title: Finite Element Analysis of Sacroiliac Joint Fixation under Compression Loads.
abstract: BACKGROUND
  Sacroiliac joint (SIJ) is a known chronic pain-generator. The last resort of treatment is the arthrodesis. Different implants allow fixation of the joint, but to date there is no tool to analyze their influence on the SIJ biomechanics under physiological loads. The objective was to develop a computational model to biomechanically analyze different parameters of the stable SIJ fixation instrumentation.
  
  
  METHODS
  A comprehensive finite element model (FEM) of the pelvis was built with detailed SIJ representation. Bone and sacroiliac joint ligament material properties were calibrated against experimentally acquired load-displacement data of the SIJ. Model evaluation was performed with experimental load-displacement measurements of instrumented cadaveric SIJ. Then six fixation scenarios with one or two implants on one side with two different trajectories (proximal, distal) were simulated and assessed with the FEM under vertical compression loads.
  
  
  RESULTS
  The simulated S1 endplate displacement reduction achieved with the fixation devices was within 3% of the experimentally measured data. Under compression loads, the uninstrumented sacrum exhibited mainly a rotation motion (nutation) of 1.38° and 2.80° respectively at 600 N and 1000 N, with a combined relative translation (0.3 mm). The instrumentation with one screw reduced the local displacement within the SIJ by up to 62.5% for the proximal trajectory vs. 15.6% for the distal trajectory. Adding a second implant had no significant additional effect.
  
  
  CONCLUSIONS
  A comprehensive finite element model was developed to assess the biomechanics of SIJ fixation. SIJ devices enable to reduce the motion, mainly rotational, between the sacrum and ilium. Positioning the implant farther from the SIJ instantaneous rotation center was an important factor to reduce the intra-articular displacement.
  
  
  CONCLUSIONS
  Knowledge provided by this biomechanical study enables improvement of SIJ fixation through optimal implant trajectory.
authors.affiliation: Department of Mechanical Engineering, Polytechnique Montréal, Montreal, Canada; iLab - Spine International Laboratory - Spine Imaging and Biomechanics.
authors.forename: Claire
authors.initials: C
authors.lastname: Bruna-Rosso
authors.affiliation: iLab - Spine International Laboratory - Spine Imaging and Biomechanics; Laboratoire de Biomécanique Appliquée, Aix-Marseille Université, Marseille, France.
authors.forename: Pierre-Jean
authors.initials: PJ
authors.lastname: Arnoux
authors.affiliation: Department of Mechanical Engineering, Polytechnique Montréal, Montreal, Canada; iLab - Spine International Laboratory - Spine Imaging and Biomechanics; Laboratoire de Biomécanique Appliquée, Aix-Marseille Université, Marseille, France; Sainte-Justine University Hospital Center, Montreal, Canada.
authors.forename: Rohan-Jean
authors.initials: RJ
authors.lastname: Bianco
authors.affiliation: iLab - Spine International Laboratory - Spine Imaging and Biomechanics; Laboratoire de Biomécanique Appliquée, Aix-Marseille Université, Marseille, France.
authors.forename: Yves
authors.initials: Y
authors.lastname: Godio-Raboutet
authors.affiliation: Department of Mechanical Engineering, Polytechnique Montréal, Montreal, Canada; iLab - Spine International Laboratory - Spine Imaging and Biomechanics; Laboratoire de Biomécanique Appliquée, Aix-Marseille Université, Marseille, France.
authors.forename: Léo
authors.initials: L
authors.lastname: Fradet
authors.affiliation: Department of Mechanical Engineering, Polytechnique Montréal, Montreal, Canada; iLab - Spine International Laboratory - Spine Imaging and Biomechanics; Sainte-Justine University Hospital Center, Montreal, Canada.
authors.forename: Carl-Éric
authors.initials: CÉ
authors.lastname: Aubin
keywords: arthrodesis; biomechanics; finite element analysis; sacroiliac joint