Stress Distributions of Hip Cartilage During Gait Cycle and its Effects in Curved Periacetabular Osteotomy / 医用生物力学

Objective To study stress distributions of the cartilage around the hip joint in stress environment of complete gait cycle, and explore the optimal correction angle of bone block in curved periacetabular osteotomy (CPO), so as to provide theoretical references for clinical operation. Methods Based on CT scans from a healthy volunteer and a patient with development dysplasia of hip (DDH), the three-dimensional (3D) model including pelvis and proximal femur was reconstructed. The cortical bone and cancellous bone were distinguished by dividing the masks, and the material attributes were assigned to the finite element model. A total of 100 different postoperative models were obtained by simulating CPO in DDH model, by adjusting lateral center edge angle (LCEA) and anterior center edge angle (ACEA). According to hip joint stresses in complete gait cycle, the model was loaded respectively, and stress changes of normal, preoperative and postoperative acetabular cartilage were analyzed and compared. ResultsThe minimum peak contact stresses of acetabular cartilage of DDH patient at heel landing phase, start phase of single leg support, mid phase of single leg support, end phase of single leg support and double support phase after simulated CPO operation were 5.273, 6.128, 7.463, 6.347, 6.582 MPa, which were decreased by 2.159, 2.724, 2.249, 2.164, 2.119 MPa,respectively, compared with those before operation. The contact area between femoral head and acetabulum was significantly increased after operation, but it was still smaller than that of normal volunteers. Conclusions The optimal correction angle of LCEA and ACEA can be obtained by using finite element method, and the simulation of CPO surgery on different patients is of great significance to improve surgical accuracy and efficiency.

Biomechanical analysis of ankle-foot complex during a typical Tai Chi movement-Brush Knee and Twist Step / 生物医学工程学杂志

The purpose of this study is to analyze the biomechanics of ankle cartilage and ligaments during a typical Tai Chi movement-Brush Knee and Twist Step (BKTS). The kinematic and kinetic data were acquired in one experienced male Tai Chi practitioner while performing BKTS and in normal walking. The measured parameters were used as loading and boundary conditions for further finite element analysis. This study showed that the contact stress of the ankle joint during BKTS was generally less than that during walking. However, the maximum tensile force of the anterior talofibular ligament, the calcaneofibular ligament and the posterior talofibular ligament during BKTS was 130 N, 169 N and 89 N, respectively, while it was only 57 N, 119 N and 48 N during walking. Therefore, patients with arthritis of the ankle can properly practice Tai Chi. Practitioners with sprained lateral ligaments of the ankle joint were suggested to properly reduce the ankle movement range during BKTS.

Three-dimensional model analysis of trabecular acetabular cup and solid acetabular CUP / 中国组织工程研究

BACKGROUND: Hip arthroplasty is most effective method to treat hip diseases such as femoral head necrosis, osteoarthritis, hip dysplasia and femoral neck fracture in the elderly. Therefore, it is necessary to study the biomechanical behaviors of hip arthroplasty. OBJECTIVE: To simulate the contact stress and Von Mise stress values and distributions of trabecular acetabular cup and solid acetabular cup by finite element analysis method, and to predict its effects on prosthesis and hip joint. METHODS: Two hip joint component models with different structures, trabecular acetabular cup and solid acetabular cup were designed in 3-Matic Research 11.0 software. The well-designed models were imported to Hypermesh 14.0 software to divide meshes and assign material properties. Finite element analysis software Abaqus 6.13 was used to simulate the stress values and distributions of both models. RESULTS AND CONCLUSION: The results of this study showed that the stress of the trabecular acetabular cup was scattered and distributed widely. The solid acetabular cup is prone to stress concentration, and the stress distribution is concentrated near the point of stress. Compared with the solid acetabular cup and the trabecular acetabular cup, the latter has larger contact area of stress distribution and more uniform stress distribution, which can reduce the wear between hip prostheses and the risk of aseptic loosening of hip prostheses.

Short-Term Results of Total Knee Arthroplasty with Anterior-Posterior Glide LCS Mobile-Bearing System

PURPOSE: To evaluate the clinical and radiological results of total knee arthroplasty (TKA) using the anterior-posterior glide (APG) low contact stress (LCS) mobile-bearing system. MATERIALS AND METHODS: We evaluated 130 knees in 117 patients who had undergone TKA with APG LCS mobile-bearing system between September 2005 and July 2007 and could be followed over 5 years. The mean follow-up period was 68 months. The clinical and radiological results were evaluated using the American Knee Society Scoring System, Oxford knee score and the American Knee Society Roentgenographic Evaluation and Scoring System. And we analyzed short-term postoperative complications. RESULTS: The average range of motion of the knee joint was 107.9degrees (range, 70degrees to 135degrees) preoperatively and 125.2degrees (range, 90degrees to 135degrees) at the last follow-up. The average knee and functional scores were improved from 39.1 and 42.0 to 71.2 and 75.6, respectively, between the preoperative and last follow-up evaluation. The Oxford knee score was decreased from 42.9 preoperatively to 23.1 at the last follow-up. The femoro-tibial angle (anatomical axis) changed from 10.1degrees varus preoperatively to 3.3degrees valgus at the last follow-up. Radiolucency was observed in 14% of all cases. There were 1 case of traumatic dislocation of the polyethylene liner, 1 case of aseptic loosening and 6 cases of posterior instability because of posterior cruciate ligament (PCL) insufficiency. CONCLUSIONS: TKA with APG LCS mobile-bearing system demonstrated relatively good short-term clinical and radiological results. However, further considerations for posterior instability associated with PCL insufficiency are needed.

A Comparison of the Clinical and Radiographic Results of Press Fit Condylar Rotating-Platform High-Flexion and Low Contact Stress Mobile Bearing Prosthesis in Total Knee Arthroplasty: Short term Results

PURPOSE: This study compared the results of rotating-platform high-flexion (RP-F) total knee arthroplasty with low contact stress (LCS) for clinical and radiographical assessment after a short-term period. MATERIALS AND METHODS: 68 total knee arthroplasties using a RP-F and LCS system were analyzed retrospectively. Thirty-five of the 68 were osteoarthritic knees and were followed-up for more than 2 years. The clinical evaluation included range of motion (ROM), Knee Society Knee Score and Function Score (KSKS and KSFS), tailor position and kneeling. The radiographic evaluation included femorotibial angle, position of implants, radiolucent line and position of patella. RESULTS: The postoperative ROM, KSKS, and KSFS improved statistically in both implants. Comparing RP-F with LCS there were statistically no differences in ROM (p=0.863), KSKS (p=0.835), KSFS (p=0.535) and tailor position (p=0.489). There were no significant radiographic differences. CONCLUSIONS: Total knee arthroplasty with RP-F and LCS showed similar clinical and radiographic results; it also showed excellent and predictable results at the short-term follow up. However, in RP-F there was 1 case of early osteolysis, 1 case of patella clunk syndrome and 1 case of painful patella crepitus; therefore, further case studies and follow-up are needed.

Biomechanical Analysis of Wrist under Axial Static Compressive Force on Metacarpals / 航天医学与医学工程

Objective To study the force and pressure transmission through normal wrist,and the effect of transverse carpal ligament release on the biomechanics of carpal tunnel.Methods A 3-D finite element model of the wrist based on CT scan images was established.The load transmission of carpus and the distribution of contact stress on radiocarpal joint under axial compressive force on metacarpals as well as the effect of transverse carpal ligament(TCL)release on the displacement of carpal bones were computed and analyzed.Results The computational results of force and pressure transmission through normal carpus matched well with previous studies.The release of TCL resulted in radial and palmar displacement of the scaphoid,flexion and radial rotation of radiocarpal joint as well as a further radial deviation of the whole carpal tunnel.Conclusion A 3-D finite element model of the wrist that includes the carpal tunnel,distal radius and ulna and proximal metacarpals is developed.This model may simulate the load transmission better and contact stress distribution of carpal tunnel and radiocarpal joint,as well as provide an operational plateform for further deeply studing on biomechanical behavior of carpal structure.The computed and analyzed results of the effect of TCL release on the displacements of carpal bones can be served as related theoratic base on carpal tunnel syndrome,carpal tunnel release surgery and recovery after operation.

Axisymmetric Contact Stress analysis of an Artificial Hip Joint of the Conical Fitting Type / 대한정형외과학회잡지

The purpose of this study is to investigate the effect of the ball-cone contact interface variation on the ceramic ball stress which is the dominant factor of the design of the moldular artificial hip joint. A contact stress analysis problem is formulated using the optimization principle and finite element analysis technique on the ball-cone system of three dimensional axi-symmetrical model, Numerical procedure is employed to get the solution for varying angles of cones and angular mismatches between the ball and cone interfaces. There is a fair amount of friction in the interface and included in the analysis model.