title: Comparison between mechanical stress and bone mineral density in the femur after total hip arthroplasty by using subject-specific finite element analyses.
abstract: The mechanism underling bone mineral density (BMD) loss that occurs in the femur after total hip arthroplasty (THA) remains unknown. We compared the equivalent stress and strain energy density (SED) to BMD in the femur after THA using subject-specific finite element analyses. Twenty-four patients who had undergone primary cementless THA were analysed. BMD was measured using dual-energy X-ray absorptiometry (DEXA) at 1 week and 3, 6 and 12 months after THA. Seven regions of interest (ROIs) were defined in accordance with Gruen's system (ROIs 1-7). Computed tomography images of the femurs were acquired pre- and postoperatively, and the images were converted into three-dimensional finite element (FE) models. Equivalent stress and SED were analysed and compared with DEXA data. BMD was maintained 1 year after THA in ROIs 3, 4, 5 and 6, whereas BMD decreased in ROIs 1, 2 and 7. FE analysis revealed that equivalent stress in ROIs 3, 4, 5 and 6 was much higher than that in ROIs 1, 2 and 7. A significant correlation was observed between the rate of changes in BMD and equivalent stress. Reduction of equivalent stress may contribute to decrease in BMD in the femur after THA.
authors.affiliation: a Department of Orthopaedic Surgery , Yokohama City University , 3-9, Fukuura, Kanazawa-ku, Yokohama , Kanagawa 236-0004 , Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ike
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Inaba
authors.forename: Naomi
authors.initials: N
authors.lastname: Kobayashi
authors.forename: Yasuhide
authors.initials: Y
authors.lastname: Hirata
authors.forename: Yohei
authors.initials: Y
authors.lastname: Yukizawa
authors.forename: Chie
authors.initials: C
authors.lastname: Aoki
authors.forename: Hyonmin
authors.initials: H
authors.lastname: Choe
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Saito
keywords: bone mineral density; finite element analysis; total hip arthroplasty