Optimization of the position of the acetabulum in a ganz periacetabular osteotomy by finite element analysis

Abstract

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. Keywords: developmental dysplasia of the hip; periacetabular osteotomy; finite element Developmental dysplasia of the hip (DDH) is an abnormal development of the acetabulum, the femoral head or both. It affects between 1% and 3% of newborn babies and was shown to be the cause of 29% of hip replacements in people under the age of 60. 1 Apart from the pain and discomfort associated with DDH, lack of treatment may lead to osteoarthritis and significant disability. In childhood, early diagnosis and treatment may allow appropriate bony development and avoid complicated and hazardous surgical procedures. However in adults, osteotomy is often the most appropriate treatment. The success largely depends on the surgeon's experience. [2][3][4][5][6][7][8] The diagnosis of DDH is based on the center edge (CE) angle formed by a vertical line passing through the center of the femoral head and a line from the center of the head to the edge of the acetabulum (Fig. 1). The CE angle in a normal hip is >258. A hip with a CE angle <208 may be diagnosed as DDH. 9,10 The periacetabular osteotomy (PAO) to correct DDH depends on the clinical condition of the patient and the severity of the disease. 8 Bernese PAO is a type of pelvic osteotomy described by Ganz et al. 11 that changes the position of the acetabulum to increase coverage of the head, stabilizing the joint and reducing contact pressure. [4][5][6][7][8][9][10]12 The advantages of the Ganz PAO over other pelvic osteotomies are: the cuts are reproducible and can be performed with one incision; post-operatively the posterior column is intact and patients do not need a cast or brace;...

How Are Dysplastic Hips Different? A Three-dimensional CT Study

“…Finite element analysis has shown that reconstructive procedures such as the Bernese periacetabular osteotomy (PAO) can increase joint contact area and decrease joint contact pressures [6,36] but cannot reach predicted normal values, probably because of the irregular shape of dysplastic hips [20,74]. Medium-term results (5.5 years to 15 years) after PAO show a rate of conversion to THA between 7% and 15% [19,36,43,68].…”

Computationally Efficient Magnetic Resonance Imaging Based Surface Contact Modeling as a Tool to Evaluate Joint Injuries and Outcomes of Surgical Interventions Compared to Finite Element Modeling

“…Computational modeling has been extensively applied to the lower extremity to evaluate in vivo joint mechanics [4][5][6][7][8][9][10][11]18]. In the wrist, studies have evaluated in vivo joint mechanics during functional activities [12,14,16,17] and have also simulated the effects of some carpal fractures and limited fusions [13,15,19].…”

“…The common techniques include image-based FEM [4][5][6][7][8][9][10][11][12][13], rigid body spring modeling/discrete element analysis (RBSM) [14][15][16], or SCM [17][18][19]. The models are either displacement driven or force driven.…”

“…The models are either displacement driven or force driven. Generally, model geometries are acquired from modalities such as computed tomography (CT) [4][5][6][7][8]14,15,19] or MRI [9][10][11]17,18]. Kinematics are determined through external (surface markers) or internal (biplanar radiography) measures, while tendon forces are estimated from corresponding musculature electromyography (EMG) and cross-sectional area, and ground reaction forces are measured using force platforms [11,20].…”

Theoretical Implications of Periacetabular Osteotomy in Various Dysplastic Acetabular Cartilage Defects as Determined by Finite Element Analysis

“…Recently, variability in the extent of acetabular cartilage development has received increasing research interest and has been investigated as a major cause [6]. Steppacher et al [7] found that patients with acetabular dysplasia had a clearly decreased lunate surface size, decreased outer acetabular rim, and increased acetabular fossa.…”