Absorbable polylactide pins versus metallic Kirschner wires in the fixation of cancellous bone osteotomies in rats

A transverse transcondylar osteotomy of the distal femur was fixed with biodegradable self-reinforced polylevolactide (SR-PLLA) pin in 42 rats and with metallic Kirschner wire in 42 rats. Consolidation of the osteotomy and periosteal callus formation was examined within standardised sample fields histologically, histomorphometrically and microradiographically one week, 3, 6, 12, 24, 36 and 48 weeks postoperatively. The intact contralateral femur served as control. From 3-week to 48-week follow-up time the total trabecular bone area of the SR-PLLA group at the osteotomy site was significantly larger in the operated femora than in the intact control femora at the corresponding site. The specimens of the Kirschner wire group showed significantly larger total bone area only at 12 weeks postoperatively as compared with the nonoperated femora. In the SR-PLLA group 28 and in the metallic group 31 osteotomies showed solid bony union. In both experimental groups the osteotomies with solid bony union showed only scantly periosteal callus formation. More abundant callus formation in both experimental groups was related to incomplete union of the osteotomy. No signs of degradation of the SR-PLLA implant could be noticed within the follow-up times of this study. Only mild foreign body reaction to both SR-PLLA pins and metallic Kirschner wires was observed during the observation period. The fixation properties of both SR-PLLA pins and metallic Kirschner wires seem to be sufficient for the fixation of small cancellous bone fragments, but by using SR-PLLA pins instead of Kirschner wires subsequent second operation for removal of the implants can be avoided.