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• Numbness of the radial 3'/2 digits

• Full knowledge of the anatomy to avoid a complication on exploration is essential.

Diagnosis

Pronator Syndrome of the Right Arm

Pronator syndrome is defined by functional problems of the median nerve due to some mechanical abnormality at the level of the forearm. This disturbance in function is often related to the path of the nerve through the middle of the pronator teres muscle. A concise and clear physical exam is the best indicator for diagnosis of pronator syndrome, which is similar to carpal tunnel, but less common. Both syndromes involve the median nerve and therefore have similar symptoms; the syndromes are usually differentiated based on the physical exam. Keys to the physical exam are to note the areas of tenderness and the presence of a positive Tinel's sign. It is possible that both conditions coexist with medial nerve entrapment at the proximal forearm and the wrist. Correlating the physical exam with the EMG study aids in correctly diagnosing the patient's symptoms. No motor symptoms or weakness is present with a pronator syndrome.

Surgical Management

The initial incision usually begins 5 cm proximal to the elbow flexion crease unless either a supracondyloid process or accessory bicipital aponeurosis has been identified. If this is the case, the incision should begin no less than 10 cm proximal to the crease (Fig. 13-1).

The incision curves distally just medial to the biceps tendon, zigzags across the antecubital crease, and curves back medially for 5 cm in the proximal forearm.

Next, the medial antebrachial cutaneous nerve is identified and isolated as it continues along the basilic vein. The median nerve is then identified and isolated in a similar manner.

If a supracondyloid process or accessory bicipital aponeurosis had been identified preoperatively, the median nerve is identified and isolated in the most proximal portion of the incision and then traced distally. The supracondyloid process or accessory bicipital aponeurosis is then dealt with if present. It is important to explore the median nerve completely, as other, more proximal, sites of compression may exist at the same time.

The median nerve is then dissected distally. The bicipital aponeurosis is incised and the nerve followed to the proximal end of the superficial or humeral head of the pronator teres. Retraction of the head is needed to identify any variation in the nerve's path in relation to the two pronator heads. Any tendinous or fibrous bands within the pronator are identified and incised (Fig. 13-2).

In those cases where the median artery penetrates the median nerve, interfasci-cular dissection may be used to enlarge the passage. Great care should be taken to avoid ligation of the artery. It is the dominant blood supplier to the median nerve

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Figure 13—2. (A) The median nerve passes between the superficial and deep heads of the pronator teres muscle. (B) Anatomy of the median nerve in the forearm of a patient with pronator syndrome. (C) The median nerve passing superficial to the deep head and through the superficial head and being compressed by a fibrous arch of this anatomic variant muscle. (D) The median nerve accompanies the anterior interosseous nerve (AIN) underneath a tight arch of the flexor digitorum superficialis (FDS) muscle.

Figure 13—2. (A) The median nerve passes between the superficial and deep heads of the pronator teres muscle. (B) Anatomy of the median nerve in the forearm of a patient with pronator syndrome. (C) The median nerve passing superficial to the deep head and through the superficial head and being compressed by a fibrous arch of this anatomic variant muscle. (D) The median nerve accompanies the anterior interosseous nerve (AIN) underneath a tight arch of the flexor digitorum superficialis (FDS) muscle.

30% of the time and also significantly serves the index and long fingers in some cases.

Next, the superficialis arcade is explored. The arch should be incised, especially if thickened, as it may be a source of compression. The surgeon should carefully dissect distal to the arch, paying attention to the possible presence of anatomic variations such as accessory muscles. All sites of nerve compression should be released as the nerve is isolated.

At this time the tourniquet should be deflated. Hemostasis should be verified, and a bipolar cautery can be used as needed.

The pronator teres is reattached if detachment was necessary. When reattaching the pronator teres, careful attention should be paid so as not to shorten and therefore tighten the attachment. This by itself could cause a new compressive lesion. Epineurotomy, internal neurolysis, and subcutaneous transposition of the median nerve are not necessary and may even prove harmful.

The subcutaneous layer is closed with 4—0 absorbable sutures and the skin edges with 5—0 simple sutures. The extremity is then placed in a bulky, plaster-reinforced, sterile, above elbow dressing. It should be positioned such that it maintains 90 degrees of flexion at the elbow, 45 degrees of pronation in the forearm, and slight flexion in the wrist to keep the nerve in a position ofminimal tension.

Postoperative Care

Ten days postoperatively, the sutures are removed and replaced with Steri-strips. Immobilization in a long arm cast in the same position is continued for 2 additional weeks, after which all immobilization is discontinued. At this time, gentle range of motion exercises are started.

The patient should be instructed to avoid resistive activities for 6 to 8 weeks after surgery. Although there are some individual variations, most patients with pronator syndrome surgery are back to full function within 3 months.

Alternative Methods of Management

In general, the pronator syndrome can often be treated using protection (Fig. 13—3), rest, ice, compression, elevation, medications, and modalities. Protection entails modifying activity and equipment to allow proper healing and prevention of further injury. It is important to explain to the patient that rest does not mean cessation of

activity, but modifying activities that may further aggravate the injury. Ice is used to alleviate pain and help control swelling. Compression is used to prevent swelling, but it should be used with caution because if compression is not placed correctly, it could aggravate the nerve entrapments.

Elevation is used to prevent venous stasis around the injury, which can lead to increased inflammation and pain. Medications used include nonsteroidal antiinflammatory drugs (NSAIDs) and corticosteroids, although very rarely. Modalities include ultrasound, electrical stimulation, and friction massage.

Complications

There are few surgical complications reported. The medial antebrachial cutaneous nerve is at risk during exposure. The entire course of the nerve must be explored in the cubital region to inspect all possible sites of compression. Scars may become hypertropic or unsightly.

Suggested Readings

Dawson DM. Entrapment neuropathies of the upper extremities. N Engl J Med 1993;329:2013-2018.

Mysiew WJ, Colachie SC III. The pronator syndrome: an evaluation of dynamic maneuvers for improving electrodiagnoistic sensitivity. Am J Phys Med Rehabil 1991;70:274-277.

Nuber GW, Assenmacher J, Bowen MK. Neurovascular problems in the forearm, wrist, and hand. Clin Sports Med 1998;17:585-610.

OlehnikWK. Manske PR, Szerzinski J. Median nerve compression in the proximal forearm. J Hand Surg 1994;19A:121-126.

Plancher KD, Peterson RK, Steichen JB. Compressive neuropathies and tendinopa-thies in the athletic elbow and wrist. Clin Sports Med 1996;15:331-371.

Rehak DC. Pronator syndrome. Clin Sports Med 2001;20:531-540.

Weinstein SM, Herring SA. Nerve problems and compartment syndromes in the hand, wrist, and forearm. Clin Sports Med 1992;11:161-188.

ANTERIOR INTEROSSEOUS NERVE SYNDROME|

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Responses

  • mezan
    How deep is the pronator teres?
    6 years ago

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