Critical analysis of in vitro stability testing of spinal implants and proposal for standardization

Background The American Society for Testing and Materials (ASTM), considered the gold standard worldwide, requires only testing in physiological saline solution to simulate in vivo conditions in standard testing of spinal implants. Research design and methods We conducted an in vitro study to identify an industrial lubricant with characteristics that are most similar to those of biologically lubricating fat, blood, and tissue fluids. The use of such a material could standardize the results of in vitro mechanical tests for better clinical applications. Results Our study has shown that the lubricity of physiological saline was well below that of human soft tissues and tissue fluids, and among the motor oils, Castrol GTX3 provided a testing environment similar to that of a living organism. Conclusions With the intention of standardizing and preventing a biological hazard, we have developed a reproducible mechanical testing proposal based on our experiments, which, in addition, would allow us to avoid many misunderstandings and contingencies.