INTRODUCTION: Total Disc Arthroplasty (TDA) can be used to replace a damaged intervertebral disc in the spine. There are different designs of prosthetic discs, but one of the most common is a ball‐and‐socket combination. In such designs, ball‐andsocket surfaces are in direct contact at all times, hence friction is created. Friction results in wear debris creation. The aim of this work was to look at the effects of change in dimensions on the friction and wear of a ball‐and‐socket disc arthroplasty.
METHODS: A generic ball‐and‐socket model was designed and manufactured based on the dimensions and geometry of a metal‐on‐metal Maverick (Medtronic, Minneapolis, USA) device. Keeping the radial clearance similar to the Maverick (i.e. 0.015 mm), the ball dimensions varied between 10 to 16 mm, in order to enable the comparison between different dimensions. The implants were made out of Cobalt Chrome Molybdenum alloy, with a surface roughness of 0.05 μm. A Bose spine simulator (Bose Corporation, ElectroForce Systems Group, Minnesota, USA) was used to apply an axial compressive force to the TDA. Flexion of +6° and extension of ‐3° was then applied at various frequencies and the resulting frictional torque measured. The tests were performed under an axial load of 50, 600, 1200 and 2000 N and frequencies of 0.5, 1.0, 1.5 and 2.0 Hz, with Newborn Calf Serum as lubricant.
RESULTS AND DISCUSSION: The results showed variation of frictional torque in different frequencies for all four samples under constant axial load. It was observed that the frictional torque had the lowest value for the implant with ball radius of 16mm. It could be concluded that the implant with larger ball radius may create less friction and therefore less wear debris.