Limited Bilateral Advancement of the Sternocostal Head of Pectoralis Major for Sternal Reconstruction: Preserving the Axillary Fold

In 1957, Julian et al¹ first described the median sternotomy for use in cardiac surgery. It provides good access to the anterior mediastinum but carries the risk of becoming infected postoperatively in 0.5% to 8.4% of open heart surgeries, leading to the possible sequelae of dehiscence, osteomyelitis, and death.

The treatment options in the past for sternotomy infections ranged from leaving the wound open to heal by secondary intention to debridement and rewiring coupled with antibiotic irrigation therapy.^2–5 In 1976 Lee et al⁶ initiated the concept of an omental flap for closure of this deficit, followed in 1980 by Jurkiewicz et al⁷ reporting on the use of pectoral muscle flaps. The use of well-vascularized flaps has improved mortality rates from 70% in early studies involving conservative treatment⁸ to 5% and 10% in recent reports.⁹

Pectoralis major and rectus abdominis have become first-line flaps, with the pectoral being the preferred one.^9–13 The omentum is generally considered a second-line treatment choice.¹⁰ Multiple variations of the pectoralis major flap in sternotomy wounds have been described. However, unresolved limitations of this flap include poor cosmesis and problematic coverage of the inferior third of the sternotomy wound.

We describe a technique that addresses these issues. By using the caudal half of pectoralis major bilaterally with limited advancement, we achieved wound closure with preservation of the anterior axillary fold and good coverage of the inferior third of the sternotomy wound.

Surgical Anatomy

The pectoralis major, a large, flat muscle, has two heads of origin: the clavicular head, which arises from the medial half of the clavicle and inserts into the bicipital groove of the humerus, and the sternocostal head, arising from the anterior surface of the sternum, the upper six costal cartilages, and the aponeurosis of the external oblique muscle over the costal attachment of the rectus abdominis.¹³ The rounded appearance of the anterior axillary fold is formed as the lower sternocostal and abdominal fibres course upwards and laterally to be inserted progressively higher into the posterior lamina of the tendon (Fig. 1).

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The blood supply, according to the classification of Mathes and Nahai, is a type 5 circulation, with one dominant vascular pedicle and a number of secondary segmental pedicles.^14–17 The dominant pedicle is based on the thoracoacromial artery, and the secondary segmental pedicles are based on the internal mammary artery. The secondary pedicles are located 2 to 3 cm lateral to the sternal border (Fig. 2). In addition, there are branches of the lateral thoracic and intercostal arteries that contribute to the blood supply.^16,17

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The motor innervation is via the lateral and medial pectoral nerves, supplying the upper part of the muscle and lower third respectively.¹⁸ The medial nerve accompanies the thoracoacromial pedicle and its branches. Branches of the lateral nerve pass either lateral to or through the pectoralis minor muscle and into the pectoralis major muscle.^16,17

Operative Technique

Prior to the procedure, as described by Godina,^19,20 infected sternal wounds require early radical debridement involving the removal of foreign bodies and the excision of nonviable tissue. Subsequently, pulsatile lavage is performed with 6 to 9 L of normal saline, secondary debridement occurs, and a suction-assisted dressing (e.g., vacuum-assisted closure) is applied to eliminate dead space. Given skeletal stability, this process is then repeated in 24 to 48 hours.

Preoperative imaging with computed tomography (CT), and in particular CT angiography, can delineate the anatomy of the pectoralis major muscle, musculotendinous unit, and vascular anatomy. This can be used to establish the remaining vascular pedicles after serial debridements, and help select the side of choice for turnover versus advancement based on the vascular anatomy (Figs. 1 and 2).

The left pectoralis major muscle is harvested through the existing wound. The skin and subcutaneous tissue are dissected off the muscle medially to laterally to the axillary border. By blunt dissection, the fibers of the muscle are undermined and elevated from the underlying ribs and pectoralis minor muscle. The thoracoacromial pedicle is identified, after lateral dissection, and followed on the undersurface of the muscle. The intramuscular perforator branches are then divided. Both sets of nerves are also visualized and separated to preserve the motor supply to the lateral one third of pectoralis major. Muscular fibers attached close to the clavicular origin are divided to facilitate flap transposition; attachments to the sternum are cut medially, caudally, and laterally. Most of the caudal portion of the left pectoralis major is divided up to the cranial level and then across to the tendon, keeping the attachment of the superior portion of the muscle to the humerus. The sternocostal head is advanced medially and rotated anticlockwise, with this portion used to fill the sternoclavicular and sternal portion of the defect.

The right pectoralis major muscle fibers are detached at the same level as those on the left; however, perforator vessels are maintained and the caudal portion is instead advanced and folded over into the lower end of the wound as a turnover flap (Figs. 3–7). Two drains are placed subcutaneously at the lower end of the dissected left chest, and two drains are placed on the right chest—one above and the other below the muscle. The skin is directly closed over the flaps. Wounds were dressed with Collatamp (gentamicin-impregnated Gelfoam), active drainage, and Op-Site film. A breast girdle was worn for support and pain control. In addition, patients had epidural catheters and intravenous or oral analgesia for pain management. They were continued on long-term intravenous antibiotics.

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Results

The study population (n = 32) comprised a 5-year period (1996–2001). A total of 18 of these patients had osteonecrosis, 6 had osteomyelitis, 5 had mediastinitis, and 3 had superficial infection of the presternal region. In addition to the technique, early diagnosis, early debridement, antibiotic therapy, and pain control were required to achieve a successful outcome.

Risk factors for sternal wound infection included use of the left internal mammary artery (80%) and diabetes (68%), as well as nonsymmetrical osteotomy, history of smoking, reexploration, and postoperative bleeding. Wound microbiology revealed coagulase-negative Staphylococcus in 65% of patients, Staphylococcus aureus in 30% of patients, and mixed organisms in the remaining 5% of patients.

In all patients, the anterior axillary fold had been preserved bilaterally and the infection completely resolved (Fig. 8). Complications included 3 cases of hematoma, 2 cases of coagulopathy, and 1 late bone sequestrum (aseptic). No deaths were reported in the patient group studied.

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Discussion

Deep sternal wound infection is a rare but devastating complication. It occurs in approximately 1% to 3% of patients following median sternotomy.^16,17 Commonly accepted risk factors for the development of sternum wound complication are diabetes, obesity, history of smoking, reexploration, mediastinal hematoma, and immunosuppressive medications.^2,3,21,22 In our patients, diabetes was present in 68% of patients. It should be noted that 80% of our patients with infected wounds had their left internal mammary artery harvested—this large number could be a confounding result rather than a significant risk factor, because the left internal mammary artery is increasingly being used for grafting. The literature is inconclusive in this respect—some studies reported that harvesting the left and right internal mammary arteries may compromise sternal vascularity^21,23,24 and predispose a patient to sternal infection, whereas no significant difference was seen in others.^25,26

Pairolero and Arnold classified sternal wounds into 3 categories based on the timing of presentation of infection^11,12,27 Type I wounds occur in the first few days postoperatively and are characterized by serosanguineous drainage without cellulitis, osteomyelitis, or costochondritis. These wounds respond well to intravenous antibiotics and wound debridement. Direct closure with suction drainage of the mediastinum is usually the only treatment required. Type II wounds occur within the first few weeks and are characterized by purulent drainage, cellulitis, mediastinal suppuration, and positive cultures. There is usually associated fulminating mediastinitis and osteomyelitis, although costochondritis is rare. Patients in this group are optimally treated by drainage, debridement, and immediate or delayed flap closure. Type III wounds occur months to years later and are characterized by the presence of chronic draining sinus tracts, localized cellulitis, osteomyelitis, costochondritis, or retained foreign body, but mediastinitis is rare. Debridement and extensive resection of the sternum and costal cartilages followed by flap obliteration of the mediastinum are necessary. The key in treating types II and III wounds is the obliteration of the dead space within the mediastinum.

Greig et al⁸ introduced an anatomic classification of types II and III sternal wounds to aid in the choice of flap for reconstruction. Wounds in the upper half of the sternum were classified as type A. Wounds in the lower half of the sternum were classified as type B, and wounds involving the whole sternum were classified as type C.

Multiple approaches for sternal wound reconstruction have been described. The greater omentum was transplanted into the sternal defect, with its immunological properties further accelerating wound healing.^28,29 However, this procedure requires laparotomy, which can lead to additional complications in septic and critically ill patients. It also does not improve sternal stability and frequently necessitates skin transfer.

Another option is the transfer of the rectus abdominis muscle, but this technique requires extensive dissection and may result in postoperative abdominal hernia formation.³⁰ The previous use of mammary arteries may compromise blood supply,^31,32 and substernal chest tube placement at the primary operation commonly affects the rectus abdominis muscles and may impair the results of the muscle transfer. The use of latissimus dorsi muscle flaps for coverage of such defects and chest stabilization is limited by the required large incisions and the resulting functional impairment.² It is also difficult to perform because of the need to change the position of the patient during the procedure. Furthermore, only the most distal part of the muscle can be used for wounds in the lower half of the sternum, and this has a less reliable blood supply. The limitations of the aforementioned flaps have allowed the pectoralis major flap to gain increasing acceptance for sternal wound reconstructions.

Several variations of the pectoralis major muscle flap for sternal wound reconstruction have been described. It can be transposed into the mediastinum based on either the thoracoacromial pedicle as an advancement flap (unilateral or bilateral), or as a turnover flap based on perforators of the internal mammary artery. Nahai et al^16,17 described a modification of the turnover pectoralis major flap by dividing the muscle medial to the thoracoacromial pedicle and using only the medial two thirds of the pectoralis major for coverage of the sternotomy wound. By preserving the thoracoacromial pedicle, this modification attempts to reduce loss of the anterior axillary fold and functional deficits. Other techniques used to increase preservation of muscle motor function have been described by Tobin et al^33–37 and Morain.³⁸ Tobin et al^33–37 described splitting the pectoralis major into sternocostal, external, and clavicular segments, and preserving the thoracoacromial pedicle. The sternocostal segment can be advanced into the mediastinal wound, and the muscle segments can be reapproximated in a V-Y fashion. Morain³⁸ split the pectoralis major segmentally, leaving some of the segments intact to preserve muscle function for smaller defects requiring only a small portion of muscle.

The major limitation of these techniques is the problematic coverage of the inferior third of the sternotomy wound. Studies have shown that the lower portion of wounds near the xiphisternum is the most common site of dehiscence after flap repair.^{6,11,12,27,31,32,39–43}

This technique preserves the axillary fold and addresses this pertinent issue of inferior wound coverage by preserving the humeral attachments and advancing bilateral muscles in a limited fashion. The left sternocostal head is advanced medially and rotated anticlockwise, using this portion to fill the upper half of the sternum while the caudal portion of the right pectoralis muscle is used as a turnover flap at the lower half of the wound.

Of note, if the right internal mammary artery has been used for coronary grafting, the technique that uses the right pectoralis muscle as a turnover flap based on perforators of the right internal mammary artery will not be appropriate. Although the study had a limited sample size, we had a high rate of success and few complications. With the ability to preserve bilateral axillary folds, achieve good cosmesis and establish adequate wound coverage, we recommend this modification of the pectoralis major flap in all, and even complicated, cases of mediastinitis.