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.