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Anterior Interosseous Nerve Syndrome

synonyms:

AIN ICD-9

  • 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

AIN Anatomy

  • 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 Complications

  • Loss of AIN function

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
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