# Novel Design of Expandable Spinal Cage for Efficient Lumbar Spine Fusion Operation
## 6 Conclusions  
In this study, we introduced a novel linkage mechanism and slider adjustment method to design an expandable spinal cage capable of sufficient height and angle expansion, independent adjustment, and continuous fine-tuning. This design was validated through FEM analysis and mechanical testing. Key findings are summarized as follows:  
* The new linkage mechanism applied in this design enables the independent control of height and angle, a functionality that is difficult to achieve with traditional rack-and-pinion or wedge-type designs. Additionally, continuous fine-tuning facilitated by sliders allows surgeons to achieve precise alignment tailored to the anatomical characteristics of individual patients during surgery. * Experimental results showed trends similar to calibrated FEM analysis, particularly demonstrating a high correlation between two evaluation methods in predicting yield locations at anterior sliding block and lower plate shaft regions. FEM analysis was calibrated considering elastic deformation of testing apparatus, enhancing the reliability of the FEM model. * In compression and compression-shear tests, the designed spinal cage exhibited an ultimate load exceeding the lower fifth percentile of FDA-approved products, thereby satisfying clinical requirements. These findings confirm that proposed design offers significant improvements over existing products and demonstrates high potential for clinical application as a patient-specific spinal fusion device. * However, this study has several limitations. Firstly, the evaluation was limited to static load testing, without performing dynamic fatigue testing, leaving durability under prolonged cyclic loading inadequately assessed. Since real clinical environments involve tens of millions of repetitive loads, fatigue testing is necessary to confirm long-term mechanical stability. Moreover, as this research was confined to in vitro testing, clinical trials or animal studies evaluating actual in vivo applicability have not yet been conducted. Future research should include such validation processes to establish clinical efficacy. Overall, this study provides essential baseline data for design and performance assessment of expandable spinal cages, highlighting the potential for developing safer and more effective spinal fusion instruments. Future dynamic fatigue testing and clinical studies are needed to evaluate long-term durability and real-world clinical applicability, paving the way for advancements in spinal fusion technology. Conceptualization, J.Y. ; methodology, C.P. and T.T.K.D. ; validation, S.-J.P., D.-S.C. and S.H.C. ; formal analysis, C.P. ; investigation, C.P. and T.T.K.D. ; resources, J.Y. ; writing--original draft, C.P. ; writing--review & editing, S.-J.P., D.-S.C., S.H.C. and J.Y. ; supervision, J.Y. ; funding acquisition, J.Y. All authors have read and agreed to the published version of the manuscript. This research was financially supported by the Ministry of Trade, Industry, and Energy (MOTIE), Korea, under the \"Innovative Digital Manufacturing Platform\" program (reference number P00223311) supervised by the Korean Institute for the Advancement of Technology (KIAT). This work was also supported by the Ministry of Trade, Industry, and Energy (MOTIE), Korea, under the \"170 k closed section roll forming and free curvature bending technology development for electric vehicle body\" grant (reference number 20022814) supervised by the Korea Institute for Advancement of Technology (KIAT). Finally, this work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (RS-2025-00555072). The authors have no conflicts of interest to declare. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author. **Conflicts of Interest:** The authors declare no conflict of interest.