**5. Conclusions**

The stress distribution for a pelvis reconstructed by an individual endoprosthesis with four different screw forces was analysed. The obtained optimal screw pretension force for tightening the implant to the bone was from 500 N to 1000 N for this specific model.

Screw tightening with a force less than 500 N seemed to be insufficient for firm fixation of the implant. At the same time, the results show that a tightening force exceeding 1000 N may result in a local bone fracture. Therefore, the optimal and critical screw forces are determined, and the stress states are calculated for the walking condition. The peak stresses occur near the holes in the bones, implant, and screws. Screw tightening with a force of 500–1000 N should be optimal because the stress state of the bones did not exceed the limits globally. This value for screw force provides reliable fixation of the implant to the bones.

When conducting the subsequent surgery, it is strongly recommended to monitor the value of the actual screw pretension force. In this case, the endoprosthesis will be reliable and durable. To prevent the undesirable development of degenerative effects during the patient's recovery process after osteosynthesis surgery, the rehabilitation plan should be adjusted to reduce the loads on the reconstructed bone by providing additional support when the person is walking.

As a result of the arthroplasty described in current research, the patient has fully recovered with no limitations in motion or activities [8]. This fact confirms the relevance of the performed studies and the significance of further development of computer modelling methods and approaches for solving the problems of personalized orthopaedics. The technology of implant development using computer modelling, finite element analysis, and 3D printing makes it possible to create anatomical prostheses with sufficient safety margins, anatomical designs, and reliable fixation methods.

**Author Contributions:** Conceptualization, L.M.; methodology, L.M. and M.Z.; validation, I.M. and D.S.; formal analysis, I.M. and F.T.; investigation, I.M.; data curation, F.T.; writing—original draft preparation, L.M. and I.M.; writing—review and editing, L.M. and M.Z.; visualization, D.S.; supervision, A.B. and L.M.; project administration, A.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was partially funded by the Ministry of Science and Higher Education of the Russian Federation as a part of the World-class Research Center program: Advanced Digital Technologies (contract No. 075-15-2020-934 dated 17 November 2020).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Acknowledgments:** We gratefully thank Evgeniy Sushentsov (N. N. Blokhin NMRCO) for the provided anonymous CAD models and other biomedical data concerning the implant design and useful discussions regarding the paper.

**Conflicts of Interest:** The authors declare no conflict of interest.
