ABSTRACT
Objective To analyze and evaluate a new acetabular revision component with three wings. Methods The finite-element models of a new acetabular component and acetabulum with bone loss were established to calculate the interface stresses during a normal gait cycle with use of the finite-element formulations. Results The finite-element analysis demonstrated that stress and strain at the interfaces of bone-shell and metal-polyethylene liner had the same direction of change but no remarkable difference between them. In the study, the result indicated increased contact stresses with an increased joint load and orientation. The peak stress was tested at the second stage of gait cycle. The stress of wings increased gradually from rim to root. Its peak stress that was significantly lower than yield force of the Co-Cr alloy was at the joint between the wing and the shell. The stress of graft had the same change rule as the joint force. The part of graft near to acetabular component was subjected to higher stress conditions. Conclusion The hip forces can transfer from acetabular component and implant to acetabulum. The result of the finite-element analysis underlined the importance of wings of the new acetabular component. The wing can help to improve the antitorsion ability of acetabular component and to minimize its aseptic loosening rate. Therefore, based on results of this study and clinical application, the acetabular component with wings is known a viable means for acetabular revision in the presence of bone loss. But further research is needed as to this acetabular component.
ABSTRACT
BACKGROUND:Alternative implants affect stability of prostheses,and freeze-dried bone allografts are most selected as implants.The crack between grafts and host bone is unavoidable,which would weaken the bone integration.Bone cement can fill the cracks quickly and completely,however,the effects of bone cement on the stress of prostheses and its own remains poorly understood.OBJECTIVE:To evaluate the effect of the different grafting for bone loss in the presence of the new acetabular component with wings at the time of acetabular revision.METHODS:The finite-element models of acetabular component with three wings and acetabulum with bone loss were established.Following prostheses implantation,the gaps were filled with bone cement and freeze-dried bone allograft,respectively,stress of the graft and its effect on prostheses were analyzed under 2 158 N and 426 N acetabular loads.RESULTS AND CONCLUSION:The finite-element analysis demonstrated that stress and strain at the interfaces of bone-shell and metal-polyethylene liner had the same direction of change but no significant difference between them.In the study,the result indicated increased contact stresses with an increased hip force and orientation.The stress of wings increased gradually from rim to root.Its peak stress was at the joint between the wing and the shell.The different grafts did not affect the stress of the acetabular component.But the stress of bone cement was significantly higher than that of particulate bone.The study demonstrated that change of the graft could not make remarkable effect on the stress of the acetabular component.But the stress of bone cement increased significantly.The result of the finite-element analysis indicated that particulate bone graft is benefit to improving itsstability and to minimize aseptic loosening rate of acetabular component.
ABSTRACT
Alternative designs have been explored in an attempt to improve the longevity of acetabular prostheses in revision surgery. Many studies had been designed to test the result of the extra-large uncemented hemispherical acetabular components used for acetabular revision in the presence of bone loss. A clinical study of a new acetabular component consisting of a porous metal shell with three wings and an all-polyethylene liner had attained a satisfying result. The purpose of this study was to evaluate the new acetabular component by comparison with the hemispherical acetabular component. The finite-element models of the two acetabular components and the acetabulum in the presence of bone loss were established to calculate the interface stresses during a normal gait cycle with use of the finite-element formulations. Results of the finite-element analysis demonstrated that stress and strain of the two acetabular components had the same direction of change, but the new component had higher stress at the root of wings. In the study, the result indicated reduced contact stresses with a reduced abduction angle of wings. The stress was lower in the new acetabular component of 15° angle of wings compared with the new acetabularcomponent of 30°of wings and hemispherical acetabular component (P < 0.05). The stress of acetabular component with wings showed no remarkable difference by comparison with the extra-large uncemented hemispherical acetabular component. Reducing abduction angle of wings seemed to be a viable means of reducing the stress of the acetabular component while improving its stability.
ABSTRACT
Objective: To investigate the gene expression of bone morphogenetic protein(BMP)in human cervical disc.Methods:cervical disc specimen were obtained from patients undergoing anterior disc surgery,who had the signs of cervical disc herniation.Immunohistochemical and in situ hybridization studies were conducted to detect cells with BMP gene expression.Results:It showed positive staining of BMP-like immunohistoreactivity and its mRNA gene expression in degenerated discs,osteophytes,posterior longitudinal ligments,amd periosteum of vertebra.Conclusion:BMP may be relate to intervertebral disc degeneration as prolifertion-stimulating factor of chondrocytes that replace normal anular cells during disc degeneration but its mechanism needs further study.