Wear Characteristics of Artificial Lumbar Disc Spine Implant on Various Center of Radius Position

Abstract

Various center of radius (CoR) positions have been applied in lumbar disc designs; however their influence on wear performance remains unclear. This study investigates the effect of CoR position on the wear volume and surface roughness of an artificial lumbar disc implant. Wear tests were conducted using a UHMWPE ball against a CP-Ti artificial lumbar disc under dynamic loading up to 150 N for one million cycles. The tests involved flexion-extension, lateral bending, and axial rotation motions at different CoR positions (8, 10, and 12 mm). The wear volume of the CP-Ti component increased from 0.981 ± 0.076 to 2.011 ± 0.162 mm³/MC, while the surface roughness decreased from 0.512 ± 0.047 µm to 0.382 ± 0.039 µm as the CoR increased from 8 to 12 mm. Similarly, the wear rate of the UHMWPE ball increased from 7.86 ± 0.786 to 12.13 ± 0.605 mm³/MC, accompanied by a surface roughness reduction from 0.421 ± 0.0591 to 0.341 ± 0.0679 µm. The dominant wear mechanisms observed were plowing, scratching, and abrasive wear. At a CoR of 10 mm, the wear volumes of CP-Ti and UHMWPE were 1.581 ± 0.206 and 9.97 ± 0.454 mm³/MC, respectively—values below 10 mm³/MC, meeting the standard for lumbar disc implant applications. Meanwhile, the surface roughness values of the CP-Ti and UHMWPE components were and 0.382 ± 0.0481 µm, respectively. The artificial lumbar disc configuration with a CoR position of 10 mm demonstrated an optimal balance between contact pressure and contact area at the ball–plate interface. Therefore, a CoR 10 mm is recommended to achieve superior performance in lumbar disc implant applications.