Wear characterization of the A-MAV™ anterior motion replacement using a spine wear simulator

Total disc replacement emerged as an alternative to fusion for the treatment of degenerative disc disease. Optimization of the bearing surfaces is critical to mitigate wear-related biological reaction. The purpose of this study was to characterize the wear of the A-MAV™ metal-on-metal total disc replacement using a spine wear simulator, per the ASTM F2423-05 standard guide. Six specimens were tested under flexion-extension (FE) conditions for ten million cycles (MC), followed by lateral bending (LB) combined with axial rotation (AR) for an additional ten MC. A run-in wear period was observed during the first 0.5 MC for both testing conditions, followed by a steady-state wear rate of 0.33 ± 0.12 mm3/MC in FE and 0.43 ± 0.06 mm3/MC in combined motion. Phasing between LB and AR led to a crossing-path motion as observed on explanted devices. This study suggests that clinically-realistic surface morphology may be achieved by carefully selecting the wear test parameters specified in the ASTM standard guide. Furthermore, the use of metal-on-metal bearings in spinal arthroplasty may be viable in view of the low wear exhibited by this material combination.