Use of the Bone Substitute SintLife® in Vertebral Arthrodesis Procedures. A Pilot Study.

1. INTRODUCTION AND RATIONALE The vertebral arthrodesis is one of the surgical procedures most used for the treatment of deformities, trauma and degenerative diseases with instability of the spine (Rajaee et al., 2012; Yoshihara and Yoneoka, 2015).

Using bone grafts and tools, such as metal rods and screws, this procedure creates a fusion between two or more adjacent vertebrae, in order to stabilize the spine.

The success of fusion, intended as the neo-formation of trabecular bone radiographically detectable, may depend on the characteristics of the bone graft used and its properties as well as the surgical technique used. In the absence of autologous bone the biological process that leads to bone regeneration is characterized by three critical elements: the osteogenic potential, the osteoinductive factors, the osteoconductive scaffold. The ideal bone substitute possesses all three of these properties, combined with excellent compatibility and biological safety (Ludwig et al., 2000; Park et al., 2013).

The local autologous bone harvested from the iliac crest has been and is still considered the "gold standard" in the treatment of spinal fusion. However, contraindications and potential complications associated with the use of autologous bone are well known (Dimar et al., 2009; Gruskay et al., 2014; Kim et al., 2009; Miyazaki et al., 2009). In order to overcome these limitations, several alternatives have been developed, clinically tested and are today available on the market: growth factors (BMPs) (Carragee et al., 2011; Kannan et al., 2015), allogenic bone or heterologous ( Gupta et al., 2015; Park et al., 2013), demineralized bone matrix (DBM) and synthetic ceramic materials to name a few (Abdullah et al., 2011; Fischer et al., 2013; Hsu et al., 2012) . Despite all of these materials have been extensively studied (Abdullah et al., 2011; Alsaleh et al., 2012; Hsu et al., 2012; Miyazaki et al., 2009) the available data are often uneven in quality, type of study, assessments performed and conclusions reached (Hsu et al., 2012; Kannan et al., 2015; Miyazaki et al., 2009).

The ceramic bone substitutes of synthetic origin (Nickoli and Hsu, 2014), such as collagen, tricalcium phosphate (TCP) (Dai and Jiang, 2008), calcium phosphate (CaP), calcium sulphate (CaS) and hydroxyapatite (HA), have been designed and developed as osteoconductive scaffolds with characteristics and properties very similar to those of human bone, able to support the regeneration and bone remodeling, and go into slow resorption (Alsaleh et al. , 2012; Gao et al., 2014; Hsu et al., 2012; Kaiser et al., 2014; Kho and Chen, 2008; Korovessis et al., 2005; Lee et al., 2009; Zhou and Lee, 2011) .