An Investigation of the Mechanism of Adjacent Segment Disease in a Porcine Spine Model

Chow N, Sinopoli SI, et al.

Clinical Biomechanics

Wilfrid Laurier University, McMaster University

RESEARCH SUMMARY

This study investigated how spinal fixation and injury affect the mechanical properties of adjacent intervertebral discs, using porcine and human cadaveric models. Fifty-two porcine cervical spines were divided into control, injured, immobilized, and injured+immobilized groups, subjected to cyclic axial compression (300–1200 N, 0.5 Hz, 2 hours). Annular tissue samples from the adjacent disc (C3/4) were tested for intralamellar and interlamellar mechanical properties. Immobilization significantly reduced toe-region and failure stresses of the intralamellar matrix (p < 0.03), particularly in the posterior annulus, while peel strength between lamellae was unchanged. Similar reductions in toe-region stress were observed in human lumbar discs. These findings reveal how immobilization weakens annular integrity, providing a mechanistic basis for adjacent segment disease following spinal fusion.

Single lamellae were mounted using five-prong tungsten BioRakes on a CellScale BioTester with collagen fibers oriented perpendicular to the rakes to isolate intralamellar matrix response. Samples were preconditioned (3×10% strain, 1%/s) and pulled to failure at 1%/s to determine stiffness, toe-region, and failure properties. Multilamellar annular samples were tested on a CellScale UStretch in a 180° peel configuration (0.5 mm/s) to assess interlamellar adhesion. Results showed immobilization reduced intralamellar failure stress from 0.53 ± 0.58 to 0.13 ± 0.06 MPa (p = 0.003), with minimal changes to interlamellar peel strength, demonstrating selective weakening of annular layers adjacent to fixation.

AUTHORS

Noah Chow, Sabrina I. Sinopoli, Mitchel C. Whittal, Drew A. Bednar, Diane E. Gregory.

PUBLICATION DETAILS

JOURNAL

Clinical Biomechanics

YEAR

2025

INSTITUTIONS

Wilfrid Laurier University, McMaster University

COUNTRIES

Canada

INSTRUMENT USED

BioTesterUStretch

TESTING METHODS

Hydrated and Temperature Controlled TestingMicro-Mechanical TestingPeel TestingTensile Testing

RESEARCH APPLICATIONS

Fibrosis & Tissue RemodelingIntervertebral Disc BiomechanicsMechanotransductionMusculoskeletal Tissue Engineering & Mechanics

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