Intramedullary fixation of distal femoral diaphyseal osteotomies with absorbable self-reinforced poly-L-lactide and metallic intramedullary rods assessed by plain radiographs, quantitative computed tomography, and magnetic resonance imaging: an experimental study in rabbits.

Osteotomies of distal femoral diaphysis were fixed intramedullary with self-reinforced poly-L-lactide acid (SR-PLLA) rods in 19 and with metallic rods in 34 adult rabbits. The follow-up times were 8, 16, 24, and 48 weeks. Plain radiographs, computed tomography (CT), quantitative computed tomography (QCT), and magnetic resonance imaging (MRI) were used to evaluate the bone changes at two different levels of the osteotomy region. There were no significant differences in cortical bone density compared to the intact in the SR-PLLA fixed femurs at the osteotomy site. In the metallic-fixed femurs, the density values were significantly lower as compared to the contralateral femurs. There was a significant reduction of the cortical bone density values in SR-PLLA fixed femurs compared to the intact control side outside the osteotomy area at 8 (p = 0.01), at 16 (p = 0.0001), and at 24 weeks (p = 0.0003). In the metallic-fixed femurs significant reductions at 8 weeks (p = 0.02), at 16 weeks (p = 0.01), at 24 weeks (p = 0.009), and at 48 weeks (p = 0.002) were found compared with the intact control. MRI depicted well the SR-PLLA cases allowing studies without removal of the implant. On the contrary, abundant disturbing metallic artifacts were detected during investigation of the metallic-fixed femurs. In conclusion, our results indicated that CT is useful to evaluate the quality of reduction and internal fixation. Furthermore, the constant presence of internal metallic fixation seems to eventually cause osteoporosis in the cortical region of the femur. However, this stress protection effect of intramedullary fixation on the femoral diaphysis seems to be avoided by using an absorbable SR-PLLA rod, thus resulting in a better quality of bone when the osteotomies are healed.