Background: Stainless steel wires are commonly used to close the sternum after cardiac-related operative procedures. However, complications have been reported associated with fracture of wires and subsequent migration into the chest cavity. The objective of this study was to biomechanically evaluate the role of surgeons in contributing to wire failure. We hypothesized that surgeons may impose damage to the sternal wire, which may be exacerbated by postoperative wire degradation and patient movement.

Methods: A biomimetic sternal model and custom test fixture simulated a median sternotomy. The sternum was closed by a fellowship-trained cardiothoracic surgeon using figure-of-eight and simple closure techniques. Closures were completed using No. 7 gauge wires made of 316 L stainless steel. Force data were collected at each costal cartilage level (six or eight levels), at each closure stage (three or two stages), for all 10 figure-of-eight and simple closures (n = 20 bones), respectively. Post hoc analysis of ultimate tensile stress in the wires determined potential for failure.

Results: The mean (SD) force for all tests was 220.5 N (59.4 N) using the figure-of-eight technique and 182.8 N (79.5 N) using the simple technique. The mean ultimate stress in the wires was 346 MPa and 286 MPa for figureof- eight and simple techniques, respectively. We found that a significant number of observed forces exceeded the yield strength of the wire during closure (figure-of-eight, 126 of 178; simple, 73 of 160).

Conclusions: Weakened areas of the wire likely define the locations of wire fracture, initiated by the surgeon, but exacerbated by wire degradation or patient movement.

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