Evaluation of sternum closure methods by means of a nonlinear finite element analysis.

The main purpose of this study is to develop a validated three-dimensional finite element model of sternum closure techniques. For this aim, the finite element method analysis results of three closure methods were compared with experimental test results. Also, three more closure techniques are simulated numerically to study the effect of the number of wires used in the manubrium and xiphoid regions. A three-dimensional model of polyurethane sternum foam was created based on computed tomography images. Six different closure techniques using steel wire, steel bands and ZipFix bands were modeled on the sternum and transferred into a three-dimensional finite element model. The sternum was modeled as an isotropic bilinear-elasto-plastic material, and nonlinear contact conditions were applied. The models were analyzed under lateral distraction loading, and load-displacement curves were obtained from displacements at the incision line. Allowable loads and stiffness values of the methods were evaluated from these curves. The results showed the importance of the including material as well as geometric nonlinearities in the simulations to obtain realistic results from the numerical analyses. Also, the analyses showed that closures that include steel or ZipFix bands are superior to conventional wiring, and addition of a single wire at the manubrium and xiphoid regions significantly improved the efficiency of the closure techniques.

A biomechanical study of 4 different sternum closure techniques under different deformation modes.

OBJECTIVES: This study experimentally compares the efficiency of the 4 most preferred sternal closure tehniques, in 3 different deformation modes of the chest. METHODS: Polyurethane sternum models fixed by conventional wiring, steel band, ZipFix band and figure-8 wiring are tested statically under lateral distraction, longitudinal shear and torsional deformation modes. As a result, load-deformation curves are obtained. The closure efficiency of the techniques is then compared with respect to allowable load (corresponding to 2 mm displacement), rigidity, rupture load and rupture displacement. A comparison in terms of cost and ease of application has also been presented. RESULTS: The highest allowable load and rigidity values in simple tension and longitudinal shear are obtained by the steel and ZipFix band techniques, respectively. In torsion mode, the highest allowable load is provided by the ZipFix band and the highest rigidty is attained by the steel band technique. The highest rupture loads under simple tension, longitudinal shear and torsion modes are observed in ZipFix, steel band and conventional wiring, respectively. Steel band closure provides the least rupture displacement in simple tension as well as torsion, whereas ZipFix bands give the smallest rupture displacements in longitudinal shear. However, in every loading mode there were no statistically significant differences in allowable load, rigidity and rupture load values between the closure methods, and only rupture displacement values were statistically different for each method. CONCLUSIONS: Our results showed that conventional wiring is the most advantageous closing method when compared to the others.