Microcomputed tomography imaging in a rat model of delayed union/non‐union fracture

We aimed to develop a clinically relevant delayed union/non‐union fracture model to evaluate a cell therapy intervention repair strategy. Histology, three‐dimensional (3D) microcomputed tomography (micro‐CT) imaging and mechanical testing were utilized to develop an analytical protocol for qualitative and quantitative assessment of fracture repair. An open femoral diaphyseal osteotomy, combined with periosteal diathermy and endosteal excision, was held in compression by a four pin unilateral external fixator. Three delayed union/non‐union fracture groups established at 6 weeks—(a) a control group, (b) a cell therapy group, and (c) a group receiving phosphate‐buffered saline (PBS) injection alone—were examined subsequently at 8 and 14 weeks. The histological response was combined fibrous and cartilaginous non‐unions in groups A and B with fibrous non‐unions in group C. Mineralized callus volume/total volume percentage showed no statistically significant differences between groups. Endosteal calcified tissue volume/endosteal tissue volume, at the center of the fracture site, displayed statistically significant differences between 8 and 14 weeks for cell and PBS intervention groups but not for the control group. The percentage load to failure was significantly lower in the control and cell treatment groups than in the PBS alone group. High‐resolution micro‐CT imaging provides a powerful tool to augment characterization of repair in delayed union/non‐union fractures together with outcomes such as histology and mechanical strength measurement. Accurate, nondestructive, 3D identification of mineralization progression in repairing fractures is enabled in the presence or absence of intervention strategies. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:729–736, 2008