Posterior Interosseous Nerve Syndrome (PIN)
Compression of the deep branch of the radial nerve (posterior interosseous nerve) in the radial tunnel, mainly at the Fröhse arcade. Causes purely motor weakness in finger and wrist extension without sensory deficit. Distinguished from lateral epicondylitis and resistant tennis elbow.
Characteristics
The posterior interosseous nerve syndrome (PIN syndrome) results from compression of the deep motor branch of the radial nerve (posterior interosseous nerve) in the radial tunnel [1]. The PIN is a purely motor branch innervating the finger and thumb extensors (extensor digitorum communis, extensor indicis, extensor digiti minimi, extensor pollicis longus and brevis, abductor pollicis longus) and the supinator. The main compression site is the Fröhse arcade (proximal edge of the supinator), a fibrous arch present in 30-80% of the population.
It manifests as progressive painless weakness of finger and wrist extension, or as lateral forearm pain that may mimic or coexist with lateral epicondylitis (resistant tennis elbow). The distinction is crucial because treatment differs fundamentally [2].
Other compression sites include the fibrous bands anterior to the radial head, the recurrent radial vessels (leash of Henry), the proximal edge of the ECRB, and lipomas or ganglia. Diagnosis relies on EMG/NCS showing denervation of PIN-innervated muscles. Treatment is surgical decompression if no improvement after 3 months of conservative management [3].
- The radial nerve divides at the level of the radial head into a superficial sensory branch and the deep motor branch (PIN). The PIN enters the radial tunnel and passes beneath the Fröhse arcade (proximal supinator edge). It innervates the supinator, extensor digitorum communis, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis longus and brevis, and extensor indicis.
- Five potential compression sites in the radial tunnel: 1) fibrous bands anterior to the radial head, 2) recurrent radial artery leash (leash of Henry), 3) proximal ECRB edge, 4) Fröhse arcade (most common, 70%), 5) distal supinator edge. Space-occupying lesions (lipomas, ganglia, rheumatoid synovitis) may also cause compression.
- Risk factors: repetitive forearm pronation-supination (manual workers, musicians), rheumatoid arthritis (synovitis), space-occupying lesions (lipoma, ganglion), forearm fractures with callus, post-surgical fibrosis, Monteggia fracture. Slight female predominance in some series.
- Complications: progressive finger drop (inability to extend MCP joints), loss of thumb extension, weakness of wrist extension in ulnar deviation (ECU paralysis), radial wrist deviation during extension (preserved ECRL/ECRB with paralyzed ECU). If untreated, complete motor loss may become irreversible after prolonged denervation.
Medical and Surgical Management
- Conservative treatment (3 months trial): activity modification, NSAIDs, splinting (wrist and finger extension splint), physical therapy. Avoid repetitive pronation-supination. Indicated for mild cases or diagnostic uncertainty. Success rate 50-60%.
- Surgical decompression of the radial tunnel: release of all potential compression sites from proximal to distal (fibrous bands, leash of Henry, ECRB edge, Fröhse arcade, distal supinator edge). Anterior (Thompson) or posterolateral approach. Results best when performed before 18 months of symptoms.
- Post-decompression tendon transfers if incomplete nerve recovery after 12-18 months: pronator teres to ECRB, FCR to EDC, palmaris longus to EPL. Restores finger and wrist extension. Indicated when EMG shows no reinnervation potential.
Physiotherapy treatment
- Conservative phase: wrist and finger extension splint to prevent flexion contracture during nerve recovery. Active and passive range of motion maintenance. Electrical stimulation of denervated muscles to prevent atrophy. Neural mobilization techniques.
- Post-surgical decompression: immediate active mobilization of the elbow, wrist and fingers. Continue dynamic extension splinting. Nerve gliding exercises from week 2. Progressive strengthening of recovering muscles as reinnervation progresses (clinical and EMG monitoring).
- Reinnervation phase (3-18 months post-decompression): progressive strengthening of recovering extensors. Biofeedback and EMG-guided exercises to facilitate muscle recruitment. Functional reintegration with progressive activities. Scar management and desensitization.
- Functional rehabilitation: coordination and manual dexterity training, fine grip and object manipulation exercises. Reintegration of daily activities (door opening, writing, cutlery use). Gradual return to occupational activities. Assessment of need for permanent assistive devices or orthoses.
After the session
You may feel slight fatigue or tightness: this is normal. Continue the exercises taught at home to maintain session benefits.
Questions About Elbow Rehabilitation
When should I start physiotherapy after elbow surgery?
Rehabilitation generally begins between 3 and 21 days after the operation, depending on the type of procedure and the stability of the surgical fixation. For fractures treated with stable internal fixation (screw plate), early mobilization is often authorized from D+3 to D+5 to prevent joint stiffness. In cases of elbow replacement or complex ligament repair, the delay may be extended to 2-3 weeks with initial immobilization in a splint. A systematic review published in the Journal of Shoulder and Elbow Surgery confirms that early mobilization after elbow surgery significantly improves final range of motion without increasing the risk of complications [Hackl et al., 2023] . Your surgeon will advise the optimal timing based on your specific procedure.
What are the goals of elbow rehabilitation?
Elbow rehabilitation pursues several complementary goals, adapted to each phase of recovery. In the initial phase (0-6 weeks), the priority is to restore range of motion in flexion-extension (goal: 30°-130° minimum for daily activities) and in pronation-supination (50° in each direction minimum). In the intermediate phase (6-12 weeks), the focus is on progressive muscle strengthening of the flexors, extensors and rotators of the forearm, as well as restoring joint stability through proprioceptive exercises. In the advanced phase (3-6 months), the emphasis is on functional reintegration: daily activities, work tasks and return to sports. Scientific literature highlights that the minimum functional arc of the elbow (30°-130° of flexion-extension, 50° of pronation and 50° of supination) is necessary to perform 90% of daily activities [Mofidi et al., 2020] . Scar treatment and adhesion prevention complete this comprehensive care approach.
Is elbow rehabilitation painful?
The techniques used are progressive and adapted to your tolerance. The elbow is a joint particularly prone to stiffness and inflammatory reactions: overly aggressive rehabilitation can paradoxically worsen the situation by causing heterotopic ossifications (abnormal bone formations in soft tissues). Exercises must be regular but never forced . The physiotherapist always adapts the intensity to stay below the pain threshold, following the "no pain, more gain" rule specific to the elbow. Gentle, regular active mobilization spread across the day in short sequences is generally preferred to prevent stiffness, with early active mobilization recommended after an elbow injury [Akhtar et al., 2021] . Complementary techniques such as cryotherapy , microcurrents and Novafon vibration therapy also help control pain during sessions.
Scientific sources
Average duration
6 to 18 months for nerve recovery post-decompression