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.

Preoperative Planning of Acetabular Arc Osteotomy Using Finite Element Method / 医用生物力学

Objective In order to simulate different angles of acetabular blocks that need to be adjusted during operation, the optimal angle was determined through analyzing the contact stress and contact area of cartilage around the hip joint, so as to provide an individual scheme for acetabular osteotomy. Methods The finite element models for development dysplasia of hip (DDH) and normal pelvis were established to investigate morphological characteristics of the acetabulum and the causes of stress concentration. To simulate osteotomy for the DDH model, a total of 20 postoperative osteotomy models were obtained through the combination of different angles for anterior rotation and lateral rotation of acetabular blocks, and the differences in optimal results of the models during simulated one legged-standing were compared and analyzed. Results The maximum contact pressure of acetabular cartilage in normal model was 7.85 MPa. The maximum contact pressure of acetabular cartilage in DDH model was 13.42 MPa. The optimal contact pressure after simulated osteotomy decreased to 8.49 MPa, and the contact distribution was improved more significantly. Conclusions Changing the anterior rotation angle can significantly improve the contact pressure distribution and size, as well as stay away from the preoperative lesion area, which has a positive impact on postoperative outcomes. Personalized osteotomy plan based on actual situation of each patient before the operation is crucial for the surgical effect.

The Effect of Pelvic Modeling on Outcome in Preoperative Planning for Bernese Acetabular Osteotomy / 医用生物力学

Objective To explore the influence of different model scopes on acetabular stress distribution and optimal osteotomy result in preoperative planning of Bernese acetabular osteotomy. Methods Two patients with hip dysplasia were established according to different model ranges. Model 1 included the affected hip and femur, and Model 2 included the complete pelvis and affected femur. Compare and analyze the acetabular cartilage contact pressure, area and distribution of the two models under single-leg standing conditions, and simulate osteotomy. Results Compared with Model 1 before surgery, Model 2 had higher contact pressure, smaller contact area and closer distribution to the meniscus edge of acetabulum. Compared with 11 postoperative plans, the variation amplitude of contact pressure and the optimal osteotomy angle for Model 1 were all smaller than those of Model 2. Conclusions The preoperative analysis result of the model with affected hip bone and femur would underestimate the degree of stress concentration and misjudge the location of stress concentration, and the obtained optimal osteotomy rotation angle would be relatively small. The research findings provide certain theoretical basis for preoperative planning and modeling of osteotomy.