Gradual Bone Segment Transportation in Mice

All surgeries and handling were performed based on the guidelines of the Animal Ethics Committee of Kitasato University (Permission number: 2018-087). A total of 32 six-month-old male C57BL/6J mice (Charles River Laboratories Japan, Inc., Yokohama, Japan) were used for this study. The mice were fed a standard laboratory diet, CRF-1 (Oriental Yeast, Tokyo, Japan), and housed under controlled temperature (23 ± 2°C) and humidity (55 ± 10%) conditions and a 12-hour light/dark cycle. Mice were randomly divided into four treatment groups of eight mice each, namely, Group CONT (immobile control), Group 0.2, Group 1.0, and Group 1.0/BMP-2. A 2.0-mm critical sized bone defect was created in the right femur according to previous studies (see below for details) [19 (link), 20 (link)]. In Group CONT, the defect was fixed with the Segmental MouseDis without transportation of the bone segment. Mice in Groups 0.2 and 1.0 underwent fixation with the device and the bone segment was moved 0.2 mm/day for 10 days and 1.0 mm/day for 2 days, respectively. Mice in Group 1.0/BMP-2 underwent fixation with the device and received an injection of 2.0 μg of rhBMP-2 into the bone defect site immediately after the defect-creating surgery and the bone segment was moved 1.0 mm/day for 2 days.