Stress distribution of amodified periacetabular osteotomy for treatment of dysplastic acetabulum

The Bernese periacetabular osteotomy has become popular in treatment of dysplastic acetabulum. However, the polygonal shape of the osteotomy can create osseous gaps when the fragment is repositioned, especially when a large correction is needed. This study compared the stress distribution of a modified periacetabular osteotomy (spherical osteotomy with smooth and round surface) with those of traditional Bernese osteotomy using finite element analysis. Computed tomography images of a standard composite pelvis were used to create the three-dimensional finite-element intact pelvis model. Based on the intact model, finite-element models simulating the modified and Bernese periacetabular osteotomy were created. The von Mises stress distributions of each model were analyzed and compared for a loading condition simulating single-legged stance. The results indicated that the deformity of the modified periacetabular osteotomy model was less than that of the Bernese-osteotomized model. A large gap and high local stress of 17.2 MPa in peak value were found at the most medial corner of the osteotomized site for the pelvic fragment in Bernese-osteotomized model, which is much higher as compared to 7.6 MPa in peak value for the modified osteotomized model. The stress distribution was more uniform surrounding the osteotomized areas for modified periacetabular osteotomy as a result of a more smooth and round surface surrounding the osteotomized site. Additionally, a high local stress of 336.2 MPa in peak value was also found on the most medial fixation screw for the Bernese-osteotomized model, which was much higher as compared to 224.3 MPa in peak value of the modified osteotomized model. The results from finite element simulation were consistent with clinical outcomes. Our study demonstrated the superiority of modified periacetabular osteotomy in achieving a more physiological stress distribution, making it a better choice for treatment of dysplastic acetabulum.