## 1 Introduction  
Tibial plateau fractures represent a common orthopaedic care problem accounting for 1-2% of all human fractures and are particularly frequent in patients over 50 years old [1], most commonly due to high-energy traumas. A stable, congruent, well-aligned, and painless knee joint along with a restored range of motion are all goals of treatment of such fractures, in order to reduce the risk of potentially severe complications, for example, post-traumatic osteoarthritis [2].  
Several surgical and non-surgical approaches for the management of tibial plateau fractures have been described, but open reduction and plating still remain the treatment of choice in most centres [3; 4].  
In some cases, due to comminuted fractures or excessive bone substance loss, it may be necessary to integrate surgery with bone grafting. Many bone grafting strategies have been investigated so far, each displaying advantages and limitations [5; 6]. As a general paradigm, an ideal bone substitute should be both osteeconductive, meaning that it should allow vascular ingrowth and bone remodelling, and osteoinductive, stimulating mesenchymal stem cells (MSCs) to differentiate into osteoblast progenitors [7]. Autologous iliac bone graft (AIBG) is the current clinical gold standard for bone transplantation, however donor site morbidity, the need for an additional surgery incision and limited available material to be harvested are still not negligible restrictions to this approach [8; 9; 10]. Bone allograft, from live donor or cadaver, have also been proposed, though risk of disease transmission and biocompatibility of such scaffolds are still challenging issues for clinical use [11]. Hence, alternative strategies, such as synthetic bone grafts, have gained increasing attention since they are readily available, easily tailored in different shapes, osteeconductive, and display a predictable absorption rate [12]. Nonetheless, biocompatibility and biomechanical stability requirements of bone substitutes are well met by the use of calcium phosphates (CP) materials; in particular, it has been shown in animal studies that CP-containing grafts are completely remodelled and reabsorbed in 12 to 26 weeks [13; 14; 15]. Bovine xenografts are also valid scaffolds for bone grafting, resembling very closely the structure of human cancellous bone [16]. Still, the need for sterilization of raw animal derived material could alter its biological and mechanical properties; hence, more recently, the application of low temperature processing and composite technologies to xenograft in order to improve biological and mechanical performances is giving promising results, both in investigational and clinical settings [17; 18].  
SmartBone(r) (SB) (Industrie Biomediche Insubri SA, Switzerland) is a composite xenohybrid scaffold (CXS), obtained from a bovine bone-derived mineral matrix, reinforced with aliphatic polyester poly(L-lactide-co-\(\epsilon\)-caprolactone) (PLCL) and RGD-containing collagen fragments (obtained from animal-derived gelatin, where RGD is the tripeptide Arg-Gly-Asp consisting of Argin, Glycine, and Aspartate), which improve elasticity, blood affinity and cell attachment respectively [18; 19; 20].  
This presents the clinical and radiological findings of a cohort of patients suffering tibial plateau fracture treated with percutaneous or open reduction and internal fixation (ORIF) augmented with the CXS described above. Primary objectives of the study were: to assess both clinical and radiological mid-term outcomes of patients included in the study (primary endpoint); to evaluate the mid-term safety of implants on patients, recording any adverse effect or complication related to the procedure.  
Secondary endpoint was to evaluate the ability of the xenograft to integrate with the surrounding bone tissue and promote new bone matrix deposition.