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ORIGINAL ARTICLE |
Division of Cardiothoracic Surgery
1 Division of Cardiothoracic Anaesthesia, Heart and Lung Centre, Universiti Kebangsaan Malaysia Medical Centre, Kuala Lumpur, Malaysia
Abdul-Rahman Mohd Ramzisham, MS, Tel: +60 3 91456201, Fax: +60 3 91737831, Email: cardsurg2008{at}gmail.com, Division of Cardiothoracic Surgery, Department of Surgery, Heart and Lung Centre, Universiti Kebangsaan Malaysia Medical Centre, Kuala Lumpur, Malaysia.
ABSTRACT
Sternal dehiscence is a rare but devastating complication following median sternotomy for cardiac surgery. The optimal technique for sternal closure is unclear. We conducted this prospective randomized trial to compare the incidence of sternal dehiscence after figure-of-8 and simple interrupted suturing in patients undergoing coronary artery bypass grafting. Between January 2007 and June 2008, 98 patients had figure-of-8 suturing and 97 had interrupted sutures. The mean age of the patients was 60.9 ± 7.6 years. The overall sternal dehiscence rate was 8%; 7 cases in the in figure-of-8 group and 9 in the interrupted group. Thirteen patients had no wound infection and healed with conservative treatment. Only 3 patients had sternal dehiscence with infection: 2 with simple interrupted closure and 1 with figure-of-8 sternal closure. There was no significant difference in rates of sternal dehiscence between the 2 groups. It was concluded that figure-of-8 sternal suturing is equally effective as simple interrupted suturing in preventing sternal dehiscence.
Key Words: Bone Wires • Coronary Artery Bypass • Sternum • Surgical Wound Dehiscence
INTRODUCTION
Median sternotomy for cardiac surgery was first advocated in 1957 by Julian and colleagues.1 Since then, it has been the standard approach for many open heart operations including coronary artery bypass grafting (CABG). Although sternotomy closure is straightforward, it is not without complications. The reported incidence of sternal dehiscence varies from 20%–25%.2 If not recognized early, instability of the bone fragments interferes with healing and can lead to complete sternal breakdown, sternal wound infection, and mediastinitis, which are major causes of morbidity and mortality after open-heart surgery.3 Various studies have shown mediastinitis rates of 1%–2.5% and mortality rates of 15%–50%.3–6 Other risk factors for sternal dehiscence include chronic obstructive pulmonary disease (COPD), redo surgery, renal failure, diabetes mellitus, chronic steroid use, obesity, concurrent infection and immunosuppression.6,7 Intraoperative risk factors such as off-midline sternotomy, osteoporosis, prolonged cardiopulmonary bypass, transverse fractures of the sternum, and bilateral internal mammary artery harvest have been identified.6 The standard median sternotomy closure involves wiring with stainless steel wires in a figure-of-8 or the simple interrupted manner. Typically, the wires are passed directly through the sternum, but peristernal and pericostal placement, circumferential encirclement, and alternating patterns, have been described to minimize sternal cut-through and wire failure.2 Various materials have been used, including steel bands, polydioxanone sutures, nylon bands, and custom-made titanium-H plates.7,8 Figure-of-8 suturing is believed to be more secure and less likely to cut the sternum, because of redistribution of shearing forces, compared to simple interrupted closure. However, disruption of a single figure-of-8 suture is equivalent to that of 2 interrupted sutures. Biomechanical studies on human cadavers and animals have assessed the efficacy of these techniques, with different results.9,10 In view of these conflicting data and the lack of randomized clinical trials, we conducted this study to compare the incidence of sternal dehiscence between these 2 techniques.
PATIENTS AND METHODS
This prospective randomized clinical trial took place between January 2007 and June 2008. The trial was approved by the institutional research and ethical committee. All patients scheduled for elective CABG in our center were included. Exclusion criteria were redo surgery, additional surgical procedures, reoperation for bleeding, and sternal fractures. Informed consent was obtained, and the patients were randomized into 2 groups. Group A had figure-of-8 suturing, and group B had interrupted suturing. The groups were matched for age and risk factors. All patients received antibiotic prophylaxis of amoxicillin/clavulanate 1.2 g intravenously at induction. Prior to surgery, the skin was cleaned with 10% povidone iodine solution, and covered with polyurethane drapes. CABG was performed through a standard median sternotomy by 3 cardiothoracic surgeons. Bone wax and diathermy were used sparingly for hemostasis upon closure. Two drains were usually left in the mediastinal and pleural cavities. The sternum was closed primarily using no. 6 steel wires in either a figure-of-8 or interrupted manner. In group A, the wires were passed through the sternum approximately 1.5 cm lateral to the midline. Each wire was inserted through the sternum at the manubrium, across the sternal angle, sternal body, and just above the xiphisternum. The 2 free ends of the wire were pulled and then crossed in a figure-of-8 configuration. Using a rotary movement of the wrist along with a vertical pull on the wires, the wires were twisted tightly until the 2 bone edges approximated. In group B, 6–8 single wires were used, depending on the length of the sternum: 2 at the manubrium, and 4–6 at the body of the sternum. The 2 free ends of the wire were pulled vertically until tight, and twisted around each other to form a loop approximating the 2 fragments of sternum. In both groups, the wounds were irrigated with sterile water and 10% povidone iodine. The subcutaneous tissue was closed in 2 layers using Polyglactin 1/0 and Vicryl 3/0 subcuticularly.
A diagnosis of sternal dehiscence was made on clinical findings of a sternal click or evidence of sternal instability during coughing or respiration. Chest radiography aided the diagnosis of dehiscence by revealing a mid-sternal strip sign, with or without wire abnormalities (Figures 1
and 2).11,12 All patients were assessed clinically and radiologically for sternal dehiscence on postoperative day 2 and daily until discharge. In cases of sternal dehiscence, patients were assessed for superficial or deep sternal wound infection. All patients were followed up at the clinic at 6 weeks and 3 months postoperatively.
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RESULTS
There were 200 patients recruited, but 5 were lost due to postoperative death within 3 months and reoperation for bleeding, giving a total of 195 included in the study (Table 1). There were 98 patients in group A and 97 in group B. Diabetes mellitus and chronic obstructive pulmonary disease (COPD) were the most common comorbidities; all patients with COPD were smokers. The patients were well matched in each group (Table 2). The overall sternal dehiscence rate was 8%. There were 16 sternal dehiscence cases documented: 7 in group A and 9 in group B. Of the patients diagnosed with sternal dehiscence, 13 (6.7%) were asymptomatic and free from sternal wound infection. The diagnosis was made solely on chest radiography showing a mid-sternal strip sign <3 mm. These patients were treated conservatively, and repeat chest radiography after 3 months showed complete resolution of dehiscence. Only 3 (1.5%) patients were diagnosed to have sternal dehiscence with infection; 2 had simple interrupted closure, the other had figure-of-8 closure. These patients required surgical wound debridement and the modified Robiscek technique to correct the dehiscence. Although the incidence of sternal dehiscence was higher in group B, it was not statistically significant (p = 0.294). The characteristics of patients with and without sternal dehiscence are shown in Table 3. Patients with sternal dehiscence were older, smokers, and suffered from COPD, diabetes mellitus, endstage renal failure, and obesity. There were no differences between patient characteristics according to CABG techniques or use of the internal mammary artery.
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Midline sternotomy remains the most popular technique for heart exposure because it is quick and easy to perform and provides excellent access to the heart and great vessels. On the other hand, it is associated with many sternal wound complications including infection and dehiscence, leading to prolonged hospitalization, increased costs, devastating morbidity, and even mortality. Dehiscence often occurs within the first 2 weeks postoperatively, due to failure of the sternal wires to keep the 2 halves of the sternum immobilized before healing occurs. The wires can cut through the bone, especially osteoporotic bone, and eventually loosen. The wires can also fracture or simply become untwisted and loosen the sternum after repeated physiological tension, e.g., coughing and respiration. Thus chest radiography will normally show dehiscence of the sternum with either a ruptured wire, malpositioned wire, or cut-through of the wire by the bone fracture.13 The key factor in preventing sternal dehiscence is a stable sternal approximation until significant bone healing occurs; bony union depends on adequate reduction, fixation, and immobilization of the sternum. This relies on several factors: the technique of sternal closure, quality of the material used for sternal closure, and patient factors.
We focused on 2 common techniques of sternal closure. To determine the effectiveness of each technique, one should consider the number of wires used, number of wire twists, the strength of each twisted wire, the force distribution, and the likelihood of each twisted wire to cut through the bone or untwist. Krejca and colleagues14 determined the force distribution in sternal wiring and the consequences of sternal closure rigidity between these 2 techniques. They concluded that simple interrupted wires provide good fixation stability for durability of the sternum, but lower strength than figure-of-8 suturing. This can be compensated for by increasing the number of sutures. The figure-of-8 wire has more strength and is less likely to cut the sternum because of an advantageous redistribution of shearing forces on the wire compared to straight closure. Several other reports also favored figure-of-8 wires because they are less likely to loosen or fracture the sternum, due to an oblique and horizontal angle of shearing forces instead of the direct perpendicular forces in simple interrupted suturing.15,16
In terms of the strength of each twisted wire, Shih and colleagues16 reported that one figure-of-8 twisted wire can sustain a force of 92.8 ± 1.3 kg in a chest closed before the wire starts to fracture, but it requires 2 straight twisted wires to withstand a force of 98 ± 4.8 kg. Casha and colleagues9 calculated that the force generated during coughing is 150 kg, or 25 kg of force transmitted across each wire if 6 are used to closed the sternum. We used 6–8 simple interrupted wires or 4 figure-of-8 wires; both closure techniques seem to ensure maximum strength and prevent sternal dehiscence. In terms of the number of twists, Glennie and colleagues10 showed that twisting a wire more than 4 times did not produce more strength, but it damaged wire, leading to early failure. Thus we standardized to 4 twists of each wire in both techniques, and we believed this would not affect our endpoint outcomes as long as the sternal edges approximated firmly. We found neither technique to be superior in preventing sternal dehiscence. Most patients with dehiscence were asymptomatic, and the diagnosis was based on a mid-sternal strip sign on chest radiography. Our incidence of sternal dehiscence without infection of 6.5%, and with infection of 1.5%, is comparable to results of several studies showing sternal dehiscence with mediastinitis in 1%–5% of cases.17 Sternal dehiscence is associated with significant morbidity and mortality rates of 14%–50%; in our study, no patient died due this complication.
In our literature review, there was no classification of sternal dehiscence based on symptoms, signs, and radiological findings. We would like to propose the following classification: type 1, asymptomatic with a mid-sternal strip <3 mm; type 2, mild to moderate sternal pain, rocking sternum, and a mid-sternal strip of 4–10 mm with no infection; type 3, severe pain, sunken sternum during breathing, mid-sternal strip >10 mm, and mediastinitis. The importance of this classification is in determining which patients can be treated conservatively. For type 1, conservative management may be advocated, and assessment by serial chest radiographs is important to determine whether the dehiscence has resolved. For types 2 and 3, surgical intervention is imperative at the time of diagnosis to reduce the rates of morbidity and mortality.
Risk factors for sternal dehiscence have been classified into 3 groups. Preoperative risk factors include advanced age and comorbidities, intraoperative factors include prolonged duration of operation and the need for reoperation, and postoperative factors comprise intraaortic balloon pumping, massive blood transfusion, prolonged mechanical ventilation, and pneumonia. Our results confirm that advanced age, obesity, COPD, diabetes mellitus, and renal insufficiency are the main preoperative risk factors. Intraoperative risk factors, including left internal mammary artery use and duration of bypass, were not significant. Careaga Reyna and colleagues18 found that risk factors for sternal dehiscence without infection were age >60 years, antiplatelet agents, beta blockers, and postoperative infections such as pneumonia. There was no significant pneumonia our patients and we did not analyze postoperative risk factors.
It was concluded that the current method of wire encirclement should remain as the standard technique for sternotomy closure. This trial proved that figure-of-8 sternal suturing is equally effective as simple interrupted suturing in preventing sternal dehiscence after CABG. The idea that one or other technique is superior should be discarded, and we recommended that the surgeon’s preference should be used for sternal closure.
REFERENCES
a P, Skarysz J, Bochenek K, Ulczok R, Bis J, et al. Force distribution in wire sternum sutures: the consequences for sternal closure rigidity. Med Sci Monit 2003;9:134–44.Asian Cardiovasc Thorac Ann 2009;
17:587-591
© 2009 by SAGE Publications
DOI: 10.1177/0218492309348948
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