The development and in vivo validation of an external fixation device with standardized micromotion for accelerating fracture healing.

Micromotion can accelerate fracture healing, with critical parameters being range of motion, frequency of motion, duration of motion, as well as initial timing of the motion. However, these parameters of micromotion have not been optimized. It is because in previous studies large animals were used. The displacement among fracture fragments caused by animal activity brings a considerable systemic error to experimental data. Also, the sample size is limited by time and cost. Thus, the rat with femur fracture can be a good animal model in investigating this problem as its advantages on high consistency of experimental results, short convalescence, and low maintenance cost. The challenge in using a small animal model in the micromotion study include 1) highly specific stiffness of the fixator; 2) lightweight fixator to bring less interference to animal's activity; 3) high accuracy on measurement method. This study aims to solve this problem by integrating 1) an aluminum fixator with a solid construction; 2) a modularized experimental device with dismountable parts; 3) a non-contact measurement model based on video identification technology. Our preliminary validation results confirmed the reliability and reproducibility of the external fixation device used in the investigation on the effect of applied micromotion on bone healing.