Intervertebral disc distraction stiffness predicts endplate subsidence following transforaminal interbody cage expansion: an ex vivo study
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Author(s)
Type
Journal Article
Abstract
Purpose: Expandable cages have the potential to mitigate the currently high subsidence rates following transforaminal lumbar interbody fusion (TLIF), but are liable to over-distraction in situ. This may be due to the undefined patient-specific expansion threshold of the intervertebral disc (IVD) space. This study aimed to elucidate whether IVD properties affect the torque required to expand the cage within the IVD space, and determine the association between achieved torque, distraction stiffness, and subsidence severity.
Methods: Fifteen cadaveric L3-L4 and L4-L5 samples were prepared with the TLIF approach. Under 100N compression, the torque required to expand the cage per half-turn, alongside the changes to IVD and cage height, were recorded until maximum cage expansion. Subsidence
depth was measured after subsequent cyclic loading, and the surface area of removed IVD tissue was quantified post-test.
Results: Peak torque was inversely associated with preloaded IVD height (B: -0.34, p < 0.001) and the percentage of IVD removed (B: -0.04, p < 0.01). IVD distraction stiffness was associated with preloaded IVD height only (B: -0.19, p < 0.001). There was no association with IVD or facet degeneration. When subsidence depth was normalised to bone mineral density, a positive correlation was observed with peak torque and cage expansion stiffness (both p < 0.05).
Conclusion: The torque required to expand interbody cages in situ is relevant to subsidence risk, and depends on IVD geometry and the amount of residual tissue. Thus, short IVDs should be thoroughly prepared to alleviate excessive stiffness during cage expansion.
Methods: Fifteen cadaveric L3-L4 and L4-L5 samples were prepared with the TLIF approach. Under 100N compression, the torque required to expand the cage per half-turn, alongside the changes to IVD and cage height, were recorded until maximum cage expansion. Subsidence
depth was measured after subsequent cyclic loading, and the surface area of removed IVD tissue was quantified post-test.
Results: Peak torque was inversely associated with preloaded IVD height (B: -0.34, p < 0.001) and the percentage of IVD removed (B: -0.04, p < 0.01). IVD distraction stiffness was associated with preloaded IVD height only (B: -0.19, p < 0.001). There was no association with IVD or facet degeneration. When subsidence depth was normalised to bone mineral density, a positive correlation was observed with peak torque and cage expansion stiffness (both p < 0.05).
Conclusion: The torque required to expand interbody cages in situ is relevant to subsidence risk, and depends on IVD geometry and the amount of residual tissue. Thus, short IVDs should be thoroughly prepared to alleviate excessive stiffness during cage expansion.
Date Issued
2026-07-01
Date Acceptance
2025-12-29
Citation
European Spine Journal, 2026, 35 (7), pp.3774-3783
ISSN
0940-6719
Publisher
Springer
Start Page
3774
End Page
3783
Journal / Book Title
European Spine Journal
Volume
35
Issue
7
Copyright Statement
© The Author(s). This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/
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Publication Status
Published
Date Publish Online
2026-01-09