The sternum provides structural support for the thoracic skeletal structures and stabilizes the shoulder girdle through the clavicles. In addition, it provides a protective barrier to the mediastinum, particularly the great vessels and the heart. Surgical principles governing resection of the sternum or clavicle emphasize the importance of a complete resection with clear margins. Repair or reconstruction of these bony defects requires the selection of appropriate prosthetic and/or autologous replacement material. It is important to stabilize the chest wall and sternum to maintain the normal dynamics of respiration and to protect mediastinal structures. Current techniques most often entail the use of rigid prostheses and soft tissue (muscle or omentum) coverage to ensure adequate healing. The use of soft tissue reconstructive techniques is imperative in any irradiated field to prevent incisional dehiscence and wound infection. Local wound complications have attendant risks for prosthetic contamination and may delay initiation of adjuvant therapy depending on the tumor type.
Preoperative placement of a thoracic epidural is used routinely for postoperative pain management unless contraindications exist, such as coagulopathy, systemic infection, anticipated cardiopulmonary bypass (CPB), or immediate need for postoperative therapeutic anticoagulation. Antibiotic prophylaxis is administered prior to incision. Subcutaneous heparin and pneumatic compression stockings are used for deep vein thrombosis prophylaxis, especially since the majority of patients have an underlying malignancy. General anesthesia is induced with initial single-lumen intubation for bronchoscopic examination followed by exchange to a double-lumen endotracheal tube to facilitate resection in the supine position. Single lung isolation is useful especially if there is involvement of adjacent lung parenchyma, concomitant chest wall or rib resection, or to facilitate resection of the sternochondral junction during sternectomy.
Positioning of the Patient
Sternectomy or claviculectomy generally requires the patient to be in the supine position. The chest and abdomen should be prepped widely to provide adequate access to potential muscle or omental flaps. The thighs should be prepped if skin grafting becomes necessary. Prior to tumor resection, there should be consideration for initial harvest of the pedicled latissimus dorsi muscle flap in the full lateral decubitus position through a vertical incision along the anterior edge of the muscle to the axilla or through a standard posterolateral thoracotomy incision. Sterile prepping of the entire ipsilateral upper extremity can facilitate dissection of the latissimus dorsi muscle but is not mandatory. In this case, all intravenous or arterial catheters should be placed in the contralateral arm. The lateral decubitus position is essential for adequate exposure for optimal latissimus dorsi muscle flap harvest. The dissected muscle flap can be tucked into the axilla and later retrieved during sternal or clavicular resection in the supine position. The latissimus dorsi muscle is our preferred flap for soft tissue coverage following sternectomy or claviculectomy. If the latissimus dorsi muscle is not available or suitable, then the pectoralis major muscle (ipsilateral and/or contralateral), transverse rectus abdominus myocutaneous (TRAM) flap, or omentum are alternatives, and can be harvested in the supine position during or after tumor resection. The pectoralis muscle is ideally suited for upper chest wall/sternal defects. The TRAM and omental flaps can reach essentially any part of the anterior and lateral thorax and sternum. However, the use of a superiorly based pedicled TRAM flap is limited given the need for preservation of ipsilateral internal mammary artery, which is generally resected in total sternectomy.
Supine positioning is the ideal position for sternal or clavicular resection. A transverse shoulder roll can be helpful to allow mild neck extension (Fig. 136-1A). In addition, a slight elevation or lateral decubitus position at 30- to 45-degree rotation ipsilateral to the clavicular resection or concomitant chest wall rib resection will provide a wider field for the tumor resection and ease retrieval of the latissimus dorsi muscle flap from the axilla (Fig. 136-1B). The ipsilateral arm should be tucked to the side. This positioning also facilitates the insertion of a thoracoscope when there is involved lung that requires en bloc resection or to evaluate the entry point into the chest wall lateral to the sternum to ensure that adequate margins are achieved in cases of concomitant sternal and chest wall tumor resection or when there is a significant intrathoracic/mediastinal component compared to the extrathoracic sternal part of the tumor.
A. Supine position with shoulder roll placed transversely. B. A slight elevation at 30- to 45-degree angle ipsilateral to site of resection.
A variety of incisions can be used depending on the location of the tumor. For a sternal or manubrial tumor, a vertical midline incision is made centered over the portion of the involved manubrium or sternum (Fig. 136-2A). For a clavicular/manubrial tumor, or upper sternal tumor, a reverse hockey stick incision can be made (Fig. 136-2B). For a lower sternal tumor involving the sternochondral junctions or chest wall ribs, a partial hemiclamshell incision (Fig. 136-2C) or lower midline vertical incision can be made. In women, the hemiclamshell incision can be extended from the midline sternum to along the ipsilateral breast crease to permit utilization of the ipsilateral pectoralis muscle and breast tissue for soft tissue coverage during reconstruction. Any previous incisional biopsy scars should be excised in an elliptical manner incorporating the entire open biopsy site.
Various incisions dependent upon tumor location. A. Vertical midline. B. Reverse hockey stick. C. Hemiclamshell.
Total Sternectomy (Resection of Costal Cartilages and Sternum)
Strict adherence to aseptic technique is mandatory to avoid incisional wound and prosthetic infection. Perioperative antibiotics are administered within 1 hour before incision. Antimicrobial surgical drapes with an iodophor impregnated adhesive (3M™ Ioban™ 2 Antimicrobial Incise Drape, 3M, St. Paul, MN) is used to maintain adherence of the drape to the patient and prevent contamination of the operative field. This also prevents contact of prosthetic materials to the patient's skin and flora.
A midline sternotomy incision is made from the sternal notch to the xyphoid. If the tumor extends close or invades the skin, then the overlying skin is resected en bloc with the sternal tumor. Subcutaneous flaps are created circumferentially by dissecting down onto the fascia of the pectoralis major muscles bilaterally. If the tumor invades the pectoralis major muscle, then en bloc resection of the muscle with the tumor is performed with a wide soft tissue margin of at least 4 cm for high-grade, primary sternal malignancies. Otherwise, the pectoralis major muscles are elevated as flaps off the sternum and costal cartilages bilaterally. Dissection is extended to expose the costal cartilages and the sternochondral junctions. Blunt dissection on the inner table of sternum at the sternal notch and at the xyphoid level is performed to release strap muscle attachments and the diaphragm attachments from the inner table of the sternum, respectively. The costal cartilages are divided from a caudal to cranial direction allowing for at least a 4-cm margin (Fig. 136-3A,B). The bilateral pleural cavities are entered. The inferior epigastric arteries are ligated bilaterally. The intercostal neurovascular bundles are ligated and divided. The lower part of the sternum is lifted anteriorly allowing visualization of the sternal undersurface. The anterior mediastinal/pericardial fat, thymus, or pericardium can be resected en bloc if tumor invasion is present. The internal mammary arteries are identified, ligated, and divided bilaterally in the upper sternal area. When the entire sternum is involved by tumor or total sternectomy is required to achieve margin negativity, the sternum is resected in its entirety with the manubrium with or without resecting the clavicular heads. When the manubrium must be resected in its entirety, the sternoclavicular joint can be disarticulated with preservation of the medial clavicular heads bilaterally. In general, the extent of margin clearance is determined primarily by tumor type and grade. For benign and metastatic lesions, negative margins are adequate. For low- and high-grade primary sternal sarcomas, 2- and 4-cm margins are required, respectively. For associated sternal and chest wall tumor resections, one rib above and below the tumor are resected to achieve adequate margins.
Total sternectomy. A. Dotted lines represent incision for centrally located sternal tumor allowing for at least 4-cm margins. B. Area representing fully resected sternum and associated ribs.
A partial resection of the sternum with or without chest wall and ribs may be sufficient for smaller tumors and is accomplished either by division of the ribs or cartilages bilaterally for centrally located tumors or by division of the ribs or cartilages on the ipsilateral side of an eccentrically located sternal tumor (Fig. 136-4A,B). The tumor is resected with the same principles as described for a complete sternectomy. If complete resectability is not compromised, preservation of at least part of the manubrium or lower part of the sternum can provide chest wall stability and facilitate an easier reconstruction.
Partial sternectomy. A. Lower midline vertical incision. Inset A. Patient positioned supine with 30- to 45-degree elevation on ipsilateral side of resection. B. Resection area for eccentrically located sternal tumor.
Reconstruction after sternal resection is necessary to provide chest wall stability for support of respiration and to protect the underlying organs (e.g., heart and great vessels). Reconstruction is performed at the time of sternal resection unless there is associated infected tissue requiring dressing changes and systemic antibiotics before definitive reconstruction with autologous grafts. Sternal reconstructions entail autologous soft tissue transpositions and prosthetic substitutes.2,5 Autologous tissue transpositions include omentum and muscle flaps that can be harvested with or without overlying skin (Chapter 138). Prosthetic substitutes include polytetrafluoroethylene (PTFE), methyl methacrylate (MMC), and polypropylene mesh.2,5
Preferential use of autologous tissue rather than prosthetic substitutes in sternal reconstruction is not clearly established except in cases of infection. Exclusive use of prosthetic materials in cases of active or deep tissue infection is contraindicated for final reconstruction but is appropriate occasionally for interim stabilization during dressing changes. In many instances, definitive reconstruction requires the combined use of prosthetic material and autologous tissue flaps.
PTFE is flexible and durable, and easily conforms to the contour of the chest wall. Although not an essential characteristic, it is impermeable to fluids and gases. It is available in a variety of thicknesses. Gore DualMesh (2-mm thickness) is used most often for chest wall reconstructions and in combined chest wall and partial sternal reconstructions. The radiolucency of this prosthesis permits easier radiographic surveillance for cancer recurrence.
Prolene or Marlex mesh, a double-stitch knit mesh with relative rigidity, is a commonly used polypropylene mesh. It is semipermeable, permitting fibroblast in growth, which is responsible for tenacious incorporation into the surrounding soft tissues.
MMC is a flammable liquid. When activated by an appropriate resin, it develops into a semisolid prosthetic substance that remains malleable for only a brief period (approximately 2 minutes) before it hardens. Since the exothermic reaction can reach temperatures of 50°C, causing necrosis of surrounding tissue, it should be molded to the appropriate contour and allowed to harden without making direct contact with the patient's tissues. Studies have proved that the rigidity and limitation of chest wall movement caused by this prosthetic material do not impair postoperative pulmonary function. MMC is radiolucent. It is commonly used in combination with polypropylene mesh in a sandwich technique discussed in detail below.
Reconstruction for sternal tumors begins with an assessment of size and location of the defect. These factors guide the choice for sternal prosthetic substitutes or autologous tissue transpositions.
Reconstruction for Total Sternectomy
Complete sternectomy requires reconstruction with rigid prosthesis to provide sturdy support to the chest wall and protection of the mediastinum and soft tissue coverage of the prosthesis. The polypropylene/MMC sandwich technique is employed. A Prolene mesh (30 cm × 30 cm) is folded over itself creating a double-layered polypropylene mesh (Fig. 136-5A). The viscera retainer should be placed over the anterior mediastinum to protect the heart and great vessels from the exothermic reaction of the MMC hardening process (Fig. 136-5B). There should be at least a 2- to 3-cm redundant overlap of polypropylene mesh from the resected sternal edge circumferentially (Fig. 136-5B). Interrupted #1 Prolene sutures are placed through each transected costal cartilage or resected rib and the clavicles to anchor the polypropylene mesh to the resected sternal edges. Use of a power drill through the ribs or clavicle may be necessary to allow suture placement through bone. The Prolene sutures are tied down in three of the four sides of the sternal defect (except for the left or right parasternal area) (Fig. 136-5C). The mesh should be tight to allow a rigid prosthetic reconstruction to prevent flail chest and respiratory complications. The clavicles should be sutured to the prosthesis to provide stability to the chest wall and improve shoulder function. Refinements to the prosthesis size and shape are carried out during the anchoring process so that it is sculpted and anchored to bony structures, producing a taut cover over the defect. The MMC cement is administered between the two layers of polypropylene mesh to create at least a 5- to 10-mm thick MMC layer (Fig. 136-5C). As the MMC hardens, it is molded into the shape of the patient's native sternum. The sternal notch should be contoured and created from the hardening MMC. Angiocatheters (14 or 16 gauge) are placed through and through the double-layered polypropylene mesh and MMC sandwich creating holes in the prosthesis to facilitate drainage of any postoperative seroma over the prosthesis into the mediastinum, alleviating the need to place any drains directly over the prosthesis (Fig. 136-5D). The viscera retainer provides protection of the heart during angiocatheter placement and heat created from the MMC. The needles are removed from the angiocatheters while the MMC is hardening. Upon completion of the exothermic reaction from the MMC, the angiocatheters and the viscera retainer are removed, and the remaining untied interrupted Prolene sutures are tied down (Fig. 136-5E).
A. 30 cm × 30 cm prolene mesh folded onto itself creating a double-layered polypropylene mesh. B. Viscera retainer protecting the anterior mediastinum with 2-cm overlap of polypropylene mesh. C. Methyl methacrylate infused in the double-layered polypropylene mesh on the free suture side. (Inset C) Layers from anterior to posterior including a 2- to 3-cm overlap of mesh from resected sternal edge. D. Angiocatheters strategically placed to allow proper drainage of postoperative seroma formation. E. Angiocatheters and viscera retainer removed after completion of exothermic reaction. Fa. Latissimus dorsi muscle flap sutured to pectoralis major and rectus abdominus muscles. Fb. Bilateral pectoralis major muscles sutured together along with rectus abdominus inferiorly. G. Layers from anterior to posterior in relation to blake drain and muscle flap placement.
The choice of autologous tissue for sternal reconstruction depends not only on the resulting sternal defect, but also on the patient's previous operations and incisions. The viability of muscle and omental transposition, advancement, and island flaps depends on a specific blood supply, which may have been disrupted during past surgical procedures or damaged from radiation exposure (Chapter 138).
The muscle or omental flap is then placed over the sandwiched prosthesis to provide soft tissue coverage. In Figure 136-5F, the use of the right latissimus dorsi muscle is depicted after being brought out from the right axilla, placed over the sternal prosthesis, and sutured to the mobilized bilateral pectoralis major muscles and rectus abdominis muscles inferiorly (Fig. 136-5F,G). Blake (19F) drains (Ethicon, Somerville, NJ) are placed over the muscle layer in the sternal reconstruction site to prevent seroma development. Drains are not placed directly over the prosthesis given the presence of holes within the prosthesis created by the angiocatheters. Drains should also be placed in the muscle harvest sites. The overlying skin is closed over the muscle flap (Fig. 136-5G). Bilateral chest tubes (28F) should be placed for pleural drainage.
Reconstruction for Partial Sternectomy
If resection has been limited to a partial sternectomy, then a rigid prosthesis may not be required depending on the location. The advantage of a partial sternectomy is that it provides the chest wall with stability due to the intact remaining thoracic skeleton. Although resection of the manubrium alone does not require reconstruction, placement of a prosthetic mesh may assist in improving the cosmetic outcome. Our preference in this instance is placement of a PTFE patch and local advancement of the bilateral pectoralis major muscles or use of the latissimus dorsi muscle for soft tissue reinforcement. The PTFE patch is fenestrated to allow seroma drainage into the pleural cavity and mediastinum. If the partial sternectomy involves the sternomanubrial junction with partial resections of the first and second ribs, then prosthetic reconstruction with the polypropylene/MMC sandwich technique is recommended to provide chest wall stability. If less than one third of the lower sternum is resected, then reconstruction is not necessary. However, our preference is placement of a PTFE patch to improve cosmetic outcome. Larger resections of the sternum will expose the heart necessitating reconstruction with the prosthetic sandwich technique. Combined partial sternal and right parasternal chest wall resections can be reconstructed usually with PTFE patch placement. However, combined partial sternal and left parasternal chest wall resections usually require reconstruction with a rigid prosthesis to provide protection of the heart mandating the prosthetic sandwich technique.
Postoperative Care and Complications
The most common complications of sternal resection and reconstruction are seroma formation, wound infection, flap necrosis, reconstruction dehiscence, and respiratory complications (i.e., pneumonia and respiratory failure).2,5 Seroma development can occur over prosthetic materials, especially after reconstruction with PTFE. The key to seroma management is prevention by fenestrating the PTFE patch or creation of holes through the prosthetic sandwich to allow seroma drainage into the mediastinum and pleural space. In general, we do not place drains directly over the PTFE patch or prosthetic sandwich reconstruction site. However, drains are placed over the muscle flap at the reconstruction and harvest sites until drainage is less than 30 mL per day for 2 consecutive days. Seromas usually resorb over weeks but may occasionally require aspiration with strict sterile technique. This can take 2 to 4 weeks from surgery before removal, particularly at the latissimus dorsi muscle harvest site. A first generation cephalosporin antibiotic is given until drain removal.
Postoperative wound infection is a significant concern given the attendant risk of prosthetic contamination. If a wound infection occurs, then aggressive local wound care and intravenous antibiotics directed against cultured organisms are warranted. Removal of the prosthetic material is generally required, particularly in the early postoperative period. If the prosthesis requires removal, a biologic material can be used for temporary reconstruction to maintain chest wall stability, such as Alloderm (Lifecell Inc., Branchburg, NJ), along with soft tissue flap coverage.
Muscle graft failure is rare.2,5 During harvesting of the flap, preservation of the associated vascular supply is critical to preventing graft necrosis. Loss of muscle flap viability generally requires reconstruction with another flap. Omental transposition is an excellent alternative in situations of muscle flap related complications. Avoidance of vasopressor utilization and optimizing the patient's hemodynamic status perioperatively are beneficial. Tension should be avoided when soft tissue flaps are anchored to neighboring tissues to prevent reconstruction dehiscence.
Respiratory complications are infrequent but contribute significantly to perioperative mortality.2,5 The occurrence of pulmonary atelectasis and pneumonia are minimized with aggressive postoperative pain management with routine placement of preoperatively placed thoracic epidural catheters, early patient mobilization, frequent ambulation, and chest physiotherapy. Therapeutic suctioning of airway secretions with liberal use of flexible bronchoscopy is encouraged when patients have a difficult time coughing up secretions and when aspiration pneumonia is suspected.