title: Intraoperative biomechanics of lumbar pedicle screw loosening following successful arthrodesis.
abstract: Pedicle screw loosening has been implicated in recurrent back pain after lumbar spinal fusion, but the degree of loosening has not been systematically quantified in patients. Instrumentation removal is an option for patients with successful arthrodesis, but remains controversial. Here, we quantified pedicle screw loosening by measuring screw insertion and/or removal torque at high statistical power (beta = 0.02) in N = 108 patients who experienced pain recurrence despite successful fusion after posterior instrumented lumbar fusion with anterior lumbar interbody fusion (L2-S1). Between implantation and removal, pedicle screw torque was reduced by 58%, indicating significant loosening over time. Loosening was greater in screws with evoked EMG threshold under 11 mA, indicative of screw misplacement. A theoretical stress analysis revealed increased local stresses at the screw interface in pedicles with decreased difference in pedicle thickness and screw diameter. Loosening was greatest in vertebrae at the extremities of the fused segments, but was significantly lower in segments with one level of fusion than in those with two or more.
  
  
  
  These data indicate that pedicle screws can loosen significantly in patients with recurrent back pain and warrant further research into methods to reduce the incidence of screw loosening and to understand the risks and potential benefits of instrumentation removal. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2673-2681, 2017.
authors.affiliation: Department of Aerospace and Mechanical Engineering, University of Notre Dame, 142 Multidisciplinary Research Building, Notre Dame, Indiana 46557.
authors.forename: Hope B
authors.initials: HB
authors.lastname: Pearson
authors.affiliation: Spine Center Atlanta, 3161 Howell Mill RoadSuite 400, Atlanta, Georgia 30327.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Dobbs
authors.affiliation: Spine Center Atlanta, 3161 Howell Mill RoadSuite 400, Atlanta, Georgia 30327.
authors.forename: Eric
authors.initials: E
authors.lastname: Grantham
authors.affiliation: Department of Aerospace and Mechanical Engineering, University of Notre Dame, 142 Multidisciplinary Research Building, Notre Dame, Indiana 46557.
authors.forename: Glen L
authors.initials: GL
authors.lastname: Niebur
authors.affiliation: Spine Center Atlanta, 3161 Howell Mill RoadSuite 400, Atlanta, Georgia 30327.
authors.forename: James L
authors.initials: JL
authors.lastname: Chappuis
authors.affiliation: Department of Aerospace and Mechanical Engineering, University of Notre Dame, 142 Multidisciplinary Research Building, Notre Dame, Indiana 46557.|Departments of Orthopaedic Surgery and Bioenegineering, University of Pennsylvania, Claire M. Fagin Hall, 418 Curie Blvd, Philadelphia, Pennsylvania 19104.
authors.forename: Joel D
authors.identifier: 0000-0003-3126-3025
authors.initials: JD
authors.lastname: Boerckel
mesh_terms: D000328:Adult; D000368:Aged; D004576:Electromyography; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D058748:Pain Perception; D010149:Postoperative Pain / Q000209:etiology*; D065289:Pedicle Screws / Q000009:adverse effects*; D012189:Retrospective Studies; D013123:Spinal Fusion / Q000009:adverse effects / Q000295:instrumentation*; D013314:Stress, Mechanical; D019415:Torque
keywords: biomechanics; loosening; lumbar spinal fusion; pedicle screw