Purpose: Micro-CT is efficient, non-destructive, and accurate for qualitative and quantitative studies of bone microarchitecture during fracture healing. A cell-based vascular endothelial growth factor (VEGF) gene delivery system can increase fracture healing. Three dimensional structural variation of new bone formation in rabbit fracture segmental defects was studied with micro-CT to determine how VEGF affects these microarchitectural differences for bone healing in various periods.
Method: All animal procedures were approved by the Animal Care Committee at St. Michael’s hospital. Ten millimeter segmental bone defects were treated by local injection with cell-based VEGF gene transfer (n=15), or control group with fibroblasts alone or saline only (n=15), to stimulate differences in bone healing. The animals were sacrificed and fracture healing specimens collected at 4, 8 and 12 weeks post surgery. The region of interest (ROI) was set where the segmental defect was located, and was selected for analysis from the recognizable margins of the original defect. To describe the topographic pattern of bone healing, the ROI was divided into three areas of equal volume: proximal, middle and distal. The new bone formation and mineralization at the defect sites were evaluated by bone structural parameters from the 3-D reconstruction of micro-CT.
Results: Macroscopic evaluation of the interfragmentary section from reconstructed micro CT scans, in the VEGF treated rabbits, showed abundant fragmentary bone filling the gap of the osteotomy at 4 weeks and abundant callus bridging the gap at 8 and 12 weeks. In the control group, only small amounts of sparsely formed bone were seen in the gap at 4 weeks. In the control group, the regenerate bone was ovoid around the bone sites and a big gap remained in the segmental bone defects at 8 and 12 weeks. The bone healing micro-structural differences between the two groups varied with the period of treatment, with more differences seen at 4 than 8 or 12 weeks.
Conclusion: Cell-based VEGF gene therapy enhances fracture healing of segmental defects, and this effect is best seen in the early period following defect creation.
