The critical size bony defect in a small animal for bone healing studies (I):: Comparative anatomical study on rats femur

Laboratory rats are small animal models which are often used for scientific investigations in medicine. So far there are only few scientific data about the meaning of these small animal models for in vivo bone healing studies available in literature. Although the rat's femur with its cyclic loadings during gait is an appropriate model for investigations in the field of experimental orthopaedics and traumatology there is a lack of morphometric information with respect to its anatomy. The aim of this study is to evaluate the anatomy of rat, femurs in two species, which are often performed in animal experimental medicine. These morphometric data should contribute to develope an appropriated osseous fragment fixation system in the rats femur. The femurs of Wistar (WR) and Sprague Dawley (SDR) cadavers were prepared and analysed by x-rays in two standard planes. The results were compared with the corresponding data for humans by literature. It could be demonstrated that SDR showed a higher caput-collum-daphyseal and antetorsion angle, but a lower transcondylar femur valgus angle compared to WR. Cortical thickness, bone marrow cavity diameter and femur length were higher in WR. Wistar rat's femur anatomy shows more similarities to human anatomy than Sprague Dawley rats.