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Ann Thorac Surg 2003;75:1618-1621
© 2003 The Society of Thoracic Surgeons

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Original article: general thoracic

Lower sternal reinforcement improves the stability of sternal closure

^a Department of Cardiothoracic Surgery, Allegheny General Hospital, Pittsburgh, Pennsylvania, USA

Accepted for publication December 12, 2002.

^* Address reprint requests to Dr Magovern, Department of Cardiothoracic Surgery, Allegheny General Hospital, 320 East North Ave, 14^th St, Pittsburgh, PA15212, USA
e-mail: jmagover{at}wpahs.org

	Abstract

Top Abstract Introduction Material and methods Data collection and statistical... Results Comment Conclusions References

 
BACKGROUND: This study uses a mechanical testing system to evaluate three methods of sternal closure.

METHODS: Twelve sternal replicas composed of a polyurethane foam bone analogue were divided in the midline and reapproximated using three stainless steel wire techniques: six simple wires (6S), six figure-of-eight wires (6F8), or seven simple wires (7S), which included an extra wire at the lower sternum. The closures were subjected to increasing lateral distraction from 0 to 400 Newtons (N) (1 N = 0.224 lbs), and motion was measured using transducers stationed across the manubrium, midsternum, and lower sternum.

RESULTS: With each method of closure, the manubrium was the most stable, the lower sternum the least stable, and the midsternum intermediate between the other two. There were also differences between sternal closure methods, but only at the lower sternum. Less sternal distraction was measured with the 7S than the 6S and 6F8 methods, starting at 100 N (0.20 ± 0.06 mm vs 0.48 ± 0.19 and 0.39 ± 0.10, p = 0.003), and progressively increasing until the study was stopped at 400 N (1.64 ± 0.39 mm vs 4.92 ± 1.73 and 5.1 ± 1.43 mm, p = 0.003).

CONCLUSIONS: These data show that the lower sternum is the site of greatest instability and that reinforcement of this area with an additional wire effectively stabilizes the closure. Figure-of-eight wires are not superior to simple wires.

	Introduction

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Median sternotomy for access to the heart and great vessels is a familiar and time-tested approach, but major morbidity occurs when dehiscence or mediastinitis develops. This occurs with an incidence of 0.5% to 2.5%, and results in considerable excess morbidity and mortality [1]. Various methods for sternal closure have been published, but most are based on practical experience rather than biomechanical testing.

This laboratory has published a biomechanical analysis of sternal closure, which demonstrated that physiologic levels of force were sufficient to cause minor sternal instability and that the lower aspect of the sternum was more prone to disruption than the manubrium [2]. We subsequently developed a sternal-closure testing model using a bone analogue, and validated this model against a human cadaver model [3]. This project was undertaken using the bone analogue model to compare two commonly used sternal closure techniques: interrupted simple wires versus interrupted figure-of-eight wires. In addition, we have tested the effect of additional reinforcement at the lower end of the sternum.

	Material and methods

Top Abstract Introduction Material and methods Data collection and statistical... Results Comment Conclusions References

 
Bench analyses were performed using 15 artificial sternal models molded from rigid polyurethane foam, a material commonly used as an alternative test medium for cancellous bone [4]. The sternal models were checked to ensure uniform size and weight before being divided equally among the three test groups. The models were manufactured by Sawbones Corporation, Pacific Research Labs, Inc (Vashon Island, WA) using foam densities of 20 lbs/ft³ to reproduce the pull-through properties observed in human cadaveric sterna [2]. The artificial sterna were transected using a reciprocating saw and reapproximated using No. 5 stainless steel sternal wire (US Surgical Corporation, Norwalk, CT ). Three methods of closure were evaluated: (1) six simple wires (6S); (2) six figure-of-eight wires (6F8); and (3) seven simple wires (7S) (Fig 1). In each method, the first wire was placed through the manubrium. In the 6S group, an additional five wires were placed around the sternum. In the 6F8 group, four additional figure-of-eight wires were placed in a parasternal location. The 7S group was the same as the 6S group, except that one additional wire was placed through the sternum at the sterni-xiphoid junction.

View larger version (136K): [in this window] [in a new window]   Fig 1. The three sternal wire configurations. The hatched area indicates the xiphoid process.

A set of three model LP804-01 linear potentiometers were used to measure sternal separation at the manubrium, midsternum, and xiphoid regions. Each potentiometer was securely mounted across the fissure using eyelet screws to fix both a transducer body and measurement arm. Signals were calibrated against a high-resolution linear positioner (Velmex, Inc, Bloomfield, NY) and displayed on a laptop computer using Windaq data acquisition software (Dataq Instruments, Akron, OH).

	Data collection and statistical analysis

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Sternal separation data were recorded at 20-N intervals of lateral traction force held steady for at least 10 seconds before data recording. Tests for significant differences among the three closure techniques (p < 0.05) were made at each sternal location using two-way analysis of variance. Correction for repeated measures was computed using Tukey’s HSD. All summary data are presented as mean ± SD.

	Results

Top Abstract Introduction Material and methods Data collection and statistical... Results Comment Conclusions References

 
The amount of sternal distraction at the manubrium, midsternum, and lower sternum was analyzed for each closure method. This showed significant differences at each location, with stability decreasing from the manubrium to the lower sternum. These findings are shown graphically in Figure 2.

View larger version (22K): [in this window] [in a new window]   Fig 2. Sternal separation as a function of distracting force for (A) six simple wires, (B) figure-of-eight wires, and (C) seven simple wires. Data are presented at means ± SD.

View larger version (19K): [in this window] [in a new window]   Fig 3. Comparison of sternal separation at the lower sternum with the three methods of wire closure. Data are presented as means ± SD.

	Comment

Top Abstract Introduction Material and methods Data collection and statistical... Results Comment Conclusions References

There is no consensus among surgeons on the optimal method for sternal closure. Many techniques have been described, including various wiring configurations, mersiline tapes, and nylon bands. For the most part, surgeon preferences are based on personal experience rather than scientific analysis [5–11]. This study shows no difference between simple wires and figure-of-eight wires with regard to sternal stability. This has also been reported by several other authors who have done mechanical analysis of closure techniques [12]. Many surgeons believe that figure-of-eight wires provide better stability, but there is no scientific demonstration of this in the literature. Recently, rigid internal fixation with specifically designed hardware has been described and recommended. This approach has been universally adopted in orthopedics and cranio-facial surgery, but has not been popular in cardiac surgery, probably because of the increased time required for internal fixation, and concern that these methods will hinder rapid reentry [7].

Fundamental to this controversy is a lack of information on the mechanical forces that can disrupt or retard sternal union. This study shows that distracting forces are not equally born by all regions of the sternum and that the lower sternum is especially susceptible to dehiscence, a situation that can be readily addressed by reinforcement of the closure in this region. It follows that the materials and configurations are probably less important than recognition of anatomic and mechanical considerations. The key issue is to fully stabilize the sternum, especially the lower end, to insure reliable healing. This can be done with plates, but also with the use of additional wires.

The relative instability of the lower sternum can be explained by several anatomic factors. During normal respiration, the abdomen and lower thorax move a greater distance than the upper thorax. In addition, ribs 7 through 10 all attach to the seventh costal cartilage at the lower sternum, a situation that tends to concentrate forces at this region. Other factors that may contribute include the greater transverse and anterior-posterior dimensions of the lower versus upper thorax and the reduced thickness of the lower sternum in comparison with the manubrium.

Optimal sternal wound healing is the result of many factors, but the most important is a secure closure. Additional factors such as acuity of surgical procedure, cigarette smoking, obesity, hypertension, interior mammary artery utilization, diabetes, and prior sternotomy increase the incidence of wound complications, but may be less important than mechanical instability [13]. In most instances, sternal wound infection is precipitated by sternal instability rather than the other way around. Increased attention to the lower end of the sternum by means of additional wires or rigid internal fixation should reduce the morbidity of the midline sternotomy incision.

	Conclusions

Top Abstract Introduction Material and methods Data collection and statistical... Results Comment Conclusions References

 
These data show that the lower sternum is a site of potential instability and that reinforcement of this area significantly stabilizes the closure. The clear implication is that more wires, especially at the lower aspect of the sternum, will reduce the complication rate of sternal closure. Figure-of-eight wires provide no improvement in sternal stability in comparison to simple wires.

	References

Top Abstract Introduction Material and methods Data collection and statistical... Results Comment Conclusions References

 

1. Casha A.R., Yang L., Kay P.H., Saleh M., Cooper G.J. A biomechanical study of median sternotomy closure techniques. Eur J Cardiothoracic Surg 1999;15:365-369.[Abstract/Free Full Text]
2. McGregor W.E., Trumble D.R., Magovern J.A. Mechanical analysis of midline sternotomy wound closure. J Thorac Cardiovasc Surg 1999;117:1144-1150.[Abstract/Free Full Text]
3. Trumble D.R., McGregor W.E., Magovern J.A. Validation of a bone analog model for studies of sternal closure. Ann Thorac Surg 2002;74:739-745.[Abstract/Free Full Text]
4. Szivek J.A., Thomas M., Benjamin J.B. Characterization of a synthetic foam as a model for human cancellous bone. J Appl Biomater 1993;4:269-272.[Medline]
5. Cheng W., Cameron D.E., Warden K.E., Fonger J.D., Gott V.L. Biomechanical study of sternal closure techniques. Ann Thorac Surg 1993;55:737-740.[Abstract]
6. Ozaki W., Buchman S.R., Iannettoni M.D., Frankenburg E.P. Biomechanical study of sternal closure using rigid fixation techniques in human cadavers. Ann Thorac Surg 1998;65:1660-1665.[Abstract/Free Full Text]
7. Hendrickson S.C., Koger K.E., Morea C.J., Aponte R.L., Smith P.K., Levin L.S. Sternal plating for the treatment of sternal nonunion. Ann Thorac Surg 1996;62:512-518.[Abstract/Free Full Text]
8. Goodman G., Palatianos G.M., Bolooki H. Technique of closure of median sternotomy with trans-sternal figure-of-eight wires. J Cardiovasc Surg (Torino) 1986;27:512-513.[Medline]
9. Taber R.E., Madaras J. Prevention of sternotomy wound disruptions by use of figure-of-eight pericostal sutures. Ann Thorac Surg 1969;8:367-369.[Medline]
10. Robicsek F., Daugherty H.K., Cook J.W. The prevention and treatment of sternum separation following open-heart surgery. J Thorac Cardiovasc Surg 1977;73:267-268.[Abstract]
11. Sirivella S., Zikria E.A., Ford W.B., Samadani S.R., Miller W.H., Sullivan M.E. Improved technique for closure of median sternotomy incision: mersilene tapes versus standard wire closure. J Thorac Cardiovasc Surg 1987;94:591-595.[Abstract]
12. Casha A.R., Ashraf S.S., Kay P.H., Cooper G.J. Routine sternal closure using interlocking multitwisted wires. Eur J Cardiothoracic Surg 1999;16:353-355.[Abstract/Free Full Text]
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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): Uday K. Dasika James A. Magovern Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Dasika, U. K. Articles by Magovern, J. A. Search for Related Content PubMed PubMed Citation Articles by Dasika, U. K. Articles by Magovern, J. A. Related Collections Chest wall