PRONATOR SYNDROME

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Pronator syndrome is the most proximal entrapment neuropathy of the median nerve. Compression can occur at one of several anatomic locations in the elbow region. It is extremely rare in comparison with carpal tunnel syndrome, which presents with similar sensory symptoms. Electrodiagnostic studies are often normal, and objective findings can be difficult to demonstrate clinically, particularly if they are related to activity. The condition is misdiagnosed frequently, and many patients undergo unsuccessful operations before the correct diagnosis is made. Timely diagnosis and treatment are required to prevent progression to a more permanent condition.

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ANATOMY

In the region of the elbow, the median nerve travels with and medial to the brachial artery in a plane between the brachialis muscle anteriorly and the medial intramuscular septum posteriorly.4 It passes beneath the bicipital aponeurosis superficial to the brachialis muscle, usually beneath a portion of the origin of the flexor muscle mass (Fig. 1).2 It then separates from the brachial artery and passes between the humeral (superficial) and ulnar (deep) heads of the pronator teres muscle

ACTIVITY-RELATED CAUSES OF PRONATOR SYNDROME

Repetitive, and often forceful, pronation and supination have been indicated as possible causes of pronator syndrome.2 McCue et al6 indicated that pitching, rowing, weight training, and racquet sports could cause the syndrome. Throwing can generate a significant amount of force about the elbow because it requires repetitive, forceful pronating and gripping that accentuates compression at the proximal edge of the pronator. Grip-intensive sports such as archery can cause compression of the median

SYMPTOMS

Patients who have pronator syndrome usually experience vague, aching pain in the volar aspect of the elbow and forearm.3, 4, 6, 8, 10, 11 This pain is the most common symptom of pronator syndrome and can extend from the distal upper arm, across the elbow, to the proximal forearm.6 Pain and other symptoms frequently begin or worsen during activities that require repetitive grasping or pronation, or both.3 The pronator teres muscle along the course of the median nerve can be tender.3, 5, 8, 12

PHYSICAL EXAMINATION

Tenderness with palpation over the pronator muscle mass is the most common physical finding in pronator syndrome.1, 4, 11 Tense firmness in the pronator muscle belly can also be present.1, 10 Motor weakness is variable and often subtle, and the affected side should be compared with the unaffected side.11, 13 Gross weakness, which can be seen with anterior interosseous nerve syndrome, does not occur. A positive Tinel sign can be present. Decreased sensation can be present in the median

ELECTRODIAGNOSTIC STUDIES

Electrodiagnostic studies rarely help the clinician to diagnose pronator syndrome. They are indispensable, however, in evaluating and ruling out other sites of compression of the median nerve, such as the carpal tunnel.1, 11 Although they are frequently normal, the studies can help confirm the diagnosis of pronator syndrome. Normal electrodiagnostic studies should not be used to exclude the diagnosis of pronator syndrome in the presence of a classic history and physical examination.2, 3 Studies

DIFFERENTIAL DIAGNOSIS

The differential diagnosis of pronator syndrome includes cervical radiculopathy, brachial plexopathy, thoracic outlet syndrome, carpal tunnel syndrome, and overuse syndrome. When contemplating the diagnosis of pronator syndrome, the examiner needs to evaluate the entire length of the median nerve from the cervical spine to the carpal tunnel, determining whether one or more potential sites of compression is involved. Pronator syndrome can occur simultaneously with compression at another level

TREATMENT

Nonoperative treatment is indicated initially and includes modification of activities, rest, immobilization, anti-inflammatory medication, oral steroids, local steroid injection, and physical therapy. Changes in posture and equipment can help relieve symptoms.6, 13 Modification or elimination of the provocative activity often results in resolution of the syndrome.4 The elbow should be immobilized in 90° of flexion; the forearm, in neutral to slight pronation; and the wrist, in neutral to slight

SURGERY

The key to decompressing the median nerve in the region of the elbow is to understand the anatomy and to address each of the potential sites of compression. Despite the provocative tests, it is difficult to predict with certainty which site is responsible for compressing the median nerve. Consequently, all potential sites of pathology should be decompressed.1, 2, 4, 6, 11

The arm is extended onto a hand–extremity table. Use of a pneumatic tourniquet and loupe magnification is recommended. The

SURGICAL RESULTS

Stern and Fassler found that approximately 90% of patients had satisfactory results after decompression.11 Johnson et al reported that all patients who had decompression of the median nerve in the forearm for only sensory problems had relief the day after surgery.5 Olehnik found no statistically significant difference when he compared patients who had abnormal nerve conduction studies with patients who had normal studies.7 When evaluating the site of compression he found no statistically

SUMMARY

Although pronator syndrome is often misdiagnosed and does not occur as frequently as carpal tunnel syndrome, its clinical features are well described, and the diagnosis should be made if the clinical features are understood and reasonable suspicion exists. The differentiating features between carpal tunnel syndrome and pronator syndrome should be understood, and evaluation for one site of compressive neuropathy of the median nerve always should include the other potential sites. When the

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Address reprint requests to David C. Rehak, MD, The Hughston Clinic, PC, 6262 Veterans Parkway, PO Box 9517, Columbus, GA 31908–9517

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The Hughston Clinic, PC, Columbus, Georgia

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