The relation between micromotion and screw fixation in acetabular cup

Authors:
Jui-Ting Hsu;Kuo-An Lai;Qingshan Chen;Mark E. Zobitz;Heng-Li Huang;Kai-Nan An;Chih-Han Chang
Affiliations:
Institute of Biomedical Engineering, National Cheng Kung University, Tainan 701, Taiwan, ROC;Orthopaedic Department, National Cheng Kung University Medical Center, Tainan 701, Taiwan, ROC;Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic College of Medicine, Rochester, MN 55905, USA;Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic College of Medicine, Rochester, MN 55905, USA;Institute of Biomedical Engineering, National Cheng Kung University, Tainan 701, Taiwan, ROC;Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic College of Medicine, Rochester, MN 55905, USA;Institute of Biomedical Engineering, National Cheng Kung University, Tainan 701, Taiwan, ROC
Venue:
Computer Methods and Programs in Biomedicine
Year:
2006

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Abstract

One of the major causes inducing loosening in the cementless acetabular cup implanting is its insufficient initial stability. In this study, three-dimensional finite element models of the pelvis and acetabular components were developed to investigate the relationship between relative micromotion, initial stability, and screw fixation under six daily activity loadings. A commercial available hemispheric cup with five screw holes was used as the target acetabular cup. The simulation results showed that if screws were placed closed together, when the screw number increased from 1 to 5, the peak micromotion decreased less than 14%, from 126.5 to 108.8@mm, while the stable region, micromotion less than 28@mm, enlarged only by 40%, from 46.1% to 64.7%. However, if the screw could be placed near the cup rim, a single rim screw, 202.1@mm micromotion, could provide better stability than that of four dome screws, 209.6@mm micromotion, placed closed together. To conclude, multiple cup screws should be placed near cup rim and as separate as possible to enlarge the stable region and reduce the peak micromotion between cup and acetabulum.