Development and Validation of a Physiological Testing Method for Sternal Closure Systems

After a median sternotomy, the sternal bone has to be refixated using implants such as wires, plates or clamps. However, there is still a lack of specifically applicable test methods to investigate the mechanical safety and effectiveness of such implant systems. The aim of this study was to develop a new test method that replicates the in vivo loads acting on the sternum and that is applicable to all types of sternal closure systems. Based on the scientific literature a setup was developed that incorporates the physiological loads acting on the sternum during breathing (91 N) and coughing (328 N). These loads are applied to a sternum replicate at 5 Hz for approximately 1.8 million cycles. This cycle number is assumed to represent the healing period. For validation, the new method was applied to two different sternal closure systems: a PEEK clamp system and wires. The new test method proved to be easily applicable. The validation tests with the two sternal closure systems showed reasonable and reproducible results regarding all outcome parameters. The pre-tension exerted by the implants significantly differed between the two implant groups and decreased after the first coughing cycles. The fracture gap separation during breathing also significantly different between the two test groups but it was similar during coughing. No implant failed. Using this new test method it is possible to compare sternal closure systems under reproducible conditions and interpret their mechanical characteristics regarding their in vivo safety and effectiveness.