Characteristics of polyethylene wear particles isolated from synovial fluid after mobile-bearing and posterior-stabilized total knee arthroplasties.

The size, shape, and number of polyethylene wear particles found in synovial fluids of patients 1 year after implantation of 22 well-functioning total knee prostheses (11 contemporary mobile-bearing type, 11 posterior-stabilized type) were determined. Polyethylene wear particles were isolated from synovial fluids and examined by scanning electron microscopy. Particle size (equivalent circle diameter) was 0.81 +/- 0.12 microm (mean +/- standard error) in mobile-bearing types and 0.78 +/- 0.08 microm in posterior-stabilized types. Particle shape (aspect ratio) was 1.94 +/- 0.13 in mobile-bearing types and 2.30 +/- 0.22 in posterior-stabilized types. Total numbers of particles were (1.75 +/- 1.02) x 10(8) in mobile-bearing and (1.16 +/- 0.57) x 10(8) in posterior-stabilized types. The differences in these parameters between the two groups were not statistically significant. In the early stages after surgery, contemporary mobile-bearing types were comparable to posterior-stabilized types in terms of polyethylene wear-particle generation. The present results do not support the proposition that has been put forward in the literature; namely, that the contemporary mobile-bearing design has an advantage, in terms of the polyethylene wear rate. These data suggest that the advantage of complete conformity in the femoro-tibial articulating surface of contemporary mobile-bearing design may be offset by wear of the mobile undersurface and slot, apart from the articulating surface.