A common location for radius fracture is the proximal radial head. With the arm in neutral position, the fracture usually happens in the anterolateral quadrant (Lacheta et al., 2019). If traditional surgeries are not enough to induce bone stabilization and vascularization, or the fracture can be defined grade III or grade IV (Mason classification), a radial head prosthesis can be the optimal compromise between bone saving and recovering the “terrible triad”. A commercially available design of radial head prosthesis such as Antea (Adler Ortho, Milan, Italy) is characterized by flexibility in selecting the best matching size for patients and induced osteointegration thanks to the Ti-Por. ®. radial stem realized by 3D printing with laser technique (Figure 1). As demonstrated, Ti-Por. ®. push-out resistance increased 45% between 8 −12 weeks after implantation, hence confirming the ideal bone-osteointegration. Additional features of Antea are: bipolarity, modularity, TiN coating, radiolucency, hypoallergenic, 10° self-aligning. The osteointegration is of paramount importance for radius, in fact the literature is unfortunately reporting several clinical cases for which the fracture of the prosthesis happened after bone-resorption. Even if related to an uncommon activity, the combination of mechanical resistance provided by the prosthesis and the stabilization due to the osteointegration should cover also accidental movements. Based upon Lacheta et al. (2019), after axial compression-load until radii failure, all native specimens survived a compression-load of 500N, while the failure happened for a mean compression force of 2560N. The aim of this research study was to test the mechanical resistance of a radial head prosthesis obtained by 3D printing. In detail, a finite element analysis (FEA) was used to understand the mechanical resistance of the core of the prosthesis and the potential bone fracture induced in the radius with simulated bone- resorption (Figure 2a). The critical level was estimated at the height for which the thickness of the core is the minimum (Figure 2b). Considered boundary conditions:. - Full-length prosthesis plus radius out of the cement block equal to 60mm (Figure 2a);. - Bone inside the cement equal to 60mm (Figure 2b);. - Load inclined 10° epiphysiary component (Figure 2c);. - Radius with physiological or osteoporotic bone conditions;. - Load (concentrated in the sphere simulating full transmission from the articulation) of 500N or 1300N or 2560N. Figure 3 shows the results in terms of maximum stress on the core of the prosthesis and the risk of fracture (Schileo et al., 2008). According to the obtained results, the radial head prosthesis shows promising mechanical resistance despite of the simulated bone-resorption for all applied loads except for 2560N. The estimated mechanical limit for the material in use is 200MPa. The risk of fracture is in agreement with the experimental findings (Lacheta et al. (2019)), in fact bone starts to fail for the minimum reported failure load, but only for osteoporotic conditions. The presented FEA aimed at investigating the behavior of a femoral head prostheses made by 3D printing with simulated bone-resorption. The prosthesis shows to be a skilled solution even during accidental loads. For any figures or tables, please contact the authors directly

Introduction:. Total hip arthroplasty has became one of the most successful standard procedures in the orthopaedic surgery. With a more frequent use in young and active patients bone saving procedures become more important. On the other hand, the ever increasing trend toward minimal excision of the healthy bone during implantation of the total hip replacement has led to a range of implants that can be classified according their means of anchorage in the various anatomic segments. The Nanos-short-stem endoprothesis presented here requires metaphyseal anchorage. Material and methods:. From juli 2005 to march 2009 a total of 112 (70 males, 52 female) uncemented Nanos-short-stem prothesis were implanted in 111 patients in Westpfalz academic hospital –University Mainz. The patiens average age was 53 years (33–73). The indication for this procedure was predominantly coxarthrosis. In all cases dorsal approach was used. The mean follow up period was 2,5 years (range 6 months–4,5 years). The patients were assessed using Harris Hip Score and radiologically to detect any bone changes, the stand of the prothesis and peri-articular ossifications. Results:. The perioperative Harris Hip Score was 53 (28–77), postoperative was 94 (86–100). We did not have discovered any prothesis specific complications. Radiological follow up examinations showed the development of increasing trabecular reinforciment of the femoral neck and pertrachanteric regions. There is no evidence of any loosing or migration of the prothesis. Conclusion:. the stem design of Nanos-short-stem prothesis allowed a metaphyseal intertrochanteric multipoint primary fixation. The surgical technique is simple. It offers alternative to convenential total hip arthroplasty especially in young patients and save bone stock for later revision (1–2). Long term studies still be needed