Radial Tunnel Syndrome (RTS) is a compressive neuropathy of the posterior interosseous nerve (PIN), a branch of the radial nerve, occurring as it passes through the radial tunnel in the proximal forearm. Characterized by pain without motor or sensory deficits, RTS poses diagnostic challenges due to symptoms overlapping with lateral epicondylitis (tennis elbow). Proper distinction between these conditions is crucial for effective treatment.
The radial tunnel extends from the humeroradial joint to the distal border of the supinator muscle. The PIN may become compressed at several anatomical sites:
Fibrous bands anterior to the radiocapitellar joint.
Tendinous margin of the extensor carpi radialis brevis (ECRB).
The “leash of Henry” (radial recurrent vessels).
Arcade of Frohse (most common site of compression, proximal supinator edge).
Distal edge of the supinator muscle.
Compression at these points causes nerve ischemia and mechanical irritation, resulting in localized pain without significant motor or sensory impairment.
RTS presents with these characteristic features:
Pain Location: Deep, aching pain approximately 4-5 cm distal to the lateral epicondyle in the dorsoradial forearm.
Tenderness: Localized tenderness over the radial tunnel, exacerbated by palpation.
Pain with Resisted Supination: Increased pain during resisted forearm supination, especially with the elbow extended.
Pain with Resisted Middle Finger Extension (Middle Finger Test): Pain elicited by resisted middle finger extension.
Pain on Passive Stretching: Pain reproduced by passive pronation combined with wrist flexion.
Nocturnal Pain: Symptoms often worsen during sleep due to positioning.
Absence of Motor Weakness: Unlike PIN syndrome, RTS does not present muscle weakness.
Lack of Sensory Deficits: No numbness or tingling, as PIN carries no cutaneous sensory fibers.
Pain with Elbow Extension: Increased symptoms with elbow extension due to tension in the radial tunnel.
Aggravation by Repetitive Activities: Symptoms worsen with repetitive forearm rotation or wrist extension.
Differentiation between RTS and lateral epicondylitis is critical due to overlapping symptoms:
Pain Location: Lateral epicondylitis tenderness is directly over the lateral epicondyle, whereas RTS tenderness is distal along the radial tunnel.
Pain with Resisted Movements: Epicondylitis pain occurs with resisted wrist extension and grip, RTS pain is provoked by resisted supination and middle finger extension.
Sensory and Motor Findings: Neither typically has sensory deficits or weakness; presence suggests alternate conditions like PIN syndrome.
Treatment Response: Epicondylitis responds to conservative management; RTS may require specific nerve decompression interventions.
Physical Examination: Middle finger test, tenderness over radial tunnel, provocative maneuvers.
Electrodiagnostic Studies (EMG/NCS): Usually normal in RTS; used primarily to rule out PIN syndrome or cervical radiculopathy.
Imaging (MRI, Ultrasound): Occasionally useful to identify structural compression (ganglion cysts, tumors) or muscle edema.
Management involves conservative and surgical interventions based on symptom severity and duration:
Activity Modification: Avoid repetitive forearm activities or prolonged elbow extension.
Physical Therapy: Exercises focusing on muscle stretching and strengthening to improve nerve mobility.
Splinting: Wrist splints to reduce forearm muscular activity and nerve irritation.
Nonsteroidal Anti-Inflammatory Drugs (NSAIDs): Reduce inflammation and manage pain.
Corticosteroid Injections: Temporary relief through reduction of local inflammation.
Surgical Decompression: Indicated after 3–6 months of failed conservative therapy, releasing compressive structures within the radial tunnel.
Surgical outcomes vary (60–70% success), emphasizing the importance of accurate patient selection and diagnosis.
Radial Tunnel Syndrome presents diagnostic challenges due to symptom subtlety and overlap with conditions like lateral epicondylitis. Accurate clinical assessment, differentiation through targeted physical exams, and diagnostic tests ensure proper management. A combination of conservative and surgical treatments, tailored to the patient’s presentation, optimizes outcomes and symptom relief.