Bone tissue response to biodegradable polymers used for intra medullary fracture fixation: a long-term in vivo study in sheep femora.

Since the degradability of the synthetic polymers used for fracture fixation is still unclear, a research project with biodegradable interlocking nails with a longterm implantation period has been started. In 21 female sheep a complete mid-shaft osteotomy of the left femur was performed to mimic a fracture of the femoral shaft. For the fixation, an intramedullary stainless-steel interlocking nail, a PLA rod or a PLA/PGA rod was used. After 30 months of implantation the histological results of these three materials were examined. In contrast to most reports the degradation rate of both polymers was much lower than the suggested ultimate period of two years. Even the tissue response was more pronounced than expected and this reaction can imply certain risks for repulsion. One can conclude that the volume quantity of polymeric implant in the bony tissue must be reduced if possible to avoid severe foreign body responses. The immunologic responses and the clinical consequences need more studies. The degradation behavior of the polymer is still not under control.