The relationship between the convexity on the ultimate bearing surface of a structure and the second- order effects of loads is discussed. All of generalized non-overload forces acted on a structure forms a convex set...The relationship between the convexity on the ultimate bearing surface of a structure and the second- order effects of loads is discussed. All of generalized non-overload forces acted on a structure forms a convex set when ignoring the second-order effects （coupling effects between the generalized forces）. It is true also when the Hessian matrix composed of the second-order partial derivatives on the hypersurface about the ultimate bearing of the structure is negative definite. The outward convexity is kept when the surface is expressed by certain dimensionless parameters. A series of properties based on the convexity are pointed out. Some applications in the analysis of bearing capacity of structures were illustrated with examples. The study shows that an evaluation about the bearing capacity state of a complex structure can be made on the basis of several points on the surface of the ultimate bearing of the structure.展开更多
Background Ceramic bearing surfaces have been introduced to prevent osteolysis after total hip arthroplasty （THA）,but little is known about the difference in clinical and radiological results between pure alumina an...Background Ceramic bearing surfaces have been introduced to prevent osteolysis after total hip arthroplasty （THA）,but little is known about the difference in clinical and radiological results between pure alumina and sandwich alumina bearings.The purpose of this study was to analyze the results obtained with third-generation alumina-on-alumina THA with two different designs both in liner and femoral stem fixation after a minimum follow-up of 4.2 years.Methods The results of 195 primary alumina-on-alumina THAs in 167 patients were evaluated.The procedures were performed between January 1998 and October 2006.Three patients died and 11 patients were lost to follow-up,leaving a total of 153 patients （181 hips） available for study.In the 88 group A patients,107 hips were implanted using pure alumina bearings with cementless femoral stems.These patients were followed for （6.84±1.49） years.In the 65 group B patients,74 hips were implanted using sandwich alumina ceramic bearings with cemented femoral stems.These patients had a follow-up period of （7.73±1.60） years.Patients in both groups were evaluated clinically and radiographically.Results One ceramic liner fracture occurred in group A and five took place in group B （P 〈0.05）,four of them revised for liner fracture.In each group,one acetabular shell migration happened without liner breakage and two hips developed deep infections,and all these six hips received revisions.Nine femoral components loosened in group B,with seven undergoing revisions.Kaplan-Meier survivorship at 5 years for revision of any component for any reason in group A was 96.26% compared to 90.54% in group B （P 〈0.05）.Better function was determined in group A （average Harris hip scores：92.13±2.85） than in group B （average Harris hip scores：86.03±4.21） and the difference was significant （P 〈0.05）.Squeaking was not recorded in either group.Conclusions The sandwich design of the acetabular bearings can not reduce the migration rate in ceramic bearings but increase the liner fracture rate compared to pure ceramic liners.The high loosening rate in fluted and taped designed cemented stems with sandwich liners warrant caution to their use.展开更多
文摘The relationship between the convexity on the ultimate bearing surface of a structure and the second- order effects of loads is discussed. All of generalized non-overload forces acted on a structure forms a convex set when ignoring the second-order effects （coupling effects between the generalized forces）. It is true also when the Hessian matrix composed of the second-order partial derivatives on the hypersurface about the ultimate bearing of the structure is negative definite. The outward convexity is kept when the surface is expressed by certain dimensionless parameters. A series of properties based on the convexity are pointed out. Some applications in the analysis of bearing capacity of structures were illustrated with examples. The study shows that an evaluation about the bearing capacity state of a complex structure can be made on the basis of several points on the surface of the ultimate bearing of the structure.
文摘Background Ceramic bearing surfaces have been introduced to prevent osteolysis after total hip arthroplasty （THA）,but little is known about the difference in clinical and radiological results between pure alumina and sandwich alumina bearings.The purpose of this study was to analyze the results obtained with third-generation alumina-on-alumina THA with two different designs both in liner and femoral stem fixation after a minimum follow-up of 4.2 years.Methods The results of 195 primary alumina-on-alumina THAs in 167 patients were evaluated.The procedures were performed between January 1998 and October 2006.Three patients died and 11 patients were lost to follow-up,leaving a total of 153 patients （181 hips） available for study.In the 88 group A patients,107 hips were implanted using pure alumina bearings with cementless femoral stems.These patients were followed for （6.84±1.49） years.In the 65 group B patients,74 hips were implanted using sandwich alumina ceramic bearings with cemented femoral stems.These patients had a follow-up period of （7.73±1.60） years.Patients in both groups were evaluated clinically and radiographically.Results One ceramic liner fracture occurred in group A and five took place in group B （P 〈0.05）,four of them revised for liner fracture.In each group,one acetabular shell migration happened without liner breakage and two hips developed deep infections,and all these six hips received revisions.Nine femoral components loosened in group B,with seven undergoing revisions.Kaplan-Meier survivorship at 5 years for revision of any component for any reason in group A was 96.26% compared to 90.54% in group B （P 〈0.05）.Better function was determined in group A （average Harris hip scores：92.13±2.85） than in group B （average Harris hip scores：86.03±4.21） and the difference was significant （P 〈0.05）.Squeaking was not recorded in either group.Conclusions The sandwich design of the acetabular bearings can not reduce the migration rate in ceramic bearings but increase the liner fracture rate compared to pure ceramic liners.The high loosening rate in fluted and taped designed cemented stems with sandwich liners warrant caution to their use.
