Exploring the Influence of Facet Orientation and Tropism On Neutral Zone Properties

Rory M Trevorrow; Jackie D Zehr; Jeff M Barrett; Jack P Callaghan; Kayla Fewster

doi:10.1115/1.4065406

Exploring the Influence of Facet Orientation and Tropism On Neutral Zone Properties

J Biomech Eng. 2024 Apr 26:1-20. doi: 10.1115/1.4065406. Online ahead of print.

Authors

Rory M Trevorrow¹, Jackie D Zehr², Jeff M Barrett¹, Jack P Callaghan², Kayla Fewster¹

Affiliations

¹ School of Kinesiology, The University of British Columbia, Vancouver, BC.
² Department of Kinesiology, University of Waterloo, 200 University Avenue West, Waterloo, ON, Canada N2L 3G1.

PMID: 38668721
DOI: 10.1115/1.4065406

Abstract

Lumbar spine pathologies have been linked independently to both neutral zone (NZ) properties and facet joint anatomical characteristics; however, the effect of facet joint orientation (FO) and tropism (FT) on NZ properties remains unclear. The aim of the present study was to investigate how axial plane FO and FT relate to NZ range and stiffness in the human lumbar spine and porcine cervical spine. Seven human lumbar functional spine units (FSUs) and 94 porcine cervical FSUs were examined. FO and FT were measured, and in-vitro mechanical testing was used to determine anterior-posterior (AP) and flexion-extension (FE) NZ range and stiffness. FO and FT were found to have no significant relationship with AP and FE NZ range. Increases in FT were associated with greater FE and AP NZ stiffness in human FSUs, with no FT-NZ stiffness relationship observed in porcine specimens. A significant relationship (p < .001) between FO and FE NZ stiffness was observed for both porcine and human FSUs, with a more sagittal orientation of the facet joints being associated with decreased FE NZ stiffness. Given the link between NZ stiffness and pathological states of the lumbar spine, further research is warranted to determine the practical significance of the observed facet joint anatomical characteristic-NZ property relationship.