Injection Technique for Anterior Interosseous Syndrome

Indications and Clinical Considerations

The injection technique for anterior interosseous syndrome, which is also known as Kiloh-Nevin syndrome, is useful in treating pain and muscle weakness secondary to median nerve compression syndrome below the elbow by the tendinous origins of the pronator teres muscle and flexor digitorum superficialis muscle of the long finger or by aberrant blood vessels ( Fig. 74.1 ). The onset of symptoms is usually after acute trauma to the forearm or after repetitive forearm and elbow motions, as in using an ice pick. An inflammatory cause analogous to Parsonage–Turner syndrome also has been suggested as a cause of anterior interosseous syndrome, as has myositis ( Fig. 74.2 ). Other causes of anterior interosseous syndrome are listed in Box 74.1 .

Clinically, anterior interosseous syndrome manifests as an acute pain in the proximal forearm. As the syndrome progresses, patients with anterior interosseous syndrome may report a tired or heavy sensation in the forearm with minimal activity, as well as the inability to pinch items between the thumb and index finger because of paralysis of the flexor pollicis longus and the flexor digitorum profundus ( Fig. 74.3 ). Positive “Playboy bunny” and Spinner signs may also be present ( Figs. 74.4 and 74.5 ).

Physical findings include the inability to flex the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger because of paralysis of the flexor pollicis longus and the flexor digitorum profundus (see Fig. 74.5 ). Tenderness over the forearm in the region of the pronator teres muscle is seen in some patients with anterior interosseous syndrome. A positive Tinel sign over the anterior interosseous branch of the median nerve 6 to 8 cm below the elbow also may be present.

The anterior interosseous syndrome also should be differentiated from cervical radiculopathy involving the C6 or C7 roots, which may at times mimic median nerve compression. Furthermore, it should be remembered that cervical radiculopathy and median nerve entrapment may coexist as the so-called double crush syndrome, which is seen most often with median nerve entrapment at the wrist or with carpal tunnel syndrome. Anterior interosseous syndrome must also be differentiated from what has been termed “pseudo-anterior interosseous syndrome,” which encompasses pathologic processes that occur above the site of anterior interosseous nerve entrapment that mimic the clinical syndrome of true anterior interosseous nerve entrapment ( Fig. 74.6 ). The differential diagnosis will be added by careful physical examination, electromyography and nerve conduction testing, and magnetic resonance and ultrasound imaging ( Fig. 74.7 ).

Clinically Relevant Anatomy

The median nerve is made up of fibers from C5-T1 spinal roots. The nerve lies anterior and superior to the axillary artery. Exiting the axilla, the median nerve descends into the upper arm along with the brachial artery. At the level of the elbow, the brachial artery is just medial to the biceps muscle. At this level, the median nerve lies just medial to the brachial artery. As the median nerve proceeds downward into the forearm, it gives off numerous branches, which provide motor innervation to the flexor muscles of the forearm, including the anterior interosseous nerve ( Fig. 74.8 ). These branches are susceptible to nerve entrapment by aberrant ligaments, muscle hypertrophy, and direct trauma. The nerve approaches the wrist overlying the radius. It lies deep to and between the tendons of the palmaris longus muscle and the flexor carpi radialis muscle at the wrist. The terminal branches of the median nerve provide sensory innervation to a portion of the palmar surface of the hand, as well as the palmar surface of the thumb, the index and middle fingers, and the radial portion of the ring finger. The median nerve also provides sensory innervation to the distal dorsal surface of the index and middle fingers and the radial portion of the ring finger.