Finite Element Simulation of Bernese Periacetabular Osteotomy for Development Dysplasia of Hip

Abstract

Developmental dysplasia of the hip (DDH) is a deformation of constituent parts of the hip during the growth period. DDH hips usually cannot get sufficient contact area in the hip joint, so stress concentration occurs, causing pain. This issue can be treated by Ganz periacetabular osteotomy (PAO) which cuts down a portion of acetabulum from pelvis and then reorients the acetabular fragment to increase acetabular coverage to the femoral head. Although Ganz PAO is a popular surgical method to treat DDH, its procedure is very challenging and its success is highly depending on the surgeon's experience. The aim of this research is to investigate the mechanical behaviour of the DDH joint before and after PAO operation and find an optimal position of the acetabulum fragment for the PAO surgery. To achieve this aim, finite element models of five generic human dysplastic hips were developed from their CT scans. Virtual PAO operations were then performed on these hip models and acetabular fragments were reoriented in lateral-medial and anterior-posterior planes. Finite element analysis was conducted to determine the contact area and contact pressure in the hip joints during five common daily activities: one-leg stance, normal walking, descending/ascending stairs and knee bending. The effect of reorientation of acetabular fragment on the range of motion (RoM) of the hip joints was also checked. The FE simulations show that contact area and contact pressure in the cartilage of the hip joint are varied as expected when the acetabular fragment is reoriented to different positions through virtual Ganz PAO. It is found that the existing method for finding the optimal position of acetabulum fragment for patients of DDH based on maximizing total contact area and minimizing average contact pressure is problematic, as the area of high contact pressure may become larger than before surgery. A new method is therefore proposed for the optimal position of acetabular fragment based on minimizing the high contact pressure areas. The optimal position of acetabular fragment is found as subject-dependent and activity-dependent. It is difficult to find one single optimal position for all activities and for some patients. The present study also found that the optimal position does increase the anterior acetabular coverage, it also reduces the range of motion of the hip. It is therefore necessary to check RoMs when selecting the optimal position to avoid hip joint impingement after surgery. The parametric study shows that labrum, cartilage thickness, and material properties of cartilage and bones are definitely important model parameters for an accurate contact prediction for hip joint, but the optimal position of acetabular fragment for patients of DDH is not sensitive to them.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Zhenmin Zou (Supervisor)