Bone changes after experimental osteotomies fixed with absorbable self-reinforced poly-image-lactide screws or metallic screws studied by plain radiographs, quantitative computed tomography and magnetic resonance imaging

The healing of the distal femoral osteotomy fixed with self-reinforced poly-image-lactide (SR-PLLA) or metallic screws in 16 rabbits was evaluated with plain radiographs, quantitative computed tomography and magnetic resonance imaging (MRI). At 36 weeks in the metallic fixation there was significantly more external callus than in the SR-PLLA fixation. On the metallic fixation side the cortical bone mineral density was significantly lower than on the non-operated side at 6 weeks as well as at 36 weeks. This decrease was not found in the SR-PLLA fixation. On the MRI on T1-weighted images a dark zone (signal void), and on the T2-weighted images a bright zone (increased signal intensity), was seen surrounding the screws, indicating oedema. At 36 weeks these oedematous zones were significantly smaller in the SR-PLLA fixation group than in the metallic one. The results give indirect evidence towards a more rapid and better osteotomy healing with the more physiologically elastic SRPLLA screws than with the metallic screws. Fixation with SR-PLLA screws may prevent stressprotection atrophy and weakening of the fixed bone usually caused by the rigid metallic fixation.