| OBJECTIVEUsing the three-dimensional finite element to research the biomechanics of hip joint after implanting artificial femoral head with different diameters during the hemiarthroplasty in treating the elderly femoral neck fracture.Analyze the stress distribution of hip joint to provide experimental bases for the clinical selection of a suitable size of artificial femoral head.METHODSFinite element models of hip joint which respectively equipped with different diameters of artificial femoral head after femoral head arthroplasty were established by using data of thinner CT scan and related parameters of prosthesis(M0 :Preoperative model;M1 :diameter of prosthesis= diameter of original femoral head;M2:diameter of prosthesis= diameter of original femoral head+1mm;M3:diameter of prosthesis= diameter of original femoral head-1mm;M4:diameter of prosthesis= diameter of original femoral head-2mm).Meshing and material attribute assigning to five models by using finite element software Geomagic Studio and Hyper Mesh.Then import to software MSC Nastran2012 to constrain the boundary and load joint loading and related muscles strength.Finally,simulating people walking slowly,one foot standing in each model to get the stress nephogram and maximum stress of biomechanical data of the pelvis,acetabulum,acetabulum cartilage,artificial femoral head,upper femur and prosthesis stem.RESULTSThe maximum stress of M0-M4 in the pelvic region is 39.5mpa,47.3mpa,54.2mpa,44.8mpa,50.2mpa respectively and the stress increasement of M1-M4 is 13.42%-37.22%.The maximum stress of M0-M4 in acetabular area is 22.2mpa,24.0mpa,20.1mpa,23.6mpa,25.1mpa respectively and the stress increasement of M1-M4 is-9.46%-13.06%.The maximum stress of M0-M4 on the acetabular cartilage is 18.2mpa,22.5mpa,25.4mpa,18.5mpa,22.9mpa respectively and the stress increasement of M1-M4 is 1.65%-39.65%.The maximum stress of M0-M4 on artificial femoral head is 54.9MPa,80.7MPa,98.1MPa,70.8MPa,90.5MPa respectively and the stress increasement of M1-M4 is 28.96%-78.69%.The maximum compressive stress of M0-M4 at femoral neck(prosthesis neck)was 80 Mpa,241Mpa,277 Mpa,196Mpa,262 Mpa respectively.Simultaneously,it was found that the stress distribution of the upper femur were generally consistent in five models,but the stress of upper femur in m1-m4 show occlusion with varying degrees compared with M0,and the stress of prosthesis stem at corresponding parts show the concentration with varying degrees.The maximum compressive stress of M0-M4 on the medial of proximal femur is 207 Mpa,127Mpa,108 mpa,135Mpa,118 Mpa respectively and the stress decrement of M1-M4 by 34.78%to 47.83%.The maximum tensile stress of M0-M4 on the lateral of proximal femur is 159 Mpa,106Mpa,90.3mpa,112 Mpa,98.2mpa respectively and the stress decrement of M1-M4 by 29.56%-43.21%.The maximum compressive stress of M1-M4 on the medial prosthesis stem is 273 Mpa,311Mpa,251 Mpa,295Mpa respectively.The maximum tensile stress of m1-m4 on the lateral prosthesis stem is 213 Mpa,243Mpa,196 Mpa,230Mpa respectively.CONCLUSIONAfter the replacement of artificial femoral head prostheses with different diameters,each model maintained the original mechanical conduction pathway in the pelvic area,which was transmitted backward and upward along the acetabular parietal cortex to the posterolateral side of the sacroiliac joint region.The stress concentration areas were in the upper part of the upper edge of the acetabulum and the great notch of the ischium,and there was no obvious deviation.In the acetabular and cartilage area,the stress concentration area of each model is transferred from the top of the acetabular to the medial and central area of the acetabular top,and the larger ball head of the prosthesis will lead to the stress dispersion at the top of the acetabulum.At the same time,the stress concentration area on the cartilage moves outward or inward with the increase of the diameter of the ball head.Because the elastic modulus of the ball head and neck of the prosthesis is much higher than that of the cortical bone,the stress concentration of each model appears in these two parts,and the stress concentration area of the ball head is located in the outer upper quadrant of the ball head,that is,the contact with the top of the acetabulum.Stress shielding appears below it.The upper part of the femur after prosthesis replacement still maintains the original axial stress pattern,the medial side of the femur is compressive stress,the lateral part is tensile stress,and the compressive stress value is higher than the tensile stress.However,the original mechanical conduction path from the femoral neck to the femoral shaft was changed from the prosthetic neck to the prosthetic stem and then to the femoral shaft after the placement of a rigid prosthetic stem,resulting in obvious stress shielding in the upper part of the femur.In the experiment,the maximum stress increase of M3(ball head diameter = original femoral head diameter-1mm)in pelvis,acetabulum,cartilage and ball head was the smallest among all postoperative models,and the stress shielding effect in the upper part of femur was the slightest than other models,followed by M1(ball head diameter = original femoral head diameter).Therefore,in bipolar hemiarthroplasty.we recommended to give priority to using the prosthetic ball head with a smaller 1mm diameter than the original femoral head,followed by the prosthetic ball head with the same diameter as the original femoral head,so as to obtain the closest natural mechanical properties of the hip joint before replacement and reduce the risk of complications such as acetabular wear and prosthesis instability caused by size differences. |
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