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Introduction: Little is known about the association between well-fixed polished tapered cemented stems (PTCS) implanted by the line-to-line technique and changes of stem migration, or the change of functional anteversion of the femur after total hip arthroplasty (THA). Materials and methods: This retrospective study included 422 two-stage bilateral primary THAs performed using PTCS implanted by the line-to-line technique. CT scans were made on both the target side (first postoperative CT) and on the contralateral side (second postoperative CT) 1 week postoperatively. The mean follow-up was 7.8 months. CT data for each scan were transferred to 3D template software (Zed hip, Lexi, Japan). The postoperative changes of anatomical stem anteversion (ASA), functional femoral anteversion (FFA), and stem subsidence were evaluated. Results: A total of 20 THAs with CT scans were available on 3D template software. The ASA and the FFA had migrated − 0.68° ± 0.62° and − 5.5° ± 9.7°, respectively, over the follow-up period. A significant positive correlation was observed between the change of subsidence and ASA (r2 = 0.34, p = 0.007), between the FFA on the second postoperative CT and ASA on the first postoperative CT (r2 = 0.26, p = 0.02) and between the FFA on the second postoperative CT and FFA on the first postoperative CT (r2 = 0.52, p = 0.0003). Conclusion: This study indicates that the change in axial rotation of a PTCS implanted by the line-to-line technique was less than that reported by other studies and the preoperative external rotation contracture was substantially improved after THA. [ABSTRACT FROM AUTHOR]

Background: The purpose of this study was to validate a diaphyseal femoral fracture model using a finite element analysis (FEA) with mechanical testing in fresh-frozen cadavers. Methods: We used 18 intact femora (9 right and 9 left) from 9 fresh-frozen cadavers. Specimens were obtained from 5 males and 4 females with a mean age of 85.6 years. We compared a computed tomography (CT)-based FEA model to diaphyseal femoral fracture loads and stiffness obtained by three-point bending. Four material characteristic conversion equations (the Keyak, Carter, and Keller equations plus Keller's equation for the vertebra) with different shell thicknesses (0.3, 0.4, and 0.5 mm) were compared with the mechanical testing. Results: The average fracture load was 4582.8 N and the mean stiffness was 942.0 N/mm from actual mechanical testing. FEA prediction using Keller's equation for the vertebra with a 0.4-mm shell thickness showed the best correlations with the fracture load ( R 2 = 0.76) and stiffness ( R 2 = 0.54). Shell thicknesses of 0.3 and 0.5 mm in Keller's equation for the vertebra also showed a strong correlation with fracture load ( R 2 = 0.66 for both) and stiffness ( R 2 = 0.50 and 0.52, respectively). There were no significant correlations with the other equations. Conclusion: We validated femoral diaphyseal fracture loads and stiffness using an FEA in a cadaveric study. [ABSTRACT FROM AUTHOR]

Introduction: Cemented femoral component design including its mechanical behavior in total hip arthroplasty (THA) has influenced the occurrence of postoperative periprosthetic femoral fracture (PPFF). The main aim of this study was to investigate the influence of the calcar collar and surface finish in the cemented femoral component on the risk of PPFF.Materials and Methods: This retrospective review was undertaken of 1082 primary THAs in 912 patients using cemented femoral components followed for a minimum of five years (mean, 9.4 years; range, 5-24 years). The incidence of PPFF, patients' demographics and surgical details were evaluated. Kaplan-Meier survivorship analysis was performed for four different outcomes: any PPFF, revision of the femoral component for PPFF, aseptic loosening, and for any reason.Results: The overall incidence of PPFFs was 1.0% (n = 11): 1.4% (n = 10) in the collarless polished (CLP) group, none in the collared polished (CP) group and 0.6% (n = 1) in the collared non-polished (CNP) group (p > 0.05). Kaplan-Meier survival analysis for the femoral component at 12 years with PPFF as the end point was 97.4% (95% confidence interval [CI], 94.9 to 99.8) in the collarless group and 99.7% (95% CI, 99.1 to 100) in the collared group (p = 0.048). With revision of the femoral component for aseptic loosening as the end point, survivorship was 100.0% in the CLP and CP groups, and 98.1% (95% CI, 95.9 to 100) in the CNP group (CLP vs CP, p > 0.999; CLP vs CNP, p = 0.001; CP vs CNP, p = 0.112).Conclusion: This study demonstrated that the calcar collar in the cemented femoral component could play an important role to reduce the incidence of PPFF. The surface finish in the cemented femoral components influenced the incidence of femoral component revision for aseptic loosening over 5-12 years. Surgeons should consider not only the geometry and the mechanical function of the femoral components based on different design philosophies, but also potential complications associated with different designs that may require revision arthroplasty. [ABSTRACT FROM AUTHOR]