome from Tennis Elbow
RTS is commonly misidentified as Lateral Epicondylitis, or “Tennis Elbow,” due to the overlapping location of pain in the lateral elbow area. A key distinction is the precise location of maximum tenderness. Tennis Elbow pain is localized directly on the bony lateral epicondyle, while RTS tenderness is found more distally, several centimeters down the forearm over the radial tunnel.
The nature of the pain also differs. Tennis Elbow pain is tendon-based and provoked by resisted gripping or extending the wrist. RTS pain, which stems from nerve irritation, is often reproduced by resisted supination (turning the palm upward). A positive test for RTS can also be elicited by resisted extension of the middle finger, a maneuver that stresses the nerve.
Confirming Diagnosis and Treatment Protocols
Diagnosing RTS relies heavily on a thorough clinical examination, as there is no single definitive test. The healthcare provider searches for the specific point of maximal tenderness in the proximal forearm and performs provocative maneuvers, such as resisted supination and resisted middle finger extension, to reproduce the characteristic pain.
Diagnostic imaging, such as X-rays or MRI, is primarily used to rule out other causes of pain, like fractures or tumors. Nerve conduction studies are frequently normal in RTS because the compression is often intermittent. A local anesthetic injection directly into the radial tunnel that temporarily relieves the pain can also serve as a diagnostic tool.
The management of RTS begins with conservative, non-surgical approaches. This includes activity modification to avoid repetitive forearm rotation and forceful gripping. A splint may be recommended to keep the forearm and wrist in a neutral position, reducing tension on the nerve.
Over-the-counter NSAIDs may be used to manage pain and reduce localized swelling. Physical therapy focuses on nerve gliding exercises and ergonomic adjustments. If symptoms do not improve after a consistent trial of conservative treatment, typically lasting three to six months, surgical decompression may be considered. The surgical procedure involves releasing the pressure on the nerve by cutting the fibrous and muscular structures in the radial tunnel, including the Arcade of Frohse.