Anterior Interosseus Nerve Syndrome

Other Names

• Kiloh-Nevin Syndrome
• AIN Compressive Neuropathy
• AINS
• Anterior Interosseus Nerve Syndrome

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Background

• This page refers to neuropathy of the Anterior Interosseus Nerve (AIN)

Epidemiology

• Represents <1% of upper extremity neuropathies

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Pathophysiology

• General
  • Typically presents with forearm pain, weakness in the FPL, FDP of the index finger
  • Sensation is intact
  • Diagnosis is aided by EMG, MRI
  • Symptoms are typically self limited, surgery is indicated if symptoms don't resolve spontaneously

Etiology

• Pathoanatomy
  • Most common site of compression is the tendinous edge of the deep head of the Pronator Teres
  • Also must consider
    • Proximal edge of the Flexor Digitorum Superficialis arch (the FDS arcade)
    • Gantzer's muscle (accessory head of the FPL muscle)
    • FDS or FDP accessory muscles
    • Arterial thrombosis (radial or ulnar artery have been implicated)
    • Lacertus fibrous
• Etiology of the disease is controversial
  • Traumatic etiologies:
    • Supracondylar fractures,
    • Penetrating injuries and stab wounds
    • Cast fixation
    • Venipuncture
    • Complication of open reduction and internal fixation of fractures
  • Spontaneous etiologies:
    • Brachial plexus neuritis
    • Compartment syndrome
    • Compression neuropathy
• Martin-Gruber Anastomosis
  • Anatomical variant in which AINM gives off branches to ulnar nerve, patients can then present with symptoms in ulnar nerve patterns

Pathoanatomy

• Anterior Interosseus Nerve (AIN)
  • Terminal motor branch of the Median Nerve
• Innervates:
  • Flexor Pollicus Longus
  • Flexor Digitorum Profundus (index, long fingers)
  • Pronator Quadratus

Associated Conditions

• Parsonage Turner Syndrome
  • Be suspicious if patient has bilateral AIN symptoms, shoulder pain, viral prodrome

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Risk Factors

• Needs to be updated

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Differential Diagnosis

Differential Diagnosis Wrist Pain

• Fractures
  • Distal Radius Fracture
    • Barton's Fracture
    • Chauffer's Fracture
    • Colles' Fracture
    • Die-Punch Fracture
    • Radial Styloid Fracture
    • Smith's Fracture
  • Distal Ulna Fracture
  • Carpal Fractures
    • Scaphoid Fracture
    • Lunate Fracture
    • Triquetrum Fracture
    • Pisiform Fracture
    • Trapezium Fracture
    • Trapezoid Fracture
    • Capitate Fracture
    • Hamate Fracture
  • Essex Lopresti Fracture
• Dislocations
  • Carpometacarpal Joint Dislocation
  • Distal Radioulnar Joint Dislocation
  • Lunate Dislocation
  • Perilunate Dislocation
• Instability & Degenerative
  • Scapholunate Instability
  • Lunotriquetral Instability
  • Scaphoid Nonunion Advanced Collapse
  • Distal Radial Ulnar Joint Instability
  • Kienbocks Disease
  • Dorsal Wrist Impingement
• Tendinopathies & Ligaments
  • De Quervain's Tenosynovitis
  • Intersection Syndrome
  • TFCC Injury
  • Wrist Tendinopathies
  • Extensor Carpi Ulnaris Instability
• Neuropathies
  • Carpal Tunnel Syndrome
  • Pronator Teres Syndrome
  • Anterior Interosseus Nerve Syndrome
  • Posterior Interosseus Nerve Syndrome
  • Guyon Canal Syndrome
• Pediatric Considerations
  • Distal Radial Epiphysitis (Gymnast's Wrist)
  • Torus Fracture
• Arthropathies
  • Wrist Osteoarthritis
  • Rheumatoid Arthritis
  • Gout
• Cartilage
  • Osteochondral Defect
• Vascular
  • Hypothenar Hammer Syndrome
• Other
  • Ganglion Cyst of Wrist
  • Ulnar Impingement Syndrome
  • Infectious Tenosynovitis

Differential Diagnosis Forearm Pain

• Fractures
  • Distal Radius Fracture
    • Barton's fracture
    • Chauffer's Fracture
    • Colles' Fracture
    • Die-Punch Fracture
    • Radial Styloid Fracture
    • Smith's Fracture
  • Radius Ulna Fracture (Both Bone)
  • Proximal Radius Fracture (Head, Neck)
  • Isolated Ulna Fracture
  • Monteggia Fracture
  • Galeazzi Fracture
  • Distal Ulna Fracture
  • Essex Lopresti Fracture
• Pediatric Specific Fractures
  • Torus Fracture
  • Greenstick Fracture
  • Salter Harris Fracture
  • Plastic Deformation
• Dislocations & Instability
  • Distal Radioulnar Joint Dislocation
  • Proximal Radioulnar Joint Instability
• Soft Tissue Trauma
  • Acute Compartment Syndrome
• Tendinopathies
  • De Quervain's Tenosynovitis
  • Intersection Syndrome
• Neuropathies
  • Radial Tunnel Syndrome
  • Posterior Interosseus Nerve Syndrome
• Pediatric Considerations
  • Distal Radial Epiphysitis

Other Considerations

• Thoracic Outlet Syndrome
• Cervical Radiculopathy
• Parsonage Turner Syndrome

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Clinical Features

• History
  • Poorly localized pain from forearm to anticubital fossa
  • The patient will not report any parasthesias
  • Inability to make "OK" sign
• Physical Exam: Physical Exam Wrist
  • This disease is characterized by motor deficits only, there are no sensory deficits
  • Weakness of index and thumb pincer movement
• Special Tests
  • Pinch Test: Patient unable to hold sheet of paper between thumb and index finger

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Evaluation

Radiographs

• Standard Radiographs Wrist
  • 3 View radiographs typically acquired to evaluate for other etiologies
  • No role in diagnosis of atraumatic disease

EMG/NCS

• Sensory nerve conduction studies of median nerve should be normal
• Can help differentiate neuralgic amyotrophy verse a compression neuropathy

MRI

• Identifying compression of the AIN on MRI can be difficult
  • Entrapment may not be visualized
  • Enhancement within the muscles affected by the nerve root entrapment

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Classification

• N/A

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Management

Nonoperative

• Most patients improve with 6-12 weeks of relative rest and conservative care
• Relative rest, especially from provocative activities
• Splint elbow at 90° flexion
• Physical Therapy
• Medications including NSAIDS

Operative

• Indications:
  • Failure of conservative measures
• 75% of patients improve following surgery if clear space occupying lesion(need citation)
• Procedure:
  • Surgical decompression of AIN

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Return to Play

• Needs to be updated

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Complications

• Motor weakness
• Chronic pain

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See Also

• Hand and Wrist Anatomy (Main)
• Wrist Pain (Main)
• Forearm Pain (Main)
• Elbow Pain (Main)
• Physical Exam Wrist
• Neuropathies (Main)

External

• Sports Medicine Review Wrist Pain: https://www.sportsmedreview.com/by-joint/wrist/

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