J.-M. Bouler, E. Verron, H. Pascal-Moussellard, A. Wajeck, I. Khairoun, B. Bujoli, O.Gauthier, (Nantes, France)
INTRODUCTION: Osteoporosis has been defined as « a systemic disease characterized by low bone mass and micro architectural deterioration of bone tissue, with consequent increase in bone fragility and susceptibility to fracture ». Resorbable calcium phosphate (CaP) biomaterials have proved a noticeable efficacy in bone reconstruction surgery. Furthermore bisphosphonates (BPs) are well known antiresorptive agents largely used in systemic clinical treatments of osteoporosis. An injectable BP-combined CaP matrix has been developed in order to reinforce locally osteoporotic bone by increasing bone mineral density and improving bone micro architecture [2-4]. The purpose of this study was to implant such a combined device in ewes’ vertebrae and to quantify bone structure modifications. The properties of bone reinforcement after implantation of BP-loaded and unloaded CaP cements were investigated by three-dimensional microtomography (3D-µCT) that was first developed for nondestructive analysis of trabecular bone architecture 
MATERIALS AND METHODS: Calcium deficient apatite was loaded with alendronate (7%w/w) according to a method previously described . The resulting powder was gamma sterilized and integrated within a specific apatitic cement formulation. Two cubic centimeters of the tested biomaterials were implanted in three vertebral bodies of 4 mature ewes. 3D-µCT analysis was conducted on the 12 implanted vertebral bodies. Bone specimens were collected immediately after sacrifice and conserved frozen. Vertebras were sectioned with respect to the implanted area to fit into the analysis chamber of the µ-CT device. For the analysed samples, bone or newly formed bone volume density (BV/TV), trabecular thickness (TbTh), space between trabeculae (TbSp) and number of trabeculae (TbN) were measured. A non-parametric Mann & Witney test (a=O.O5) was applied for statistic analysis.
RESULTS AND DISCUSSION: After 12 weeks of implantation significant differences of the bone density and micro architecture were observed between the two groups. Those modifications have been quantified by measuring conventional histomorphometric parameters . Comparing BP-loaded cement implants with unloaded ones for µ-CT histomorphometric measurements showed significant increases (p<0.05) for bone volume density (+50.4%), trabecular thickness (+5.4%) and trabecular number (+60.4%) and a significant decrease for trabecular space (-15.0%). For the first time to our knowledge, a local combined effect of calcium phosphate cement and bisphosphonate is evidenced on sheep vertebral bodies. Those preliminary results can be considered as a first step for a local approach that aims in delaying or even preventing osteoporotic fractures. Reinforcing specific bone sites like vertebral bodies, proximal femurs or wrists by implanting calcium phosphate cements that can promote bone ingrowth and release controlled quantities of bisphosphonates could be considered, in the near future, as an alternative to current systemic injections. Indeed, this combined device allows using small quantities of BPs that present a pure local effect because of the high affinity of BPs for bone apatite. This way of delivery could then decrease described side-effects (e.g. jaw osteonecrosis), due to regular and long-term BPs treatments. Obviously complementary in vivo experiments (mechanical tests, undecalcified histology) have to be conducted in order to better characterize the potential efficacy and eventual limits of such a local approach. Figure:: Scanning electron microscopy images of vertebras implanted respectively with cement (up) and BP-loaded cement (down) REFERENCES: Consensus development conference, Am. J Med 94: 646-650 1993 Josse, S.,...& Bouler, J.M. Adv. Mater. , 16: 1423-27, 2004. Josse, S.,.. & Bouler, J.M. Biomaterials, 26: 2073-80, 2005 Roussiere, H... & Bujoli, B. J. Mater. Chem. 15: 3859-68. M¸ller, R. et al. Bone 23: 59-66, 1998 AKNOWLEDGEMENTS : This Work was supported by ANR - RNTS 2005 and GRAFTYS. Authors would like to thank Mrs Julie Lesoeur for histology.