title: Instrumentation failure following pedicle subtraction osteotomy: the role of rod material, diameter, and multi-rod constructs.
abstract: Pedicle subtraction osteotomy (PSO) has a complication rate noticeably higher than other corrective surgical techniques used for the treatment of spinal sagittal imbalance. In particular, rod breakage and pseudoarthrosis remain burning issues of this technique. Goal of this study was to investigate the biomechanical performance of several hardware constructs.
  
  
  
  The study was performed using two validated finite element models of the lumbosacral spine (L1-S1) incorporating a PSO on L3 and L4, respectively. Both models were instrumented two levels above and below the osteotomy site. Different combinations of materials (Ti6Al4V and Cr-Co) and device configurations (bilateral single vs. double rod, rod diameters of 5 and 6 mm) were investigated. The loading was represented considering a force of 500 N (imposed along the spinal curvature and connecting the vertebral bodies) and pure moments of 7.5 Nm in flexion-extension, lateral bending and axial rotation. The results were evaluated in terms of range of motion (ROM), load, and stresses acting on the instrumentation.
  
  
  
  A comparable ROM was found for all the models. The simulations showed a different behavior of the devices: increasing the stiffness an 8-19% increase of the load was calculated on the rod. However, the stress on the instrumentation resulted higher on Cr-Co devices and on smaller rods. The highest stress reduction (up to 50%) was ensured using double rod constructs.
  
  
  
  The bilateral double parallel rods configuration resulted the best to reduce the stresses on the spinal fixators at the osteotomy site. However, the high loads acting on the rods with respect to the physiologic condition could slow down the bone healing at the osteotomy site.
authors.affiliation: Department of Spine Surgery III, IRCCS Istituto Ortopedico Galeazzi, Milan, Italy. aluca.md@gmail.com.
authors.forename: Andrea
authors.identifier: http://orcid.org/0000-0001-8626-6376
authors.initials: A
authors.lastname: Luca
authors.affiliation: Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, Milan, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Ottardi
authors.affiliation: Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, Milan, Italy.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Sasso
authors.affiliation: Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, Milan, Italy.
authors.forename: Liliana
authors.initials: L
authors.lastname: Prosdocimo
authors.affiliation: Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, Milan, Italy.|IRCCS Istituto Ortopedico Galeazzi, Milan, Italy.
authors.forename: Luigi
authors.initials: L
authors.lastname: La Barbera
authors.affiliation: Department of Spine Surgery III, IRCCS Istituto Ortopedico Galeazzi, Milan, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Brayda-Bruno
authors.affiliation: IRCCS Istituto Ortopedico Galeazzi, Milan, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Galbusera
authors.affiliation: Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, Milan, Italy.|IRCCS Istituto Ortopedico Galeazzi, Milan, Italy.
authors.forename: Tomaso
authors.initials: T
authors.lastname: Villa
mesh_terms: D019544:Equipment Failure Analysis; D020342:Finite Element Analysis; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008954:Models, Biological; D010027:Osteotomy / Q000295:instrumentation*; D016059:Range of Motion, Articular
keywords: Finite elements; Lumbar spine; Osteotomy; Pedicle subtraction osteotomy; Spinal fixation