| Background: Avascular necrosis of the femoral head and osteoarthritis of hip are common, the late results are severe hip pain and dysfunction. Total hip replacement (THR) has proved to be a very successful operation in terms of pain relief and improvement in patients’ quality of life. The published data has shown a high level of patient satisfaction and very low revision rate at 15-20 years follow-up. These excellent results in the elderly population but in young patients with significant comorbidity do not reflect the picture in young active patients. Several authors have reported higher rates of failure ranging from 30% to 56%, in patients under 40 years of age after 10-12 years when conventional hip arthroplasty has been performed. The level of a patient’s activity correlates highly with early failure of the prosthesis. This leaves the patient and the surgeon facing the difficulties of revision surgery, with less chance of success than the original primary operation. Revision THR is technically demanding and the surgeon is usually faced with scarred, less pliable tissue and loss of the bone stock. Femoral head resurfacing has several advantages over conventional total hip arthroplasty which include minimal bone resection, easier revision, and maintenance of physiological stresses within the proximal femur. The short-term performance of modern hip resurfacing arthroplasty is impressive,with low rates of migration, revision , and femoral neck fracture.Hip resurfacing arthroplasty has always been an more attractive option in the treatment of end-stage arthritis of the hip in young and active patients. Bone conservation and non-violation of the femoral shaft make it a less invasive option. Normal load transmission and better biomechanics hold the promise of better preservation of the conserved bone. The life expectancy of a young patient is very likely to be more than the longevity of any artificial device. When the implant needs to be revised, resurfacing offers better revision options.Hip resurfacing is not a new concept and attempts to treat hip arthritis without resecting the femoral head and neck as it have been made since the 1950s. The current generation of metal-on-metal hip resurfacing arthroplasty components is the third attempt by their pro-ponents to eliminate a femoral component inserted into the diaphysis. The earliest resurfacing arthroplasties failed by osteolysis. Further development produced the first generation of metal-on-metal (MoM) resurfacing arthroplasties. These early MoM implants suffered from poor manufacturing quality resulting in ’stiction’ between femoral and acetabular components, aseptic loosening and femoral neck fracture During the 1990s development of MoM bearings in total hip replacement lead to rejuvenation of MoM resurfacing arthroplasties. The resurgence of new and better-engineered metal-on-metal bearings has provided the means to develop aviable prosthetic solution from a concept that was once abandoned.FEA of hip resurfacing has developed from simplistic 2D models to more complicated 3D,geometrically precise, models using physiologically suitable loading conditions. These Computer-Tomography (CT) based models can more accurately predict stresses for an individual. Previous FEA on the resurfaced femur has shown that resurfacing induces stress shielding in the proximal sections of the femoral head.Currently, FEA of hip resurfacing focused on the stress change in the femoral neck, the disadvantage is that there do not take into account the acetabular prosthesis on the stress change.FEA of hip overall is more in line with the normal physiology of human activity. In this stuty,it regarded acetabular and femoral head contact stress, models using physiologically suitable loading conditions. The simulation closer to the actual conditions, the more real response the stress changes of hip, resulting in higher reliability.Objective: 1. Set up the hip resurfacing arthroplasty systems’ finite element model ,and master the stress distribution under physiological loads.2. To determine stress distribution of prosthesis and femoral neck after the hip resurfacing arthroplasty to provide biomechanical evidence for Improving the surgical effect of hip resurfacing arthroplasty.3. To analyze the different stress distribution on the different part of femoral neck after the hip resurfacing arthroplasty,and analyses Stress shielding inside the femoral head exist or not.Method Three-dimensional FE model intact right proximal femur and aproximal femur with resurfaced femoral head were developed using computed tomography (CT) scan data, Mimics 10.01 and the solid modeler of abaqus6.5FE software. The femur was implanted with a 48mm diameter femoral head resurfacing prosthesis(zimmer).The inner surface of the implant was fixed to the bone using bone-cement(PMMA).The tapered stem was inserted into aparallel side hole and was modeled as completely debonded. The Young’s modulus for the PMMA and the implant were assumed to be 2500 and 235000 MPa,respectively.A Poisson’s ratio of 0.3 was assumed for all materials.Mesh generation and solutions were obtained using Mimics 10.01 and abaqus 6.5 software. The model were divided into 5 parts: acetabular prosthesis, femoral prosthesis, bone cement, os integumentale and cancellous bone. The model were divided by hexahedron unit.the part of acetabular prosthesis contains 5465unit and 11062 nodes, the part of femoral prosthesis contains 6883 unit and 9880 nodes.the part of bone cement contains 9829 units and 12295 nodes;the part of os integumentale contains 80222 units and 104306 nodes, the part of cancellous bone contains 62346 units and 73689 nodes.the FE model were analysed by abaqus 6.5.These loading conditions were applied to the FE model as static load cases. The body weight was assumed to be 60kg. these loads were uniformly distributed over the area of contact (for the hip joint reaction force) .Nodes located on the distal end of the femur were constrained in all directions.The femoral part of model were divided into 8 parts .the stress distribution and stresses were measured; measure the Von Misses stress on different points; the qualitation data would be described by mean±standard deviation;before been analysised;all datas should be tested by one-way anova and Iindependent Samples T Test; all these test would be finished by SPSS16.0 stastical soft.Result: 1 .The stress pattern of implanted femur is similar to that of intact femur as the stress shielding at femoral neck. Peak strain is presented in the lower regions of femoral neck and Bone - prosthesis interface in the resurfaced femur.2.As for the prosthesises, Peak strain exists in the superior top regions of the acetabular and femur prosthesises and Bone-prosthesis interface (P <0.001) . In order to reduce the rate of fermoral neck fracture,these regions should be protected during the operation.3.Stress shielding exists inside the femoral head after hip resurfacing arthroplasty. Which caused changes in bone density within the resurfaced femoral head,and would lead to bone remodeling and consequently reduction in bone density in the superior femora head region.Conclusion: 1.The stress pattern of implanted femur was similar to the one of intact femur with the obvious stress shielding at femoral neck. Peak strain concentrations occurr at the inferior and superior parts of the femoral head-neck junction, in order to reduce the rate of fermoral neck fracture,these regions should be protected during the operation.2.Stress shielding exists inside the femoral head after hip resurfacing arthxoplasty. Which caused changes in bone density within the resurfaced femoral head,and would lead to bone remodeling and consequently reduction in bone density in the superior femora head region. |
PDF Full Text Request