## 3 Results and Discussion
### Medical Aspects  
#### 3.3.1 Clinical Outcomes and Challenges  
In their case report, [PERSON] et al. [18] used a 3D-printed titanium truss cage for the treatment of a tibial plafond nonunion. The case was one with multiple previous surgeries and failure in acquiring tibiotalcanean fusion (TTC), despite multiple options being used. Moreover, the entire approval process was laborious, and the implant cost was high. Fortunately, the result was good at the 1-year follow-up. At that time, the authors considered 3D-printed implants as a \"new frontier in surgery and medicine\" and outlined the lack of regulatory legislation for routine cases. Four years later (2019), [PERSON] et al. [33] reported a posttraumatic case in which a 3D-printed truss cage, retro nail, and allograft were used to obtain TTC fusion in a case with severe bone loss, both on the distal tibia and talar bone. The follow-up time was the longest reported--5 years--but it came with additional benefits of bone osseointegration, as well as construct stability and the absence of the stress shielding phenomenon. It is also worth mentioning that, within 4 years, the legislation for these cases had already moved forward, so that this reported case was performed with FDA approval. Similarly, in 2018, [PERSON] et al. [37] disseminated a revision for failed TAR in which a TTC arthrodisis was obtained using a 3D-printed truss cage, retro nail, and bone graft. Short-term follow-up--1 year--with a good functional status was reported. Since talar subsidence is one of the most commonly reported modes of failure in TAR, the use of customized 3D-printed implants for its partial revision appears both promising and restorative in such cases. In 2019, [PERSON] et al. [35] reported a successful partial revision with a customized 3D-printed talar component and with an additional truss cage, achieving good primary stability and graft incorporation. The results at the 1-year follow-up were good in terms of the range of motion and functional results. In the early stages of 3D printing technology, authors reported combined cases treating various pathologies, such as ankle fusion, deformity correction, and osteotomies, as seen in [PERSON] et al. 's 2018 study [30]. However, after 2020, studies began focusing on more specific pathologies. Still, particular cases were reported, as in [PERSON] et al. 's paper from 2020 [17]. The most important aspect presented in [17] is that the 3D-printed cage worked in a severe segmental bone defect in a pediatric patient. A similar case, with a segmental defect on the tibia of about 8.5 cm, was previously reported to be successful by [PERSON] et al. [31] in 2016. The 3D-printed titanium truss successfully managed to restore the tibial length and achieve ankle fusion. In this paper, 3D-printed cutting guides were also mentioned, with their purpose being to allow the proper accommodation of the implant, while performing controlled, minimal bone cuts. In 2020, [PERSON] et al. [15] published the first retrospective comparative study analyzing custom-made implant spheres versus bulk femoral allografts in TTC arthrodeis for various etiologies. Despite some bias (retrospective, non-randomized, small number of cases), the results documented the usage of customized sphere implants as being safe and achieving a significantly higher number of joints to be fused. One year later, [PERSON] et al. [34] reported 12 cases in which truss customized implants were used in various pathologies of the foot and ankle. In 91% of the cases, the fusion of the TTC, in the metatarsophalangeal and subtalar joints, was obtained while using various types of truss cages and allografts, proving that 3D-printed cages may be extremely helpful in malalignment, malunion, nonunion, severe acquired deformities, or large osseous defects. However, CT scan examinations were used to document fusion in only 7 of the 12 operated cases, and the follow-up period was 12 months. In the same year, [PERSON] et al.