Biomechanical Comparison of Wire Circlage and Rigid Plate Fixation for Median Sternotomy Closure in Human Cadaver Specimens

Abstract

Background:Over 700,000 patients per year undergo open-heart surgery. Healing complication rates can be up to 5% of patients who undergo this procedure, with a morbidity rate of 50% if mediastinitis supervenes. A secure and rigid fixation of surgically divided sternum is critical to avoid healing complications. The purpose of this study was to compare the yield load, construct stiffness, ultimate load, displacement at ultimate load, and post-yield behavior of three sternotomy closure methods (Peristernal wires or Sternalock titanium plates) when stressed in each of three directions: lateral distraction, rostro-caudal (longitudinal) shear distraction, and anterior-posterior (transverse) shear in a cadaveric model. Methods:Forty-two fresh cadaver models were divided into three test groups: group A, B, and C. A cardiothoracic surgeon divided each cadaveric sternum longitudinally and repaired peristernal wires or one of two Sternalock configurations. Tests were performed using a materials testing system that applied force at a constant displacement rate in a uniaxial direction until the construct catastrophically failed. Mechanical behavior was monitored using a 3D texture correlation system to create a real-time three-dimensional representation of strain directions. The resulting displacement pattern is analogous to a finite element contour plot of displacements, Lagrange Strain, or velocity. Statistical analysis was used to show the different mechanical properties of each closure method. Results:When loaded in lateral distraction, both Sternalock configurations surpassed the rigidity of peristernal wires by 600%. Some evidence was also found linking Sternalock with stiffer behavior in the rostro-caudal direction. Though not statistically significant, a trend was observed showing that constructs using the Sternalock also had higher yield loads, as well as, less post-yield displacement when compared to peristernal wires. Conclusions:Data gathered showed the superior performance of the Sternalock system in stiffness in both longitudinal distraction and rostro-caudal shear. Implications for use of the Sternalock system are faster healing times, lower complication rates, and success of the procedure.