Preoperative placement of a thoracic epidural is used routinely for postoperative pain management unless contraindications exist, such as coagulopathy or systemic infection. In cases of sternal infection after cardiac surgery, cardiopulmonary bypass must be available. Antibiotic prophylaxis is administered in the setting of sternal resection, tumor, or noncontaminated osteoradionecrosis. Continuation of specific antibiotic therapy is used for sternal infection. Subcutaneous heparin and pneumatic compression stockings are used for deep vein thrombosis prophylaxis. General anesthesia is induced with single-lumen intubation. A double-lumen endotracheal tube for lung isolation may be required if there is involvement of adjacent lung parenchyma.
Supine positioning with a vertical shoulder roll enhances exposure of the sternum. After standard sterile skin preparation and draping, Ioban film is applied to the skin to minimize contamination of the incision and prosthetic reconstruction material by skin flora.
Resection Technique for Postoperative Sternal Infection
The previous incision is reopened. Cultures are obtained. The infected or necrotic edges of the sternum are debrided or resected. Curets and rongeurs are often used to accomplish this nonanatomic resection. Debridement is continued to the level of viable bleeding bone. It may be necessary to resect medial portions of cartilages or ribs to accomplish a complete resection. A smooth contour is fashioned with rasps and rongeurs of various sizes to dull sharp edges that may cause injury to adjacent structures or ensnare dressings. (Wet-to-dry saline dressing changes are often an appropriate intermediate step to delayed reconstruction.) Copious irrigation is used.
Resection Technique for Sternal Tumors or Sternal Osteoradionecrosis
A vertical midline incision is made centered over the portion of the sternum requiring resection if skin is not involved in the primary process (Fig. 116-1). If overlying skin is involved, it is advisable to resect a rim of at least 0.75 cm of grossly normal skin to achieve adequate margins. Subcutaneous skin flaps or submyocutaneous flaps are raised circumferentially for superiorly or inferiorly located tumors. A plane is dissected digitally beneath the sternum (depending on overlying soft tissue involvement and tumor type), superior to the xiphoid, and inferior to the manubrium. Presence and extent of mediastinal structure invasion are determined primarily preoperatively but are confirmed digitally. The involved mediastinal structures are resected en bloc if physiologically appropriate and technically feasible. The lateral extent of resection is determined preoperatively and then visually at the time of surgery. The goal of the resection is to obtain free margins circumferentially. Margin size is determined primarily by tumor type and site of origin. In general, smaller margins are indicated for metastatic lesions and larger margins (up to 4 cm) are indicated for primary sarcomas.2,6 Often these resection margins will require excision of one or more ribs or costal sternal junctions anteriorly.
A vertical midline or paramedian incision over the tumor offers access for sternal resection in most situations. Inset A shows placement of the shoulder roll.
The bony resection is begun over the ribs or costosternal junction, allowing for an appropriate resection margin. The rib or cartilage is isolated from surrounding soft tissues using electrocautery and blunt dissection. For sternal resections of malignant tumors, the associated neurovascular bundle medially is sacrificed and taken with the resection specimen. For nonmalignant processes, dissection of the ribs and cartilages is best carried out in a subperiosteal or subperichondral plane using periosteal elevators. The ribs and cartilages are divided using rib cutters.
Care is taken to either avoid or to ligate the internal thoracic vessels, which run approximately 1.5 cm laterally to the costochondral junction of the sternum on each side. Whenever possible, depending on the location and extent of the sternal tumor, it is preferable to keep a portion of the sternum intact for stability and to facilitate reconstruction.
Resection of the sternum 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. 116-2). Occasionally, ribs can be disarticulated at the costochondral or chondrosternal junction if the required free margin is small. The sternum then is incised using a sternal saw or osteotome after the extent of the resection is scored in the periosteum using electrocautery. Necrotic edges of the bone are debrided using a curet or rongeur. Vancomycin antibiotic paste, Gelfoam, or bone wax is used as an adjunct for hemostasis of the divided bony structures.
The area of resection is confirmed at surgical exposure of the sternum. Presence and extent of mediastinal structure invasion are determined.
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 it is determined that the associated infected tissues require dressing changes and systemic antibiotics before definitive reconstruction with autologous tissue or grafts. The two major options for sternal reconstructions are prosthetic substitutes and autologous tissue transpositions.8 Autologous tissue transpositions include omentum, muscle flaps that can be harvested with or without overlying skin, and bone such as rib. Autologous fasciae latae and preserved animal tissues (e.g., bovine pericardium) are mostly of historical interest. Prosthetic substitutes include polytetrafluoroethylene (Gore-Tex), polypropylene mesh (Marlex or Prolene), and methylmethacrylate.2,3,9
Preferential use of autologous tissue over 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 use of prosthetic substitutes and autologous tissue flaps simultaneously.
Polytetrafluoroethylene (Gore-Tex) is flexible and durable and easily conforms to various shapes. Although not an essential characteristic, it is impermeable to fluids and gases. It is available in a variety of thicknesses. “Tissue weight” (2 mm) Gore-Tex is used most often for sternal reconstruction. The radiolucency of this prosthetic permits easier radiographic surveillance for cancer recurrence (Figs. 116-3 and 116-4). The two most common types of polypropylene mesh are Prolene, a double-stitch knit mesh with relative rigidity, and Marlex, a single-stitch knit mesh expansile in one direction and rigid in the other. Both are semipermeable, permitting fibroblast ingrowth, which is responsible for tenacious incorporation into the surrounding soft tissues.
After complete resection of the sternal tumor and surrounding bony chest wall structures with a margin, assessment is made for reconstruction. Gore-Tex is used widely because of patient comfort and ease of use. The patch is tailored to match the defect.
The patch is sutured to the edge of the defect using a combination of interrupted mattress and running nonabsorbable stitches.
Methylmethacrylate is a flammable liquid. When activated by an appropriate resin, it develops into a semisolid prosthetic substance with a characteristic odor that remains malleable for only a brief period before it hardens (∼60 seconds). For sternal reconstruction, it is often sandwiched between two layers of precut polypropylene mesh (Fig. 116-5). 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. However, it is not radiolucent, limiting radiographic surveillance for recurrent cancer. Although none of the prosthetic materials just described has clearly demonstrated superiority, we prefer to use 2-mm-thick Gore-Tex mesh.
Creation of methylmethacrylate and polypropylene mesh prosthesis. A. The polypropylene mesh is cut into two patches somewhat larger than the area of defect requiring reconstruction. B. After the methylmethacrylate compound has been activated but is still pliable, it is spread on one of the patches. Care must be taken to fashion the methylmethacrylate such that it is the exact shape of the defect, but minimally smaller in size, with a methylmethacrylate-free margin of less than 1 cm on all sides for securing the prosthesis. C. The second polypropylene patch is rotated 90 degrees before it is placed on the hardening methylmethacrylate to create a sandwich. The polypropylene is rotated to limit the intrinsic stretch of the mesh border of the prosthesis (as shown in A).
Reconstruction Technique for Sternal Infection
Before postoperative reconstruction for sternal infection, an assessment is made of the sternal wound, including quantitative tissue cultures, if appropriate. If a decision is made to proceed with reconstruction, and if straightforward soft tissue or pectoralis major muscle rotation flap reconstruction is not considered feasible, the plastic surgery service is consulted preoperatively. Skin flaps are raised in all directions around the median sternotomy incision with effort concentrated laterally to expose the pectoralis major muscles. Pectoralis major muscle flaps then are raised using electrocautery beginning medially and progressing laterally, taking care to ligate perforating vessels. These muscles are left connected to their origins superiorly but may be released from their insertions inferiorly, providing a larger radius for coverage superiorly.10,11 The remaining sternum, if present, should be reapproximated using a combination of nonabsorbable and absorbable sutures and sternal wires whenever possible. This often may be achievable only for a modest portion of the length of the sternum but does, when possible, add to postoperative stability. Gentle curettage may be necessary before securing the sternal wires.
Pectoralis muscle advancement flaps are either approximated in the midline over the sternum or may be placed one on top of the other medially to fill a deep sternal defect. These muscle flaps are also secured to sternal edges or soft tissue, whenever possible, to maintain appropriate positioning.
If the defect in the sternum requires additional autologous tissue to fill the defect, or if the remaining sternal halves cannot be reapproximated and the defect extends inferiorly, then omentum can be recruited through an upper abdominal incision after release from its attachments, particularly to the transverse colon. It can be inserted through a subcutaneous tunnel into the median sternotomy wound, often through pectoralis major muscle flaps.10
Soft tissue and skin are reapproximated over the bone, muscle, and omental reconstructions. If approximation cannot be accomplished primarily as a consequence of skin and soft tissue loss, split-thickness skin grafts can be applied directly on top of the reconstruction or a Vac sponge can be applied to promote skin closure.
Reconstruction Technique for Sternal Tumors or Osteoradionecrosis
Reconstruction for sternal tumors or osteoradionecrosis begins with an assessment of wound size, as well as location and stability of the remaining structures that can be employed in the reconstruction. These factors guide the choice for sternal prosthetic substitutes or autologous tissue transpositions. If resection has been limited, then occasionally, reconstruction with localized advancement flaps similar to those described previously can be used. Sternal reconstruction inferiorly or superiorly of a sternoclavicular joint requires stabilization. In this case, the reconstruction is straightforward, and Gore-Tex is the most comfortable option for the patient given the proximity to either costal margins inferiorly or neck structures superiorly. When the resulting sternal defect is very large, associated with the need for stabilization of a large number of bony structures, or if it exposes the heart and great vessels, the sternal reconstruction most often used involves creation of a rigid prosthetic replacement.
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.
Strict adherence to aseptic technique is used to avoid wound and prosthetic infection. Perioperative antibiotics are administered beginning ½–1 hour preoperatively. Foreign-body prosthetic implantation is avoided in infected wounds. Autologous tissue coverage is used if overlying tissues are insufficient for wound coverage or are of poor quality. Prosthetic material is soaked in antibiotic irrigation and is never allowed to come into contact with the patient's skin before insertion.
Once the sternal resection is completed and hemostasis is confirmed, the chosen prosthesis is cut to appropriate dimensions using a paper template, if necessary (see Figs. 116-3 and 116-5). The prosthesis is anchored circumferentially by approximating it to ribs or muscle fascia using nonabsorbable sutures. Often interrupted sutures are used when securing the prosthesis directly to bony structures, but a combination of interrupted and running sutures can be used for approximating the prosthesis to soft tissue. Gore-Tex or Teflon pledgets may be used to avoid suture tear through muscle fascia (see Figs. 116-4 and 116-6). 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 lie over the defect. Fairly precise measurements are required if the prosthesis used involves a methylmethacrylate sandwiched technique because this will not be easily altered during implantation. Familiarity with the individual properties of prosthetic placement is mandatory because the direction of stretch and long-term elasticity of the material need to be taken into account to create a tight and smooth reconstruction. This tension helps to create chest wall stability.
The methylmethacrylate and polypropylene prosthesis is anchored to the defect by placing nonabsorbable sutures through the polypropylene mesh rim.
Excess mesh can be folded onto itself to add thickness and solidity to that margin, if appropriate. Sternoclavicular joints can be reconstructed by suturing the free end of the divided clavicle to an extension of the mesh. Portions of clavicle and ribs that cannot be reimplanted into the sternal reconstruction should be stabilized by some other means. K-wires inserted by means of a drill or paracostal sutures should be used as needed to prevent undesired movement of these structures during patient activity.
If there is a concomitant soft tissue defect either overlying the prosthetic material or deep within the mediastinal space that requires additional soft tissue coverage, an autologous tissue flap can be used. This tissue flap is best secured before sternal prosthetic reconstruction. Alternatively, a soft tissue flap can be used to cover the prosthetic material at this point. Pleural drains should be inserted if either pleural cavity is violated. Soft drains, such as a Jackson-Pratt or Blake, are left in place to prevent seromas by draining serous fluid, which frequently accompanies prosthetic or muscle flap reconstruction. Postoperative IV antibiotics are continued for 24 hours. A brief summary of frequently used muscle and omental flaps is provided in Table 116-2.
Table 116-2. Autogenous Tissue Available for Sternal Reconstruction
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Table 116-2. Autogenous Tissue Available for Sternal Reconstruction
Muscle flaps (rotation, island, or free)