Sternal closure following negative pressure wound therapy: a safe approach with a new titanium device

INTRODUCTION

Mediastinal wound complications after cardiac surgery are a significant source of postoperative mortality and increased cost (1). Wound infections may be classified as superficial or deep (i.e., bone and retrosternal space). The sternum may dehisce with or without an infection. The incidence of deep sternal wound infection varies from 0.4% to 5%. Staphylococcus aureus and Staphylococcus epidermidis are cultured from 70% to 80% of the wounds. Deep and organ-related surgical infections result in increased length of stay, costs of care, and mortality (2). Long-term survival is decreased in these patients (3). In one series, sternal infections developed in 40 out of 3760 patients (1.1%). Early mortality was the same in the control group, but at five years, patients without sternal infections had a survival rate of 73% compared with 51% in patients with infections (3). Clinical predictors of sternal infections are diabetes, obesity, preoperative hemodynamic instability, preoperative renal failure on dialysis, use of bilateral internal mammary arteries, sepsis, and transfusions of more than four units of packed red blood cells after surgery (3, 4). Preoperative patient management may lessen the impact of these risk factors. Both accurate timing of preoperative antibiotics and tight control of perioperative blood sugar concentration in diabetic patients have been suggested as means to decrease these infections (5). Prevention of infection begins prior to surgery with identification of patient-related risk factors, careful antibiotic prophylaxis, and preoperative hair removal. Intraoperative considerations include surgical technique, with judicious use of electrocautery, and foreign bodies, including bone wax.

Once mediastinitis is diagnosed, treatment options vary from debridement and closure to sternectomy and muscle flaps. Negative pressure wound therapy (NPWT) devices may be an important adjunct in many cases of sternal wound treatment (6). NPWT is based on the application of continuous negative pressure to the infected wound, resulting in arteriolar dilatation and granulation tissue proliferation (7, 8). This technique is widely used in various surgical settings (9-10-11-12). It has been suggested that NPWT is more effective than conventional treatment strategy (13-14-15). However, management of residual sternal diastasis with soft or bone tissue defect remains challenging, even in the era of modern stabilization systems, thereby limiting the risk of injury related to sub-sternal preparation.

METHODS

Between January 2009 and August 2012, 88 patients with deep wound infection and sternal diastasis received NPWT (by Vacuum Assisted Closure Device©; KCI, San Antonio, TX, USA). Following our internal policy, patients with early (<7 days) clinical evidence of sternal instability underwent mediastinal re-exploration. In the absence of intraoperative signs of infection, the surgeon proceeded to rewiring and direct closure. Otherwise, after disinfection and removal of infected or necrotic tissues, a NPWT device was applied and changed every three days until formation of macroscopically evident granulation tissue. After that, the sternum was closed and the patient was discharged with antibiotic therapy for four weeks. Of these patients, 16 out of 88 (18.2%) underwent sternal closure after NPWT with the ASCS^® system. The ASCS^® was applied on the basis of the surgeon’s judgment, considering the presence of strong adherence under the sternum, and the consistency of the bone.

DISCUSSION

The ASCS^® system is a new, innovative device that can be routinely used for sternal approximation after NPWT. It is a simple, titanium closure device that encircles the sternum and achieves a stable and consistently powerful closure. It can reduce the risk of important structures such as the right ventricle or a bypass graft from being damaged in cases of potentially extreme adhesion. Several years ago, comparable strategies were developed successfully by Robicsek et al (16), who used additional longitudinal wires to prevent sternal instability. Multiple solutions for sternal repair are possible, in combination with NPWT or not. These include: primary closure and local irrigation with antibiotics; sternal reinforcement using a parasternal wire suture (Robicsek’s cage); sternal refixation using sternal plating; flap closure by regional myocutaneous flaps (e.g., pectoralis muscle, rectus abdominus muscle, and latissimus dorsi flap), or by the transposition of the greater omentus.

In one study, debridement, rewiring, and delayed skin closure resulted in shorter healing time (17). In a series of 5337 patients, 62 patients developed deep sternal infections (1.1%). Thirty-two were treated with debridement, rewiring, and delayed primary closure. This treatment failed in six initially and ultimately in two patients, with a median length of stay of 32 days and a median time to healing of 85 days. Twenty-five patients had muscle flap closure without sternal reapproximation, with a median length of stay of 31 days and a median time to healing of 161 days.

Recently, in a propensity-score matching analysis with 40 patients, Zeitani et al demonstrated the superiority of pectoralis muscle flap reconstruction versus sternal rewiring in terms of late survival, procedure failure, and quality of life (18). Schols et al, reviewing the experience of their collegial work by cardiac and plastic surgeons, recommend initial preservation of the sternum with NPWT followed by delayed sternal refixation and bilateral pectoralis major flap advancement (19). These conclusions are in line with the experience of Baillot et al in a 15-year experience on 23499 patients (20).

The use of titanium plate fixation provides more sternal stability and faster healing. Sergant et al demonstrated faster healing of primary closure in an animal model (21). Fawzy et al documented improved sternal stability in a human cadaver model by the use of transverse sternal plating (22). In a study by Baillot et al, the incidence of recurrences in patients treated with the titanium plate fixation system was 9.72% (9 out of 92 patients), three of whom were infected preoperatively with methicillin-resistant Staphylococcus aureus (MRSA). However, in these patients the infectious process was well circumscribed and, after appropriate antibiotic therapy and hardware removal, chest-wall integrity and survival were achieved in all patients.

Recently, new devices for sternal closure after cardiac surgery have been introduced. In most cases there is a lack of evidence about their effectiveness and costs. The Sternal ZipFix™ System (Synthes, Oberdorf, Switzerland) consists of PEEK (Poly-ether-ether-ketone) strips with an attached, blunt, stainless steel needle and it passes around the intercostal spaces. Grapow et al applied this system for the primary closure of 50 patients, resulting in sternal stability in all patients, and mediastinitis (requiring the removal of the system) in two patients (23). The authors reported that the costs of this new device are, at the moment, about 5 to 8 times more expensive than conventional wires.

Nitinol is a shape-memory alloy of nickel and titanium that is highly flexible at low temperatures (<8°C) and that recovers its original shape at temperatures of 35°C or above. Nitinol thermoreactive clips (Nitillium Research, Naples, Italy) are a sternal closure system with two coupling points implanted in the intercostal space to attain traction on the sternum. Gucu and coworkers used it in ten patients after the development of non-infective sternal dehiscence. They found the method safe, easy, and efficient (24).

A product based on the same mechanism (Flexigrip; Praesidia, Bologna, Italy) was used by Bejko et al. In their propensity-matched comparison of the nitinol clips versus standard parasternal wiring for primary sternal closure, the incidence of sternal instability secondary to wound infection was significantly lower in 464 patients who received nitinol clips (1.9 vs. 0.2%). Moreover, the authors reported in this population a cost reduction of 13% compared to standard technique (25).

New systems such as titanium plate, the Rapid Sternal Closure Talon System (KLS Martin Group, Jacksonville, FL, USA), the Sternal Closure Device™ (SuturTek, North Chelmsford, MA, USA) or nitinol clips may reduce the risks described above (damage of right ventricle, coronary grafts, and postoperative bleeding due to adhering tissue dissection) but they also have some drawbacks, such as expensive equipment and the steep learning curve they require (26). Using ASCS^® System, the approach is similar to the standard wiring approach using the sternal wire, while minimizing the risk of postoperative bleeding due to its technique, and the learning curve is fairly easy. Moreover, the use of ultrapure titanium (medical grade 1) ensures that chromium or nickel allergies will be avoided. The ASCS system also protects the patent internal mammary artery more efficiently, with subsequent improvement in sternal perfusion and healing. The smooth, larger work surfaces of the hooks reduce the risk of sternal rupture and allow for better protection of the sternal cortical layers in the intercostal position. The ASCS^® System made of titanium provides better sternal stability and decreases the risk of intrasternal bleeding, which can occur after needle penetration when traditional wires are used for sternal closure (wiring).

Due to the limited study population, a cost analysis of ASCS^® use and a comparison with others system was not possible, which is the major limitation of this study.

CONCLUSIONS

In our opinion, the ASCS^® device can be routinely used for sternal approximation after NPWT. Our experience, however, is limited and larger case series are necessary to fully evaluate this new, innovative technique.