Abstract
OBJECTIVES
During the last decade, various plate fixation systems have been developed for the treatment of complicated sternal dehiscence after open-heart surgery. One of them is the Modular Sternal Cable System© (MSCS), which promises optimal distribution of forces along the whole sternum by using plates, cannulated screws and cables. However, in comparison with other systems, there is a lack of outcome data.
METHODS
Sternal reconstruction with the MSCS was performed in 11 patients (male n = 10, age 72.0 ± 7.3 years) with complicated sternal dehiscence following cardiac surgery, and 73% of them had a history of sternal infection. Sternal reconstruction included bilateral longitudinal plating and thoracic re-closure with 4–9 cables. Patients received postoperative examination, focusing on sternal wound conditions and clinical stability. If there was any suspicion of recurrent wound infection, computed tomographic scans were done in the early postoperative period or in the long term, in order to evaluate bony consolidation and integrity of osteosynthetic material.
RESULTS
The mean operation time was 165 ± 59 min, the mean intubation time 4.7 ± 5.3 min and the mean intensive care unit length of stay was 1 day (median) (range 1–23 days), with a total hospital stay of 9 days (median) (range 5–64 days). Operative mortality was 0%. One patient died on the 65th postoperative day of a non-MSCS-related cause. Sternal wound infection occurred in 6 patients (54.5%) and made hardware removal necessary in 5 of them early postoperatively (median 14 days) and in 1 patient late postoperatively (1058 days). In another patient, material was removed 715 days after MSCS application due to persisting sternal pain.
CONCLUSIONS
A high incidence of postoperative wound infections was observed after implantation of the MSCS. It may be speculated that hardware design (e.g. the absence of a locking system, large screws) compromises osseous microcirculation, favouring the development of infection. This should be kept in mind for further development of sternal reconstruction systems.
Keywords: Sternal dehiscence, Rigid plate fixation, Osteosynthesis
INTRODUCTION
Median sternotomy remains the most common access for cardiac exposure, since first described by Milton in 1897 [1]. Sternal closure is routinely performed using steel wires [2]. One of the major complications after median sternotomy is sternal dehiscence, occurring in 0.3–5.0% [3]. Although the incidence is low, this complication is accompanied by a high morbidity and mortality rate [4–6]. The key factor for preventing sternal dehiscence and infection is a stable sternal approximation. In cases of frail bone, fractured sternum or excessive loss of sternal bone, readaptation with wires or sternal bands may be challenging [7].
In the last decade, specialized sternal plate fixation systems have been developed to treat complicated sternal dehiscence. One of the most applied systems is the Titanium Sternal Fixation System© (Synthes™, Switzerland). We, as well as various other authors [8–16], published our/their experience with this system, demonstrating excellent results in sternal restabilization (97–100%) [9, 11, 16–18]. In the following study, a different system is described, the Modular Sternal Cable System© (MSCS; Synthes™, Switzerland), a mixture of cable closure and rigid plate fixation. Postoperative outcome data concerning this system have not yet been reported. We present our results using the MSCS in 11 patients with complicated sternal dehiscence after median sternotomy.
MATERIALS AND METHODS
Modular Sternal Cable System fixation system
The MSCS consists of a set of stainless steel implants, such as sternal reconstruction plates, cannulated screws and multifilament sternal cables, respectively. Plates (3 mm thickness, 8 mm wide) are positioned in a longitudinal fashion on both sides of the sternum and fixed with specialized cannulated screws (diameter 4.5 mm). After sternal stabilization is achieved, thoracic closure can be performed by 4–9 sternal multifilament cables, passing through the holes of the cannulated screws (Fig. 1 ). This kind of reconstruction is indicated either to stabilize multiple transverse fractures and/or to serve as a partial sternal replacement in case of widely resected or lost sternal bone. All surgical procedures were done by a single, highly experienced surgeon. A detailed description of the system's application has been presented previously [19].
Figure 1:
Operating principle of the MSCS using two plates, cannulated screws and cables (Courtesy of the German Heart Center Munich). MSCS: Modular Sternal Cable System.
Patients
Sternal plate reconstruction was performed in 11 patients (male n = 10, age 72.0 ± 7.3 years, range 59.1–84.6 years) with sternal non-union after median sternotomy. Patients were considered for sternal plate reconstruction with the MSCS if standard rewiring failed before (n = 2) and failure of standard rewiring was expected due to one or more serious risk factors (e.g. nearly complete loss of sternal bone, multiple fractured sternum, excessive overweight and insulin-dependent diabetes mellitus). In 8 patients (73%), sternal dehiscence was associated with infection and 3 patients (27%) presented a sterile sternal dehiscence.
Initial cardiac procedures included coronary artery bypass grafting (CABG, n = 6), aortic valve replacement (AVR, n = 2), CABG and carotid thromboendarterectomy (n = 1), CABG combined with AVR (n = 1), CABG combined with AVR and tricuspid valve repair with closure of persistent foramen ovale (PFO, n = 1). The initial heart operation was performed 173 ± 295 days (median 36 days) prior to sternal plate osteosynthesis. All patients had several comorbid factors (Table 1). Further baseline data are listed in Table 1.
Table 1:
Preoperative patient data
| Patient characteristics | All patients (N = 11) |
|---|---|
| Age (years) | 72 ± 7 |
| LVEF (%) | 47 ± 9 |
| Time from original heart operation to sternal plate refixation (days) | 173 ± 295 |
| Body mass index (kg/m2) | 31 ± 3 |
| Hypertension (%) | 100 (n = 11) |
| Dyslipidaemia (%) | 91 (n = 10) |
| Insulin-dependent diabetes mellitus (%) | 55 (n = 6) |
| COPD (%) | 18 (n = 2) |
| Renal failure (%) | 55 (n = 6) |
| Nicotine abuse (%) | 64 (n = 7) |
| Infectious sternal dehiscence (%) | 73 (n = 8) |
| Sterile sternal dehiscence (%) | 27 (n = 3) |
| Multiple sternal fractures (%) | 64 (n = 7) |
| Nearly complete sternectomy after previous debridement (%) |
27 (n = 3) |
| Previous standard rewiring (%) | 18 (n = 2) |
| Number of previous VAC therapiesa (n) | 3 ± 2 |
| VAC sponge change timesa (days) | 4 ± 1 |
Preoperative patient data presented as mean ± standard deviation, unless otherwise indicated.
LVEF: left ventricular ejection fraction; COPD: chronic obstructive pulmonary disease; VAC: vacuum-assisted closure.
aOnly patients with an infectious sternal dehiscence (n = 8).
The diagnosis of sternal dehiscence was made clinically and was confirmed by computed tomographic (CT) scan. In 64% of the patients, CT examination revealed multiple sternal fractures after median sternotomy.
In case of infectious sternal dehiscence (n = 8), swabs were taken and an antibiotic therapy was started, according to the bacterial sensitivity. A systematic wound debridement was performed, followed by recurrent pulse-jet lavage and vacuum-assisted closure (VAC) therapy (Table 1). Due to the existence of avital and instable bone tissue, extensive intraoperative sternal resection and/or partial costal resection were necessary in three patients (27.3%). We first decided to finish VAC therapy and continue with sternal reconstruction if the following criteria for wound sterility were given: advanced local signs of healing process like the formation of well-vascularized granulation tissue, negative bacteriological cultures and a decline in serological inflammatory parameters. Patients with previously sterile sternal dehiscence received our standard perioperative antibiotic regimen, including the administration of cefuroxime pre-, intra- and postoperatively.
After sternal reconstruction with the MSCS, patients were seen daily until hospital discharge revealing early signs of sternal instability or infection. Additional CT scans were done late postoperatively (3–12 months). Former CT examination was performed, if there was any suspicion of sternal infection and/or recurrent dehiscence. One patient declined a CT examination and 1 patient passed away on the 65th postoperative day before a CT scan was done.
RESULTS
The mean operation time was 165 ± 59 min. The mean extubation time was 4.7 ± 5.3 h and the mean ICU length of stay was 1 day (median) with a range from 1 to 23 days. Complete time from operation to hospital discharge was 9 days (median), ranging from 5 to 64 days. In 6 patients, sternal reconstruction using the MSCS was successful in achieving sternal restabilization. Sternal wound infection after reconstruction with the MSCS occurred in 6 patients (54.5%), in 5 of them early (13.2 ± 6.5 days) and in 1 patient late postoperatively (1058 days). Bacteriological investigation revealed isolated coagulase-negative Staphylococcus (CNS, n = 2), isolated Escherichia coli (E. coli, n = 1), E. coli and CNS (n = 1), CNS and Candida (n = 1) and Enterococcus faecalis in combination with Propionibacterium acne and CNS (n = 1). In 3 patients with postoperative wound infection, a previous infection had been the reason for the sternal dehiscence. In 1 of these 3 patients, bacteriological investigations revealed the same germ as had been found preoperatively (E. coli).
Due to sternal wound infection, hardware had to be removed in all patients (n = 6), in 5 patients within the first 46 days (early infection) and 1 after 1058 days (late infection). Intraoperative findings revealed a break in of all sternal cables in 1 patient (initially sterile dehiscence; Fig. 2) and parasternal costal avulsion in 2 other patients (n = 1 initially sterile dehiscence; n = 1 initially infectious dehiscence; Fig. 3). Explantation (n = 6) was followed by wound debridement, recurrent pulse-jet lavage, VAC therapy and antibiosis. Secondary wound closure with a pectoralis plasty was performed in 1 patient. The remaining patients (n = 5) showed a great substantial loss of bone and tissue, making a latissimus dorsi flap necessary. Another patient complained about plate-related pain, despite a solid sternum and the absence of infection. This made hardware removal necessary 715 days after reconstruction.
Figure 2:
(A) Postoperative CT scan showing sternal separation. (B and C) Break in of all multifilament cables (Courtesy of the German Heart Center Munich). CT: computed tomography.
Figure 3:
(A) Sufficient sternal refixation using the MSCS. (B) Parasternal costal avulsion postoperatively (Courtesy of the German Heart Center Munich). MSCS: Modular Sternal Cable System.
One patient died on the 65th postoperative day, as a consequence of severe right heart failure. This patient had initially received AVR, tricuspid valve repair and PFO closure. Sternal cable reconstruction was preceded by two failed attempts of standard rewiring due to sternal dehiscence. Seventeen days after successful cable reconstruction, the patient was transferred to a nearby hospital for further treatment. At the time of hospital discharge, sternal wound conditions were bland, showing no signs of infection or recurrent dehiscence.
The postoperative data are summarized in Table 2.
Table 2:
Intraoperative and postoperative patient data
| Patient characteristics | All patients (N = 11) |
|---|---|
| Operation time (min) | 165 ± 59 |
| Time of intubation (h) | 5 ± 5 |
| Stay on intensive care unit (days) | 5 ± 8 |
| Hospital discharge (days after operation) | 24 ± 26 |
| Sternal wound infection (%) | 55 (n = 6) |
| Need of hardware removal (%) | 64 (n = 7) |
| Due to wound infection (n) | 6 |
| Due to thoracic pain (n) | 1 |
| Time from sternal reconstruction to hardware removal (days) | 267 ± 435 |
Intra- and postoperative patient data presented as mean ± standard deviation, unless otherwise indicated.
DISCUSSION
Sternal dehiscence with or without infection is a rare but serious complication after median sternotomy [3]. Usually, sternal dehiscence without infection is treated by simple rewiring or in cases of poor bone tissue vitality, modified wire techniques may be applied, as described by Robicsek et al. [20]. In cases of a multiple fractured sternum or a widely resected sternal bone, other strategies have to be considered to achieve sternal stability, such as an extended osteosynthesis with plates and screws. One of the most applied systems is the Titanium Sternal Fixation System© (Synthes™, Switzerland), which has been described in the past by different authors [8–14]. This system consists of titanium unilock screws and different locking plates (e.g. sternal body plates, star-shaped and H-shaped plates as well as straight plates), which allow transversal and longitudinal plate reconstruction. Attaching the plate on the bone, the screw head locks securely into the threated plate hole. With this ‘locking mechanism’, the plate functions like an external fixator applied internally, providing stable fixation, even in complicated sternal dehiscence [15, 16]. In contrast, the MSCS (Synthes™, Switzerland) is a set of stainless steel implants without a locking mechanism (reconstruction plates, cables and cannulated screws), only allowing sternal refixation in a longitudinal fashion. However, the following theoretically advantages convinced us to work with this type of reconstruction system:
Longitudinal plate fixation allows immediate stabilization of multiple fractured fragments in case of widely resected or lost sternal bone [19]. This effect cannot be reached by transverse plate fixation.
Sternal approximation after longitudinal stabilization is achieved by using 4–9 flexible cables that perfectly adapt to the shape of the sternum, differing from other longitudinal fixation techniques, where sternal closure is achieved by wires or plate cross connections [16, 21]. This cable mechanism increases the force between broken segments, hypothetically leading to faster callus formation.
In combination with the cannulated screws as metal cannula for cable passage, the sternal bone is particularly reinforced, minimizing the risk of sternal cutting [19].
Theoretically, this should lead to a sufficient distribution of forces along the whole sternal area, making the MSCS a useful tool to treat patients with complicated sternal dehiscence [19].
The application of the MSCS is cumbersome and thus, prolongs the long operation time (165 ± 59 min). In comparison, our mean operation time after longitudinal and transversal plate fixation, using the Titanium Sternal Fixation System in a previous study, was 133 ± 21 and 110 ± 12 min, respectively [16]. This difference is mainly due to the more complex operative technique using plates, cannulated screws and cables, which are guided with a cable passer through the cannulated screws and the transverse holes of the plates (Fig. 1). Therefore, both sternal halves have to be dissected widely prior to fixation, which is time-consuming. The postoperative time on the intensive care unit (4.6 ± 7.7) and the total hospitalization time (24 ± 26 days) were comparatively long after sternal reconstruction with the MSCS [16]. This was mainly due to a high incidence of sternal wound infections (54.5%), the majority of them developing early after the operation. Sternal infection rates after reconstruction with the Titanium Sternal Fixation System have been reported to be lower, ranging from 2 to 18% in the literature [9, 11, 14, 16–18]. We also used the Titanium Sternal Fixation System in 15 patients with complicated sternal dehiscence. Here, sternal wound infection occurred in only 1 patient [16]. Sternal wound infection after reconstruction with the MSCS made hardware removal necessary in 63.6% of patients (n = 7). In the literature, the need for hardware removal after sternal plating has been reported between 8 and 45% [9–11, 14, 17, 18, 22, 23], mainly due to wound infection and plate-related pain.
Postoperative infections in our patients might have been boosted by the specific design of the MSCS. For example, the absence of a ‘locking mechanism’ made it necessary to attach the plates onto the whole sternum to achieve stable sternal fixation. This procedure may compress periosteal blood vessels, resulting in an inadequate bony blood supply. Additionally, sternal bone is hurt by each drilling mechanism. The cannulated stainless steel screws are bigger than those of other systems, causing a larger osseous damage. Also, the filament cables with their broad surface make a colonization of potential germs easier. These facts as well as the material texture itself, namely stainless steel, could influence postoperative wound healing. Cicilioni et al. [18] explained his low infection rate of 2.7% after sternal plate osteosynthesis by using ‘bacteriostatic’ titanium plates. Orthopaedic and trauma surgery studies showed the superiority of titanium over steel implants concerning the release of toxic and allergic ions and the resistance against bacterial infection [24, 25].
We believe that using specialized reconstruction systems for the treatment of complicated sternal non-union after median sternotomy is principally justified. However, on the basis of the high incidence of wound infections in our postoperative course, we decided against a further application of the MSCS. Our doubts about this system were confirmed as it was taken off the market only a short time later.
CONCLUSION
The MSCS initially convinced with its theoretical advantages, promising good results in the treatment of complicated sternal dehiscence. However, we observed a high incidence of sternal wound infection after reconstruction in most cases. We speculate that this complication might be inherent in the specific design of the MSCS. Our report may influence further developments of sternal reconstruction systems.
Conflict of interest: Bernhard Voss had a consultant agreement with Synthes GmbH from 2007 to 2009. He has been a consultant to Stryker Craniomaxillofacial since June 2015.
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