Bone response to polymers based on poly-lactic acid and having different degradation times

Authors studied two degradable and resorbable polymers derived from lactic acid: poly-L-Lactic acid (PLLA), with a relatively long time of degradation (longer than 6 months, PL10 Purac NL); poly-DL-Lactic acid (PDLLA), with a relatively short time of degradation (shorter than 6 months, PDL Purac NL) . The animal species was the young adult New Zealand White rabbit. The in-v ivo study was performed by implantation of small cylinders of 10 x 3 mm in size (length x diameter) in the distal metaepiphysis of the femur; 34 cylin ders have been implanted. Retrievals of PLLA specimens took place at 3, 6, 9, 12 and 24 months; for PDLLA specimens at 1, 2, 4 months. Polarized light microscopy of undecalcified tissue sections was performed. The analysis fo r PLLA and PDLLA has shown a favorable response of bone tissue: alterations in the bone repair, growth and remodeling have not been observed. PLLA is persistent at the times studied; there is never a tight apposition between bone and PLLA implant and an intervening fibrous layer has often been obser ved. PDLLA is not persistent at the times studied and it degrades quite fas t; bone repair of the empty implantation's hole occurs by bony growth from the endosteal trabeculae. The newly formed bone covers the hole's walls wit h an elongation parallel to them. For both polymers, whether the degradatio n is fast or slow, the material's substitution by newly formed bone never s tarts from the walls of the implantation hole. Only after the complete disa ppearance of the polymeric material newly formed bone begins to fill the ho le. (C) 2001 Kluwer Academic Publishers.