Objective: To assess the tibio‐femoral contact forces before and after total knee arthroplasty (TKA) in patients with knee osteoarthritis (KOA) by three‐dimensional (3D) finite element analysis (FEA) models and gait analysis.Methods: Two hospitalized patients with Kellgren–Lawrence grade IV varus KOA and two healthy subjects were enrolled in this study. Both patients underwent unilateral TKA. FEA models were established based on CT and MR images of the knees of the patients with KOA and healthy subjects. Gait analysis was performed using a three‐dimensional motion capture system with a force plate. Three direction forces at the ankle joints were calculated by inverse dynamic analysis, which provided the load for the FEA models. The total contact forces of the knee joints were also calculated by inverse dynamic analysis to enable comparisons with the results from the FEA models. The total knee contact forces, maximum von Mises stress, and stress distribution of the medial plateau were compared between the patients and healthy subjects. The distributions of the medial plateau force at 2 and 6 months postoperatively were compared with the distributions of the forces preoperatively and those in the healthy subjects.Results: During static standing, the medial plateau bore the most of the total contact forces in the knees with varus KOA (90.78% for patient 1 and 93.53% for patient 2) compared with 64.75 ± 3.34% of the total force in the healthy knees. At the first and second peaks of the ground reaction force during the stance phase of a gait cycle, the medial plateau bore a much higher percentage of contact forces in patients with KOA (74.78% and 86.48%, respectively, for patient 1; 70.68% and 83.56%, respectively, for patient 2) than healthy subjects (61.06% ± 3.43% at the first peak and 72.09% ± 1.83% at the second peak). Two months after TKA, the percentages of contact forces on the medial tibial plateau were 79.65%–85.19% at the first and second peaks of ground reaction forces during the stance phase of a gait cycle, and the percentages decreased to 53.99% – 68.13% 6 months after TKA.Conclusion: FEA showed that TKA effectively restored the distribution of tibio‐femoral contact forces during static standing and walking, especially 6 months after the surgery. The changes in the gait were consistent with the changes in the contact force distribution calculated by the FEA model.

Background: Prosthesis subsidence and mechanical failure were considered significant threats after vertebral body replacement during the long-term follow-up. Therefore, improving and optimizing the structure of vertebral substitutes for exceptional performance has become a pivotal challenge in spinal reconstruction. Methods: The study aimed to develop a novel artificial vertebral implant (AVI) with triply periodic minimal surface Gyroid porous structures to enhance the safety and stability of prostheses. The biomechanical performance of AVIs under different loading conditions was analyzed using the finite element method. These implants were fabricated using selective laser melting technology and evaluated through static compression and subsidence experiments. Results: The results demonstrated that the peak stress in the Gyroid porous AVI was consistently lower than that in the traditional porous AVI under all loading conditions, with a maximum reduction of 73.4%. Additionally, it effectively reduced peak stress at the bone-implant interface of the vertebrae. Static compression experiments demonstrated that the Gyroid porous AVI was about 1.63 times to traditional porous AVI in terms of the maximum compression load, indicating that Gyroid porous AVI could meet the safety requirement. Furthermore, static subsidence experiments revealed that the subsidence tendency of Gyroid porous AVI in polyurethane foam (simulated cancellous bone) was approximately 15.7% lower than that of traditional porous AVI. Conclusions: The Gyroid porous AVI exhibited higher compressive strength and lower subsidence tendency than the strut-based traditional porous AVI, indicating it may be a promising substitute for spinal reconstruction.

Objective: To compare the biomechanical properties of percutaneous cement discoplasty (PCD) in the spinal column between different implant‐endplate friction.Methods: A validated L3‐Scarumfinite element (FE) model was modified for simulation. In the PCD model, the L4/5 level was modified based on model 1 (M1) and model 2 (M2). In M1, the interaction between bone cement and endplate was defined as face‐to‐face contact with a friction coefficient of 0.3; in M2, the contact was defined as a Tie constraint. 7.5 N m moments of four physiological motions and axial load of 15, 100 and 400 N preload were imposed at the top of L3. The range of motion (ROM) and interface stress analysis of endplates, annulus fibrosus and bone cement of the operated level were calculated for comparisons among the three models.Results: The ROM of M1 and M2 increased when compared with the intact model during flexion (FL) (17.5% vs 10.0%), extension (EX) (8.8% vs −8.8%), left bending (LB) (19.0% vs −17.2%) and left axial rotation (LR) (34.6% vs −3.8%). The stress of annulus fibrosus in M1 and M2 decreased in FL (−48.4% vs −57.5%), EX (−25.7% vs −14.7%), LB (−47.5% vs −52.4%), LR (−61.4% vs −68.7%) and axis loading of 100 N (−41.5% vs −15.3%), and 400 N (−27.9% vs −27.3%). The stress of upper endplate of M1 and M2 increased in FL (24.6% vs 24.7%), LB (82.2% vs 89.5%), LR (119% vs 62.4%) and axis loading of 100 N (64.6% vs 45.5%), and 400 N (58.2% vs 24.3%), but was similar in EX (2.9% vs 0.3%). The stress of lower endplate of M1 and M2 increased in FL (170.9% vs 175.0%), EX (180.8% vs 207.7%), LB (302.6% vs 274.7%), LR (332.4% vs 132.8%) and axis loading of 100 N (350.7% vs 168.6%), and 400 N (165.2% vs 106.7%).Conclusion: Percutaneous cement discoplasty procedure could make effect on the mobility or stiffness. The fusion of bone cement and endplate might have more biomechanical advantages, including of the decreasing rate of implant subsidence and dislocation, and the increase spine stability.

Objective: The gait analysis of patients after surgery for tumors around the knee joint relies on the use of a three‐dimensional motion capture system. However, obtaining long‐term, free‐standing, real‐world gait data with three‐dimensional gait analysis is challenging. In this study, we utilized a portable gait analyzer to collect gait data from patients who underwent rotating hinge knee megaprosthesis (RHK) and total knee arthroplasty (TKA), this study aims to compare via gait analysis patients who underwent megaprosthesis with patients with TKA.Methods: A retrospective study was conducted on eight patients with knee bone tumors (RHK group) and ten patients with knee osteoarthritis who underwent standard TKA (TKA group) from January 2018 to January 2022. Gait analysis, was conducted using the Intelligent Device for Energy Expenditure and Activity (IDEEA), and the results were compared with those of a healthy control group. The lower limb alignment of the RHK and TKA groups was evaluated, and the KSS scores of the two groups were collected and compared. Energy consumption during a 20‐m walk was measured and compared among the RHK, TKA, and healthy control groups using one‐way ANOVA. Paired t‐tests were used to compare the operated and nonoperated limbs within groups.Results: All patients exhibited slower walking speeds and cadence than the healthy control participants (p < 0.01), While no significant differences were found between the RHK and TKA groups. The single support time (521.15 ± 94.56 ms) of the RHK‐operated limb was significantly shorter than that of the nonoperated limb (576.53 ± 77.40 ms, p = 0.004). The pulling acceleration of the RHK group (0.71 ± 0.27 G) was lower than that of the TKA group (1.04 ± 0.31 G, p = 0.029). The push‐off angle in the RHK group (24.91° ± 10.91°) was significantly greater than that in the TKA group (10.64° ± 5.41°, p = 0.007). The RHK group showed significant differences between the operated and nonoperated limbs in terms of swing power, ground impact, footfall, and push‐off. The RHK (0.03 ± 0.01 kcal/min/kg) and TKA (0.029 ± 0.01 kcal/min/kg) groups had significantly greater energy expenditures than did the healthy control group (0.02 ± 0.00 kcal/min/kg, p < 0.05). The comparison of HKA angles and KSS scores between the TKA and RHK groups showed statistically significant differences.Conclusion: A portable gait analyzer appears to be suitable for evaluating the effects of RHK. RHK patients demonstrate more pronounced gait abnormalities than TKA patients, reflected in greater energy expenditure, implying reduced walking efficiency. This suggests the need for increased energy expenditure in RHK patients to compensate for abnormal knee joint conditions during walking and maintain body balance.