Skip to main content
Hand Surgery Source
Toggle navigation
Main navigation
HOME
Anterior Interosseous Nerve (AIN) Sign
Test, Exam and Signs
Historical Overview
Anterior interosseous nerve (AIN) syndrome was first reported by Kiloh and Nevin in 1952.
1,2
In 1965, the first description of an operation for AIN syndrome was credited to Fearn and Goodfellow.
2
Description
The AIN sign helps to identify AIN syndrome, which involves partial or complete loss of motor function of the flexor pollicis longus (FPL), the flexor digitorum profundus (FDP), and the pronator quadratus (PQ).
Pathophysiology
AIN syndrome often arises from the neuritis, Parsonage-Turner syndrome.
3
AIN syndrome also may arise from pronator teres syndrome, carpal tunnel syndrome, or peripheral neuropathy.
Some patients with AIN syndrome may have suffered a viral illness before experiencing pain in the forearm.
3
Instructions
Obtain an accurate and complete patient history. Ask the patient if s/he experiences any difficulty with writing, knitting, or other pinching motions.
Check the patient for weakness in the thumb, index finger, and/or middle finger.
Examine the patient for lack of distal interphalangeal (DIP) flexion in the index finger and interphalangeal (IP) flexion in the thumb.
Examine the patient for a dull pain in the proximal forearm.
2,4
Check the contralateral hand, wrist and forearm.
Variations
The AIN sign is also referred to as the “OK” sign.
5
Related Signs and Tests
Pinch strength
2
Muscle test: FDP
Muscle test: FPL
Range of motion (ROM), active
Sensory exam by nerve
Flexor pollicis manual compression
Electrodiagnostic studies
6
Magnetic resonance imaging (MRI), without contrast
Additional Information
Flexor Pollicis Manual Compression
Grip Strength
Muscle Test and Tendon Exam: Flexor Digitorum Profundus (FDP)
Muscle Test and Tendon Exam: Flexor Pollicis Longus (FPL)
Muscle Testing by Nerve
Pinch Strength
Range of Motion: Active
Presentation Photos and Related Diagrams
AIN Palsy Sign
Note lack of index DIP and thumb IP flexion (arrows) in patient with Anterior Interosseous Nerve Palsy
Definition of Positive Result
A positive result occurs when the patient presents with lack of index DIP and thumb IP flexion.
Definition of Negative Result
A negative result occurs when the patient does not present with lack of index DIP and thumb IP flexion.
Comments and Pearls
AIN syndrome may resolve spontaneously after continued observation.
2,6
Three months after an EMG has shown no evidence of reinnervation, operative treatment would include surgical decompression, and a complete release of the median nerve in the proximal forearm.
3
Magnetic resonance imaging (MRI), without contrast can also be helpful
Diagnoses Associated with Tests, Exams and Signs
ANTERIOR INTEROSSEOUS NERVE PALSY
CARPAL TUNNEL SYNDROME
MANNERFELT'S SYNDROME
MEDIAN NERVE LACERATION
PRONATOR SYNDROME
References
Kiloh LG, Nevin S. Isolated neuritis of the anterior interosseous nerve.
Br Med J
1952;1(4763):850-1.
PMID: 14916168
Gardner-Thorpe C. Anterior interosseous nerve palsy: spontaneous recovery in two patients.
J Neurol Neurosurg Psychiatry
1974;37:1146-50.
PMID: 4374508
Culp R, Jacoby S.
Musculoskeletal Examination of the Elbow, Wrist and Hand: Making the Complex Simple
. New Jersey: SLACK Incorporated, 2012
Collins DN, Weber ER. Anterior interosseous nerve syndrome.
South Med J
1983;76(12):1533-7.
PMID: 6359461
Rayan G, Akelman E.
The Hand: Anatomy, Examination and Diagnosis
. Philadelphia: Lippincott Williams & Wilkins, 2012
Rodner CM, Tinsley BA, O’Malley MP. Pronator syndrome and AIN syndrome.
J Am Acad Orthop Surg
2013;21(5):268-75.
PMID: 23637145