Biocompatibility of intraosseously implanted predegraded poly(lactide): an animal study

During degradation of high molecular weight as-polymerized poly(l-lactide) (PLLA) late complications such as swelling of the subcutaneously implanted bone plates have been observed in patients. However, in the same patients the intraosseously implanted PLLA screws did not give rise to any complications. To investigate a possible difference in the degradation and histological response due to the site of implantation, subcutaneous and intraosseous implantation studies are necessary. In the present study rods of PLLA and a copolymer poly(96l/4d-lactide) (PLA96) and predegraded PLLA and PLA96 were implanted intraosseously in rabbit tibiae. In vitro predegradation at elevated temperatures was used to obtain an enhanced degradation rate to simulate long-term physiological degradation. Animals were sacrificed after a postoperative period varying from 2 to 26 weeks. The predegraded PLLA and PLA96 implants showed a high rate of fragmentation and internalization of particles by macrophages. In the medullary cavity large fields of macrophages and, with the predegraded PLA96 implants, haemorrhages and infiltrates were noted, but no osteolytic changes were observed in the cortical bone. It can be concluded that, based on the disintegration of the implants and the accompanying histological reaction, a reaction similar to that found with subcutaneous implants in former studies had occurred. This indicates that not only the site of implantation, subcutaneous or intraosseous, but a number of other factors will affect the degradation process and the corresponding histological response.