Orthopedics

Original Research 

MODIFIED EXPOSURE FOR PRONATOR SYNDROME DECOMPRESSION: A PRELIMINARY EXPERIENCE

Barry J Gainor, MD

Abstract

ABSTRACT

Because hypertrophic and symptomatic scarring is not infrequent from a lazy S incision across the antecubital fossa, a new surgical approach to the pronator tunnel has been developed. Preliminary experience with this modified incision has proven to be encouraging in seven cases (five patients). The exposure is composed of two off-set linear incisions which allow visualization of the median nerve and brachial artery distal and proximal to the lacertus fibrosis. An intact bridge of skin at the antecubital fossa protects the medial cutaneous nerves of the arm and forearm from injury. The median nerve is exposed by splitting the pronator teres along its length, and fractional step cutting of the pronator aponeurosis relaxes the muscle. Postoperative scar management with a compressive wrap and elastomer insert is helpful for cosmetic healing of the incisions.

Abstract

ABSTRACT

Because hypertrophic and symptomatic scarring is not infrequent from a lazy S incision across the antecubital fossa, a new surgical approach to the pronator tunnel has been developed. Preliminary experience with this modified incision has proven to be encouraging in seven cases (five patients). The exposure is composed of two off-set linear incisions which allow visualization of the median nerve and brachial artery distal and proximal to the lacertus fibrosis. An intact bridge of skin at the antecubital fossa protects the medial cutaneous nerves of the arm and forearm from injury. The median nerve is exposed by splitting the pronator teres along its length, and fractional step cutting of the pronator aponeurosis relaxes the muscle. Postoperative scar management with a compressive wrap and elastomer insert is helpful for cosmetic healing of the incisions.

The antecubital fossa and its perimeter is an irksome scar zone. Unfavorable scarring from exploration of the pronator tunnel occurs in up to 20% of patients.1 Skin sutures must be removed early,2 as the integument of the volar forearm does not tolerate interrupted sutures that provoke unsightly cross-hatched scars (Fig 1). The traditional lazy S incision for pronator tunnel exploration has potential healing problems in the radial corner of the incision which may be dependent on flap thickness.3 To prevent a potentially disfiguring scar, a wavy incision has replaced the straight incision for decompression of radial tunnel syndrome.4 A Z-plasty revision of an unacceptable scar over the radial tunnel can leave a rippled contour to the skin over the mobile wad.

This report describes the author's preliminary experience with a modified exposure for pronator syndrome decompression which is designed to address these and other problems encountered in the standard surgical approach.

TECHNIQUE

The procedure is done in a bloodless field under tourniquet control. The pronator exposure is accomplished through two offset linear incisions that delete the transverse component of the traditional lazy S incision (Fig 2). The intact intervening skin bridge acts as a protective shield for the brachial cutaneous nerves, and it is mobilized and elevated to facilitate release of the lacertus fibrosis (Fig 3). The two incisions allow identification of the median nerve and the brachial artery both proximal and distal to the bicipital aponeurosis. After lysis of the lacertus fibrosis, the median nerve is exposed by direct visualization while the pronator teres is split longitudinally. Fascial bands and compressive vascular elements are released or ligated. As the dissection progresses distal Iy, the median nerve is kept in the surgeon's full view. The flexor digitorum superficialis arch is exposed and decompressed at the distal most portion of the forearm incision. At its insertion on the radius, the aponeurosis of the pronator teres is fractionally step cut to lengthen the resting length of the muscle (Fig 4). The tourniquet is released to assure hemostasis. The subcutaneous tissue is closed in a routine fashion, and the skin is closed with a subcuticular nylon suture.

Fig 1: The antecubital fossa is a highly visible portion of the anatomy. Skin sutures from a pronator tunnel release performed by another physician resulted in hypertrophic cutaneous cross-hatching in this 30-year-old woman.

Fig 1: The antecubital fossa is a highly visible portion of the anatomy. Skin sutures from a pronator tunnel release performed by another physician resulted in hypertrophic cutaneous cross-hatching in this 30-year-old woman.

Fig 2: Unlike the conventional lazy S incision in which the cutaneous nerves become a target, the modified exposure protects them with a skin bridge over the lacertus fibrosis.

Fig 2: Unlike the conventional lazy S incision in which the cutaneous nerves become a target, the modified exposure protects them with a skin bridge over the lacertus fibrosis.

Fig 3: The two-incision technique allows access and direct visualization of all important structures about the pronator tunnel.

Fig 3: The two-incision technique allows access and direct visualization of all important structures about the pronator tunnel.

The elbow is splinted in 90° of flexion for about 12 days, and then motion exercises are begun after suture removal. The incisions are covered with elastomer inserts and a compressive sleeve to flatten the healing scars; this flexible garment is worn for 6 to 8 weeks (Fig 5).

MATERIALS AND METHODS

Five consecutive patients were surgically treated for pronator syndrome. Two of the patients had bilateral entrapment. Four of the five patients had a so-called double crush syndrome with simultaneous carpal tunnel syndrome as weil as entrapment of the median nerve in the pronator tunnel. AU of the patients were female, and the average age was 33 years (range: 27 to 36). The average duration of symptoms was 15 months (range: 2 to 54). The average follow up was 10 months (range: 6 to 14).

Fig 4: The resting muscle length of the pronator teres is relaxed by fractional lengthening. Note the serial incisions in the aponeurosis of the pronator where it inserts on the radius in the right forearm.

Fig 4: The resting muscle length of the pronator teres is relaxed by fractional lengthening. Note the serial incisions in the aponeurosis of the pronator where it inserts on the radius in the right forearm.

Fig 5: Patches of elastomer are secured over the healing incisions with a compressive wrap to prevent hypertrophy of the scars. This sleeve-like garment does not interfere with activities of daily living.

Fig 5: Patches of elastomer are secured over the healing incisions with a compressive wrap to prevent hypertrophy of the scars. This sleeve-like garment does not interfere with activities of daily living.

All of the patients had forearm symptoms. On physical examination, all had a positive Tmel's sign at the pronator teres muscle and a positive pronator compression test. Each patient had electromyography for pronator syndrome, and none of these studies were positive for it. Two of the five patients were noted to have carpal tunnel syndrome by electrodiagnostic testing.

Three of the patients, with concurrent carpal tunnel syndrome, had a simultaneous carpal tunnel release at the time of pronator decompression. The carpal tunnel surgeries were uneventful. The surgical findings at pronator tunnel exploration revealed fascial bands in two cases, and a bulky pronator teres muscle in the other five cases.

Four of the patients did well postoperatively and returned to their previous level of activities of daily living and work. One patient, a 27-yearold with an eighth grade education on workers' compensation was referred for vocational rehabilitation after surgery because she was unable to resume her job as a house painter.

DISCUSSION

The problems with the conventional lazy S exposure of the median nerve in the antecubital fossa are more than skin deep. The disadvantages of the standard surgical approach to the pronator muscle are: 1) it can cause unintended injury to the brachial cutaneous nerves; 2) it does not attain direct visualization of the median nerve in the mid-forearm until the flexor carpi radialis/pronator teres interval is dissected; 3) it does not change the resting length of the pronator teres; and 4) it is prone to produce an unsightly or symptomatic scar.

All of the terminal branches of the posterior arborization of the medial antebrachial cutaneous nerve, and more than three fourths of the arborization of the medial brachial cutaneous nerve, are in the fascia directly over the medial epicondyle and flexor pronator muscle.5 Injury to these cutaneous branches can result in a dysesthetic dermatome or loss of sensation over the volar distal forearm (Fig 6). These sensory branches are safeguarded in the modified exposure by deleting the transverse component of the lazy S incision.

The median nerve should be kept in full view by splitting the pronator. The proximal arch of the flexor digitorum superficialis is readily exposed in the modified approach, as well as the aponeurosis of the pronator at its insertion on the radius. The resting length of the pronator teres is relaxed by fractional lengthening of the muscle with serial incisions in the aponeurosis. The amount of physiologic length gained by these step cut incisions varies with each case, but sometimes up to 1 .5 cm will be gained by a single incision if the muscle is hypertrophied. This technique is not new, but the author is unaware of it being reported in the literature pertaining to pronator syndrome.

Fig 6: A dysesthetic island of skin (striped area) persists 18 months after pronator decompression with a lazy S incision (dotted (ine) in this 23-year-old woman.

Fig 6: A dysesthetic island of skin (striped area) persists 18 months after pronator decompression with a lazy S incision (dotted (ine) in this 23-year-old woman.

The antecubital fossa is a highly visible portion of the anatomy. All of the author's patients were female, and most were very interested in the outcome of the scar. They would report comments garnered from the check-out line in supermarkets or from friends in their social circles; some patients related accounts of unsightly sears in the antecubital fossa area of acquaintances. All of the patients were pleased with their cutaneous healing. A vermillion hue lingers in the scar for up to 6 months. No one objected to wearing the sleeve garment and elastomer inserts. Although a more acceptable scar results from the modified exposure, it is not invisible.

The modified exposure for pronator syndrome offers protection of the cutaneous nerves, direct visualization of the median nerve, fractional lengthening of the pronator teres muscle, and an improved cosmetic scar.

REFERENCES

1. Gainor BJ. The pronator compression test revisited. A forgotten physical sign. Orthop Rev. 1990; 19:888-892.

2. Littler JW. Principies of reconstructive surgery of the hand. In: Converse JM. Littler JW. eds. Reconstructive Plastic Surgery. Philadelphia, Pa: WB Saunders; 1964:1613.

3. Spinner M. Injuries to the Major Branches of Peripheral Nerves in the Forearm. Philadelphia, Pa: WB Saunders: 1978:217.

4. Lister GD, Belsole RB, Kleine« H. The radial tunnel syndrome, J Hand Surg. 1 979; 4:52-59.

5. Race CM, Saldana MJ. The anatomic course of the medial cutaneous nerves of the arm. J Hand Surg. 1991; I6A:48-52.

10.3928/0147-7447-19931201-07

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