RESUMEN
BACKGROUND:After the internal fixation of cannulated screws in femoral neck fractures,because the affected limb is often unable to bear weight in the short term and the implants with high stiffness have a stress shielding effect on the fracture end,it is easy to cause osteoporosis of the affected limb and changes in the biomechanical distribution of the proximal femur,the incidence of osteonecrosis of the femoral head is high after surgery.At present,few studies have been conducted on the biomechanical effects of osteoporosis at the proximal end of the femur occurring after femoral neck fracture surgery on femoral neck fracture treated with cannulated screws. OBJECTIVE:Using finite element analysis,to investigate the biomechanical effects of osteoporosis occurring after femoral neck fracture surgery on femoral neck fracture treated with cannulated screws and explore the role of biomechanical factors in osteonecrosis of the femoral head. METHODS:Based on the obtained CT scan data of the femur in a patient with a femoral neck fracture,a proximal femoral model for internal fixation for femoral neck fracture was established by Mimics 19.0,3-Matic,UG 11.0,Hypermesh 14.0,and Abaqus software.One finite element model of the proximal femur without osteoporosis and three finite element models of the proximal femur with osteoporosis were analyzed using Abaqus software.The stress,contact pressure,displacement peak and cloud map under different components of the four models were measured and analyzed,and the internal stress changes and distribution of the femoral head were compared and analyzed. RESULTS AND CONCLUSION:The stresses and contact pressures of the femoral head and lower anterior cannulated screws varied more with the degree of osteoporosis.The peak displacement of the four models increased slowly with the degree of osteoporosis.By one-way analysis of variance,there was no significant effect of the degree of osteoporosis on the peak stress,contact pressure,and displacement of the different components.The internal stress distribution of the femoral head changed with the degree of osteoporosis.Changes in the biomechanical environment of the proximal femur have an important impact on osteonecrosis of the femoral head.
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Objective To understand the cause of chest pain (precordium indisposition) in children and explore the thread of thought in its analysis.Methods Clinical data of 314 children with chest pain who visited the cardiovascular department for children of our hospital were collected and analyzed to study its causes.Results The cause could be attributed to organic cardiac diseases in 43 of 314 children (13.7%) with chest pain,to non-organic cardiac diseases in 108 (34.4%),to psychiatric-psychological factors in 60 (19.1%) and to unknown cause in 41 (13.1%).Average age of children with organic cardiac diseases was younger than that of children with other causes (P<0.05).Symptoms accompanied simultaneously in children with organic cardiac diseases were much more frequent significantly than those in them with non-organic cardiac chest pain and unknown causes (P<0.05).Conclusions Chest pain in children could be caused by a few causes,which was non-specific symptom for organic cardiac diseases,so, more should be taken into account in analyzing the cause of chest pain in children.