Failure Analysis on Interface Stress in Unicompartmental Knee Arthroplasty / 医用生物力学

Objective To analyze interface stress of cemented tibial prosthesis platform and determine the interface stress damage area, so as to provide references for stress failure of tibial platform in clinical single condylar replacement. Methods The full cycle gait was simulated by human dynamics software to obtain the load-bearing condition of knee joint. A complete model of the knee joint was established by medical imaging and three-dimensional (3D) reconstruction software, and unicompartmental replacement was performed. The distribution of interfacial stress of tibial prosthesis platform after single condylar replacement was analyzed by finite element method. ResultsIn gait, force and angle of the knee joint changed periodically with time, a cycle lasted 1.3 s, and the peak of knee joint resultant force was 760 N. The maximum shear stress of the interface was 11.82 MPa and the maximum tensile stress was 6.849 MPa, both occurred at inner front end of the corner of prosthesis cement interface. The maximum interface stress of titanium alloy prosthesis was lower than that of stainless steel prosthesis. Conclusions The decrease in elastic modulus of prosthesis can reduce the maximum principal stress at the interface. Considering the interface stress, titanium alloy prosthesis is better than stainless steel prosthesis. The area of tibial prosthetic platform interface damage is mainly at the medial anterior and posterior corners and lateral middle ends,so improving the ability of prosthesis cement bonding in this area can prevent the loosening of tibial prosthesis of unicompartmental knee joint.The findings have practical implications for the prevention of tibial prosthetic platform loosening after unicompartmental knee arthroplasty in clinic.

Static Finite Element Analysis on Hip Disarticulation Prosthesis Socket-Residual Limb in Stance Phase / 医用生物力学

Objective To study mechanical properties of the interface between hip residual limb and hip socket during the stance phase by using the finite element analysis (FEA) method, so as to provide the theoretical basis for structure optimization and design of hip socket, as well as the research basis for comfort evaluation of hip socket. Methods According to CT scan images of the patient’s residual limb, the model of bone, soft tissues and socket was reconstructed by reverse modeling. The distribution of normal stress and shear stress on the interface between hip residual limb and hip socket was analyzed and a pressure acquisition module system was designed to verify the stress distribution condition. Results The interfacial stress between hip residual limb and hip socket was mainly distributed in the waist and the bottom of the residual limb, and the interfacial stress was more evenly distributed in the rest of the residual limb. The results of finite element calculation were in good agreement with the system measurement results of pressure acquisition module. Conclusions In order to improve force transfer and safety and comfort of the hip socket, it is necessary to fully consider stress condition of the waist and bottom of the residual limb, as well as the coordination degree between residual limb and hip socket.

Evaluation of stress contours on a maxillary molar subjected to simulated tooth loads by finite element analysis technique

Forces applied by dental occlusion generate stresses which are transmitted to the surrounding bone via the periodontal ligament causing a tissue response. The purpose of this study was to evaluate the response of a maxillary molar under secondary trauma from occlusion by observing the changes in its stress patterns. In order to visualize the exact pattern of stress distribution, three dimensional finite element analysis models were developed. A force of 3 N, moment of 27 Nmm and a counter rotation moment of 15 Nmm were applied to simulate orthodontic forces. Stresses produced at the periodontal ligament-tooth interface on a maxillary molar model with normal bone height subjected to an orthodontic force were compared with molar models showing bone loss and analyzed using finite element analysis technique. As the bone loss increased, it was observed that, the concentration of stresses at the apical one-third of the tooth also increased and there was high tendency for tooth displacement. The results suggest that an alteration in the magnitude of forces applied may be necessary in teeth with an increased crown to root ratio to maintain a healthy periodontium.