Ann Thorac Surg 2005;80:968
© 2005 The Society of Thoracic Surgeons
Original article: Cardiovascular
Invited commentary
Julian E. Losanoff, MD
Department of Surgery, MC 5026, Room J 517, University of Chicago, 5841 South Maryland Ave, Chicago, IL 60637
(Email: jelosanoff{at}yahoo.com).
The report by Pai and colleagues [1] documents significantly reduced lateral motion using wire fixation in a polyurethane bone model. This and other previously published biomechanical studies of median sternotomy closure suggest that standardized nonbiologic sternal analogues are inexpensive and obviate the variability of bone density, size, thickness, shape, and geometry common among biologic specimens. It should be noted, however, that only detailed biomechanical comparisons between human cadaveric and bone analogue sterna can show whether the manufactured material adequately replicates all features of the biologic tissues. Well-supported conclusions about one or the other method’s superiority have not yet been established.
The authors have not discussed in much detail the results of an earlier in vivo trial comparing cerclage wires and compression plates in skeletally mature baboons. The study showed that rigid fixation resulted in earlier osseous union at 4 weeks, and no clinical difference between the treatment groups at 8 weeks [2]. The results of this and several clinical studies [3–5] suggest that the plates provide greater inherent stability. The limited study enrollment, short follow-up, and variability in internal fixation methods preclude definitive conclusions about their superiority over more established wire closure methods, however [6].
Pai and colleagues [1] observed that plates provided more stable fixation in the xiphoid region, where the largest separation typically occurs [7]. It remains unclear whether plates positioned at the xiphoid process provide equivalent support in living patients, in whom the region is primarily cartilaginous.
The authors’ conclusions are based entirely on biomechanical analysis of static traction forces; it is uncertain whether their model would respond differently if tested under repetitive loads. The forces used in the Pai study ruptured sternal union at 200–400 N (Newtons). These findings are not consistent with the results of available human cadaveric trials. A German median sternotomy study using increasing traction found that wires cut through the bones at forces between 390 and 490 N [8]; a more recent trial using repetitive cycling loads found that even at 800 N, the wires did not typically cut through or fracture sterna [6].
Pai and colleagues [1] show that sternal plating provides a more stable union than cerclage wires in polyurethane sterna models stressed by a static traction. Future studies comparing the biomechanical behavior of the plates in biologic and non-biologic sterna, and using repetitive cycling loads that more closely approximate breathing and coughing, can be expected to authoritatively establish the best models for biomechanically testing this and other median sternotomy closure techniques.
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- Pai S, Gunja NJ, Dupak EL, et al. In vitro comparison of wire and plate fixation for midline sternotomies Ann Thorac Surg 2005;80:962-968.[Abstract/Free Full Text]
- Sargent LA, Seyfer AE, Hollinger J, Hinson RM, Graeber GM. The healing sternuma comparison of osseous healing with wire versus rigid fixation. Ann Thorac Surg 1991;52:490-494.[Abstract]
- Hendrickson SC, Koger KE, Morea CJ, Aponte RL, Smith PK, Levin LS. Sternal plating for the treatment of sternal nonunion Ann Thorac Surg 1996;62:512-518.[Abstract/Free Full Text]
- Song DH, Lohman RF, Renucci JD, Jeevahandam V, Raman J. Primary sternal plating in high-risk patients prevents mediastinitis Eur J Cardiothorac Surg 2004;26:367-372.[Abstract/Free Full Text]
- Cicilioni OJ, Stieg FH, Papanicolaou G. Sternal wound reconstruction with transverse plate fixation Plast reconstr Surg 2005;115:1297-1303.[Medline]
- Losanoff JE, Collier AD, Wagner-Mann CC, Richman BW, Huff H, Hsieh F, Diaz-Arias A, Jones JW. Biomechanical comparison of median sternotomy closures Ann Thorac Surg 2004;77:203-209.[Abstract/Free Full Text]
- Dasika UD, Trumble DR, Magovern JA. Lower sternal reinforcement improves the stability of sternal closure Ann Thorac Surg 2003;75:1618-1621.[Abstract/Free Full Text]
- Schade K, Greve H. refixation of the sternum after median sternotomyexperimental investigations of its stability. Langenbecks Arch Chir 1989;374:20-24.[Medline]
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References