Altered bioreactivity and limited osteoconductivity of calcium sulfate-based bone cements in the osteoporotic rat spine.

Abstract

Previous studies documenting the osteoconductive nature of calcium sulfate (CaSO(4))-based biomaterials have been largely limited to animal models exhibiting nonosteoporotic bone biology. In addition to diminished bone mineral density (BMD) and altered bone microarchitecture, the osteoporosis phenotype is associated with a proinflammatory and pro-osteolytic state. Thus, osteoporosis may elicit an amplified bioreactivity to common orthopedic biomaterials, potentially limiting their full osteoconductive capabilities in vivo. The purpose of this study is to test the hypothesis that CaSO(4)-based bone cements exhibit altered bioreactivity and limited osteoconductivity in response to osteoporotic conditions. 1) Microcomputed tomography (micro-CT) radiomorphometry study and 2) histological analysis. Our laboratory has previously established a preclinical model of osteoporosis using the rodent osteoporotic spine (OS). Caudal vertebral defects were filled with either CaSO(4) or CaSO(4)/CaPO(4) (Hybrid) cement for each group (n=4). Over 8 weeks, cement resorption profiles, BMD, average cortical thickness, average trabecular thickness, average trabecular spacing, and diaphyseal bone volume fraction were assessed via micro-CT radiomorphometry. Histological analysis was performed on vertebrae obtained postsurgery and at Week 8. Both materials displayed an accelerated cement resorption profile after implantation into the OS vertebrae. Hybrid cement exhibited slower resorption compared with that of CaSO(4) under both normal female rats (NL) and OS conditions. The cement-mediated bone augmentation observed in the NL spine was altered under OS conditions. This study suggests that cement bioreactivity is heightened and osteoconductivity may be limited in a preclinical model of the OS. The disparity between the two resorption profiles suggests that this accelerated cement resorption is a material-dependent phenomenon. The proinflammatory and pro-osteolytic bone environment associated with the osteoporosis disease state may contribute to the accelerated resorption and altered osteoconductivity exhibited by both materials. Future study of potential biomaterials intended for use within the OS may necessitate further exploration of the relationship between biomaterial performance and osteoporosis bone biology.