Zhenxian Chen

This study aims to investigate the impact of tibial tray fixation peg structure in posterior stabilized (PS) knee prostheses on its initial fixation stability, a finite element model and a micromotion prediction model of PS total knee arthroplasty (TKA) were established to comparatively study the differences in the von Mises stress of the proximal tibia and the micromotion at the bone-prosthesis fixation interface under four PS tibial tray fixation peg design, namely cylindrical plus hemispherical, cylindrical plus conical, hexagonal prism, and cruciform. The results showed that, at the moment of the maximum force of knee joint during level walking activity, there was no significant difference in the tibial von Mises stress between the tibial tray with or without fixation peg designs. However, the peak micromotions at the prosthesis fixation interface of all tibial trays with fixation peg design were significantly reduced. Among them, the micromotion suppression effect of the cruciform fixation peg was the most obvious. At the moment of the maximum flexion angle of knee joint during squatting activity, the tibial von Mises stress for tibial trays with fixation peg design was clearly lower than that without fixation peg design, meanwhile the peak micromotion at the prosthesis fixation interface was also significantly reduced. Overall, the cruciform fixation peg design showed the best fixation stability and effectively reduced the loosening risk at the prosthesis fixation interface. This study recommended that the backside of the tibial tray in non-cemented PS knee prostheses adopted a design combining a cylindrical stem with a serrated keel and a cruciform fixation peg. This study provided an important reference basis for improving the initial fixation stability of non-cemented PS knee prostheses by optimizing the backside design of the tibial tray.

The potential risks of osteoarthritis (OA) progression in the lateral compartment during the progression of medial knee OA and after medial unicompartmental knee arthroplasty (UKA) remain to be elucidated. Thus, five medial knee OA models with different progression stages and one medial UKA model were established using the finite element method to investigate the biomechanical differences of lateral compartment articular cartilage (AC). The AC and meniscus were constructed by fibril-reinforced biphasic material, and the real biphasic contact conditions were adopted. The results showed that biomechanical differences in lateral compartments were within 2% between the healthy knee model (OARSI 0–1) and early medial knee OA models (OARSI 2–3). However, in advanced medial knee OA (OARSI 4.5), up to a 7.0% increase in stress and a 22.2% increase in a strain of the lateral compartment AC were predicted. After medial UKA surgery, the maximum shear strain of the lateral compartment AC was reduced by about 22.2% when compared with advanced medial knee OA. In conclusion, the progression of medial knee OA may cause OA development in the lateral compartment. In contrast, medial UKA surgery might help to lower the risks of OA progression in the lateral compartment when in the advanced medial knee OA stage.

Loading modes and parameters on wear testing of unicompartmental knee prostheses are important. The difference in wear assessments of unicompartmental knee prosthesis under total knee loading mode and unicompartmental loading mode was investigated via computational simulation. The ISO standard testing protocol and the measured personalised load and kinematic data were further used to reveal the influence of the testing parameters on wear assessments. Compared with the total knee loading mode, the unicompartmental loading mode produced a larger peak contact pressure of the tibial insert throughout the wear cycle. Under ISO 14243‐3 and Stan’s CAMS testing parameters, the predicted volumetric wear of tibial inserts of the unicompartmental loading mode increased by 28.21% and 15.18%, respectively, compared with the total loading mode. Compared with ISO 14243‐3, volumetric wear increased by 42.64% for total knee loading mode and 28.14% for unicompartmental loading mode under Stan’s CAMS loading conditions. Both loading mode and parameters played an important role in the wear of unicompartmental knee arthroplasty simulation. Therefore, wear testing and computational simulation of wear predictions for unicompartmental knee prostheses should be performed in a unicompartmental loading mode, and it is more reasonable to use the patient’s in vivo measurement data.

Aseptic loosening is the primary cause of failure following posterior-stabilized total knee arthroplasty. It is unclear whether tibial post loading of posterior-stabilized prosthesis increases the risk of aseptic loosening of the tibial prosthesis. The purpose of this study is to investigate the biomechanical effects of tibial post loading on the tibial prosthesis fixation interface during level walking, squatting, stair descent, and standing up-sitting down activities. In this paper, finite element models with and without post were established to compare the effects of tibial post loading on the von Mises stress of the proximal tibia, shear stress of the cement, and the bone-prosthesis interface micromotion during four physiological activities. The tibial post loading had an insignificant influence on tibial biomechanics and bone-prosthesis interface micromotion during leveling walking activity. However, compared to the insert without post condition, tibial post loading significantly increased the maximum tibial von Mises stress, the maximum shear stress in the medial of cement, and the bone-prosthesis interface peak micromotion by 912.84%, 612.77%, and 921.09%, respectively, at the moment of the maximum flexion angle for the stair descent activity, and 637.92%, 351.43%, and 519.13%, respectively, at the moment of the maximum flexion angle for the standing up-sitting down activity. Tibial post loading increased the risk of postoperative aseptic loosening of tibial prosthesis in patients with posterior-stabilized total knee arthroplasty, and it was recommended that the post-cam contact mechanism of posterior-stabilized prosthesis should be optimized to reduce the biomechanical impact of tibial post loading on tibial prosthesis fixation.

Biphasic models have been widely used to simulate the time-dependent biomechanical response of soft tissues. Modelling techniques of joints with biphasic weight-bearing soft tissues have been markedly improved over the last decade, enhancing our understanding of the function, degenerative mechanism and outcomes of interventions of joints. This paper reviews the recent advances, challenges and opportunities in computational models of joints with biphasic weight-bearing soft tissues. The review begins with an introduction of the function and degeneration of joints from a biomechanical aspect. Different constitutive models of articular cartilage, in particular biphasic materials, are illustrated in the context of the study of contact mechanics in joints. Approaches, advances and major findings of biphasic models of the hip and knee are presented, followed by a discussion of the challenges awaiting to be addressed, including the convergence issue, high computational cost and inadequate validation. Finally, opportunities and clinical insights in the areas of subject-specific modeling and tissue engineering are provided and discussed.

单髁膝关节置换术（UKA）中假体的手术安装精度是影响术后膝关节功能和假体寿命的重要因素。本文以UKA股骨部件相对胫骨衬垫内外侧位置的比值（a/A）为参数，分别考虑了9种不同股骨部件安装情况，建立UKA置换的骨肌多体动力学模型并模拟患者术后行走步态，研究UKA手术中股骨部件内外侧安装位置对术后膝关节接触力、关节运动和韧带力的影响。结果表明，随着a/A比值的增大，膝关节内侧假体接触力减小，外侧软骨接触力增大；膝关节内翻运动、外旋运动和关节后移运动增大；前交叉韧带力、后交叉韧带力和内侧副韧带力减小。UKA股骨部件内外侧安装位置对膝关节屈曲伸展运动、外侧副韧带力影响不大。而当a/A≤0.375时，股骨部件与胫骨会产生接触。为了避免内侧假体和外侧软骨承受过高的载荷、产生过高的韧带力以及内侧假体与胫骨碰撞等问题，本文建议医生UKA手术中安装股骨部件时a/A比值控制在0.427~0.688范围内，为UKA手术中股骨部件内外侧安装提供了参考依据。

Restoration of ankle kinematic functions is the major objective following total ankle arthroplasty (TAA). However, the clinical results of traditional ankle implants are still unsatisfactory. Anatomic ankle implant may provide better ankle kinematic functions and load distribution. In this study, the biomechanical performances between two potential anatomic ankle implants and a commercial INBONE II implant were compared using a previously developed patient-specific musculoskeletal multibody dynamics model during walking. Furthermore, the effects of the different height differences between the medial and lateral borders on the ankle biomechanics and kinematics were also investigated. Significant improvements in kinematic functions especially in internal-external rotation and inversion-eversion, and in load balance between the medial and lateral contacts of the two anatomic ankle implants were observed, as compared to the INBONE II ankle implant. The design of anatomic ankle implant with the medial peak higher than the lateral peak had better performance in restoring the internal-external rotation and balancing the medial and lateral contact forces. The kinematics and loads were not sensitive to the height difference for the anatomic ankle implant with medial border higher than lateral border. The anatomic articular surface design of artificial ankle implant can provide better tibiotalar joint kinematics and loading, therefore, anatomic ankle implant should be considered in the future implant design and surgical procedures.

This study aims to evaluate the reconstructive stability for Paprosky III acetabular defects after total hip arthroplasty using three different reconstruction strategies with trabecular metal (TM) augments. The acetabular bone defects examined were located in the ilium, the sciatic ramus and the pubic ramus. Different scenarios of acetabular reconstructions were simulated, including the non-reconstruction model (NRM), the complete reconstruction model (CRM), the two-point reconstruction model (TRM) and the superior edge reconstruction model (SRM). A primary hip replacement model (HRM) was also investigated to compare the initial stability with different reconstruction models. The gait cycle was incorporated in the model to investigate the dynamic variation within the contact mechanics parameters. By comparing the SRM and the TRM, the acetabular cup translation was more pronounced when the superior defect on the acetabulum remained unfixed. Comparison of the acetabular cup displacement and the interface micromotion of both HRM and CRM demonstrated that the prosthetic implant provided good support for the reconstructed acetabulum. With the use of a press-fit cup, the cup displacement was reduced remarkably, while its Von-Mises stress increased significantly. The results show that the CRM was the best reconstruction option. In terms of acetabular defects, future improvements should focus on the reconstructive stability in stress concentration areas, to ensure no significant stress-shielding or other factors contributing to loosening of the prosthesis.