Background: Reconstruction of large segmental bone defects is a constant challenge in orthopaedics, with mechanical stability and biological integration being essential for successful healing. Porous titanium alloy prostheses have been gradually applied in non-neoplastic bone defect reconstruction with good clinical results. Different from traditional prostheses, porous structures can match the host bone's elastic modulus by adjusting pore size and porosity, thereby creating a mechanical environment similar to natural bone that enhances bone integration. However, the biomechanical properties of additive-manufactured prostheses and their relationship with bone integration in the human body remain unclear. Methods: Finite element analysis (FEA) was performed to analyze stress distribution in the bone, prosthesis, and screws under different loads. A retrospective analysis of 29 cases of lower limb long bone defects treated with additive manufacturing prostheses was conducted. Bone callus growth around the prosthesis was recorded via X-ray. Differences in bone callus growth between stress concentration and non-stress concentration zones were evaluated. Results: The FEA results indicate that additive-manufactured prostheses exhibit good stability and consistent mechanical transmission. Stress is concentrated on the medial and posterior sides of the bone. When defected involved the metaphysis, the lateral plates effectively distribute stress. In femoral defects, no significant difference was found in bone callus growth between the stress concentration and non-stress concentration areas. However, the average bone callus length at the proximal prosthesis-bone interface showed a significant difference of 15.3mm (P=0.018). At the distal prosthesis bone interface, this difference was 8.9mm (P=0.368). In tibial defects, stress concentration did not significantly affect bone callus growth or length. The proximal lateral plate limited the bone callus growth rate on the same side (37.5% vs 90.5%, P=0.008), indicating the presence of stress shielding effects. Conclusion: Better bone callus growth around the prosthesis was observed in femoral defects. Additive manufacturing is an effective technique for lower limb bone defect reconstruction.