The number of screws, bone quality, and friction coefficient affect acetabular cup stability.
One of the major causes of loosening of cementless acetabular cup implants is insufficient initial stability. This study used three-dimensional finite element models of the pelvis and acetabular components to investigate the effects of the number of screws, bone quality, and friction coefficient of the acetabular cup on the initial stability under normal walking. A commercially available hemispherical acetabular cup with five screw holes was used as the default model. The stiffness of the pelvis and the friction coefficient of the cup were systematically varied, within a realistic range, to assess the initial stability of the acetabular cup. The simulations showed that the inserted screws provide only a localized reduction in the relative micromotion between the cup and pelvis therefore inserting several screw closed together might not be useful. Changes in the pelvic stiffness have a non-linear effect on the initial stability of acetabular cup and the subchondral bone provides good support for fixation of the cementless cup. The friction coefficient of the acetabular cup plays a limited role, comparing with the factor of bone quality, in resisting relative micromotion in the cup-pelvis interface.
Hsu
Jui-Ting
JT
Institute of Biomedical Engineering, National Cheng Kung University, Tainan 701, Taiwan, ROC.
Chang
Chih-Han
CH
Huang
Heng-Li
HL
Zobitz
Mark E
ME
Chen
Weng-Pin
WP
Lai
Kuo-An
KA
An
Kai-Nan
KN
D000497:Alloys; D001696:Biomechanical Phenomena; D001863:Bone Screws; D001842:Bone and Bones / Q000378:metabolism / Q000473:pathology*; D020342:Finite Element Analysis; D017276:Friction; D006615:Hip / Q000000981:diagnostic imaging; D006621:Hip Joint / Q000000981:diagnostic imaging; D006622:Hip Prosthesis; D006801:Humans; D008422:Materials Testing; D008962:Models, Theoretical; D010388:Pelvis / Q000033:anatomy & histology* / Q000473:pathology; D011474:Prosthesis Design; D013314:Stress, Mechanical; D014057:Tomography, X-Ray Computed
D000497:Alloys