SELF-REINFORCED POLY-L-LACTIDE SCREWS IN THE FIXATION OF CORTICAL BONE OSTEOTOMIES IN RABBITS

This study was carried out to test absorbable self-reinforced poly-L-lactide (PLLA) screws as lag screws in the fixation of cortical bone osteotomies. A right tibial osteotomy was performed in 72 rabbits, of which 36 were fixed with 4.5 mm in diameter metallic cortical screws and 36 with self-reinforced PLLA screws manufactured by a sintering method. Follow-up times were 6, 12, and 24 weeks. After killing the rabbits all operated and the control tibias were examined macroscopically and radiographed. Sixty pairs of tibias were tested for shear strength; the rest were evaluated histologically, microradiographically and by oxytetracycline fluorescence. Macroscopically, 97% of the metallic and 44% of the PLLA screw-fixed osteotomies healed well. Radiographically, the metallic group healed significantly better and there were less malpositions than in the PLLA group. The shear strengths of the operated tibias were divided by those of the controls to give comparative shear strengths. The mean comparative shear strengths were 52% at 6, 61% at 12 and 76% at 24 weeks in the metallic group and 38, 49 and 61% in the PLLA group, respectively. No statistically significant difference in shear strength was observed between the groups. A mild foreign-body reaction was found in the histological evaluation in both groups, and normal bone healing was noticed in the microradiography and in the fluorescence studies. In conclusion, the sintered self-reinforced PLLA screws were insufficiently strong to be used as a single lag screws in the fixation of tibial cortical bone osteotomies in rabbits.