In vitro wear assessment of the Charite Artificial Disc according to ASTM recommendations

Study Design. Biomechanical laboratory research. Objective. To evaluate the potential for Ultra High Molecular Weight Polyethylene ( UHMWPE) wear debris from the Charite Artificial Disc. Summary of Background Data. Cases of osteolysis from artificial discs are extremely rare, but hip and knee studies demonstrate the osteolytic potential and clinical concern of UHMWPE wear debris. Standards for testing artificial discs continue to evolve, and there are few detailed reports of artificial disc wear characterizations. Methods. Implant assemblies were tested to 10 million cycles of +/- 7.5 degrees flexion-extension or +/- 7.5 degrees left/ right lateral bending, both with +/- 2 degrees axial rotation and 900 N to 1,850 N cyclic compression. Cores were weighed, measured, and photographed. Soak and loaded soak controls were used. Wear debris was analyzed via scanning electron microscopy and particle counters. Results. The average total wear of the implants was 0.11 and 0.13 mg per million cycles, before and after accounting for serum absorption, respectively. Total height loss was approximately 0.2 mm. Wear debris ranged from submicron to > 10 mu m in size. Conclusions. Under these test conditions, the Charite ' Artificial Disc produced minimal wear debris. Debris size and morphology tended to be similar to other CoCr-UHMWPE joints. More testing is necessary to evaluate the implants under a spectrum of loading conditions.