Anterior Interosseous Nerve Syndrome
Anterior interosseous nerve syndrome is a condition in which damage to the anterior interosseous nerve, a branch of the median nerve at the elbow, causes pain and characteristic weakness in the flexor pollicis longus, flexor digitorum profundus of the index finger, and pronator quadratus. Because there is no sensory component to the syndrome it is often missed on clinical exam and the motor weakness is often undiagnosed as well. I present here a video exam of a patient with anterior interosseous nerve syndrome for review demonstrating a classic weakness in the flexor pollicis longus and flexor digotorum profundus.
Classic clinical finding in anterior interosseous nerve syndrome is weakness of the flexor pollicis longus and flexor digitorum to the index finger and the possibility of vague anterior elbow pain and forearm pain. This may manifest as difficulty with writing skills or fine pinch activities as well as complaints of hand fatigue and forearm pain. The most obvious clinical sign is the inability to make an okay sign with lack of the ability to curve the thumb and index finger into a round okay sign. Patients with anterior interosseous nerve syndrome will also have weakness of pinch strength between the thumb with difficulty holding a sheet of paper. Little sensory deficit or normal sensation over the forearm would be expected. It is important to rule out tendon rupture to the thumb or index finger DIP joint by performing a standard tenodesis effect with wrist extension. Please see the below video demonstrating a physical exam of anterior interosseous nerve syndrome.
Causes of anterior interosseous nerve syndrome can include direct trauma from a forearm or supracondylar elbow fracture, penetrating injuries, as well as compression of the anterior interosseous nerve as it branches away from the median nerve. Oher common causes can include neuritis symptoms which are often manifest with rapidly progressive symptoms and oftentimes a prodrome of viral illness preceding the onset of symptoms. Diagnosis of anterior interosseous nerve syndrome is made by classic clinical exam as well as EMG nerve conduction studies demonstrating the weakness in the flexor digitorum profundus to the index finger and flexor pollicis longus as well as the pronator quadratus muscles. Treatment of anterior interosseous nerve syndrome is usually non-surgically initially for roughly 6-12 months. Prognosis for spontaneous recovery is better in cases of neuritis. In etiologies which are suggestive of compression or penetrating trauma surgical exploration and decompression may be indicated.
Submitted by:
J. Randall Riehl, MD
Decatur Orthopaedic Clinic
Decatur, AL
