Biomechanically Optimized 3D-Printed Titanium Prostheses with Stiffener Arrangement for Critical Femoral Diaphyseal Defects: Early Weight-Bearing Capacity and Combat Readiness Validated Through Integrated Biomechanical-FEA Approach

Guo-Sen Li^1,2Hao Li²Da Liu³Rui Yi⁴Yi Cui⁵Hong-Da Lao²Xiao-Yang Nie²Min Zhao⁶Cheng-Fei Du^7*Yong-Qing Xu^5*Jiang-Jun Zhou^2*

• ¹Nanchang University, Nanchang, China
• ²908th Hospital of People's Liberation Army Joint Logistic Support Force, Nanchang, China
• ³Chinese People's Liberation Army Western Theater General Hospital, Chengdu, China
• ⁴The Seventh Medical Center of PLA General Hospital, Beijing, China
• ⁵920th Hospital of People's Liberation Army Joint Logistic Support Force, Kunming, China
• ⁶the People's Hospital of Yingtan, Yingtan, China
• ⁷Tianjin University of Technology, Tianjin, China

Critical femoral diaphyseal defects exceeding 3 cm present significant challenges in trauma and military orthopedics, particularly in blast injury scenarios requiring rapid rehabilitation. The purpose of this experiment was to evaluate the biomechanical in vitro performance of two personalized prostheses (Groups A and B) designed explicitly for critical femoral diaphyseal defects through integrated biomechanical testing and finite element analysis (FEA). Using fourth-generation composite femurs simulating 10cm defects (n=16), we compared axial compression, torsion, fourpoint bending stiffness, and cyclic fatigue performance against intact bones (Group D) and diaphyseal fractures without defects (Group C).Key findings demonstrate comparable compressive stiffness between prostheses groups (Group A: 764.12±112.63 N/mm; Group B: 693.63±136.31 N/mm) and intact femurs (808.59±18.1 N/mm, p>0.05). The torsional stiffness is comparable between prostheses groups (Group A: 2.28±0.15 Nm/°; Group B: 2.18±0.22 Nm/°) versus diaphyseal fractures without defects (2.01±0.19 Nm/°). The stiffness results comply with mobilization requirements. FEA revealed maximum von Mises stresses in prosthesis fixation systems below the yield strength of Ti6Al4V, with digital image correlation validating the stress distribution patterns. The porous scaffold design achieved optimal modulus (1,132.85 MPa) between cortical and cancellous bone, reducing the "stress shielding" effect. Both prostheses endured 1800N cyclic loading (100,000 cycles ≈ , 13.3 years of physiological use) without structural failure.These customized prostheses address critical military medical needs by enabling immediate weightbearing, reducing surgical complexity compared to bone transport techniques, and maintaining longterm mechanical integrity. The stiffener design philosophy and additive manufacturing flexibility provide adaptable solutions for complex combat-related trauma, significantly advancing early functional recovery in resource-constrained environments.