Lower sternal reinforcement improves the stability of sternal closure

This study uses a mechanical testing system to evaluate three methods of sternal closure. Twelve sternal replicas composed of a polyurethane foam bone analogue were divided in the midline and reapproximated using three stainless steel wire techniques: six simple wires (6S), six figure-of-eight wires (6F8), or seven simple wires (7S), which included an extra wire at the lower sternum. The closures were subjected to increasing lateral distraction from 0 to 400 Newtons (N) (1 N = 0.224 lbs), and motion was measured using transducers stationed across the manubrium, midsternum, and lower sternum. With each method of closure, the manubrium was the most stable, the lower sternum the least stable, and the midsternum intermediate between the other two. There were also differences between sternal closure methods, but only at the lower sternum. Less sternal distraction was measured with the 7S than the 6S and 6F8 methods, starting at 100 N (0.20 ± 0.06 mm vs 0.48 ± 0.19 and 0.39 ± 0.10, p = 0.003), and progressively increasing until the study was stopped at 400 N (1.64 ± 0.39 mm vs 4.92 ± 1.73 and 5.1 ± 1.43 mm, p = 0.003). These data show that the lower sternum is the site of greatest instability and that reinforcement of this area with an additional wire effectively stabilizes the closure. Figure-of-eight wires are not superior to simple wires.