What is radial tunnel syndrome, a condition causing persistent pain in the forearm and triceps, possibly due to repetitive strain or overuse injuries?

Radial Tunnel Syndrome: Definition and Clinical Characteristics

Radial tunnel syndrome (RTS) is a compression neuropathy of the posterior interosseous nerve (the deep branch of the radial nerve) as it travels through the radial tunnel in the forearm, causing chronic lateral forearm pain without motor weakness or sensory deficits. 1, 2

Anatomical Basis

• The radial nerve divides into superficial (sensory) and deep (motor) branches in the proximal forearm, with the deep branch (posterior interosseous nerve) traveling posteriorly through the heads of the supinator muscle where compression most commonly occurs 1, 2

• The radial tunnel is a musculo-aponeurotic furrow extending from the lateral epicondyle of the humerus to the distal edge of the supinator muscle 3

• The arcade of Frohse (a fibrous arch formed by the superficial head of the supinator muscle) is the most common compression site, though it is not the exclusive location 3

• The arcade of Frohse is tendinous in approximately 87% of individuals and membranous in 13%, with the tendinous form developing in adults as a response to repeated rotary movements of the forearm 3

• Additional compression sites include the fibrous tissue surrounding the nerve supply to the extensor carpi radialis brevis (ECRB), occurring in approximately 13% of cases 3

Clinical Presentation

• RTS manifests as persistent pain in the lateral forearm and proximal forearm without motor paralysis or sensory changes, distinguishing it from other radial nerve pathologies 1, 4

• Pain typically radiates from the lateral elbow region down the forearm and can significantly interfere with daily activities 1

• The condition is often worsened by repetitive pronation and supination movements of the forearm, particularly in individuals with occupational or recreational activities involving these motions (such as gardening) 3, 1

Pathophysiology

• Repetitive pronation and supination of the forearm induces compression of the radial nerve and its branches between two inextensible structures: the fibrous arcade of Frohse and the proximal radius (radial head and radial tubercle) 3

• This repetitive compression is aggravated by repeated supinator muscle activity and promotes histological changes in the radial tunnel contents, leading to progressive development of local fibrosis 3

• The angle formed by the radial shaft and the supinator arch (approximately 23 degrees) contributes to the mechanical compression during forearm rotation 3

Diagnostic Challenges and Controversy

• RTS remains a controversial diagnosis with notable confusion due to inconsistent definitions, terminology, and diagnostic tests in the literature, particularly regarding its overlap with lateral epicondylitis ("tennis elbow") 2, 4

• The clinical validity and anatomical rationale for traditionally used provocative tests (such as Maudsley's test) remain unclear and lack strong evidence 4

• Neither imaging nor electrophysiological studies contribute significantly to clinical diagnosis 4

• Clinical diagnosis is supported by short-term improvement after injection with long-acting local anesthetic and corticosteroid 4

Epidemiology

• The prevalence of RTS in the United States is approximately 0.091%, with an annual incidence of 0.0091%, making it a relatively rare diagnosis 5

• The mean age at diagnosis is 52 years, with 55% of cases occurring in women 5

• Approximately 5.7% of patients with RTS also have ipsilateral lateral epicondylitis diagnosed within 6 months, highlighting the diagnostic overlap between these conditions 5

Treatment Approach

• Initial management consists of conservative treatment with splinting, activity modification, and anti-inflammatory medication 1, 2

• Fewer than 3% of patients receive diagnostic or therapeutic injections within 30 days of diagnosis 5

• Surgical decompression is reserved for refractory cases where conservative measures have failed 1, 2

• Only 2.4% of diagnosed patients undergo radial tunnel release within 1 year of diagnosis 5

• In patients with concurrent ipsilateral RTS and lateral epicondylitis requiring surgery, 59.1% undergo simultaneous radial tunnel release and lateral epicondyle debridement 5

• Surgical outcomes show low 90-day complication rates: 5% hospital readmission and 2.1% revision surgery 5