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Ann Thorac Surg 2004;77:2261-2262
© 2004 The Society of Thoracic Surgeons
Department of Cardiothoracic Surgery, Forum Health, Northside Medical Center, 500 Gypsy Lane, Youngstown, OH 44501, USA
Department of Cardiothoracic Surgery, Allegheny General Hospital, 320 E North Ave, Pittsburgh, PA 15212, USA
e-mail: udasika{at}forumhealth.org
e-mail: jmagouer{at}wpahs.org
To the Editor:
We thank Dr Losanoff and colleagues for their comments and interest in our report [1] that described increased separation occurring at the lower sternum as a result of increasing distracting forces to a sternal model. Our study demonstrated that sternal wire reinforcement at the lower portion resulted in less sternal distraction at correspondingly increasing distracting forces. The maximal lateral distraction force in this study was 400 newtons (N). As described in our article, lower sternal separation in the group that had an extra simple wire at the lower sternum, for a total of seven simple wires, showed a distraction of only 1.64 ± 0.39 mm at 400 N versus 4.92 ± 1.73 mm and 5.1 ± 1.43 mm in the two comparison groups tested (p = 0.003). This simulated sternal load exceeded forces described in an earlier report by McGregor and colleagues [2] revealing that a 2-mm distraction was achieved in the lateral direction at 220 ± 40 N. Cheng and co-workers [3] tested distracting forces up to 200 N on human cadaveric sternums using various methods of closure. In their report, closure with No. 5 stainless steel wire showed less distraction than closure with Mersilene ribbon or stainless steel band; their data revealed a distraction of 0.012 mm/N for stainless steel wire. We note the finding of Losanoff and colleagues that significant distraction occurred only at 800 N; however, several reports clearly have demonstrated that forces of less than 400 N can result in sternal distraction[2, 3].
We believe repetitive cycling loads should be tested, and more experiments can be carried out in the future. The finding of Losanoff and associates that separation occurred at the xiphoid end in their study further validates our model. The beauty of our mechanical model is that it allows several different variables and closing schemes to be tested in an economical and uniform fashion. This is a distinct advantage when there are subtle differences observed between biologic testing models.
The clinical implications of data accrued from the laboratory are the ultimate standard. In the past 12 months, one of us (U.K.D.) has followed a conscientious policy of rigid sternal fixation in patients weighing more than 70 kg. These patients have received Myo/Wire double-strand wire (A & E Medical Corporation/Alto Development Corporation, Farmingdale, NJ) and placement of additional wire reinforcement at the lower sternum. This has provided rigid sternal fixation and has virtually eliminated sternal wound dehiscence. This evidence closely mirrors the data and clinical outcomes published by Opie [4] and Stoney [5].
We applaud Dr Losanoff and colleagues, whose comments and data provide more information regarding the biomechanics of sternal closure. These concerted efforts translate to the ultimate goal of improved sternal-wound healing for our patients.
References
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