Biomechanical study of sternal closure techniques

Abstract

Median sternotomy is the most commonly used incision in cardiothoracic surgery. Closure of this incision is usually performed with parasternal wires, but alternate techniques have been proposed to improve closure stability. This study compares biomechanical stability of standard wire (No. 5 stainless steel) with that of three types of band closure: 5-mm Mersilene ribbon, 5-mm stainless steel band, and 5-mm plastic band. Eight bisected cadaver sterna were reapproximated using each method of sternal fixation and tested for biomechanical stability using an MTS Bionix 858 Biomechanical Tester. Loads of 50, 100, 150, and 200 Newtons (1 Newton = 1 kg.m/s2) were applied as a distracting force across the closure. A linear regression line of displacement as a function of increasing load was determined for each closure method; the slope of this line is inversely proportional to fixation stability. Displacement and load correlated linearly for each closure (r = 0.99). Mean slopes were 0.012 mm/Newton (95% confidence limits, 0.0098 to 0.0142 mm/Newton) for No. 5 stainless steel wire, 0.014 mm/Newton (95% confidence limits, 0.0118 to 0.0162 mm/Newton) for plastic band, 0.017 mm/Newton (95% confidence limits, 0.0148 to 0.0192 mm/Newton) for Mersilene ribbon, and 0.017 mm/Newton (95% confidence limits, 0.0148 to 0.0192 mm/Newton) for 5-mm steel band. No. 5 stainless steel wire provided the most stable closure, although statistical significance was achieved only in comparison with Mersilene ribbon and stainless steel band (p < 0.05). The superior stability of stainless steel wire closure may be due to tightening of the wires by twisting, which results in more tension across the reapproximated sternal halves than with other methods.