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Misaligned spinal rods can induce high internal forces consistent with those observed to cause screw pullout and disc degeneration

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dc.contributor.author Loenen, Arjan C.Y.
dc.contributor.author Noriega, David C.
dc.contributor.author Ruiz Will, Carlos
dc.contributor.author Noailly, Jérôme
dc.contributor.author Nunley, Pierce D.
dc.contributor.author Kirchner, Rainer
dc.contributor.author Ito, Keita
dc.contributor.author van Rietbergen, Bert
dc.date.accessioned 2022-06-16T06:05:42Z
dc.date.available 2022-06-16T06:05:42Z
dc.date.issued 2021
dc.identifier.citation Loenen ACY, Noriega DC, Ruiz Wills C, Noailly J, Nunley PD, Kirchner R, Ito K, van Rietbergen B. Misaligned spinal rods can induce high internal forces consistent with those observed to cause screw pullout and disc degeneration. Spine J. 2021;21(3):528-37. DOI: 10.1016/j.spinee.2020.09.010
dc.identifier.issn 1529-9430
dc.identifier.uri http://hdl.handle.net/10230/53504
dc.description.abstract BACKGROUND CONTEXT: Manual contouring of spinal rods is often required intraoperatively for proper alignment of the rods within the pedicle screw heads. Residual misalignments are frequently reduced by using dedicated reduction devices. The forces exerted by these devices, however, are uncontrolled and may lead to excessive reaction forces. As a consequence, screw pullout might be provoked and surrounding tissue may experience unfavorable biomechanical loads. The corresponding loads and induced tissue deformations are however not well identified. Additionally, whether the forced reduction alters the biomechanical behavior of the lumbar spine during physiological movements postoperatively, remains unexplored. PURPOSE: To predict whether the reduction of misaligned posterior instrumentation might result in clinical complications directly after reduction and during a subsequent physiological flexion movement. STUDY DESIGN: Finite element analysis. METHODS: A patient-specific, total lumbar (L1−S1) spine finite element model was available from previous research. The model consists of poro-elastic intervertebral discs with Pfirrmann grade-dependent material parameters, with linear elastic bone tissue with stiffness values related to the local bone density, and with the seven major ligaments per spinal motion segment described as nonlinear materials. Titanium instrumentation was implemented in this model to simulate a L4, L5, and S1 posterolateral fusion. Next, coronal and sagittal misalignments of 6 mm each were introduced between the rod and the screw head at L4. These misalignments were computationally reduced and a physiological flexion movement of 15˚ was prescribed. Non-instrumented and wellaligned instrumented models were used as control groups. RESULTS: Pulling forces up to 1.0 kN were required to correct the induced misalignments of 6 mm. These forces affected the posture of the total lumbar spine, as motion segments were predicted to rotate up to 3 degrees and rotations propagated proximally to and even affect the L1−2 level. The facet contact pressures in the corrected misaligned models were asymmetrical suggesting nonphysiological joint loading in the misaligned models. In addition, the discs and vertebrae experienced abnormally high forces as a result of the correction procedure. These effects were more pronounced after a 15˚ flexion movement following forced reduction. CONCLUSIONS: The results of this study indicate that the correction of misaligned posterior instrumentation can result in high forces at the screws consistent with those reported to cause screw pullout, and may cause high-tissue strains in adjacent and downstream spinal segments. CLINICAL SIGNIFICANCE: Proper alignment of spinal posterior instrumentation may reduce clinical complications secondary to unfavorable biomechanics
dc.format.mimetype application/pdf
dc.language.iso eng
dc.publisher Elsevier
dc.relation.ispartof The Spine Journal. 2021;21(3):528-37.
dc.rights © 2020 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license
dc.rights.uri http://creativecommons.org/licenses/by/4.0/
dc.title Misaligned spinal rods can induce high internal forces consistent with those observed to cause screw pullout and disc degeneration
dc.type info:eu-repo/semantics/article
dc.identifier.doi http://doi.org/10.1016/j.spinee.2020.09.010
dc.subject.keyword Finite element analysis
dc.subject.keyword Pedicle screw
dc.subject.keyword Rod contouring
dc.subject.keyword Spine biomechanics
dc.subject.keyword Spinal fusion
dc.rights.accessRights info:eu-repo/semantics/openAccess
dc.type.version info:eu-repo/semantics/publishedVersion

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