Bone accretion around polymethylmethacrylate and polyethylene implanted in the rabbit tibia

This study examines the accretion rate of bone surrounding orthopaedic polymeric implants in different physical forms. Forty mature, female, New Zealand white rabbits were used in the study. Bilateral 6mm drill holes were made in the anteromedial tibias, 1cm from the joint line. The right tibia received a polymeric implant and the left tibia functioned as a prepared but nonimplanted control. The animals were allocated as follows: Group 1--bulk, preformed cooled polymethylmethacrylate (PMMA) plug; Group 2--bulk, doughy PMMA implant; Group 3--cement polymer powder; Group 4--bulk ultra-high-molecular-weight polyethylene (UHMWP) plug; Group 5--UHMWP particles averaging 67.29 mum; Group 6--UHMWP particles averaging 15.68 mum. All animals received the same volume of PMMA or UHMWP. The animals were killed after four months by barbiturate overdose. Beginning four weeks prior to sacrifice, the animals were given tetracycline injections at two-weekly intervals for two consecutive days. The upper tibias were harvested bilaterally and the specimens were processed undecalcified. Using a fluorescent microscope, the distance between successive tetracycline bands was assessed. Doughy PMMA tended to suppress bone formation compared to the control side, whereas preformed PMMA plugs and particulate PMMA polymer did not. This may be due to the heat of polymerization or to the presence of residual monomer in the doughy group. Polyethylene tended to facilitate bone accretion whether in bulk or particulate form when compared to the control side or to doughy cement. This effect was less marked when the cement was in particulate form.(ABSTRACT TRUNCATED AT 250 WORDS)