Biomechanical and in vivo comparison of three fixation devices for the long lasting maintenance of a critical size bone defect in the rat femur — A proposed model for segmental bone defect research

Bone regeneration with tissue engineering constructs is a topic of active international research. The standardization of an animal model and especially the fixation method in critical size defects became a necessity in order to facilitate reliable comparison among different studies. Three hand-made fixation devices (FD), namely external fixator (EF), steel plate (SP), and cement plate (CP) made of poly-methyl-methacrylate (PMMA), were compared regarding their biomechanical properties and their long term ability to maintain a 8 mm critical size bone defect (CSD). A modified three point bending test, aimed to resemble the in vivo loading pattern and a 12-week in vivo monitoring of the FDs integrity were utilized in the femurs of rats. The biomedical bending tests showed that the CP sustained much higher loads and safely underwent longer displacements than the other two FDs. In line with the biomechanical results, the CP showed high success rate in maintaining the CSD intact for 12 weeks in vivo, whereas the other FDs showed higher failure rates. Furthermore, the CP incorporates the locking compression plate (LCP) principle by securely fixing the screws both in the plate and in the underlying bone. The high biomechanical and in vivo performance of the CPs and the incorporation of the LCP principle along with them being inexpensive and easy to produce, qualify the CP as a fixation model for the safe maintenance of prolonged absolute stability of a CSD in experimental animals.