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Eur J Cardiothorac Surg 2004;26:367-372
© 2004 Elsevier Science NL

Primary sternal plating in high-risk patients prevents mediastinitis

^a Department of Surgery, Sections of Plastic and Reconstructive Surgery, University of Chicago, MC 5040, 5841 South Maryland Ave, Chicago, IL 60637, USA
^b Department of Cardiac and Thoracic Surgery, University of Chicago, MC 5040, 5841 South Maryland Ave, Chicago, IL 60637, USA

Received 22 October 2003; received in revised form 13 April 2004; accepted 16 April 2004.

^* Corresponding author. Tel.: +1-773-834-2807
e-mail: jraman{at}surgery.bsd.uchicago.edu

	Abstract

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Summary Appendix A. Conference... References

 
Objective: Sternal wound infection leading to post-operative mediastinitis is a devastating complication of cardiac surgery carrying nearly a 15% mortality rate despite current treatment methods. Instability of bone fragments pre-disposes a patient to have non-union, mal-union and can subsequently lead to deep sternal wound infections progressing to mediastinitis. Rigid plate fixation has been utilized for acquired and surgically created fractures of virtually every bone in the body to prevent instability. However, the current standard for sternotomy closure remains the method of wire-circlage. Application of rigid plate fixation for sternal osteotomies affords greater stability of the sternum. We report on our preliminary experience with this technique in high-risk patients. Methods: From July of 2000 to December 2001, rigid plate fixation was applied to 45 patients designated as having high risk for sternal dehiscence and subsequent mediastinitis. High risk was defined as patients having 3 or more established historical risk factors, including: COPD, Re-Operative Surgery, Renal Failure, Diabetes, Chronic Steroid Use, Morbid Obesity, Concurrent Infection and Acquired or Iatrogenic Immunosuppression. Intra-operative risk factors included off-midline sternotomy, osteoporosis, long cardio-pulmonary bypass runs (>2 h), transverse fractures of the sternum. Rigid plate fixation was performed using a combination of plates secured by bi-cortical screws, after the cardiac surgical procedure was complete and hemostasis was secured. Results: Rigid plate fixation was performed on 26 males and 19 females. The average age of patients was 63 (43–88) years. The average follow-up was 15 weeks (range 8–41 weeks). While there were 4 peri-operative deaths unrelated to sternal closure: one from aspiration pneumonia (post-operative day 9), one from a pulmonary embolus (post-operative day 29), one from overwhelming sepsis from pre-existing endocarditis (post-operative day 15), and one for primary respiratory failure (post-operative day 12). All others healed successfully. One patient who had a sterile dehiscence subsequently underwent successful re-operative rigid fixation. Comparing the cohort of patients who received rigid plate fixation to a matched population of high-risk patients during a similar time period who received wire closure, revealed a significant difference in the incidence of post-operative mediastinitis. The wire closed group (n=207) had 18 deaths unrelated to sternal closure and had 28 patients who developed mediastinitis (14.8%). The rigid plate fixation group had no mediastinitis (Fisher's exact test, P=0.006). The total incidence of post-operative mediastinitis during the designated study period was 4.2%. Conclusion: Patients who benefited from sternal closure with rigid plate fixation showed a significant decrease in the incidence of post-operative mediastinitis when compared to similar population of patients whose sterna were closed with wire.

Key Words: Sternum • Plating • Rigid fixation • Mediastinitis

	1. Introduction

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Summary Appendix A. Conference... References

 
Median sternotomy is the preferred method of access for cardiac surgeons and in 2001, nearly 760,000 operations were performed in the United States [1]. While access and exposure are excellent for surgery, infectious complications leading to post-sternotomy mediastinitis are extremely morbid and the mortality rate can be as high as 15% [2]. Methods for preventing post-sternotomy mediastinitis have included different prophylactic measures including antibiotic therapy and various means of skin closure, but few have focused on rigid osseous fixation as a means for preventing infection despite experimental evidence to support it [3].

Since Julian re-introduced Milton's (1897) operation of median sternotomy in 1957 [4], numerous methods for sternal osteosynthesis have been described but despite evidence of the superiority of rigid plate osteosynthesis, the current standard for sternal closure remains circlage wire fixation. Due to the proven merits of increased stability and decreased incidence of non-union, mal-union and infection, the principles of rigid fixation have caused paradigm shifts away from wire fixation of bone for maxillofacial surgeons and more recently neurosurgeons. Circlage fixation under normal physiologic loads can prove to be inadequate and can lead to separation [5]. Bacterial contamination in the face of sternal separation and instability can then progress to deep sternal wound infections and mediastinitis. Effective rigid osteosynthesis of the sternum may prevent post-sternotomy mediastinitis from occurring by affording greater stability and promoting primary healing of the sternum.

We therefore adopted this technique of rigid plate fixation, by modifying plates that were used in mandibular fixation. Our experience with prophylactic use of this technique in high-risk patients is described.

	2. Materials and methods

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Summary Appendix A. Conference... References

 
A retrospective analysis from July 2000 through December 2001 was performed on patients who received primary rigid plate fixation after sternotomy. Forty-five consecutive patients designated as having high-risk for the development of post-sternotomy mediastinitis received primary rigid plate fixation. High-risk was defined as patients having 3 or more established historical risk factors [6].

2.1. Pre-operative risk factors included
Chronic Obstructive Pulmonary Disease, Re-Operative Surgery, Renal Failure, Diabetes, Chronic Steroid Use, Morbid Obesity (BMI>30), concurrent infection and acquired or iatrogenic immunosuppression.

2.2. Intra-operative risk factors included
Off mid-line sternotomies, osteoporosis, long cardio-pulmonary bypass runs (of greater than 2 h) and transverse fractures of the sternum. Cardiac surgeons selected all patients and rigid plate fixation was applied immediately after the cardiac procedure instead of wire-circlage.

Patients were followed up clinically and their sternal wounds assessed both during their hospital stay and in the outpatient follow-up setting. Patients were followed by the cardiac surgical team and managed irrespective of the sternal closure. Criteria for discharge and routine follow-up care did not vary. Successful sternal closure was defined by physical exam devoid of instability, pain, wound healing complications and radiographs showing unchanged location of hardware for a minimum of 8 weeks.

A biostatistician using SAS software performed the statistical analysis. Fischer's exact test was used to assess statistical significance and a P value of <0.05 was considered significant.

2.3. Surgical technique
Immediately after the cardiac surgical procedure, the 2 sternal halves are closely inspected by reflecting the pectoralis major muscle to the sterno-costal junction on both sides (Fig. 1) . This exposure allows identification of any transverse fractures and affords precise measurement of the thickness of the sternum from manubrium, to xyphoid. This direct measurement then dictates the length of the drill bit, depth of drilling and screw placement for each respective region of the sternum, thus precluding the need for a depth gauge while allowing for precise and safe drilling of both cortices.

View larger version (129K): [in this window] [in a new window]   Fig. 1. Reflection of pectoralis major muscle off the sternal surface.

View larger version (128K): [in this window] [in a new window]   Fig. 2. Reduction of the sternal halves and anatomic alignment.

View larger version (113K): [in this window] [in a new window]   Fig. 3. Completed sternal closure secured with plates.

View larger version (141K): [in this window] [in a new window]   Fig. 4. Post-operative chest X-ray of a patient with titanium plate sternal fixation.

	3. Results

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Summary Appendix A. Conference... References

There was no incidence of mediastinitis in this group.

During the same study period, analysis of a similar cohort of high-risk patients (group B) showed a total of 207 patients who were closed with standard wire-circlage. The age, gender, risk factor distribution was very similar to the study group. Within this group, there were 18 deaths unrelated to sternal circlage closure and 28 (14.8%) patients who developed post-sternotomy mediastinitis as defined by deep sternal wound cultures and systemic sepsis. All of these patients required surgical debridement, sternectomies and pectoral muscle flap closure. Of the 18 deaths in group B, 2 were attributed to post-sternotomy mediastinitis. The total number of adult cardiac procedures during the study period was 671 and the total incidence of post-sternotomy mediastinitis was 4.2%. No patients receiving rigid plate fixation (group A) developed post-sternotomy mediastinitis (Fisher's exact test, P=0.006). Post-operative deaths were not excluded when this analysis was made. A log rank test was not used because of the relatively small number of patients in the study group and the disparate nature of the groups. This was based on the advice of the consulting statistician.

	4. Discussion

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Summary Appendix A. Conference... References

 
While definitive and effective strides have been made in the management of post-sternotomy mediastinitis, few proven measures have been developed for its prevention. Existing modalities focus on adjunct methods to prevent bacterial contamination from both the surgical team and the patient [7]. Focusing on a more stable and successful technique of sternal osteosynthesis in an effort to prevent complications has been cited but most revolve around a different pattern of wire circlage or various non-rigid methods of closure [8]. Rigid plate fixation of the sternum, although not new, has not been embraced as the choice method of sternal osteosynthesis for various reasons. Drilling near and around the heart, added time and expense, the difficulty of emergent re-entry and the availability of a simple and effective plating system have all been obstacles to the development and institution of proven technology to the cardiac surgical arena.

One obstacle for the acceptance of rigid plate fixation to the sternum has been the logistics of drilling into the sternum and the inherent risks to the heart and bypass conduits. Measuring the thickness of the sternum from manubrium down to xyphoid has served as a precise guide from choosing the length of the drill bit, to engaging both cortices with screw placement. Unique to this technique is the fact that a depth gauge is not necessary as the sternotomy itself allows for direct visualization and measurement of the thickness of the bone. The drill bit is 1.5 mm in diameter allowing for the 2.4 mm screws to fit snuggly into the cancellous bone. A further layer of safety is intrinsic to this technique as each drill bit has a stop and the drill guide also stops one from over-drilling.

A second obstacle has been the issue of emergent re-entry into the mediastinum for hemorrhage. The SternaLock^® plates are specifically designed to be cut in the middle with standard wire cutters found in any re-entry tray without sacrificing the stability and integrity of the plates themselves. Salvage of the closure can then be performed with new plates and without re-drilling by exchanging the 2.4 mm screws for 2.7 mm emergency screws. These plates are made of titanium and do not interfere with magnetic resonance imaging. However, they are clearly radio-opaque and readily visible on any kind of X-ray imaging.

A third obstacle to wide acceptance has been the cost of hardware placement and the additional time it takes to implant hardware. At our institution, the average additional hospital charge for patients suffering from post-sternotomy mediastinitis is just over $500,000. Prevention of post-sternotomy complications not only can be fiscally sound, more importantly it can potentially decrease morbidity and mortality associated with this complication. The cost of the plates ranges from $700 to about $1400 depending on the number of plates and screws used. Finally, the additional 15–20 min required for rigid plate fixation to be applied can be negligible when global patient care is considered.

While effective and efficient plating systems for many other bones abound, a plating system specifically designed for the sternum has to date not been described. Previous attempts at rigid plate fixation of the sternum have employed mandibular reconstruction plates or fracture mini-plates with some success, but issues of emergent re-entry and accurate precision placement were not addressed [9]. Furthermore, fashioning mandibular reconstruction plates for the sternum was cumbersome and time consuming as each plate had to be cut specifically for each region of the sternum. Finally, drilling with drill bits designed for the mandible did not afford the controlled precision drilling needed to provide safety.

The benefits of rigid plate osteosynthesis have caused paradigm shifts away from wire fixation for orthopedic and plastic surgeons over twenty years ago. More recently, neurosurgeons have adopted plate fixation of bone flaps in the past five years. However, cardiac surgeons are the only surgeons who continue to provide bone fixation with wire-circlage. Ironically, cardiac surgeons perform the sternotomy, which is most common osteotomy worldwide on a daily basis. Yet, as a group we have not adopted the state-of-the art technique in stabilizing this osteotomy. In the setting of a surgically created osteotomy or fracture treatment, a failure rate even below 5% might be considered unacceptable but may be tolerated by the patients. However, in the setting of the sternotomy, this failure rate may have devastating complications such as non-union, persistent pain and deep sternal wound infection.

Complications of median sternotomy have been reported ever since the early and widespread adoption of this common technique [10]. Sternal stability has always been regarded as essential for normal healing of these wounds. There was a report from our unit in 1994, on the use of rigid internal fixation in post-operative mediastinitis, with bony union being achieved in over 90% of patients [9]. Others have used plates to provide a template for more rigid fixation [11] in sternal dehiscence. Cyano-acrylate glue has been used in mediastinitis even with the risk of toxicity in an attempt at improving sternal stability [12]. Negri and co-workers evaluated a new technique using thermo-reactive clips that seemed to improve the rate of wound infection but did not eliminate it [13].

Our approach was to use the best existing techniques of osteotomy closure and adapting them to the sternal situation. Application of this in a high-risk population with a historically high rate of complications seemed like the logical next step in evaluating our hypothesis. This preliminary report highlights the fact that rigid plate fixation can dramatically reduce and hopefully eliminate sternal dehiscence. This may help reduce the incidence of deep sternal wound infection dramatically.

	5. Summary

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Summary Appendix A. Conference... References

 
A safe, efficient and effective technique for rigid plate fixation of the sternum is outlined. Experience in this technique of rigid sternal osteosynthesis has shown a dramatic reduction in complications associated with sternal instability including post-sternotomy mediastinitis.

	Acknowledgments

 
The authors would like to acknowledge the contribution of Ms Lan Ting Dai, constultant statistician at the University of Chicago.

	Footnotes

 
Presented at the joint 17th Annual Meeting of the European Association for Cardio-thoracic Surgery and the 11th Annual Meeting of the European Society of Thoracic Surgeons, Vienna, Austria, October 12–15, 2003.

	Appendix A. Conference discussion

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Summary Appendix A. Conference... References

 
Dr B. Buxton (Heidelberg, Victoria, Australia): Tell me about hemostasis with this technique. Do you avoid bone wax and Gelfoam or any of the other factors during the compression before you plate the bone?

Dr Raman: We didn't use anything specific. We always used Gelfoam on sternal edges that are very vascular, but we actually bring the bone edges together and you actually get a very nice anatomic reduction.

You don't see the traditional areas of bleeding, which are often the wire related bleeding that you see around the sternal edges, with this technique. The difference is very dramatic because if you have to take someone back for bleeding and coagulopathy, often you have bleeding from around the wire sites. You don't see that with these sternal plates because the screws go into pre-drilled holes and the screws actually lock those holes very nicely and you don't see that traditional wire-related bleeding. If the sternal cut edge is actually very vascular, we do use either bone wax or Gelfoam, but none of that is routine. We use what is suitable for each patient. We have actually had very nice results with not too much bleeding with this technique.

And at the end of the procedure we actually make sure that we leave a small drain anterior to the sternum just to vacate any hematomas that might form around the screw tops.

Dr Buxton: Do you have any trouble with the screws that are placed in the lower part of the sternum where it is relatively weak? In other words, do the screws cut through the bone in the lower segment?

Dr Raman: No, the screws tend not to cut through. I was very skeptical, and I must preface all my comments by actually acknowledging the pioneer of this technique, Dr David Song our plastic surgeon who actually did all the work and convinced us to change our ways, and he is in the audience. I was very reluctant to adopt this technique, initially. We always used wire at least to try and bring the sternal edges together, and I found that with a very weak sternum, the wire tended to cut through the sternum a lot more than the plates or the screws. As long as you have sternum that is reasonably strong, (it doesn't have to be too strong), you can use it even in osteoporotic bone, and you get the reduction with these bone-reducing forceps, you can actually use screws very safely. And there are different sizes of screws. You can use screws which are as small as 8 mm in depth or you can go up to 14 mm in depth. So based on the thickness of the sternum, you can actually tailor your screws and get a very precise way of screwing the plate onto the sternum.

Dr G. Rizzoli (Padova, Italy): If you need to make an emergency re-entrance, how long does it take to get to the heart?

Dr Raman: We have now got an institutional experience of over 200 patients that have been plated. We have had to go back on five of them. And I don't know if you noticed, but the middle portion of the plates are very easy to cut through, and it is actually a lot quicker to cut through these than the traditional wires because you don't have to pull them out. You just cut through these things and the sternum will come apart very quickly.

	References

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Summary Appendix A. Conference... References

 

1. American Heart Association Statistics for Cardiac Procedures 2001: www.americanheart.org/downloadable/heart/HDSStatsBook.
2. Gummert J.F., Barten M.J., Hans C., Kluge M., Doll N., Walther T., Hentschel B., Schmitt D.V., Mohr F.W., Degeler A. Mediastinitis and cardiac surgery—an updated risk factor analysis in 10,373 consecutive adult patients. Thorac Cardiovasc Surg 2002;50(2):385.[CrossRef][Medline]
3. Krischak G.D., Janousek A., Wolf S., Augat P., Kinzl L., Claes L.E. Effects of one-plane and two-plane external fixation on sheep osteotomy healing and complications. Clin Biomech 2002;17(6):470-476.[CrossRef][Medline]
4. Dalton M.L., Connally S.R., Sealy W.C. Julian's re-introduction of Milton's operation. Ann Thorac Surg 1992;53(3):532-533.[Abstract]
5. Trumble D.R., McGregor W.E., Magovern J.A. Validation of a bone analog model for studies of sternal closure. Ann Thor Surg 2002;74(3):739-744.[Abstract/Free Full Text]
6. Gosolow L.M., Wagner J.D., Felley M., Sharp T., Havlik R., Sood R., Coleman J.J. Risk factors for predicting surgical salvage of sternal wound-healing complications. Ann Plast Surg 1999;43(1):30-35.[Medline]
7. Usry G.H., Johnson L., Weems J.J., Jr, Blackhurst D. Process improvement plan for the reduction of sternal surgical site infections among patients undergoing coronary artery bypass graft surgery. Am J Infect Control 2002;30(7):434-436.[CrossRef][Medline]
8. Tavilla G., van Son J.A., Verhagen A.F., Lacquet L.K. Modified Robicsek technique for complicated sternal closure. Ann Thorac Surg 1991;52(5):1179-1180.[Abstract]
9. Gottlieb L.J., Pielet R.W., Karp R.B., Krieger L.M., Smith D.J., Deeb G.M. Rigid internal fixation of the sternum in post-operative mediastinitis. Arch Surg 1994;129(5):489-493.[Abstract]
10. Grmoljez P.F., Barner H.H., Willman V.L., Kaiser G.C. Major complications of median sternotomy. Am J Surg 1975;130(6):679-681.[CrossRef][Medline]
11. Chase C.W., Frankling J.D., Guest D.P., Barker D.E. Internal fixation of the sternum in median sternotomy dehiscence. Plast Reconstr Surg 1999;103(6):1667-1673.[Medline]
12. Ogus T.N., Hulusi U.M., Cicek S., Ozkan S., Yuksel O.O., Isik O. Sternal cyanoacrylate gluing in mediastinitis. Effects on infection, stability and bone healing. J Cardiovasc Surg 2002;43(5):741-746.[Medline]
13. Negri A., Manfredi J., Terrini A., Rodella G., Bisleri G., El Quarra S., Muneretto C. Prospective evaluation of a new sternal closure method with thermoreactive clips. Eur J Cardiothorac Surg 2003;22(4):571-575.

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Valluvan Jeevanandam Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Song, D. H. Articles by Raman, J. Search for Related Content PubMed PubMed Citation Articles by Song, D. H. Articles by Raman, J. Related Collections Chest wall Mediastinum Cardiac - other