A Biomechanical Comparison of Three Sternotomy Closure Techniques

Background. A biomechanical study of three sternotomy closuretechniques (figure-of-eight stainless-steel wires, PectofixDynamic Sternal Fixation [DSF] stainless-steel plates, and figure-of-eightstainless-steel cables) was conducted to compare strength andstiffness variables in three clinically relevant loading modes(anterior-posterior shear, longitudinal shear, and lateral distraction). Methods. All tests were conducted on polyurethane foam sternalmodels that simulate the properties of cancellous bone. Eachmodel was divided longitudinally and reconstructed using oneof the sternotomy closure repair techniques. Tests were performedusing a materials testing system that applies a continuouslyincreasing amount of force in one direction to the model untilit catastrophically breaks. A total of six trials of each fixationtype in each of three test groups were prepared and tested,for a total of 54 tests. Strength and stiffness variables aswell as a post-yield analysis of failure were evaluated. Results. Sternums repaired using the DSF plate system are amore rigid construct than sternums repaired using the stainless-steelwires or cables in the distraction and transverse shear modesand they are not significantly different from sternums repairedwith wires or cables in the longitudinal shear mode. The DSFplate system offers a 25% improvement in resistance to failure(yield) compared to wires when a transverse shear force is appliedto the model. The cable system had a higher resistance to failurethan the wires in all modes although the differences were notstatistically significant. Additionally, the DSF plate systemprovides substantial reduction of the implant’s cuttinginto the sternal model under loading as evidenced by the post-yielddisplacement when compared with either cables or wires for thedistraction and longitudinal shear modes. For the transverseshear mode, the cables or wires would completely fail at theload for which cutting begins for the DSF. Conclusions. Both the DSF plate system and the stainless-steelcable system offer important advantages over figure-of-eightwire for sternal closure