Optimization of the position of the acetabulum in a ganz periacetabular osteotomy by finite element analysis
School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester M13 9PL, UK.Journal of Orthopaedic Research (Impact Factor: 2.99). 03/2013; 31(3). DOI: 10.1002/jor.22245
Periacetabular osteotomy (PAO) is a surgical procedure to correct acetabular orientation in developmental dysplasia of the hip (DDH). It changes the position of the acetabulum to increase femoral head coverage and distribute the contact pressure over the cartilage surface. The success of PAO depends significantly on the surgeon's experience. Using computed tomography data from patients with DDH, we developed a 3D finite element (FE) model to investigate the optimal position of the acetabulum following PAO. A virtual PAO was performed with the acetabulum rotated in increments from the original center edge (CE) angle. Contact area, contact pressure, and Von Mises stress in the femoral and pelvic cartilage were analyzed. Five dysplastic hips from four patients were modeled. Contact area, contact pressure, and Von Mises stress in the cartilage all varied according to the change of CE angle through virtual PAO. An optimal position could be achieved for the acetabulum that maximizes the contact area while minimizing the contact pressure and von Mises stress in the pelvic and femoral cartilage. The optimal position of the acetabulum was patient dependent and did not always correspond to what would be considered a "normal" CE angle. We demonstrated for the first time the interrelation of correction angle, contact area, and contact pressure between the pelvic and femoral cartilage in PAO surgery. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.
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ABSTRACT: Joint injuries and the resulting posttraumatic osteoarthritis (OA) are a significant problem. There is still a need for tools to evaluate joint injuries, their effect on joint mechanics, and the relationship between altered mechanics and OA. Better understanding of injuries and their relationship to OA may aid in the development or refinement of treatment methods. This may be partially achieved by monitoring changes in joint mechanics that are a direct consequence of injury. Techniques such as image-based finite element modeling can provide in vivo joint mechanics data, but can also be laborious and computationally expensive. Alternate modeling techniques that can provide similar results in a computationally efficient manner are an attractive prospect. It is likely possible to estimate risk of OA due to injury from surface contact mechanics data alone. The objective of this study was to compare joint contact mechanics from image-based surface contact modeling (SCM) and finite element modeling (FEM), in normal, injured (scapholunate ligament tear) and surgically repaired radiocarpal joints. Magnetic resonance images (MRI) of the normal, injured, and postoperative wrists of three subjects were acquired when relaxed, and during functional grasp. Surface and volumetric models of the radiolunate and radioscaphoid articulations were constructed from the relaxed images for SCM and FEM analyses, respectively. Kinematic boundary conditions were acquired from image registration between the relaxed and grasp images. For the SCM technique, a linear contact relationship was used to estimate contact parameters based on interactions of the rigid articular surfaces in contact. For FEM, a pressure-overclosure relationship was used estimate parameters based on deformable body contact interactions. The SCM technique was able to evaluate variations in contact parameters arising from scapholunate ligament injury and also the effects of surgical repair, with similar accuracy to FEM. At least 80% of contact forces, peak contact pressures, mean contact pressures and contact areas from SCM were within 10 N, 0.5 MPa, 0.2 MPa and 15 mm2 respectively, of the results from FEM, regardless of the state of the wrist. Depending on the application, the MRI-based SCM technique has the potential to provide clinically relevant subject-specific results in a computationally efficient manner compared to FEM.Journal of Biomechanical Engineering 04/2014; 136(4). DOI:10.1115/1.4026485 · 1.78 Impact Factor
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ABSTRACT: Background Surgical correction of acetabular dysplasia can postpone or prevent joint degeneration. The specific abnormalities that make up the dysplastic hip are controversial. Questions/purposes (1) What are the relative size, shape, and orientations of the typical nondysplastic hip? (2) How do these variables differ in the developmentally dysplastic hip? (3) Are there version differences between the acetabuli of dysplastic and nondysplastic hips? (4) Are there pairs of variables in which the change in one is always accompanied by a change in the other for both nondysplastic and dysplastic acetabuli? Methods Of 117 consecutive three-dimensional (3-D) CT scans performed for hip dysplasia between March 1988 and October 1995, 48 met criteria of developmentally dysplastic hips by plain radiography. These were retrospectively compared with 55 pelvic 3-D CT scans culled from 81 consecutive scans performed for reasons other than hip dysplasia (ie, hip pain, trauma, infection) that did not affect the hip or pelvic landmarks. The 3-D reconstructions were orientated anatomically for standardization of the measurements to be compared. Representative 3-D volumes of the acetabular space were constructed from which we could measure anatomic positions and dimensional information. One author performed all image orientation and measurements. Results Nondysplastic acetabuli are essentially hemispheric with height equal to width and twice the depth. The dysplastic acetabuli were elongated in females (52.4 ± 6.2 mm for dysplastic versus 46.5 ± 4.6 mm for nondysplastic (mean difference, 5.0; 95% confidence interval [CI], 1.9–8.0; p = 0.002) and shallower in both females (18.7 ± 4.9 mm for dysplastic versus 23.6 ± 4.0 mm for nondysplastic; mean difference, 6.5; 95% CI, 4.4–8.5; pClinical Orthopaedics and Related Research 12/2014; 473(5). DOI:10.1007/s11999-014-4103-y · 2.77 Impact Factor
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ABSTRACT: Periacetabular osteotomy (PAO) is a joint-preserving surgical procedure and it has been introduced as a surgical alternative to the total hip arthroplasty (THA) for young person. However, its clinical and biomechanical efficacies remain unknown. In this study, we constructed patient-specific finite element (FE) models of the hip joint before and after surgery to evaluate the efficacies in more quantitative fashion. 3-D FE models were constructed based on patient's computed tomography (CT) images. Post-operative geometrical changes in joint contact areas, center-edge (CE) angle and distance between the symphysis pubis and the femoral head (DBSPFH) were assessed in three dimensions. In addition, changes in peak contact pressures and peak von Mises stress (PVMS) at the hip joint were predicted. After PAO, CE angle was increased by 126.2% and DBSPFH was decreased by 3.7%. The contact area was increased by 32% while peak contact pressure was decreased by 53.8%. More even distribution of stresses at the femur were observed. Our results suggested that for this given patient PAO was an effective reconstructive surgical choice in terms of reconstructing joint congruency. Therefore, PAO can be considered a good alternative to THA especially for young patients who need to be treated with joint-preserving techniques.International Journal of Precision Engineering and Manufacturing 04/2015; 16(4):823-829. DOI:10.1007/s12541-015-0108-z · 1.50 Impact Factor
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