FILLING OF BONE DEFECTS WITH POROUS HYDROXYAPATITE REINFORCED WITH POLYLACTIDE OR POLYGLYCOLIDE FIBERS

Hydroxyapatite has intrinsically poor mechanical resistance for loading bone replacements and its clinical applications are mainly limited to use as a filling device. In the present study, hydroxyapatite blocks were reinforced with resorbable polyglycolide (PGA) or polylactide (PDLLA) fibres so that most of the implant pores remained open assuming intimate contact with the host bone. The reinforced blocks, 2 x 3 x 4 mm in size (Interpore 200), were implanted into the proximal and diaphyseal tibiae of rabbits in order to study the tissue and bone ingrowth into the implants. The samples were studied by histological, histomorphometrical, microradiological, and oxytetracycline fluorescence analyses. The results suggested that PGA or PDLLA fibre reinforcement does not hinder bony ingrowth into the hydroxyapatite implant. Maximal bone ingrowth was observed at 6 weeks but thereafter the amount of ingrowth remained constant up to the end of the 24-week follow-up period. Modest foreign body type reactions around the fibres were histologically seen and there was no difference between the two types fibres in relation to the bone ingrowth. With implants used in this study the bone ingrowth as measured with histomorphometry was 12.9 +/- 1.4% in the cancellous implantation and 17.1 +/- 1.5% in the cortical implantation. It seems that fibre reinforcement does not hinder bone ingrowth into the coralline hydroxyapatite implants and supports their further development as bone graft substitute in high loading conditions.