Micro CT Analysis of Spine Architecture in a Mouse Model of Scoliosis

Objective: Mice homozygous for targeted deletion of the gene encoding fibroblast growth factor receptor 3 (FGFR3(−/−)) develop kyphoscoliosis by 2 months of age. The first objective of this study was to use high resolution X-ray to characterize curve progression in vivo and micro CT to quantify spine architecture ex vivo in FGFR3(−/−) mice. The second objective was to determine if slow release of the bone anabolic peptide parathyroid hormone related protein (PTHrP-1-34) from a pellet placed adjacent to the thoracic spine could inhibit progressive kyphoscoliosis. Materials and methods: Pellets loaded with placebo or PTHrP-1-34 were implanted adjacent to the thoracic spine of 1-month-old FGFR3(−/−) mice obtained from in house breeding. X rays were captured at monthly intervals up to 4 months to quantify curve progression using the Cobb method. High resolution post-mortem scans of FGFR3(−/−) and FGFR3(+/+) spines, from C5/6 to L4/5, were captured to evaluate the 3D structure, rotation, and micro-architecture of the affected vertebrae. Un-decalcified and decalcified histology were performed on the apical and adjacent vertebrae of FGFR3(−/−) spines, and the corresponding vertebrae from FGFR3(+/+) spines. Results: The mean Cobb angle was significantly greater at all ages in FGFR3(−/−) mice compared with wild type mice and appeared to stabilize around skeletal maturity at 4 months. 3D reconstructions of the thoracic spine of 4-month-old FGFR3(−/−) mice treated with PTHrP-1-34 revealed correction of left/right asymmetry, vertebral rotation, and lateral displacement compared with mice treated with placebo. Histologic analysis of the apical vertebrae confirmed correction of the asymmetry in PTHrP-1-34 treated mice, in the absence of any change in bone volume, and a significant reduction in the wedging of intervertebral disks (IVD) seen in placebo treated mice. Conclusion: Local treatment of the thoracic spine of juvenile FGFR3(−/−) mice with a bone anabolic agent inhibited progression of scoliosis, but with little impact on kyphosis. The significant improvement in IVD integrity suggests PTHrP-1-34 might also be considered as a therapeutic agent for degenerative disk disorders.