Surface Texture Analysis of Artificial Disks Wear-Tested Under Different Conditions and Comparison to a Retrieved Implant

Abstract

Total disk arthroplasty is growing in popularity and becoming an alternative to fusion for the treatment of some degenerative disk diseases. To date, there is little consensus regarding the appropriate in vitro techniques with which to evaluate the biotribological properties of these devices. The current study evaluated the surface texture and topography of lumbar metal-on-metal artificial disks tested in a spine wear simulator compared to an explanted device after twelve months in situ. Six implants were tested under a constant load and unidirectional flexion-extension motion as defined by the ASTM standard guide. One implant was tested under a variable load using a combination of flexion-extension, lateral bending, and axial rotation as specified by the ISO standard. While the retrieved disk retained its initial mirror-like surface finish, implants tested under unidirectional motion were severely damaged by abrasive wear resulting in a significant increase in roughness. The implant tested under combined motions exhibited a multi-directional wear scar with limited surface damage. Although only a single retrieved implant was characterized, the current study suggests that wear testing under unidirectional motion may not produce clinically-relevant surface morphology of metal-on-metal artificial disks.