Biodegradation patterns of injected composite bone cements in porcine vertebral bodies

Abstract

Background: For vertebroplasty, newly synthesized bone cements are proposed to replace traditional polymethylmethacrylate (PMMA). Most inventors initially evaluated these newly developed cements in animal spine models. However, even these time- and work-consuming histological inspections performed meticulously by experienced hands, there are still lots of specimen lost during the processing procedures. Although the histological sections can reveal new bone formations and surrounding tissue reactions to implanted materials, it is difficult to identify the degradation processes of the injected cement. In fact, there is no standard method to quantify the volume changes of injected substitutes postoperation. Methods: Previously, we developed two new biodegradable cements and evaluated performances in fixed-volume and fixed-shaped holes in vertebral bodies of porcine lumbar spine. The animals were sacrificed and the retrieved spines were analyzed after 3 and 6 months. Herein, we further used computed tomography (CT) and three-dimensional CT (3D-CT) to quantitate volumes and biodegradation of cements inside vertebral bodies after previous attestation of CT findings. Exteriors of controls and injected materials were reconstructed with different Hounsfield units (HU); changes of HU as well as cement volumes were later calculated. Results: The results revealed that the volumes and shapes of these biodegradable cements can be determined by 3D-CT. After meticulous comparisons among gross specimens, histologies, and CT images, the different patterns observed in CT implied consistency among all three observations. Gradual reductions of HU and volumes of newly synthesized cements showed the degradability. Meanwhile, consistent HU and volumes of PMMA meant its inertness. Conclusion: CT imaging may be a preliminary, quantitative, and liable way for evaluating injectable bone cements in the vertebral bodies.