## 1 Introduction  
Since its invention in the 1980s 3D printing has developed rapidly and come to play an important role in various fields of manufacturing including the automotive, medical devices, and aerospace industries [1, 2]. Not long after this technology became available, its potential use in medicine, in particular reconstructive surgery, became obvious [3, 4, 5, 6]. Today 3D printing has numerous applications and in 2020 the International Medical Device Regulators Forum (IMDRF) published its strategic plan for 2021-2025 [7], which described it as a rapidly developing technology in the medical sector. At present many different 3D printing technologies are available, the most common are Vat Photopolymerization (Steeolithography (SLA), Digital Light Processing (DPL)), Material letting (PolyJet, NanoParticle Jetting), Powder Bed Fusion technology (Electron Beam Melting (EBM), Selective Laser Sintering (SLS), Selective Heat Sintering (SHS), Direct Metal Laser Sintering (DMLS)) and MaterialExtrusion (MEX), commonly referred to as Fused Deposition Modeling (FDM) or Fused Filament Fabrication (FFF). Of these technologies, FDM/FFF is currently the most commonly used for rapid prototyping and development of different products [2]. Additionally, this technology is most frequently used to create anatomical models that are used in medicine. This is mainly because such 3D printers have relatively low purchase costs, with a large number of manufacturers and numerous 3D printers readily available on the market. In addition, they are reasonably easy to operate and use low-cost materials [2; 8; 9; 10; 11; 12], of which Acrylonitrile Butadiene Styrene (ABS) and Polylactic Acid (PLA) are the most commonly used. The latter is particularly useful, with regard to anatomical models used in medicine, due to its biodegradability, adequate mechanical properties for such applications, ease of printing (well-defined print parameters), and low purchase costs [2; 8; 9; 10; 11; 12]. 3D printed 1:1 scale anatomical models can be used to visualize and classify complex pelvic fractures as well as optimally plan surgical access for their reconstruction. They can also serve as templates for selecting and pre-contouring surgical plates together with choosing suitable screw sizes. Furthermore, such models can also be used to plan pelvic tumor resection and custom implant design [13]. Studies have shown that such an approach shortens operative times and consequently the duration of general anesthesia; reduces patient blood loss, as well as intraoperative exposure to ionizing radiation [14]. An additional benefit is better patient communication. Of all pelvic injuries, fractures involving the acetabulum are the most challenging [15; 16; 17]. Currently, the number of low-energy osteopororotic fractures involving the acetabulum is increasing, with an estimated annual incidence of 224 per 100,000, in patients over 60 years of age [18]. Open reconstruction together with fracture stabilization, is essential for optimal long-term results and prevention of degenerative changes. In the literature [19], two main approaches to preparing and using 3D printed models as templates for pre-contouring fixation plates, have been described [19] (Figure 1). The two approaches can outlined as shown in Table 1.  
Both of these approaches can be complex and time-consuming processes. Both require knowledge of radiological anatomy and the use of different types of software that can be difficult to master. Furthermore, some basic knowledge of the many 3D printing methods available today is necessary, to choose the optimal technology for a given task. Unfortunately, most software packages used to convert CT data into virtual models as well the 3D printing technologies required to build them are prohibitively expensive. Furthermore, the technique of virtual fracture reduction that consists of accurately repositioning virtual bone fragments is unpredictable.