title: The biomechanical effect of anteversion and modular neck offset on stress shielding for short-stem versus conventional long-stem hip implants.
abstract: Short-stem hip implants are increasingly common since they preserve host bone stock and presumably reduce stress shielding by improving load distribution in the proximal femur. Stress shielding may lead to decreased bone density, implant loosening, and fracture. However, few biomechanical studies have examined short-stem hip implants. The purpose of this study was to compare short-stem vs. standard length stemmed implants for stress shielding effects due to anteversion-retroversion, anterior-posterior position, and modular neck offset. Twelve artificial femurs were implanted with either a short-stem modular-neck implant or a conventional length monolithic implant in 0° or 15° of anteversion. Three modular neck options were tested in the short-stem implants. Three control femurs remained intact. Femurs were mounted in adduction and subjected to axial loading. Strain gauge values were collected to validate a Finite Element (FE) model, which was used to simulate the full range of physiologically possible anteversion and anterior-posterior combinations (n = 25 combinations per implant). Calcar stress was compared between implants and across each implant's range of anteversion using one and two-way ANOVA. Stress shielding was defined as the overall change in stress compared to an intact femur. The FE model compared well with experimental strains (intact: slope = 0.898, R = 0.943; short-stem: slope = 0.731, R = 0.948; standard-stem: slope = 0.743, R = 0.859); correction factors were used to adjust slopes to unity. No implant anteversion showed significant reduction in stress shielding (α = 0.05, p > 0.05). Stress shielding was significantly higher in the standard-stem implant (63% change from intact femur, p < 0.001) than in short-stem implants (29-39% change, p < 0.001). Short-stem implants reduce stress shielding compared to standard length stemmed implants, while implant anteversion and anterior-posterior position had no effect. Therefore, short-stem implants have a greater likelihood of maintaining calcar bone strength in the long term.
authors.affiliation: Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto M5S 3G9, ON, Canada; Martin Orthopaedic Biomechanics Laboratory, St. Michael's Hospital, Toronto M5B 1W8, ON, Canada.
authors.forename: Peter
authors.initials: P
authors.lastname: Goshulak
authors.affiliation: Department of Mechanical and Industrial Engineering, Ryerson University, Toronto M5B 2K3, ON, Canada.
authors.forename: Saeid
authors.initials: S
authors.lastname: Samiezadeh
authors.affiliation: Martin Orthopaedic Biomechanics Laboratory, St. Michael's Hospital, Toronto M5B 1W8, ON, Canada.
authors.forename: Mina S R
authors.initials: MS
authors.lastname: Aziz
authors.affiliation: Department of Mechanical and Industrial Engineering, Ryerson University, Toronto M5B 2K3, ON, Canada.
authors.forename: Habiba
authors.initials: H
authors.lastname: Bougherara
authors.affiliation: Department of Mechanical and Industrial Engineering, Ryerson University, Toronto M5B 2K3, ON, Canada; Martin Orthopaedic Biomechanics Laboratory, St. Michael's Hospital, Toronto M5B 1W8, ON, Canada; Department of Mechanical and Industrial Engineering, University of Toronto, Toronto M5S 3G8, ON, Canada. Electronic address: rzdero@ryerson.ca.
authors.forename: Radovan
authors.initials: R
authors.lastname: Zdero
authors.affiliation: Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto M5S 3G9, ON, Canada; Martin Orthopaedic Biomechanics Laboratory, St. Michael's Hospital, Toronto M5B 1W8, ON, Canada.
authors.forename: Emil H
authors.initials: EH
authors.lastname: Schemitsch
mesh_terms: D001696:Biomechanical Phenomena; D020342:Finite Element Analysis; D006622:Hip Prosthesis; D011474:Prosthesis Design; D013314:Stress, Mechanical; D013997:Time Factors; D016474:Weight-Bearing
keywords: Biomechanics; Finite element analysis; Hip arthroplasty; Short-stem; Stress shielding