Fact-sheet: Posterior inter-osseous nerve syndrome
Updated on 09/30/2019 at 6:18 PM
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Definition
Mechanical involvement of the posterior interosseous nerve, the terminal motor branch of the radial nerve at the elbow.
Preferentially affects men and the dominant side.
Predisposing factor: repeated pronation-supination movements (watchmakers, musicians, painters, etc.)
< 5% of causes of atypical lateral epicondylalgia.
Several etiologies are possible:
- compression at an anatomic site: arcade of Frohse most frequently, inferior border of the supinator muscle, arcade of the recurrent radial artery, superomedial border of the extensor carpi radialis brevis muscle...
- extrinsic compression: benign tumor (e.g., lipoma), malignant tumor, cyst, lymphadenopathy, bicipitoradial bursitis.
- neurogenic tumor.
- post-traumatic involvement (radial fracture).
Clinical features
- Dynamic compression pattern: posterolateral forearm pain, mimicking lateral epicondylalgia.
- Permanent compression: posterolateral forearm pain and motor deficit of finger and wrist extension due to motor involvement of the posterior forearm compartment muscles.
Ultrasound
Bilateral and comparative assessment always +++:
- Thickening of the PIN with caliber discrepancy at its compression point,
- Loss of fascicular echotexture with diffuse hypoechogenicity,
- Doppler hyperemia,
- Particularity: its anteroposterior caliber decreases significantly and physiologically at the arcade of Frohse.
MRI
PD FS hyperintensity, T1 hypointensity, and thickening of the posterior interosseous nerve at its compression point.
Signs of secondary muscle denervation of the posterior forearm compartment muscles, with PD FS hyperintensity and amyotrophy with fatty involution on the T1 sequence.
Management
Symptomatic treatment in cases of dynamic compression: immobilization, NSAIDs.
Ultrasound-guided infiltration could be considered.
Surgical treatment with nerve release possible in cases of permanent compression.