## 4 Conclusions and Further Research Directions  
This review has highlighted the growing potential of 3D-printed titanium cages in foot arthropods, demonstrating their ability to overcome traditional limitations like poor anatomical fits and nonunion rates. The ability to customize implants for each patient, using techniques such as EBM, SLM, or DMLS, represents a significant advancement in orthopedic care, particularly for complex cases of bone loss and deformity.  
The data gathered from 20 papers in this field provide evidence that 3D-printed titanium cages effectively address the research question by showing their capability to achieve high fusion rates, improve osseointegration, and offer mechanical stability in foot arthropods.  
Clinically, these implants have demonstrated remarkable success in achieving high fusion rates, with osseointegration confirmed by imaging studies, indicating up to a 92% fusion rate for spherical implants, significantly outperforming traditional femoral head allografts. These outcomes underscore the implants' reliability in promoting bone integration and long-term stability. From a design perspective, the customizability of 3D-printed titanium implants represents a key advantage. The patient-specific designs, often incorporating advanced lattice structures (trusses or gyroids), can enhance the mechanical stability and facilitate osseointegration by mimicking the geometry of cancellous bone. The open architecture of these implants allows also for the integration of bone grafts, which supports faster healing and reduces the risk of nonunion, a common complication in foot and ankle arthrodesis. Moreover, the role of these implants in limb salvage is especially relevant, as in severe cases involving traumatic bone loss, with 3D-printed cages being instrumental in avoiding limb amputations.  
As 3D printing technology advances, regulatory bodies are continuously updating their frameworks to accommodate the unique aspects of this emerging field, balancing innovation with patient safety. However, despite these advancements, several challenges remain. The cost of producing custom implants, as well as the relatively long lead times for design and manufacturing, continues to be a barrier to widespread adoption. Moreover, while the short-term clinical outcomes are promising, the long-term durability and performance of these implants need further investigation. Long-term follow-up studies are essential to assess the implants' ability to maintain their structural integrity and functionality over extended periods.  
This review has also identified several key directions for future research. These include exploring alternative biocompatible materials to optimize the mechanical properties, optimizing the AM processes to enhance the efficiency and reduce the manufacturing costs, and conducting long-term studies to assess implants' durability under stress. Additionally, integrating smart sensors into implants for real-time monitoring and examining regulatory and cost-effective strategies for broader accessibility are promising areas. By focusing on these trends, the field of 3D-printed orthopedic implants can continue to evolve, offering more effective and personalized treatment options for patients.  
Conceptualization, I.B., D.L. and D.P.; methodology, I.B., D.P. and D.L.; validation, I.B., R.M. and D.L.; formal analysis, R.M., D.P., D.L. and I.B.; investigation, I.B., R.M., D.P. and D.L.; data curation, D.P., D.L. and I.B.; writing--original draft preparation, I.B. and D.P.; writing--review and editing, I.B., D.L. and D.P. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Data Availability Statement: Not applicable. Conflicts of Interest: The authors declare no conflicts of interest.