Review on the Anterior Interosseous Nerve Syndrome Introduction The anterior interosseous nerve (AIN) is a branch of the median nerve.
Review on the Anterior Interosseous Nerve Syndrome The anterior interosseous nerve (AIN) is a branch of the median nerve. The AIN is typically found approximately 5cm from the lateral epicondyle and will typically dive below or through the pronator teres before it travels through the interosseous membrane of the wrist. The AIN provides motor innervation to the flexor pollicis longus (FPL), the flexor digitorum profundus (FDP) of the second and third digit, and the pronator quadratus.
The pathophysiology of AIN syndrome is controversial. The AIN can be injured from trauma or iatrogenically from surgical injury. However, symptoms can also be secondary to entrapment from an accessory flexor digitorum profundus.
Entrapment of the AIN occurs infrequently and only amounting for less than 1% of the upper limb entrapment syndromes. AIN entrapment is found most commonly in patients in their 40s. There are alternative theories as to the pathophysiology of AIN syndrome, which includes the theory that the motor weakness seen in AIN syndrome is due to neuritis and not entrapment.
Diagnosis Patients with AIN will have no sensory deficit on examination. Hand paresthesias and forearm pain can be representative of a proximal median nerve entrapment and not AIN syndrome. Providers will find motor weakness with AIN syndrome.
This can be tested with resistance of the FPL and FDP of the index finger. During the clinical examination, patients with AIN syndrome have weakness in making an O with their thumb and index finger. This can also be tested by having the patient try to hold a piece of paper with their finger tips when somebody tries to pull the paper away.
If you are experiencing symptoms that may be related to the anterior interosseous nerve syndrome, it is important to see a sports medicine physician. Early evaluation and treatment typically lead to better outcomes. Do not ignore pain or symptoms that are limiting your activity.
*This article is for educational purposes only and does not substitute for professional medical advice. Always consult a qualified healthcare provider.*
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