Radial Tunnel Syndrome

Radial Tunnel Syndrome (RTS) is a pain condition of the proximal forearm that occurs due to compression of the posterior interosseous nerve (PIN) within the radial tunnel—most commonly at the Arcade of Frohse. The condition is clinically challenging to diagnose and is often confused with lateral epicondylitis (tennis elbow). RTS is primarily a diagnosis of exclusion, as radiological and neurophysiological findings are frequently normal.

Anatomy

The radial tunnel is a narrow anatomical passage on the lateral side of the proximal forearm.It extends from the lateral epicondyle to the proximal third of the radius and contains the following structures:

Nerve branches:

• Radial nerve, which divides into: – Ramus superficialis (sensory branch) – Ramus profundus (motor branch, also called the posterior interosseous nerve)

Muscular boundaries:

• Lateral: Brachioradialis and extensor carpi radialis longus

• Medial: Biceps tendon and brachialis

• Floor: Capsule of the humeroradial joint and the supinator muscle

Pathophysiology of Radial Tunnel Syndrome

The condition usually results from compression of the motor branch of the radial nerve (ramus profundus) as it passes through the radial tunnel, most frequently at the Arcade of Frohse, the fibrous proximal edge of the supinator muscle.

Typical characteristics:

• Deep, burning pain in the proximal lateral forearm

• Pain aggravated by pronation and supination

• No sensory loss (since the ramus profundus is purely motor)

• Pain located more distally than in lateral epicondylitis

Clinical Tests

The diagnosis of RTS relies heavily on clinical assessment.

Commonly used tests:

• Pain during resisted supination

• Pain during passive wrist extension against resistance

• Pain with resisted extension of the third finger (although not always present)

Rule of Nine Test:The proximal forearm is divided into a 3×3 grid. Gentle palpation of each area is performed.Tenderness in the two upper lateral zones indicates radial nerve irritation.The middle and distal circles serve as controls to help differentiate RTS from median nerve-related disorders.

Differential Diagnoses

Pain on the dorsal forearm and reduced grip strength may have several causes.RTS must be distinguished from:

• Lateral epicondylitis: Direct tenderness over the lateral epicondyle; coexists with RTS in 21–41% of cases

• Posterior interosseous nerve (PIN) syndrome: Characterised by motor weakness, especially in thumb and finger extensors, without pain

• De Quervain’s tenosynovitis: Often misdiagnosed when involving superficial radial nerve irritation

Other possible conditions:

• Radiocapitellar osteoarthritis

• Extensor carpi radialis brevis muscle rupture

• Synovitis or posterior plica impingement

• Biceps tendinopathy

• Cervical radiculopathy

Rehabilitation

Acute Phase

• Avoid repetitive loading (especially supination and wrist extension)

• Wrist orthosis: Wrist in slight extension, forearm in supination, elbow flexed

• Nerve mobilisation and radial nerve gliding techniques

• Soft tissue treatment and stretching of the extensor group

• Activity modification and ergonomic correction

Progressive Rehabilitation

• Restore balance between agonists and antagonists

• Focus on neuromuscular control and PNF diagonal patterns

• Integrate closed kinetic chain movements

• Introduce eccentric grip-strength exercises

• Add sport-specific and functional exercises when pain-free motion and strength are regained

Surgical Treatment

Patients who fail to respond to conservative therapy after 3–6 months may be considered for surgery.

Surgical decompression typically includes:

• Release of the PIN and SBRN (superficial branch of the radial nerve)

• Removal of pressure at the Arcade of Frohse

• Ligation of the radial recurrent vessels

Common surgical approaches:

• Trans-brachioradialis approach

• Anterior approach

Success rates:

• Vary between 67–93%, depending on whether both branches are decompressed.

Prognosis

• PIN decompression alone: 39–95% success

• Combined PIN + SBRN decompression: 67–92% success

• Athletes and compliant patients demonstrate the best long-term outcomes

Summary

Radial Tunnel Syndrome (RTS) is a rare but important differential diagnosis for lateral elbow pain without muscle weakness. The diagnosis is clinical and requires careful exclusion of other causes. Conservative treatment is first-line and includes rest, nerve mobilisation, and ergonomic correction. When non-surgical management fails, surgical decompression offers good outcomes.Rehabilitation should focus on nerve mobility, muscular balance, and functional restoration.

References

1. S. Brent Brotzman, Robert C. Manske. Clinical orthopedic rehabilitation, 2011

2. Ali Moradi, MD; Mohammad H Ebrahimzadeh, MD; Jess B Jupiter, MD. Radial Tunnel Syndrome, Diagnostic and Treatment Dilemma. THE ARCHIVES OF BONE AND JOINT SURGERY. 2015 Jul; 3(3): 156–162.