Biomechanical analysis of a trans-discal, multi-level stabilization screw (MLSS) at the upper instrumented vertebra (UIV) of long posterior thoracolumbar instrumentations

Andrew P Collins; Anoli A Shah; Niloufar Shekouhi; Vijay K Goel; Alekos A Theologis

doi:10.1007/s43390-024-00862-7

Biomechanical analysis of a trans-discal, multi-level stabilization screw (MLSS) at the upper instrumented vertebra (UIV) of long posterior thoracolumbar instrumentations

Spine Deform. 2024 Apr 5. doi: 10.1007/s43390-024-00862-7. Online ahead of print.

Authors

Andrew P Collins¹, Anoli A Shah², Niloufar Shekouhi², Vijay K Goel², Alekos A Theologis³

Affiliations

¹ Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, WA, USA.
² Engineering Center for Orthopaedic Research Excellence (E-CORE), Departments of Bioengineering and Surgery, Colleges of Engineering and Medicine, University of Toledo, Toledo, OH, USA.
³ Department of Orthopaedic Surgery, San Francisco (UCSF), University of California, 500 Parnassus Ave, MUW 3rd Floor, San Francisco, CA, USA. alekos.theologis@ucsf.edu.

PMID: 38578598
DOI: 10.1007/s43390-024-00862-7

Abstract

Purpose: To evaluate proximal junctional biomechanics of a MLSS relative to traditional pedicle screw fixation at the proximal extent of T10-pelvis posterior instrumentation constructs (T10-p PSF).

Methods: A previously validated three-dimensional osseoligamentous spinopelvic finite element (FE) model was used to compare proximal junctional range-of-motion (ROM), vertebral body stresses, and discal biomechanics between two groups: (1) T10-p with a T10-11 MLSS ("T10-11 MLSS") and (2) T10-p with a traditional T10 pedicle screw ("Traditional T10-PS").

Results: The T10-11 MLSS had a 5% decrease in T9 cortical bone stress compared to Traditional T10-PS. Conversely, the T10 and T11 bone stresses increased by 46% and 98%, respectively, with T10-11 MLSS compared to Traditional T10-PS. Annular stresses and intradiscal pressures (IDP) were similar at T9-T10 between constructs. At the T10-11 disc, T10-11 MLSS decreased annular stresses by 29% and IDP by 48% compared to Traditional T10-PS. Adjacent ROM (T8-9 & T9-10) were similar between T10-11 MLSS and Traditional T10-PS. T10-11 MLSS had 39% greater ROM at T10-11 and 23% less ROM at T11-12 compared to Traditional T10-PS.

Conclusions: In this FE analysis, a T10-11 MLSS at the proximal extent of T10-pelvis posterior instrumentation resulted in increased T10 and T11 cortical bone stresses, decreased discal annular stress and IDP and increased ROM at T10-11, and no change in ROM at the adjacent level. Given the complex and multifactorial nature of proximal junctional kyphosis, these results require additional biomechanical and clinical evaluations to determine the clinical utility of MLSS on the proximal junctions of thoracolumbar posterior instrumented fusions.

Keywords: Adjacent segment; Biomechanics; Finite element analysis; Multi-level stabilizing screw; Trans-discal screws.