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) login to view 3 more bullets 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 login to view 3 more bullets medial login to view 2 more bullets floor login to view 1 more bullet 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 login to view 11 more bullets sensory login to view 3 more bullets 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 login to view 1 more bullet provocative tests resisted long finger extension test login to view 1 more bullet resisted supination test (with elbow and wrist in extension) login to view 1 more bullet passive pronation with wrist flexion login to view 2 more bullets radial tunnel injection test login to view 1 more bullet 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 login to view 1 more bullet to evaluate compression sites login to view 1 more bullet to identify other causes of entrapment (rare) login to view 1 more bullet 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 login to view 1 more bullet technique of activity modification login to view 1 more bullet corticosteroid injection indications login to view 1 more bullet outcomes login to view 2 more bullets Operative radial tunnel release indications login to view 1 more bullet outcomes login to view 7 more bullets Techniques Radial tunnel release approach dorsal approaches to the PIN login to view 4 more bullets anterior approach to the PIN login to view 1 more bullet 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%