• Nam Lee, Gyu Yeul Ji, Seong Yi, Do Heum Yoon, Dong Ah Shin, Keung Nyun Kim, Yoon Ha, and Chang Hyun Oh.
• Yonsei University College of Medicine, Seoul, Korea, Spine and Spinal Cord Institute; Department of Neurosurgery, Spine and Joint Research Institute, Guro Teun Teun Hospital, Seoul, Korea.
• Pain Physician. 2016 Jul 1; 19 (5): E787-93.

BackgroundIt is well documented that epidural adhesion is associated with spinal pain. However, the underlying mechanism of spinal pain generation by epidural adhesion has not yet been elucidated.ObjectivesTo elucidate the underlying mechanism of spinal pain generation by epidural adhesion using a two-dimensional (2D) non-linear finite element (FE) analysis.Study DesignA finite element analysis.SettingA two-dimensional nonlinear FE model of the herniated lumbar disc on L4/5 with epidural adhesion.MethodsA two-dimensional nonlinear FE model of the lumbar spine was developed, consisting of intervertebral discs, dura, spinal nerve, and lamina. The annulus fibrosus and nucleus pulpous were modeled as hyperelastic using the Mooney-Rivlin equation. The FE mesh was generated and analyzed using Abaqus (ABAQUS 6.13.; Hibbitt, Karlsson & Sorenson, Inc., Providence, RI, USA). Epidural adhesion was simulated as rough contact, in which no slip occurred once two surfaces were in contact, between the dura mater and posterior annulus fibrosus.ResultsThe FE model of adhesion showed significant stress concentration in the spinal nerves, especially on the dorsal root ganglion (DRG). The stress concentration was caused by the lack of adaptive displacement between the dura mater and posterior annulus fibrosus. The peak von Mises stress was higher in the epidural adhesion model (Adhesion, 0.67 vs. Control, 0.46). In the control model, adaptive displacement was observed with decreased stress in the spinal nerve and DRG (with adhesion, 2.59 vs. without adhesion, 3.58, P < 0.00).LimitationsThis study used a 2D non-linear FE model, which simplifies the 3D nature of the human intervertebral disc. In addition, this 2D non-linear FE model has not yet been validated.ConclusionThe current study clearly demonstrated that epidural adhesion causes significantly increased stress in the spinal nerves, especially at the DRG. We believe that the increased stress on the spinal nerve might elicit more pain under similar magnitudes of lumbar disc protrusion.

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