## 1 Introduction  
Arthrodesis, or joint fusion, is a widely performed surgical procedure for the management of severe joint arthritis, deformity, or instability, particularly in the foot and ankle, by eliminating movements in the joint [1]. The procedure involves removing the damaged cartilage, followed by the surgical fusion of two or more bones of the joint using screws, bars, plates, intramedullary nails, implants (prefabricated or customized cages), or bone grafts [2; 3]. The most common conditions requiring arthroresis are end-stage arthritis, trauma-induced bone loss, avascular necrosis, Charcot neuropathy, rheumatoid arthritis with significant deformity, and failed total ankle replacement (TAR) [4; 5]. It is also the standard treatment for rigid and collapsing deformities, such as progressive collapsing foot deformity (PCFD), where fusion provides both stability and correction. Despite its effectiveness in addressing these severe conditions, foot and ankle arthroresis is challenging. One of the most significant complications is nonunion, when the bones do not properly fuse. The nonunion rates after foot and ankle arthroresis were reported to be as high as 13% [6]. Nonunion leads to chronic pain, functional impairment, and the need for revision surgery, which comes with increased health risks and prolonged recovery times. The factors contributing to nonunion include poor bone quality, insufficient fixation, infection, or insufficient blood supply to the fusion site. In this context, due to the wide variability in foot and ankle deformities and the complexity of cases, there is a growing need for individualized treatment strategies, as standard off-the-shelf implants often fail to address the specific anatomical and biomechanical needs of patients with large bone defects or severe deformities, resulting in poor outcomes. This highlights the interest in more personalized solutions, with 3D-printed customized implants showing promise [7]. In orthopedic surgery, the use of 3D-printed implants composed of materials such as PEEK or Ti-6 Al-4V has become increasingly frequent. While long-term clinical results are not largely available [8], various clinical case reports show outcomes with promising improvements, mainly due to the osseointegration made possible by the porous structure or the lattice structure of the implants, which promotes bone adhesion and long-term stability. Additionally, these materials offer a high strength-to-weight ratio and biocompatibility, characteristics that make them well suited for complex reconstructive surgeries. Thus, porosity and structural design are critical in the success of these implants. The reported pore size of the implants is 300-600 \(\upmu\)m in order to facilitate cell penetration and allow nutrient exchange [9; 10], and the pores should be interconnected for the same reason [11]. The volume porosity for lattice structures was reported to be between 62% and 80%, depending on the design parameters [9; 10; 11]. From the structural characteristics perspective, as mentioned, a balance between biological performance, mechanical strength, and compatibility with bone properties is needed. Thus, the literature presents the strut thickness of the 3D-printed titanium implant with an average value of around 498 \(\upmu\)m [12]. The struts or spikes are the individual structural elements of the lattice or porous structure of the implant, being the solid parts between the pores in the lattice framework. The strut thickness is a critical design parameter of the implant that ensures its structural integrity while participating in osseointegration and maintaining mechanical compatibility with the surrounding natural bone. Such structures can be produced using electron beam melting (EBM), selective laser melting (SLM), and direct metal laser sintering (DMLS) processes--all belonging to the category of powder-bed fusion AM [11]. Another significant advantage of using 3D-printed cages is the integration of bone grafts.