Testing criteria for spinal implants: recommendations for the standardization of in vitro stability testing of spinal implants.

New implants and new surgical approaches should be tested in vitro for primary stability in standardized laboratory tests in order to decide the most appropriate approach before being accepted for clinical use. Due to the complex and still unknown loading of the spine in vivo a variety of different test loading conditions have been used, making comparison of the results from different groups almost impossible. This recommendation was developed in a series of workshops with research scientists, orthopedic and trauma surgeons, and research and development executives from spinal implant companies. The purpose was to agree on in vitro testing conditions that would allow results from various research groups to be compared. This paper describes the recommended loading methods, specimen conditions, and analysis parameters resulting from these workshops.