Biomechanical comparison of sacral and transarticular sacroiliac screw fixation
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BIOMECHANICS
Biomechanical comparison of sacral and transarticular sacroiliac screw fixation Léo Fradet1,2,3 · Rohan‑Jean Bianco1,4,5 · Robert Tatsumi6 · John Coleman7 · Carl‑Éric Aubin1,2,3 Received: 4 March 2020 / Accepted: 16 March 2020 © Scoliosis Research Society 2020
Abstract Study design A detailed finite element analysis of screw fixation in the sacrum and pelvis. Objective To biomechanically assess and compare the fixation performance of sacral and transarticular sacroiliac screws. Summary of background data Instrumentation constructs are used to achieve fixation and stabilization for the treatment of spinopelvic pathologies. The optimal screw trajectory and type of bone engagement to caudally anchor long fusion constructs are not yet known. Methods A detailed finite element model of the sacroiliac articulation with two different bone densities was developed. Two sacral and one transarticular sacroiliac screw trajectories were modeled with different diameters (5.5 and 6.5 mm) and lengths (uni-cortical, bi-cortical and quad-cortical purchase). Axial pullout and flexion/extension toggle forces were applied on the screws representing intra and post-operative loads. The force–displacement results and von Mises stresses were used to characterize the failure pattern. Results Overall, sacroiliac screws provided forces to failure 2.75 times higher than sacral fixation screws. On the contrary, the initial stiffness was approximately half as much for sacroiliac screws. High stresses were located at screw tips for the sacral trajectories and near the cortical bone screw entry points for the sacroiliac trajectory. Overall, the diameter and length of the screws had significant effects on the screw fixation (33% increase in force to failure; 5% increase in initial stiffness). A 20% drop in bone mineral density (lower bone quality) decreased the initial stiffness by 25% and the force to failure by 5–10%. High stresses and failure occurred at the screw tip for uni- and tri-cortical screws and were close to trabecular–cortical bone interface for bi-cortical and quad-cortical screws. Conclusions Sacroiliac fixation provided better anchorage than sacral fixation. The transarticular purchase of the sacroiliac trajectory resulted in differences in failure pattern and fixation performance. Keywords Spinopelvic instrumentation · Sacral screws · Sacroiliac screws · Finite element analysis
Introduction Bone screws are used for the treatment of spinopelvic pathologies to achieve fixation and stabilization. Spinal surgeons have numerous options to caudally anchor long * Carl‑Éric Aubin carl‑[email protected] 1
Department of Mechanical Engineering, Polytechnique Montréal, P.O. Box 6079, Downtown Station, Montreal, QC H3C 3A7, Canada
2
Sainte-Justine University Hospital Center, 3175, Cote Sainte‑Catherine Road, Montreal, QC H3T 1C5, Canada
3
International Laboratory - Spine Imaging and Biomechanics, Montreal, Canada
fusion constructs via screw fixation in the sacrum and pelvis. Sacroiliac screw anchoring s
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