Predictive modelling of cervical disc implant wear

This study presents a chain of simulations aimed at estimating the wear in a cervical disc implant and providing insight into the in vivo biomechanical performance of the implant. The simulation chain can start with determining a representative maximum range of motion (ROM) of a person's head. The ROM is used as motion input to a kinematic simulation of the cervical spine containing a disc implant. The cervical spine geometry is obtained from computed tomography (CT) scans and converted to STL format using reverse engineering software. The time histories of the loads imposed by the adjacent vertebrae on the implant, as well as the vertebral relative rotations can be extracted from the kinematic simulation. Alternatively, force and motion profiles prescribed by wear test protocols (e.g. ISO 18192-1 and ASTM F2423-05) can be used. The force and motion profiles are applied as boundary conditions to a non-linear finite element model (FEM) of the implant to determine the time-varying contact stress and slip velocity distributions at the interface between the two halves of the implant. The stresses and slip velocities are used in a linear wear model to estimate the wear rate distribution at the FEM's nodal points where contact occurs. Reverse engineering software is used to triangulate the contact surface so that the total wear volume can be calculated. The simulation chain's predicted wear rate shows good agreement with in vitro results in the literature. The simulation chain is thereby demonstrated to be suitable for comparative pre-experimental studies of spinal implant designs.