PMMA particles and pressure--a study of the osteolytic properties of two agents proposed to cause prosthetic loosening.

Amongst the wear debris particles implicated in the particle hypothesis for prosthetic loosening are polymethylmethacrylate (PMMA), and particularly PMMA with barium sulphate contrast agent. Another suggested cause for loosening is hydrostatic pressure. PMMA particles were combined with hydrostatic pressure in a study to investigate whether there could be a synergistic or additive effect between these two factors. Titanium plates were fastened onto tibiae of 59 rats. After osseointegration, PMMA particles with barium sulphate were administered to the bone-implant interface. Further, PMMA particles were introduced into a previously published model for hydrostatic pressure induced osteolysis. There was measurable resorption in response to the PMMA particles but no additive or synergistic effect from introducing particles to the pressure model, and the effect of pressure was far greater than that of particles. These results suggest that, whereas particles can be shown to elicit an osteolytic response, the much less studied osteolytic effects of pressure could be far more important.