## 3 Results and Discussion
### Narrative Review
#### 3.1.3 Bibliometric Results: Trend Analysis and Research Gaps  
The bibliometric results presented in Figure 3 provide insights into the current research landscape for 3D-printed implant cages. The largest cluster (green, in Figure 3a) is centered on the manufacturing technologies and materials, including terms like \"additive manufacturing\", \"3D printing\", \"titanium\", and \"electron beam melting\". The red cluster is focused more on medical aspects, particularly clinical outcomes, patient demographics, and recovery, as indicated by keywords such as \"human\", \"case report\", \"bone defect\", and \"postoperative complication\". The blue cluster deals with case-specific outcomes (i.e., the evaluation of the effectiveness of 3D-printed cages in real-world surgeries), surgical techniques, and specific orthopedic applications, such as \"ankle arthrodesis\", \"bone graft\", \"fusion\", and \"pilon fracture\", which are closely related to arthrodesis procedures and clinical practices.  
The sizes of the nodes for terms like \"3D printing\", \"arthrodesis\", and \"additive manufacturing\" are the largest and most central on the map, indicating their high relevance and frequent discussion in the literature. Over time (Figure 3b), the research has expanded, reflecting an increased interest in topics related to the production processes, such as SLM, EBM, PEEK, and biomaterials, highlighting ongoing innovations in this field. The lines indicating the timeframes that connect keywords like \"pilon fracture\", \"bone graft\", and \"ankle arthrodesis\" show that these topics have been have been well established in earlier research yet are still relevant for ongoing research.  
The two maps, although visually similar, serve distinct purposes: Figure 3a highlights clusters of related research topics, illustrating the relationships between key terms and thematic areas, while Figure 3b includes the temporal dimension, using a color scale to show the progression of the research over time. The consistent positioning of the terms across both maps reflects their shared foundation in the co-occurrence analysis, with Figure 3b overlaying the publications' timing to visualize the trends. This temporal analysis indicates the increasing interest in SLM and EBM processes, as well as materials like PEEK, which appear in more recent studies (represented by green and yellow hues). Earlier research focused more broadly on general topics like \"titanium\", \"3D printing\", and \"osseointegration\", as seen in blue tones, highlighting the foundational work that set the stage for current innovations.  
The bibliometric analysis also allowed the identification of several areas for further research, with one of the most important being related to long-term follow-up studies, whose mention is limited--as indicated by the sparse connections between terms like \"follow-up studies\" and \"controlled studies\". Therefore, for researchers in this field, it will be important to take into account the assessment of the effectiveness and durability of 3D-printed arthrodesis cages. Moreover, the analysis also pointed to a growing emphasis on optimizing materials like titanium and refining the implant designs, such as lattice structures, to enhance the osseointegration and mechanical stability.  
Both maps in Figure 3 highlight specific surgical applications, but terms like \"limb salvage\" and \"large osseous defect\" suggest the types of orthopedic cases in which 3D-printed cages have been explored. Therefore, further studies should consider expanding the use of such cages to other complex orthopedic cases, particularly those difficult or rare conditions in which implant personalization is the only viable solution.