Surgical simulation of curved periacetabular osteotomy in four types of developmental dysplasia of the hip using finite element analysis and identification of the optimal rotation angle of the osteotomized bone.

Background: Patients with developmental dysplasia of the hip (DDH) undergo curved periacetabular osteotomy (CPO) to prevent progressive osteoarthritis. The acetabulum's morphology varies with in each DDH type. Therefore, developing a three-dimensional preoperative plan is important in CPO. However, the optimal rotation angle of the osteotomized bone remains unclear. This study aimed to examine the contact pressure (CP) of the acetabular cartilage in each DDH type using the finite element analysis and the optimal rotation angle of the osteotomized bone in surgical simulation.

Methods: This study included 23 patients (24 hips) with DDH who underwent CPO. The DDH type was determined based on a previously reported DDH type classification using radar charts. Four patients, with each patient presenting with one deficiency type, were selected for analysis. The preoperative computed tomography scan data of each patient were analyzed using a finite element analysis software. Based on each DDH type, the following CPO models were established: the preoperative model, the model rotated 10°, 20°, 30°, and 40° laterally, each lateral rotation model with 10° anterior rotation, and each lateral rotation model with 10° external rotation. Furthermore, the acetabular cartilage and the femoral head cartilage were created. The mesh model based on a 4-mm tetrahedron was generated from the CPO model. The load was set in the one-leg standing position (femur: 500 N, grater trochanter: 1000 N). The medial pubic bone, distal femur, and superior rim of the ilium were constrained. The CP of the acetabular cartilage and the number of contact surfaces in each model were evaluated. The rotation angle that was most effective in reducing the CP was examined.

Results: According to the mean CP, the optimal rotation angles of the osteotomized bone in mild, anterior, posterior, and global type deficiencies were 20° laterally, 30° laterally, 30° laterally with 10° anterior rotation, and 30° laterally with 10° anterior rotation, respectively. Based on the contour diagram, the CPO models rotated anteriorly or externally increased the contact surface. The CP of the models rotated 40° laterally did not improve to greater extent than that of the models rotated 30° laterally.

Conclusions: The optimal rotation angle of the osteotomized bone should be determined based on the DDH type.