Development of a sheep vertebroplasty model for bioceramic materials assessment

Development of a sheep vertebroplasty model for bioceramic materials assessment Sheep has been widely used as an animal orthopaedic model. Although several studies report anatomic and biomechanical similarities as well as distinctions of ovine lumbar vertebrae when compared to human’s, only a few studies describe its actual use as a vertebroplasty model. Due to distinct anatomic features, sheep lumbar vertebrae pose a challenge when developing a minimally invasive procedure for vertebroplasty material testing, under conditions meant to be the most similar to clinical procedure. The present work describes the development of an appropriate surgical percutaneous vertebroplasty model in the lumbar spine of sheep, applicable in vivo, that minimizes the risk of post-surgical complications. This model was mechanically evaluated ex-vivo regarding its safety, and used to evaluate the injectability and radiopacity of two new bioceramic materials when compared to a commercial bioceramic bone substitute (Cerament™ SpineSupport). Microtomography techniques helped in the development of the model and results assessment. Under fluoroscopic guidance, a defect was created through a bilateral modified parapedicular access in the cranial hemivertebrae of 30 sheep lumbar vertebrae (L4, L5 and L6). The manually drilled defect had an average volume of 1209 ±226 mm3 and allowed the novel materials injection through a standardized injection cannula placed in one of the entrance points. Adequate defect filling was observed with all tested materials. No mechanical failure was observed under loads higher than the physiological.

Ex Vivo Model for Percutaneous Vertebroplasty

The testing of novel biomaterials for percutaneous vertebroplasty depends on suitable animal models. The aim of this study was to develop ex vivo a reproducible and feasible model of percutaneous vertebroplasty, for ulterior application in vivo. A large animal model was used (Merino sheep), due to its translational properties. Vertebroplasty was performed under tactile and fluoroscopic control, through a bilateral modified parapedicular access in lumbar vertebrae (n=12). Care was taken in order to avoid disruption of the vertebral foramen. The average defect volume was 1234±240 mm3. This mean volume ensures practical defects to test novel injectable biomaterials. 6 vertebrae were injected with a commercial cement (Cerament®, Bone Support, Sweden). Adequate defect filling was observed in all vertebrae. All vertebrae were assessed by microCT, prior to and post defect creation and after biomaterial injection. All vertebrae were mechanical tested. No mechanical failure was observed under loads higher than the physiological. Ultimately, this model is considered suitable for pre-clinical in vivo studies, mimicking clinical application.