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research-article

Biomechanical Robustness of a Successful Cementless Stem to Surgical Variation in Stem Size and Position

[+] Author and Article Information
Rami M A Al-Dirini

Medical Device Research Institute, College of Science and Engineering, Flinders University, Adelaide, Australia 5043
rami.aldirini@flinders.edu.au

Dermot O'Rourke

Medical Device Research Institute, College of Science and Engineering, Flinders University, Adelaide, Australia 5043
dermot.orourke@flinders.edu.au

Daniel Huff

DePuy Synthes, Johnson and Johnson, Warsaw, USA
DHuff4@its.jnj.com

Saulo Martelli

Medical Device Research Institute, College of Science and Engineering, Flinders University, Adelaide, Australia 5043
saulo.martelli@gmail.com

Mark Taylor

Medical Device Research Institute, College of Science and Engineering, Flinders University, Adelaide, Australia 5043
mark.taylor@flinders.edu.au

1Corresponding author.

ASME doi:10.1115/1.4039824 History: Received September 02, 2017; Revised March 18, 2018

Abstract

Successful designs of total hip replacement (THR) need to be robust to surgical variation in sizing and positioning of the femoral stem. This study presents an automated method for comprehensive evaluation of the potential impact of surgical variability in sizing and positioning on the primary stability of a contemporary cementless femoral stem (Corail®, Depuy Synthes). A patient-specific finite element (FE) model of a femur was generated from computed-tomography (CT) images from a female donor. An automated algorithm was developed to span the plausible surgical envelope of implant positions constrained by the inner cortical boundary. The analysis was performed on four stem sizes: oversized, ideal (nominal) size and undersized by up to two stem sizes. For each size, Latin Hypercube sampling was used to generate models for 100 unique alignment scenarios. For each scenario, peak hip contact and muscle forces published for stair climbing were scaled to the donor's body weight and applied to the model. The risk of implant loosening was assessed by comparing the bone-implant micromotion/strains to thresholds (150µm and 7000µe) above which fibrous tissue is expected to prevail and the peri-prosthetic bone to yield, respectively. The risk of long-term loosening due to adverse bone resorption was assessed using bone adaptation theory. The range of implant positions generated effectively spanned the available intra-cortical space. The Corail® stem was found stable and robust to changes in size and position, with the majority of the bone-implant interface ...

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