Summary Radial Tunnel Syndrome is a compressive neuropathy of the posterior interosseous nerve (PIN) at the level of proximal forearm (radial tunnel). Diagnosis is made clinically with pain only (maximal tenderness 3-5 cm distal to lateral epicondyle) without any motor or sensory dysfunction. Treatment is a prolonged course of conservative management with NSAIDs, temporary splinting and CSIs with radial tunnel decompression reserved for refractory cases. Epidemeology Incidence rare ~3 per 100,000 annually Demographics male > females Etiology Pathophysiology involves same sites of compression as PIN syndrome include (from proximal to distal) fibrous bands anterior to radiocapitellar joint radial recurrent vessels (leash of Henry) medial edge of ECRB proximal aponeurotic/tendinous edge of the supinator (arcade of Frohse) most frequent site of entrapment of the PIN normal radial tunnel pressure 50mmHg with supinator stretch (forced wrist flexion) pressure increases to 250mmHg distal edge of the superficial layer of the supinator risks constant prono-supination with 1kg force and elbow in 0°-45° flexion Associated conditions lateral epicondylitis RTS is difficult to distinguish from lateral epicondylitis and coexists in 5% of patients Anatomy Radial Tunnel 5 cm in length from the level of the radiocapitellar joint, extending distally past the proximal edge of the supinator boundaries lateral brachioradialis ECRL ECRB medial biceps tendon brachialis floor capsule of the radiocapitellar joint PIN origin PIN is a branch of the radial nerve that provides motor innervation to the extensor compartment course passes between the two heads of origin of the supinator muscle direct contact with the radial neck osteology passes over abductor pollicis longus muscle origin to reach interosseous membrane transverses along the posterior interosseous membrane innervation motor common extensors ECRB (often from radial nerve proper, but can be from PIN) Extensor digitorum communis (EDC) Extensor digiti minimi (EDM) Extensor carpi ulnaris (ECU) deep extensors Supinator Abductor pollicis longus (APL) Extensor pollicus brevis (EPB) Extensor pollicus longus (EPL) Extensor indicis proprius (EIP) sensory sensory fibers to dorsal wrist capsule provided by terminal branch which is located on the floor of the 4th extensor compartment no cutaneous innervation Presentation Symptoms deep aching pain in dorsoradial proximal forearm from lateral elbow to wrist increases during forearm rotation and lifting activities muscle weakness because of pain and not muscle denervation Physical exam tenderness over mobile wad over the supinator arch maximal tenderness is 3-5cm distal to lateral epicondyle more distal than lateral epicondylitis provocative tests resisted long finger extension test reproduces pain at radial tunnel (weakness because of pain) resisted supination test (with elbow and wrist in extension) reproduces pain at radial tunnel (weakness because of pain) passive pronation with wrist flexion reproduces pain at radial tunnel passive stretch of supinator muscle increases pressure inside radial tunnel to 250mmHg (normal 50mmHg) radial tunnel injection test diagnostic if injection leads to a PIN palsy and relieves pain sensory no cutaneous sensory manifestations if changes present in the first dorsal web space consider more proximal pathology motor no motor manifestations Imaging MRI usually negative indications to identify muscle changes in muscles innervated by PIN denervation edema/atrophy within the supinator/extensor to evaluate compression sites may show thickened edge of ECRB, prominent radial recurrent vessels (leash of Henry), swelling of PIN to identify other causes of entrapment (rare) tumors, ganglia, radiocapitellar synovitis, bicipital bursitis, radial head fractures and dislocations Studies Electrodiagnostic studies EMG/NCV are inconclusive because PIN carries unmyelinated Group IV fibers (C-fibers, nociception) and small myelinated Group IIA afferent fibers (temperature) pressure on these fibers produces pain these fibers cannot be evaluated by EMG/NCV the large myelinated fibers of PIN remain normal, producing normal EMG/NCV Diagnostic injection injection of local anesthetic (LA) into the area of localized tenderness ensure that LA does not spread to lateral epicondyle Differential Key differential Lateral epicondylitis both conditions coexist in 5% of patients in lateral epicondylitis, tenderness is directly over the lateral epicondyle in RTS, tenderness is 3-5cm distal to the lateral epicondyle Cervical radiculopathy at C6-7 electrodiagnostic studies may show denervation Diagnosis Clinical diagnosis is made with careful history and physical examination Treatment Nonoperative activity modification, temporary splinting, NSAIDS indications first line of treatment for at least one year technique of activity modification avoid prolonged elbow extension with forearm pronation and wrist flexion corticosteroid injection indications both diagnostic and therapeutic outcomes 70% improvement at 6 weeks 60% pain free at 2 years Operative radial tunnel release indications extensive nonoperative treatment fails outcomes surgical release has disappointing results only 50-90% good to excellent results delayed maximal recovery of up to 9-18 months lower success rate in the following groups concomitant multiple entrapment neuropathies (60%) concomitant lateral epicondylitis (40%) workers compensation patients (30%) Techniques Radial tunnel release approach dorsal approaches to the PIN 3 planes have been described between ECRB and EDC between brachioradialis and ECRL transmuscular brachioradialis-splitting anterior approach to the PIN between brachioradialis and biceps technique release arcade of Frohse release distal edge of supinator release fibrous bands superficial to the radiocapitellar joint outcomes success rate of surgical decompression is 70-90%