Biomechanical Effectivity Evaluation of Single- and Double-Metal-Bar Methods with Rotation and Equilibrium Displacements in Nuss Procedure Simulations.

Surgical treatment of the pectus excavatum has led to the introduction of the Nuss procedure, a minimally invasive surgical procedure that involves inserting a metal bar under the sternum through a small lateral thoracic incision. An additional metal bar was inserted in patients with pectus excavatum to improve the retention of the restored chest wall after the Nuss procedure. However, a need still exists to analyze the mechanistic advantages and disadvantages of the double-bar method owing to the increased surgical time and proficiency. The purpose of this study is to compare and evaluate the efficiency of single- and double-bar methods using rotational and equilibrium displacement simulations of the Nuss procedure. A finite-element model was constructed for two types of metal bars inserted into the chest wall. Boundary conditions for the rotation and equilibrium displacements were set for the metal bar. The anterior sternal translation, Haller index and maximum equivalent stress and strain owing to the behavior of the metal bar were estimated and compared with the single-bar method and postoperatively acquired patient data. The simulation results showed that the influences of the intercostal muscle and equilibrium after rotation displacement were significant. The stresses and strains were distributed across the two metal bars, and the upper-metal bar was heavily loaded. The double-bar method was advantageous regarding the load distribution effects of the two metal bars on the chest wall. However, mechanical assessments are also important because an excessive load is typically applied to the upper-metal bar.