• Maxine Harvey-Burgess and Diane E Gregory.
• Department of Kinesiology and Physical Education, Wilfrid Laurier University, Waterloo, Ontario, Canada.
• Spine. 2019 Feb 15; 44 (4): E195-E201.

Study DesignIn-vitro study of the tissue mechanics of annulus fibrosus.ObjectiveTo determine the effect of axial torsion on the mechanical properties of the inter- and intralamellar matrices.Summary Of Background DataAxial torsion, when combined with repetitive flexion, has been associated with an increased risk of intervertebral disc herniation. However, the mechanisms behind this relationship are poorly understood.MethodsBovine intervertebral discs (IVDs) from the caudal region were exposed to a combination of either 0° or 12° of static axial torsion and 0 N or 1000 N of compression for 2 hours in an attempt to created micro-damage to the IVD. Following the loading protocol, one multilayered sample and two single layer samples were dissected from the annulus fibrosus to undergo tensile testing of the inter- and intralamellar matrices. Histological staining was also performed.ResultsThe strength of the interlamellar matrix was not affected by axial torsion or compression, suggesting that torsion did not damage the interlamellar matrix. However, intralamellar matrix strength of samples exposed to axial torsion, regardless of compressive loading magnitude, was 48% lower than those from samples that were not exposed to torsion (P < 0.001). Similarly, intralamellar matrix stiffness of samples exposed to axial torsion was 42% lower than from samples that were not exposed to torsion (P = 0.010). Additionally, histological analysis demonstrated more disruption within individual lamellae of the samples exposed to axial torsion compared with samples that were not.ConclusionThis study suggests that axial torsion damages the components of the intralamellar matrix as a result of the strain it puts on the matrix, thus making the intervertebral disc more susceptible to herniation.Level Of EvidenceN/A.

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