Anterior interosseous nerve syndrome diagnosis and intraoperative findings: A case report

Abstract

Introduction: Anterior Interosseous Nerve (AIN) is a motor branch from the Median nerve and runs deep in the forearm along with the anterior interosseous artery. It innervates three muscles in the forearm; an isolated palsy of these muscles is known as AIN Syndrome. There are several documented causes of AIN syndrome but its pathophysiology remains unclear.

Presentation of case: A 48-year old male that presented with right elbow pain and inability to flex his right interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger. MR images denoted mild atrophy of the radial half of the flexor digitorum profundus and the pronator quadratus. Although there were no compressing lesions identifiable on MRI, Electrodiagnostic studies suggested compression neuropathy affecting the AIN. During surgical decompression of the median nerve in the proximal forearm, the operative findings were several tendinous fasciae and a tight fibrous arch of the flexor digitorum superficialis compressing the median nerve at the level of the AIN branch.

Discussion: Different treatment schemes with reasonable outcome have been reported. Both nonsurgical and surgical intervention have been described in most of these schemes but differed in the timing of intervention with variable outcome.

Conclusion: Clinical suspicion should arise in the presence of isolated paralysis of the AIN-supplied muscles. MRI and electrodiagnostic studies will confirm the diagnosis and identify the etiology. The optimal treatment of AIN syndrome has not been established. We recommend surgical intervention in confirmed AIN syndrome from compression neuropathy, refractive to conservative therapy.

Keywords: Anterior; Case report; Interosseous; Nerve; Neuropathy; Palsy.

Fig. 1

Axial and sagittal fat-saturated proton density images demonstrating diffuse increased SI of the proximal portion of the flexor digitorum profundus muscle and axial T1WI demonstrates decreased muscle bulk and a few streaks of high SI within the flexor digitorum profundus muscle. Both images denote mild atrophy.

Fig. 2

Non-contrast MR images of the distal forearm: axial T1WI demonstrates few streaks of high SI seen within the pronator quadratus muscle and axial fat-saturated proton density image demonstrating diffuse increased SI of the pronator quadratus muscle. Both images denote mild atrophy.

Fig. 3

Intraoperative photograph showing compression of the median nerve by tendinous fascia off the deep head of pronator teres and the fibrous arch of the flexor digitorum superficialis proximal to it.