Objective：To model the stress transfer at the interface of the cemented prosthesis and femur, an axisymmetric model of the interfacial stress transfer was established. Methods ： Assuming that the prosthesis, the cem...Objective：To model the stress transfer at the interface of the cemented prosthesis and femur, an axisymmetric model of the interfacial stress transfer was established. Methods ： Assuming that the prosthesis, the cement and the femur were concentric cylinders with linear elastic and isotropic properties, distributions of the axial stresses in the prosthesis, the cement and the femur as well as the interfacial shear stresses at the prosthesis/cement interface and the cement/femur interface in the axial direction were obtained from the established axisymmetric stress transfer model. Results ： Interfacial failure was the main form for the prosthesis/cement/femur structure under external loads. Considering the residual thermal stresses, it was more likely to produce the mixed failure form than the pure shear failure form. Since the cement had a relatively high thermal expansion coefficient, the thermal effect accelerated the interface failure and thus aggravated the stress shielding effect. Due to a relatively high thermal residual temperature difference, the interfacial debonding and femur failure was more likely to occur for the cobalt-chromium alloy prosthesis material than the Ti-6A1-4V alloy prosthesis material. Conclusion： Assuming that the prosthesis, the cement and the femur are concentric cylinders with linear elastic and isotropic properties, distributions of the axial stresses in the prosthesis, the cement and the femur as well as the interfacial shear stresses at the prosthesis/cement interface and the cement/femur interface in the axial direction was obtained using the basic equations of axisymmetric elastic mechanics when the prosthesis bears the compressive stresses. Interface failure is the main failure form for the prosthesis/cement/femur structure under external loads. The thermal effects accelerate the failure of the prosthesis/cement interface and the cement/femur interface and the relaxation of the prosthesis, and then aggravates the stress shielding effect of the femur. Also, the thermal effects decrease the efficiencies of the interfacial stress transfer to some extent since it alleviates the failure of the interface and the femur, which was confirmed by the clinical results.展开更多
Objective： Total hip arthroplasty （THA） and hemiarthroplasty （HA） are effective methods currently used to treat femoral neck fracture in elderly patients, but the two options remain controversial in patients over...Objective： Total hip arthroplasty （THA） and hemiarthroplasty （HA） are effective methods currently used to treat femoral neck fracture in elderly patients, but the two options remain controversial in patients over 70 years old. The main purpose of our study was to determine whether THA or HA is a superior treatment of femoral fractures involving a displaced neck in patients who are over 70 years of age. Methods： A computer-based online search of Medline （1970-2011）, PubMed （1977-2011）, and the Cochrane Cen- tral Register of Controlled Trials （2002-201 l） was conducted. Six relevant randomized controlled trials with a total of 739 patients were included for the final analysis. The analysis was performed with software RevMan 5.0. Results： We found that compared with THA, HA needed shorter average time and lost less blood. While over the long-term follow-up, THA patients exhibited significantly less pain and better function and were less likely to require a revision hip surgery. Postoperative infection was equally common among HA and THA patients. Conclusions： The significant differences in outcomes suggest that THA is a valuable treatment option for active elderly hip fracture individuals. However, patients who are older, impaired or institutionalized benefit from HA.展开更多
文摘Objective：To model the stress transfer at the interface of the cemented prosthesis and femur, an axisymmetric model of the interfacial stress transfer was established. Methods ： Assuming that the prosthesis, the cement and the femur were concentric cylinders with linear elastic and isotropic properties, distributions of the axial stresses in the prosthesis, the cement and the femur as well as the interfacial shear stresses at the prosthesis/cement interface and the cement/femur interface in the axial direction were obtained from the established axisymmetric stress transfer model. Results ： Interfacial failure was the main form for the prosthesis/cement/femur structure under external loads. Considering the residual thermal stresses, it was more likely to produce the mixed failure form than the pure shear failure form. Since the cement had a relatively high thermal expansion coefficient, the thermal effect accelerated the interface failure and thus aggravated the stress shielding effect. Due to a relatively high thermal residual temperature difference, the interfacial debonding and femur failure was more likely to occur for the cobalt-chromium alloy prosthesis material than the Ti-6A1-4V alloy prosthesis material. Conclusion： Assuming that the prosthesis, the cement and the femur are concentric cylinders with linear elastic and isotropic properties, distributions of the axial stresses in the prosthesis, the cement and the femur as well as the interfacial shear stresses at the prosthesis/cement interface and the cement/femur interface in the axial direction was obtained using the basic equations of axisymmetric elastic mechanics when the prosthesis bears the compressive stresses. Interface failure is the main failure form for the prosthesis/cement/femur structure under external loads. The thermal effects accelerate the failure of the prosthesis/cement interface and the cement/femur interface and the relaxation of the prosthesis, and then aggravates the stress shielding effect of the femur. Also, the thermal effects decrease the efficiencies of the interfacial stress transfer to some extent since it alleviates the failure of the interface and the femur, which was confirmed by the clinical results.
文摘Objective： Total hip arthroplasty （THA） and hemiarthroplasty （HA） are effective methods currently used to treat femoral neck fracture in elderly patients, but the two options remain controversial in patients over 70 years old. The main purpose of our study was to determine whether THA or HA is a superior treatment of femoral fractures involving a displaced neck in patients who are over 70 years of age. Methods： A computer-based online search of Medline （1970-2011）, PubMed （1977-2011）, and the Cochrane Cen- tral Register of Controlled Trials （2002-201 l） was conducted. Six relevant randomized controlled trials with a total of 739 patients were included for the final analysis. The analysis was performed with software RevMan 5.0. Results： We found that compared with THA, HA needed shorter average time and lost less blood. While over the long-term follow-up, THA patients exhibited significantly less pain and better function and were less likely to require a revision hip surgery. Postoperative infection was equally common among HA and THA patients. Conclusions： The significant differences in outcomes suggest that THA is a valuable treatment option for active elderly hip fracture individuals. However, patients who are older, impaired or institutionalized benefit from HA.
