Objective This study aimed to investigate the differences in mechanical responses of knee joint internal tissues among older adults with varying bone qualities during unplanned gait termination (UGT) at different walking speeds, and quantify intra-articular stress distribution and changes in peak stress, so as to provide a theoretical basis for the prevention and early intervention of knee joint-related injuries in the older people.

Methods Dual fluoroscopic imaging systems (DFIS) and finite element analysis (FEA) were integrated to develop individualized three-dimensional finite element models of the knee joint based on reverse engineering. Models with different bone densities were established by assigning gradient material properties, including a normal group (NG), an osteopenia group (OG1), and an osteoporosis group (OG2). Boundary and loading conditions derived from laboratory biomechanical tests (including 3D knee angles and ground reaction force) were applied to simulate UGT under slow (1.3 m/s), normal (1.45 m/s), and fast (1.6 m/s) walking speeds. Changes in equivalent stress in the meniscus and tibial cartilage were compared.

Results Measurements from DFIS and FEA-calculated femoral-tibial relative displacements in medial-lateral, anterior-posterior, and proximal-distal directions showed good consistency (ICC=0.998, Bland-Altman mean difference=0.05 mm), validating the effectiveness of the knee joint model. FEA results indicated that meniscal stress exhibited regional variations with increasing speed: stress in the anterior horn first increased and then decreased, with the lateral anterior horn stress in the NG group under fast UGT decreasing by 19.20% and 33.55% compared to slow and normal speeds, respectively. Stress in the body and posterior horn continued to rise, with the lateral body stress increasing by 36.84% and 9.86%, and the lateral posterior horn stress rising by 42.11% and 31.71%, respectively. Tibial cartilage stress increased with speed, with the lateral stress in the NG group increasing by 37.40% and 20.00% compared to slow and normal speeds, respectively. Decreased bone density (OG1 and OG2 groups) further affected stress distribution within the knee joint. Under fast UGT, meniscal body stress in the OG2 group increased by up to 11.47% compared to the NG group, while tibial cartilage stress decreased by a maximum of 9.44%.

Conclusions At fast speed, the posture adjustments of the knee joint induced by the UGT task may alter joint contact conditions, thereby contributing to increased stress in the meniscal body and posterior horn as well as in the tibial cartilage. Decreased bone density may reduce tibial cartilage stress through load redistribution but also exacerbates meniscal load, potentially increasing its degeneration risk.