A model for evaluating injectable bone replacements in the vertebrae of sheep: radiological and histological study.

We developed a bone-defect model in the vertebrae of sheep. Forty four cavities were prepared in the upper lumbar vertebrae of 11 sheep using a biopsy trocar via a posterior-lateral extracanal percutaneous route and the location was monitored by radiology with a brilliance amplifier. The cavities were 3 mm in diameter. The histological study was performed on 15 cavities which were left empty to give reference data for the model. Histological and histomorphometry results showed that 67% of the surface area of the empty cavities was still empty 3 months after their preparation. Thus, the natural regenerative capacity of vertebral trabecular bone is limited. We performed preliminary percutaneous injections of polymethylmethacrylate (PMMA) and nacre powder to assess whether this bone-defect model would be suitable for further studies on bone repair. Cavities were successfully filled with nacre powder (21 cavities) or PMMA (8 cavities) while monitoring the process by interventional radiology. The experimental sheep vertebrae defect system is reproducible and appears to be a suitable model for testing injectable biomaterials for treating bone loss.