Eric N. Feins and Christopher R. Morse
INDICATIONS/CONTRAINDICATIONS
Resection and reconstruction of the sternum comprises a wide spectrum of surgical techniques applied to a range of clinical conditions. As methods have evolved for skeletal and soft tissue reconstruction, the ability to manage sternal pathology has greatly improved. The main conditions requiring sternal resection and reconstruction are infectious or neoplastic although radiation-induced necrosis of the anterior chest wall, as well as trauma, may also require surgical intervention.
Infection represents the most common indication for resection/reconstruction of the sternum. Sternal infections are typically a postoperative occurrence following median sternotomy for cardiac surgery although sternal osteomyelitis from IV drug use can also occur. Several patient- and surgically related factors predispose to postoperative sternal wound infections, including obesity, diabetes, recent tobacco use, urgent surgery, use of internal mammary arterial grafts (especially bilateral), and postoperative bleeding. Superficial sternal wound infections generally do not require surgical intervention and can be managed with IV antibiotics and local wound care. Deep sternal wound infections, however, require urgent surgical intervention to widely resect all infected and/or nonviable tissue. The extent of infection obviously dictates the degree of bony and soft tissue debridement, which in turn dictates the reconstructive technique. Partial sternectomy is preferred so long as the surgeon is able to debride to healthy, solid bone and soft tissue with bleeding margins. In the case of extensive sternal osteomyelitis with widely necrotic bone that is soft and/or oozing pus, a total sternectomy must be performed. The implantation of prosthetic material for skeletal reconstruction in the setting of active infection is contraindicated. Reconstructive techniques for sternal wound infections, therefore, rely on soft tissue coverage with muscle or myocutaneous flaps or omentum, typically done in collaboration with a plastic/reconstructive surgeon.
Sternal neoplasms are rare but represent another major indication for sternal resection/reconstruction. Primary sternal tumors, which are most commonly sarcomas (especially chondrosarcoma), are a clear indication for sternectomy and reconstruction because radical resection may permanently eradicate the tumor and improve long-term survival. The extent of resection follows oncologic principles. A 3- to 5-cm macroscopic margin is the goal. Depending on the extent of tumor invasion, the following sternal resections are indicated.
Total Sternectomy (sternal body, manubrium, medial 1/3 of clavicles): Large tumors involving the manubrium + sternal body, primary neuroendocrine tumors
Subtotal Sternectomy (sternal body with sparing of manubrium/clavicles): Tumors confined to the sternal body
Partial Sternectomy: Tumors limited to the manubrium or lower 1/3 of the sternal body
In cases where tumor invades deeper to involve underlying mediastinal structures, such as the pericardium or major vessels, the involved structures must be resected en block with the sternum, and appropriate reconstruction (e.g., caval reconstruction) performed.
The indication for resection of secondary sternal tumors (e.g., locally recurrent breast cancer, metastatic lung cancer, renal cell carcinoma) is more controversial given the poorer oncologic outcomes. In this setting, resection/reconstruction is often indicated for palliative purposes to relieve pain, inflammation, or bleeding related to the tumor.
Sternal reconstruction following oncologic resection takes a variety of forms, and there is some debate as to the proper approach. Because of the sternum’s important role in chest wall stability and respiratory mechanics, large bony defects that put a patient at risk for paradoxical chest wall motion (e.g., following total sternectomy) typically undergo rigid fixation with a prosthesis followed by soft tissue coverage using muscle or myocutaneous flaps. Small bony defects (i.e., <5 cm in greatest diameter), however, do not require skeletal reconstruction.
PREOPERATIVE PLANNING
Preoperative evaluation and management depend upon the surgical indication. Regardless of indication, the surgeon must be aware of any prior thoracic and/or cardiac procedures that will impact the surgical approach. This includes knowledge of prior internal mammary artery harvest for coronary artery bypass procedures, which will affect the choice of muscle flaps for reconstruction. In addition, it is critical to know the patient’s underlying cardiopulmonary status. Given that sternal resection can leave people with altered respiratory mechanics, it can be particularly morbid for those with pre-existing pulmonary disease.
For deep sternal wound infections, physical examination, standard blood work, wound cultures, blood cultures, and imaging are necessary. Clinical findings suggestive of sternal osteomyelitis include fevers/chills, wound drainage, and sternal instability upon palpation. Computed tomography (CT) is the most useful modality for assessing the extent of sternal infection. CT findings consistent with deep sternal wound infection include changes to bone configuration, fat stranding, and substernal fluid collection(s)/abscess(es). Importantly, after cardiac surgery the mediastinum will have standard postoperative changes that can make the radiographic assessment for infection more challenging. Plain films of the chest are of limited value but will show late bony findings consistent with osteomyelitis. Preoperative management should include prompt initiation of broad-spectrum IV antibiotics, as well as resuscitation in the setting of sepsis.
In patients with a sternal neoplasm, preoperative evaluation includes standard blood work and imaging. While CT is the most informative for assessing the tumor size and location, MRI can provide additional information about tumor invasion and involvement of underlying mediastinal structures. Bone scan or PET-CT is performed to rule out extrathoracic metastasis. Tissue biopsy should be obtained prior to definitive surgery to determine tumor type and grade. This is important given that sarcoma grade dictates management: Patients with high-grade tumors may require neoadjuvant therapy prior to operative resection.
SURGERY
Prior to surgery, the patient should receive standard prophylactic IV antibiotics within 1 hour of incision. For patients with deep sternal wound infections who are already receiving antibiotics, the surgeon must ensure with anesthesia that antibiotics are continued and dosed appropriately.
Positioning
The patient is placed in the supine position and is prepped and draped with sterile towels/sheets. If a single-stage procedure is planned with immediate sternal reconstruction the sterile field must be wide enough to accommodate flap preparation, including the abdomen if a rectus flap or omentum will be used.
Technique
Sternal Debridement for Infection
For deep sternal wound infections, the prior midline sternotomy incision is reopened and dissection is performed down to the sternum. Deep sternal wound cultures are obtained. A combination of cold dissection and electrocautery is used to completely debride the presternal soft tissue, until healthy, viable bleeding tissue surfaces are reached. The surgeon may have to extend the initial incision laterally on either side at the superior and/or inferior aspects of the midline incision in order to gain adequate exposure.
The sternal wires must be cut and removed, and the sternum reopened. Sternal debridement is carried out using a curette and/or rongeur to remove all necrotic/infected bone from the cut edge of the sternum until healthy, bleeding surfaces are reached. Sharp bone edges should be filed down to prevent injury to the heart. Importantly, if the sternum is widely involved then total or subtotal sternectomy must be performed (see below).
After debridement is completed the surgeon performs pulse lavage of the wound bed with antibiotic solution. There have been no randomized controlled trials proving the effectiveness of antibiotic pulse lavage, but it is a standard step in sternal debridement. Once the surgeon is satisfied with the debridement, and after confirming hemostasis, a vacuum-assisted closure device is placed in the wound. Negative pressure therapy has become an increasingly popular method of wound management following sternal debridement and serves as an effective bridge to definitive closure.
Reconstructive procedures are not performed at the time of sternal debridement in the setting of active infection, unless the surgeon (in consultation with a plastic/reconstructive surgeon) is extremely confident that the debridement was complete and there would be no benefit to an interval period of wound care. Interval flap reconstruction is typically performed in collaboration with a plastic/reconstructive surgeon once it is certain that the infection has been completely controlled.
Sternectomy
When resecting a sternal tumor, an elliptical skin incision is made over the sternum to include the prior biopsy incision. The incision extends from the manubrium to the xiphoid. Dissection is carried down to the sternum with electrocautery. In cases where there is tumor involvement of the skin and/or presternal soft tissue then the incision must be extended out laterally to normal tissue with a 3-cm macroscopic margin, and subsequent dissection down to sternum must remain wide to fully encompass the tumor (Fig. 17.1).
Once down to sternum, the medial attachments of the pectoralis major are divided to raise each muscle off the sternum and costal cartilage (Fig. 17.2). This exposes the lateral extent of the sternum. If the tumor clearly involves the pectoralis major then these muscles should be left in place and resected with the specimen.
Figure 17.1 An elliptical incision is made for sternectomy in the setting of neoplasm. The incision includes the prior biopsy incision. Macroscopic margins should be at least 3 cm if the tumor involves the presternal soft tissue and/or skin. Incision may have to be extended laterally at the superior aspect overlying the clavicles (dashed lines) in cases where resection of the manubrium and clavicles is necessary.
The sternal notch is dissected and the superior retrosternal space is developed. The xiphoid is also fully dissected up to the costal cartilages, and the inferior retrosternal space is developed. The degree of tumor invasion is assessed to define the extent of resection. The intercostal spaces are dissected out with electrocautery, and the internal thoracic arteries are identified, suture ligated, and divided.
The perichondrium is removed at each intercostal level, and the costal cartilages are divided with a sternal saw (Fig. 17.3). Division of the costal cartilage should begin on the side that has less tumor involvement and should extend to one intercostal space above the superior aspect of the tumor. Laterally the point of division is dictated by tumor invasion, with care taken to attain adequate margins (3 cm or more). Special care should be taken to identify and isolate the intercostal vascular bundle at each level and divide the vessels between clamps.
The posterior perichondrium is divided at each level to free the sternum from the ribs. The sternum is gently suspended upward to expose the underlying retrosternal tissue. The soft tissue between the pericardial fat and the undersurface of the sternum is divided with electrocautery, which gradually frees the specimen (Fig. 17.4). If the manubrium is free of disease and an adequate margin can be accomplished, then the sternum is divided with the sternal saw just above the second interspace, separating the specimen from the manubrium.
Figure 17.2 Dissection of the pectoralis major muscles off from their medial attachments to the sternum and chostochondral cartilage.
Figure 17.3 The sternum is fully exposed, with complete dissection of the intercostal spaces. The internal mammary arteries have been ligated. Division of the costochondral cartilage is performed with a sternal saw.
If the tumor involves the manubrium, then the dissection is carried superiorly to the first costochondral cartilage and laterally over the clavicles. This may require lateral extension of the skin incision. When dissecting the manubrium and clavicles, care is taken to stay directly on bone, to separate the underlying vessels from the eventual specimen. Division of the clavicles is performed lateral enough to attain adequate margins, and the whole specimen is taken en bloc.
Figure 17.4 Superior retraction of the specimen with dissection of the underlying adhesions between the endothoracic fascia and the underlying pericardial fat. The specimen is removed en bloc.
Skeletal Reconstruction
After removal of the specimen the sternal defect is assessed for reconstruction, with rigid/bony reconstruction performed for large sternal defects. A variety of materials exist for skeletal reconstruction, including rigid prostheses (polypropylene–methylmethacrylate sandwiches, cryopreserved homografts [iliac crest, rib], titanium plates, or meshes), and nonrigid prosthesis (PTFE patches, polypropylene patches).
Polypropylene–Methylmethacrylate Sandwich Reconstruction of the Sternum
A layer of polypropylene mesh is sized to the sternal defect. The sandwich is then created by suturing two layers of mesh together using a nonabsorbable suture. Methymethacrylate is injected in between the two mesh layers, which will lend rigidity to the prosthesis following implantation. The prosthesis is then molded to the sternal defect and anchored to the chest wall using interrupted, monofilament, nonabsorbable sutures at the corners. It is preferable to have the sizing of the prosthesis be slightly smaller than the defect to avoid overriding and subsequent pain. After placement of a drain behind the prosthesis, the prosthesis is fully secured to the chest wall with more nonabsorbable sutures coupled with running nonabsorbable sutures between the mesh and the cut rib edges or costal cartilages (Fig. 17.5).
Allograft Reconstruction of the Sternum
A cryopreserved allograft—typically iliac crest—can be fitted to the defect to serve as the neosternum (in lieu of a methylmethacrylate prosthesis). When the manubrium has been left in place, the allograft is anchored to the manubrium using titanium screws. Laterally, the graft can be secured to the rib edges with titanium bars, which are anchored with titanium screws (Fig. 17.6). Alternatively, methylmethacrylate sandwiches are constructed and sutured to the anterior chest wall on either side of the allograft and then sutured to the lateral aspect of the allograft with interrupted, nonabsorbable sutures through holes drilled in the graft.
Figure 17.5 Sewing in the methymethacrylate prosthesis fill the poststernectomy defect.
Figure 17.6 Allograft implantation, with titanium bars/screws used to anchor the prosthesis to the chest wall.
Titanium Plating
A variety of titanium prostheses exist that can be implanted to provide rigid fixation of the anterior chest wall. For large defects (i.e., after subtotal sternectomy), three titanium plates are implanted across the defect. Prior to implantation they are shaped to conform to the chest wall. They are secured to the ribs on each side with three titanium screws, which are sized to the thickness of the patient’s ribs.
Soft Tissue Reconstruction
When the prostheses mentioned above are implanted, an omental flap may be performed, with placement of the flap underneath the prosthesis to provide separation between the prosthesis and the heart. As a highly vascular structure, the omentum also helps promote tissue integration with the prosthesis. The omentum is secured in place with interrupted nonabsorbable sutures.
The pectoralis muscles are then reapproximated to the costal cartilage and the presternal fascia in the midline to cover the prosthesis. This is done over another drain, which lies behind the pectoralis muscle layer. The presternal soft tissue is then reapproximated with a running, absorbable suture, such as PDS. Finally the skin is closed with a running monocryl suture.
If the soft tissue defect is large, then a muscle or myocutaneous flap reconstruction can be performed, typically with a pectoralis major advancement flap, based on the thoracoacromial pedicle.
POSTOPERATIVE MANAGEMENT
Analgesia and aggressive pulmonary physiotherapy are critical in the immediate postoperative period given that anterior chest wall reconstruction can leave patients with altered respiratory mechanics. Inadequate analgesia with subsequent splinting will exacerbate this. When operating for sternal wound infections IV antibiotics are continued for 6 to 8 weeks if there was presence of osteomyelitis, with narrowing of antibiotics based on culture data. Standard perioperative antibiotics are appropriate after surgery for noninfectious reasons. Drains should be left in place until outputs reach an acceptably low level (approximately 20 to 40 cc per day) to prevent seroma formation. If patients were on anticoagulant therapy preoperatively, resumption should be delayed for as long as possible to minimize the risk of hematoma formation.
COMPLICATIONS
Respiratory and wound complications are the main concerns following sternal resection/reconstruction. Pulmonary complications, including pneumonia, respiratory failure, and prolonged ventilator support, are related to the altered chest wall mechanics and in some cases paradoxical motion of the chest wall. These complications represent a major cause of nononcologic, postoperative mortality after sternal resection/reconstruction. Wound complications include seroma formation, hematoma formation, prosthesis infection, and partial or complete flap loss. Small seromas typically resorb over several weeks without intervention; however, sterile aspiration is necessary for large seromas. Hematomas, if large enough mandate reoperation for evacuation. Prosthesis infection is a serious wound complication that usually requires reoperation to remove the infected material.
RESULTS
For patients undergoing resection for sternal neoplasm, tumor type is the most important predictor of survival. Those who undergo radical resection of a primary sternal tumor fair the best, as demonstrated in multiple studies. In a review of 49 patients undergoing sternal resection/reconstruction for malignancy at MD Anderson between 2001 and 2012, the oncologic mortality rate was 49%, with a median survival of 18 months. Patients with primary sternal tumors had a 17% oncologic mortality, compared to a 50% mortality among those with breast cancer, and an 87% mortality in those with metastatic cancer other than breast.
Lequaglie et al. reviewed 88 patients who underwent sternal resection for neoplasm over a 19-year period. The 10-year actuarial survival for patients with resected primary sternal tumors was 85%. Patients undergoing resection for breast cancer relapses had a 42% 10-year survival while none of those with other metastatic cancers were alive at 10 years.
Chapelier et al. reviewed 38 patients who underwent sternal resection/reconstruction for primary sternal tumors over a 16-year period. Tumor grade was the primary predictor of survival in this study. Local recurrence rates were nontrivial. Approximately 25% of patients had a local recurrence within 1 year of surgery, most of whom underwent reresection. Patients with radiation-induced sarcoma are at particular risk for local recurrence because the surrounding irradiated tissue is abnormal, making it difficult to be certain of negative margins.
The outcomes of patients who undergo debridement and flap reconstruction for deep sternal wound infections are largely dependent on preoperative characteristics. Those with end-stage renal disease, COPD, or poststernotomy prolonged ventilator support have an increased mortality following sternal resection/reconstruction. Patients with sepsis preoperatively have mortality rates as high as 25%, compared to only 3% in those without it.
CONCLUSIONS
Techniques for sternal resection and reconstruction play an important role in the management of sternal wound infections as well as sternal neoplasms. The extent of sternal resection depends entirely on the degree of diseased tissue and can range from limited debridement or partial sternectomy to total sternectomy. Surgical techniques have evolved for reconstructing the poststernectomy defect. Large sternal defects require rigid fixation to prevent paradoxical chest wall motion and optimize respiratory mechanics. A range of techniques and materials exist today, including mythymethacrylate, bone allograft, and titanium prostheses, which can be used alone or in combination to replace the structure and function of the sternum.
Recommended References and Readings
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