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NEW BIOMATERIALS
Christian Ryf, Markus Arigoni
NEW BIOMATERIALS chronOS Inject: An injectable, osteoconductive solution for metaphyseal fractures Prior to the introduction of LCP, many fractures with concomitant bone defects had to be treated with either autologous bone or a bone substitute to support bone healing and subsequent fusion. Although LCP reduced the number of fractures in need of bone grafts, there still remains a considerable number of impact fractures with a critical size bone defect close to the joint that make LCP fixation difficult. In these cases, the use of bone or a bone substitute is recommended. In the mid-eighties, brushite cements were investigated, named after the end-product of the setting reaction: brushite, also called dicalcium phosphate dihydrate. Since then, several in vitro and in vivo studies have been performed, but brushite cements were never used clinically. In the mid-nineties, the first calcium phosphate cement formulations were made available. Despite the good clinical performance, some users became disappointed with the slow resorption rate and the poor handling characteristics of these materials. Considering the fast remodelling rate and the good biocompatibility of brushite cements, chronOS Inject was developed to solve these problems, providing surgeons with the option to use an injectable, fast remodelling calcium phosphate cement. The challenge was to design an easily injectable, fully resorbable and simple and safe to handle biphasic bone substitute. The result of the development, chronOS Inject, consists of a fast resorbable brushite matrix in combination with β-tricalcium phosphate granules (chronOS). All components of chronOS Inject are completely synthetic. Injectability Irregular, metaphyseal bone defects can be completely filled with chronOS Inject using a minimally invasive technique. The fluid mechanics are unique due to the addition of sodium hyaluronate as part of the liquid component. The biotechnologically produced sodium hyaluronate is the most physiological and biocompatible carrier known. Studies have indicated positive effects on bone healing. In order to allow for optimal flow characteristics, the rheology of chronOS Inject was extensively tested in internal AO studies. Resorption chronOS Inject resorbs and remodels. Apelt et al (2004), Kümmerle et al (2005), Oberle et al (2005) and Theiss et al (2005) state that resorption of brushite calcium phosphates in a sheep model is mainly based on macrophage activity. The brushite matrix dissolves in the interface between implant and bone (osteoid), thus permitting excellent vascularization and the ingrowth of new bone. The spherical β-TCP granules resorb more slowly than the brushite matrix and act as an anchor for