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Biomechanical Analysis of the Spinal Cord in Brown-Séquard Syndrome

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Biomechanical Analysis of the Spinal Cord in Brown-Séquard Syndrome 1184 EXPERIMENTAL AND THERAPEUTIC MEDICINE 6: 1184-1188, 2013 Biomechanical analysis of the spinal cord in Brown-Séquard syndrome NORIHIRO NISHIDA1, TSUKASA KANCHIKU1, YOSHIHIKO KATO1, YASUAKI IMAJO1, SYUNICHI KAWANO2 and TOSHIHIKO TAGUCHI1 1Department of Orthopaedic Surgery, Yamaguchi University Graduate School of Medicine, Yamaguchi 755-8505; 2Faculty of Engineering, Yamaguchi University, Yamaguchi 755-8611, Japan Received April 23, 2013; Accepted August 6, 2013 DOI: 10.3892/etm.2013.1286 Abstract. Complete Brown-Séquard syndrome (BSS) rosis (1). There have also been a few reports of BSS associated resulting from chronic compression is rare and the majority with intradural spinal cord herniation or disc herniation (2,3). of patients present with incomplete BSS. In the present study, Furthermore, complete BSS due to chronic compression is we investigated why the number of cases of complete BSS rare and most patients present with an incomplete form of this due to chronic compression is limited. A 3-dimensional finite condition (4). element method (3D-FEM) spinal cord model was used in this In the present study, a 3-dimensional finite element method study. Anterior compression was applied to 25, 37.5, 50, 62.5 (3D-FEM) was used to analyze the stress distribution of the and 75% of the length of the transverse diameter of the spinal spinal cord under various compression levels corresponding to cord. The degrees of static compression were 10, 20 and 30% five different lengths of the transverse diameter. Three levels of the anteroposterior (AP) diameter of the spinal cord. When of static compression corresponding to 10, 20 and 30% of the compression was applied to >62.5 or <37.5% of the length anteroposterior (AP) diameter were used for each of these five of the transverse diameter of the spinal cord, no increases in conditions. This model was used to investigate why the number stress indicative of complete BSS were observed. Compression of cases of complete BSS resulting from chronic compression of 50% of the length of the transverse diameter of the spinal is limited. cord resulted in a stress distribution that may correspond to that in complete BSS cases, when the degree of compression Materials and methods was 30% of the AP diameter of the spinal cord. However, compression within such a limited range rarely occurs in Construction of the 3D-FEM spinal cord model. The clinical situations and, thus, this may explain why the number Abaqus 6.11 (Dassault Systèmes Simulia Corp., Providence, of cases with complete BSS is low. RI, USA) standard finite element package was used for FEM simulation. The 3D-FEM spinal cord model used in this study Introduction consisted of gray and white matter and pia mater. In order to simplify calculation in the model, the denticulate ligament, Brown-Séquard syndrome (BSS) is a syndrome consisting dura and nerve root sheaths were not included. Pia mater was of ipsilateral upper motor neuron paralysis (hemiplegia) and included since it has been demonstrated that spinal cord with loss of proprioception with contralateral pain and tempera- and without this component shows significantly different ture sensation deficit. BSS is usually observed in association mechanical behaviors (5). The spinal cord was assumed to be with traumatic spinal cord injuries, extramedullary spinal symmetrical about the mid-sagittal plane, so that only half the cord tumors, spinal hemorrhages, degenerative disease and spinal cord required reconstruction and the whole model could infectious and inflammatory causes, including multiple scle- be integrated by mirror image. This model simulated chronic compression of the cervical spinal cord. The vertebral canal model consisting of lamina was established by measuring 13 cervical computed tomographic myelographs (Fig. 1). A rigid flat plate was used as a compression factor from the Correspondence to: Dr Norihiro Nishida, Department of Orthopedic Surgery, Yamaguchi University Graduate School of anterior surface of the spinal cord and its width was 25, 37.5, Medicine, 1-1-1 Minami-Kogushi, Ube, Yamaguchi 755-8505, Japan 50, 62.5 and 75% of the length of the transverse diameter of E-mail: [email protected] the spinal cord (Fig. 2). The rigid flat plate was located at the longitudinal center of the spinal cord. The spinal cord consists Key words: finite element method, Brown-Séquard syndrome, of three distinct materials: the white and gray matter and the spinal cord herniation pia mater. The mechanical properties (Young's modulus and Poisson's ratio) of the gray and white matter were determined using data obtained from the tensile stress strain curve and stress relaxation tests under various strain rates (6,7). The NISHIDA et al: BIOMECHANICAL STUDY OF BROWN-SÉQUARD SYNDROME 1185 Figure 1. Three-dimensional finite element method (3D-FEM) model of the spinal cord and the vertebral canal model consisting of lamina. Figure 2. The rigid flat plate applied compression to 25, 37.5, 50, 62.5 and 75% of the length of the transverse diameter of the spinal cord. mechanical properties of the pia mater were obtained from a the transverse diameter of the spinal cord. The degrees of previous study (8). The mechanical properties of the lamina compression were 10, 20 and 30% of the AP diameter of the and flat plate were stiff enough to enable the spinal cord to be spinal cord. A 10% compression was first applied to the spinal pressed. Based on the assumption that no slippage occurs at cord, followed by compressions of 20 and 30% . In total, the interfaces of white and gray matter and pia mater, these 15 different compression combinations were evaluated. interfaces were glued together. Data concerning the fric- tion coefficient between the bone and spinal cord were not Results available. The coefficient of friction between lamina and the spinal cord was ‘glue’ at the contact line and ‘frictionless’ Under compression of 25% of the length of the transverse next to the part in contact. Similarly, the coefficient of fric- diameter of the spinal cord with a rigid flat plate, the stresses tion between the rigid flat plate and spinal cord was ‘glue’ were extremely low when the degree of compression was 10% at the contact interfaces and ‘frictionless’ next to the part in of the AP diameter of the spinal cord. The stress was confined contact. To simulate the axial injury model of the spinal cord, to part of the gray matter and to the anterior funiculus. At 20% nodes at the bottom and top of the spinal cord model were compression, the stress on the anterior horn and part of the constrained in all directions. The spinal cord and the rigid anterior funiculus was slightly increased. At 30% compres- flat plate were symmetrically meshed with 20-node elements. sion, high stresses were observed in the gray matter, anterior With a FEM model of 50% of the length of the transverse funiculus and part of the lateral funiculus, but not the posterior diameter of the spinal cord, the total number of isoparametric funiculus (Fig. 3A). 20-node elements was 12,535 and the total number of nodes Compression of 37.5% of the length of the transverse diam- was 76,993. eter of the spinal cord with a rigid flat plate resulted instresses that were very low when the compression of the AP diameter Static compression model. For the simulation of BSS, ante- of the spinal cord was 10%. The stresses on the gray matter rior static compression was applied to the spinal cord by the and anterior funiculus were slightly increased when 20% rigid flat plate at 25, 37.5, 50, 62.5 and 75% of the length of compression was applied. At 30% compression, high stresses 1186 EXPERIMENTAL AND THERAPEUTIC MEDICINE 6: 1184-1188, 2013 A B C D E Figure 3. Static compression corresponding to 10, 20 and 30% of the anteropostrior (AP) diameter of the spinal cord was applied by compression of (A) 25, (B) 37.5, (C) 50, (D) 62.5 and (E) 75% of the length of the transverse diameter of the spinal cord with a rigid flat plate. were observed in the gray matter, anterior funiculus and lateral When 50% of the length of the transverse diameter of the funiculus, while the stress was moderately increased in part of spinal cord was compressed with a rigid flat plate, the stress the posterior funiculus (Fig. 3B). was very low when the degree of compression was 10% of NISHIDA et al: BIOMECHANICAL STUDY OF BROWN-SÉQUARD SYNDROME 1187 the AP diameter of the spinal cord, and was observed only not provide details concerning whether the BSS was complete in the gray matter and part of the anterior funiculus. At or incomplete. 20% compression, the stress on the gray matter and anterior Based on these previous findings, we hypothesized funiculus was slightly increased. At 30% compression, the that pressure within a limited range of compression causes stress on the spinal cord was increased and high stresses complete BSS with static compression. To test this hypothesis, were observed in the gray matter and the anterior, lateral and we investigated three different degrees of static compression posterior funiculi. However, the stress was not increased on under five different compressions of the transverse diameter the posterior funiculus of the non-compressed side (Fig. 3C). of the spinal cord. We calculated the stress distributions inside A compression of 62.5% of the length of the transverse the spinal cord and simulated complete and incomplete BSS diameter of the spinal cord with a rigid flat plate resulted in using a 3D-FEM model. very low stresses when the degree of compression was 10% of The aim of the present study was to develop a 3D-FEM the AP diameter of the spinal cord; the stress was only slightly spinal cord model that simulates the clinical situation.
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