Anterior Interosseous Nerve Syndrome
- 354.1 (other lesion of median nerve)
AIN Etiology / Epidemiology / Natural History
- vague forearm pain with loss of function
- loss of FPL and Index finger FDP with no sensory changes
- AIN palsy = inability to flex the distal interphalangeal joint of the index finger because of weakenss and/or paralysis of the FDP to the index finger.
- may be peripheral compression or neuritis
- Origin: branches from the the median nerve 4-6cm below the elbow.
- AIN innervated muscles=radial 2 FDP, Flexor pollicis longus, Pronator quadratus. Provides sensation and pain to volar carpus.
- Sources of impingement: 1-pronator quadratus fibrous bands, 2-FDP origin, 3-lacertus fibrousus, 4-Gantzer's muscle, 5-Enlarged vessels/bursa/tumor.
- Excessory head of FPL (Gantzer's muscle) anatomic variant may cause AIN syndrome
- See also forearm anatomy.
AIN Clinical Evaluation
- A-OK signs tests FDP and FPL. Patients demonstrate weakness in pinch and grip.
- May note vague forearm pain.
- No sensory deficit.
- must rule out viral brachial neuritis(Pasonage-Turner syn) if bilateral
AIN Xray / Diagnositc Tests
- Plain films normal
- EMG diagnostic, but can be difficult due to deep location of AIN.
- MRI: may demonstrate a specific compressive process.
AIN Classification / Treatment
- AIN Palsy Treatment: maintain ROM, observation for 6 months as most will resolve by 6 months. Surgical decompression if no improvement at 6 months.
AIN Associated Injuries / Differential Diagnosis
AIN Follow-up Care
- Consider repeat EMG to evaluate for nerve recovery.
- Clinical improvement can occur for up to 18 months.
AIN Review References
- Miller-Breslow, J Hand Surg 15A:493:1990