Analysis of Polyethylene Particles Produced in Different Wear Conditions In Vitro

The production of ultrahigh molecular weight polyethylene wear particles is a major factor limiting the life of prosthetic joints. The aim of the current study was to determine whether the morphologic features and size distribution of polyethylene particles produced in wear tests were in agreement with clinical findings. Particles from two hip simulators, a pin-on-disk hip wear device and a knee wear simulator, were studied and compared with particles found from synovial fluid of a prosthetic hip, and with published findings on clinical wear particles. Scanning electron microscopy and digital image analysis were used for characterization and sizing. The average equivalent circle diameter ranged from 0.27 μm to 0.69 μm, which corresponded well with published clinical findings. Common to all wear tests was that the lubricant contained albumin or globulin, and that the relative motion was multidirectional. In the hip wear simulation, the particle size distribution was not sensitive to the type of loading, counterface material, protein content of the lubricant, and whether the polyethylene was irradiated. In the knee wear simulation, the debris on average was larger than in the hip wear simulation. The simulators produced wear particles similar to those seen clinically, which indicates that the current test methods are relevant for assessing wear of prosthetic joints.