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Mechanical analysis of a virtual Ganz periacetabular osteotomy in patients suffering hip malformations by using finite element analysis

Chavez Arreola, Arturo

[Thesis]. Manchester, UK: The University of Manchester; 2016.

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Abstract

Developmental dysplasia of the hip (DDH) refers to some hip disorders, from mildly dysplastic to hip joint dislocation. The main feature of DDH is the deficient acetabular coverage, which is related to a small contact area in the hip joint, and causes an increase in contact pressure. Ganz periacetabular osteotomy (PAO) is a surgical procedure to correct acetabular orientation in DDH. It changes the position of the acetabulum to increase the femoral head coverage and distribute the contact pressure over the cartilage surface. The procedure of Ganz PAO is technically demanding and its success depends significantly on the surgeon’s experience.The aim of this research is to investigate whether it is possible to optimize the position of the acetabular fragment in patients suffering DDH before a Ganz PAO by using finite element (FE) analysis. Using computed tomography (CT) data from patients with DDH, five three-dimensional (3D) hip models were developed. A virtual Ganz PAO was then performed on the hip models. FE analyses were carried out on the hip models before and after virtual Ganz PAO. Contact area, contact pressure and Von Mises stress in the hip cartilage were checked and analysed in order to find an optimal acetabular position.The first virtual surgery performed was only to rotate the acetabular fragment in the lateral direction to improve the acetabular coverage. Analyses were conducted under loading conditions associated with four commonly daily activities: one leg stance, normal walking, descending stairs and knee bend. Second virtual surgery performed was to rotate the fragment in both the lateral and anterior directions and FE analysis conducted for one leg stance loading condition.Contact area, contact pressure and Von Mises stress in the cartilage all varied according to the change of the acetabular fragment position through virtual Ganz PAO. The optimal lateral position of the acetabular fragment occurs close to the inferior border of its normal range. Large anterior position of the acetabular fragment results in large contact area, low contact pressure and Von Mises stress. However, an overcorrection of the acetabular fragment, especially in the anterior correction, leads to problems in performing normal hip movements. The optimal anterior position of the acetabular fragment is therefore close to the superior limit of the normal range.In conclusion, the present analysis shows that an optimal position of the acetabular fragment for patients suffering DDH which improves the acetabular femoral head coverage in the normal range, maximizes the contact area and minimizes the contact pressure and Von Mises stress can be established using 3D models and FE analysis. This information will be useful to the surgeons for the planning of PAO.