Tissue response to polyglycolide and polylactide pins in cancellous bone.

An absorbable self-reinforced polyglycolide (SR-PGA) pin, 2.0 mm in diameter and 15 mm in length, was implanted in the trabecular bone areas of the distal femur of 51 rats and a biodegradable self-reinforced poly-L-lactide (SR-PLLA) pin of the same size was inserted into the distal femur of the other hind leg of the same rats. The intact femora of eight non-operated rats were used as controls. Tissue reaction to the implants was examined within standardized sample fields radiographically, histologically, histomorphometrically, microradiographically and using oxytetracycline fluorescence studies. The follow-up periods of the groups consisting of five operated rats and one intact control rat were 1, 3, 6, 12, 24, 36, 48 and 52 weeks. Eleven extra rats were operated on to ensure five samples in each follow-up group for the final analyses. The first signs of degradation of the SR-PGA pin were seen at 3 weeks, and the pin was totally degraded by 36 weeks. No signs of degradation of the SR-PLLA pin were observed during the follow-up period. Active new bone formation was seen close to the implant profile at 1 week in both groups. At 12 weeks the mean fractional osteoid formation surface was statistically significantly (P < 0.01) higher in the SR-PGA-implanted specimens than in the SR-PLLA-implanted specimens. At that time there were also statistically significantly (P < 0.05) more phagocyting macrophages in the SR-PGA-implanted specimens than in the SR-PLLA-implanted specimens, which is in accordance with the degradation behaviour of both implants. The biocompatibility of polyglycolide and polylactide proved to be good.