Tribology of flexible and sliding spinal implants: Development of experimental and numerical models

Abstract

New fusionless devices are being developed to get over the limits of actual spinal surgical treatment, based on arthrodesis. However, due to their recentness, no standards exist to test and validate those devices, especially concerning the wear. A new tribological first approach to the definition of an in vitro wear protocol to study wear of flexible and sliding spinal devices is presented in this article, and was applied to a new concept. A simplified synthetic spine portion (polyethylene) was developed to reproduce a simple supra-physiological spinal flexion (10° between two vertebrae). The device studied with this protocol was tested in wet environment until 1 million cycles (Mc). We obtained an encouraging estimated wear volume of same order of magnitude compared to similar devices. An associated finite element (FE) numerical model has permitted to access contact information and study the effect of misalignment of one screw. First results could point out how to improve the design and suggest that a vertical misalignment of a screw (under or over-screwing) has more impact than a horizontal one. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 104-111, 2018.

A review of recent advances in tribology

“…In additional to the articulating surfaces, the fixation interface which has not received enough attention previously, was also extensively considered [358,359] and also in conjunction with wear testing of the bearing surfaces [360]. Modular interfaces with fretting corrosion were increasingly studied at the hip [318, 361−363], the knee [364], and the spine [365,366] and for new materials combinations of PEEK and XLPE [367]. The contact between implant and bone was also an important consideration [368].…”