Anterior Interosseous Nerve

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Introduction

The anterior interosseous nerve, also known as the volar interosseous nerve, is a motor branch that comes off of the median nerve in the proximal forearm. Compression of this nerve can occur at various sites along its course in the forearm.

Structure & Origin

The anterior interosseous nerve arises off the posterior surface of the median nerve in the proximal forearm, approximately 5-8cm distal to the lateral epicondyle of the humerus.

It is comprised of the C5-T1 spinal nerve roots.

Course

After branching off the median nerve in the proximal forearm, the anterior interosseous nerve courses distally between the two heads (superficial & deep) of the pronator teres muscle, deep to the flexor digitorum superficialis. It continues its descent along the anterior aspect of the interosseous membrane, between the flexor digitorum profundus and flexor pollicis longus muscles.

The anterior interosseous nerve passes deep to the pronator quadratus muscle, terminating close to the wrist joint.

Branches & Supply

The anterior interosseous nerve provides motor innervation to the deep muscles in the anterior compartment of the forearm, including:

• Flexor pollicis longus
• Flexor digitorum profundus - lateral aspect only (the medial aspect of this muscle is supplied by the ulnar nerve).
• Pronator quadratus.

The terminal branch of the anterior interosseous nerve travels through the posterior surface of the pronator quadratus, where it also provides sensory branches to the carpal bones of the wrist .

Relations

Initially, the anterior interosseous nerve sits parallel to the median nerve. As it travels into the distal forearm, it is positioned between two muscles: the flexor pollicis longus laterally and the flexor digitorum profundus medially. The anterior interosseous nerve continues to descend along the anterior aspect of the interosseous membrane where it is accompanied by the anterior interosseous artery and correlating veins .

Variants

Research suggests that the degree to which the median and ulnar nerves innervate the flexor digitorum muscle is variable.

Clinical Significance

Lesions to the anterior interosseous nerve are deemed rare, due to the nerves deep location in the forearm. Although the overlying structures provide protection, they may also be a cause of compression.

The anterior interosseous nerve may be compressed by the following structures:

• Struthers ligament
• Bicipital aponeurosis
• Fibrous arch of the pronator teres muscles (between the humeral & ulnar heads)
• Fibrous arch at the origin of the flexor digitorum muscle
• Anamalous muscles. i.e., Gantzer muscle

Other causes of compression include the following:

• Trauma i.e., supracondylar humeral fracture, fracture of the forearm (proximal third)
• Vascular disease. i.,.e thrombosis, vessel hypertrophy
• Cysts
• Abscesses
• Hematomas
• Tumors
• Iatrogenic. i.e., forearm drug injections, fracture reduction

Anterior Interosseous Nerve Syndrome

Anterior interosseous nerve syndrome refers to compression of the anterior interosseous nerve, which may occur along it's path in the anterior forearm. The most common location

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