Injection Technique for Pronator Syndrome

Indications and Clinical Considerations

The injection technique for pronator syndrome is useful in treating pain secondary to median nerve compression syndromes at the elbow, including pronator syndrome and compression of the median nerve by the ligament of Struthers. Pronator syndrome is caused by median nerve compression by the ulnar and humeral heads’ pronator teres muscle ( Figs. 73.1 and 73.2 ). Other causes of compression of the median nerve in this anatomic region are listed in Box 73.1 . The onset of symptoms is usually after repetitive elbow motions, such as in chopping wood, sculling, and cleaning fish ( Fig. 73.3 ). Clinically, pronator syndrome manifests as a chronic aching sensation localized to the forearm, with pain occasionally radiating into the elbow. Patients with pronator syndrome may complain about a tired or heavy sensation in the forearm with minimal activity, as well as clumsiness of the affected extremity. In contradistinction to carpal tunnel syndrome, nighttime symptoms are unusual with pronator syndrome.

Physical findings include tenderness over the forearm in the region of the pronator teres muscle. Unilateral hypertrophy of the pronator teres muscle may be identified. A positive Tinel sign over the median nerve as it passes beneath the pronator teres muscle also may be present. Weakness of the intrinsic muscles of the forearm and hand that are innervated by the median nerve may be identified with careful manual muscle testing. A positive pronator syndrome test—pain on forced pronation of the patient’s fully supinated arm—is highly suggestive of compression of the median nerve by the pronator teres muscle ( Fig. 73.4 ).

Median nerve entrapment by the ligament of Struthers appears clinically as unexplained persistent forearm pain caused by compression of the median nerve by an aberrant ligament that runs from a supracondylar process to the medial epicondyle. Clinically, it is difficult to distinguish from pronator syndrome. The diagnosis is made by electromyography and nerve conduction velocity testing, which demonstrate compression of the median nerve at the elbow, combined with the radiographic finding of a supracondylar process. Ultrasound and magnetic resonance imaging may help clarify the diagnosis ( Fig. 73.5 ).

Both of these entrapment neuropathies can be differentiated from isolated compression of the anterior interosseous nerve, which occurs 6 to 8 cm below the elbow. These syndromes 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 most common with median nerve entrapment at the wrist or with carpal tunnel syndrome.

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 that provide motor innervation to the flexor muscles of the forearm. 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.