Experimental and computational analysis of the spinal cord-fragment interactions during the burst...
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$532 Journal of Biomechanics 2006, Vol. 39 (Suppl 1) 5640 We-Th, no. 6 (P59) Sternocleidomastoideus Muscle Activation Index; A promising tool for evaluating functional changes following whiplash associated disorders I. Ringheim, A. Indahl. Hospital for Rehabilitation, Rikshospitalet University Hospital, Stavem, Norway Objective: To develop an objective measure for documentation of increased muscle activation in a group of patients suffering from head and neck pain following neck injury with whiplash mechanism. Subjects: Eight patients with whiplash associated disorders (grade 1-2) and eight age and gender matched healthy controls Method: During a period of three weeks, subjects were tested three times in the laboratory for movement analysis of the Hospital for Rehabilitation in Stavern, Norway. Kinematic data from the subjects was collected with 6 ProReflex MCU (Qualisys Medical AB) digital cameras. In addition sEMG from sternocleidomastoideus (SCM) was recorded bilaterally. In the analysis a model with two rigid bodies (head and trunk) was used. Angle of head rotation with respect to the trunk in the horizontal plane was calculated (Euler angles). The angles where SCM was activated and deactivated during head rotation was calculated bilaterally. From these angles the range of motion (RAM) in which SCM was activated was calculated and expressed as a Sternocleidomastoideus Muscle Activity Index (SMAI). Paired t-test was used to document differences between patients and healthy controls. Results: Considerable differences between patients and healthy controls were observed. The patients showed reduced RaM for head rotation compared to healthy subjects (910 vs. 132 °, p~< 0.05). At the same time, angular velocity was reduced (109°/s vs. 183°/s, p ~<0.05) and SMAI was higher compared to healthy controls (64 vs. 32, p~< 0.1). Conclusion: The results indicate that patients with neck pain following neck injury with whiplash mechanism have activated mechanisms with increased muscular control for head rotation with respect to the trunk. Due to small sample size the SMAI only reached a level of significance of 0.1. Yet, SMAI may be a useful measure describing increased muscle activity objectively. 5.3. Spine Kinematics and Injury Biomechanics 4114 We-Th, no. 7 (P59) Experimental and computational analysis of the spinal cord-fragment interactions during the burst fracture process R.J. aakland 1, R.K. Wilcox 1, D.C. Barton 1, R.M. Hall 28. 1School of UK, Muscoskeletal Services, Mechanical Engineering, University of Leeds, 2 School of Medicine, University of Leeds, UK Introduction: Thoracolumbar burst fractures contribute to the large number of spinal cord injuries, imposing high costs to both individuals and society [1]. Although significant advances have been made in our understanding of the pathological cascade following the initial insult [2], little is known about the mechanical response of tissue within the spinal canal during the fracture process. The purpose of the study was to model the bone fragment and spinal cord interaction that occurs during a burst fracture. Methods: An in-vitro model was developed that reliably reproduced fragment- cord impact scenarios observed in a burst fracture study [3]. An analogue bone projectile was pneumatically propelled into explanted bovine cord at different velocities. The cord, instrumented with pressure transducers, was held in tension between a simulated posterior longitudinal ligament (PLL) and an anatomically correct surrogate of the posterior elements. The complete dynamic event was captured using high-speed video techniques. A finite element model of the fragment impingement was developed and validated against the experimental high-speed video images. Results: The status of the PLL played a key role in the fragment trajectory, whilst the dura mater was found to have no significant effect on the degree of cord contusion. Greater fragment velocities caused greater levels of occlusion and higher cord pressures. The finite element model gave a high level of agreement with experimentally observed cord compression and indicated that tension in the PLL affected the response of the cord. Conclusions: The combined study shows that the PLL is critical in reducing the occlusion of the fragment into the cord. Flexion or hyperextension would change the tension in the PLL and so would alter the degree of maximum cord compression as well as the final position. The same impact energy may therefore result in very different neurological outcomes depending on patient orientation at the time of fracture. References [1] Sekhon L.H. et-al. Spine, 2001. [2] Fifford R.J. et-al. J-Neurotrauma, 2004. [3] Wilcox R.K. et-al. J-Biomechanics, 2002. Poster Presentations 7487 We-Th, no. 8 (P59) Finite element simulation of chiropractic adjustment in the cervical spine J. Dahlkvist, K. Brolin, P. Halldin. Division of Neuronic Engineering, Royal Institute of Technology, Sweden Introduction: The biomechanical effects of chiropractic treatments are unclear. To determine injury risk associated with different treatment techniques it is necessary to evaluate the transfer of loads and energy between spinal levels and tissues. Numerical simulations have becoming a useful technique in injury biomechanics. Therefore, the aim of this study is to simulate a chiropractic adjustment using the finite element (FE) technique Method: A previously developed FE-model of the human neck [1,2] was used to simulate a supine cervical adjustment, the index pillar push. A simple model of a finger was introduced in the FE-model as boundary condition to the movement. The FE-model was positioned by applying a prescribed motion of the skull that gave a rotation of 15 degrees. Secondly, flexion was compensated by axial rotation of the head to straighten the spinal curvature. Lastly, a force was introduced to simulate the application of pressure at the facet joints on the C4 to C5 level. The disc pressure and strain and ligament strain were studied for varied material properties of the surrounding ligaments and discs, and for varied magnitudes of the applied push-force. Results & Discussion: The FE-model was successfully positioned in accor- dance to filmed data, although there is a wide variation in head and spine position between different adjustments and practitioners. The finger-model was needed to obtain a realistic lordosis. The FE-model could distinguish between different push-forces in the strain responses of tissues. Also, the FE- model response differed depending on if the material data of the soft tissues represented young or elderly individuals. Hence, it is tempting to initiate further FE studies to determine when the injury risk for a specific patient motivates avoiding certain adjustments. Conclusion: The promising results of this study illustrated that the FE tech- nique can determine how the response to a chiropractic adjustment differs for degenerated patients and healthy individuals. Also, the effects of treatment implementation seem suitable to study with FE-models. References [1] Brolin Halldin. Spine 2004; 29(4): 376-385. [2] Brolin et al. Traffic injury prevention 2005; 6(1): 67-76. 4703 We-Th, no. 9 (P59) Computational analysis of the spinal cord during the thoracolumbar burst fracture R.J. aakland -1, R.K. Wilcox -1 , D.C. Barton -1 , R.M. Hall -28. 1School ef Mechanical Engineering, University of Leeds, UK, 2Muscoskeletal Services, School of Medicine, University-of Leeds, UK Introduction: Spinal cord injury (SCI) continues to challenge the healthcare and adjunct social welfare systems [1]. A significant cause of SCI is the propulsion of the bone fragment into the spinal canal during the thoracolumbar burst fracture. Although experimental studies have shown the fragments to recoil from a position of maximum occlusion [2], the short time-span of the fracture event and the need to preserve the structural integrity of the specimen limit the measurement techniques available. The purpose of the study was to develop a computational model to assess what effect the fragment propagation has on the tissue within the spinal canal during the fracture process. Methods: The computational model was constructed to accurately represent a series of in-vitro experimental tests, simulating the impact of a bone fragment on the spinal cord under a range of impact conditions. The dura mater and posterior longitudinal ligament (PLL) were also included in the model, located within a rigid body representation of the posterior elements of the spinal canal. Results: Increased tension in the PLL had significant effects on the fragment propagation, spreading the impact load and distributing the force and therefore the induced displacement more uniformly throughout the cord. The stress in the spinal cord was concentrated between the fragment and posterior elements during the initial fragment impingement, following by the propagation of perpendicular and longitudinal stress waves depending on the condition of the PLL. Deformations of the posterior surface of the cord according to the anatomical geometry of the posterior elements were noted. Conclusions: Although the cause and general patterns of injury for burst fractures have been established, the appropriate response to a stable fracture with canal occlusion is widely debated. Developing our understanding of the role the PLL plays in distributing the fragment impact force, and the associated cord displacement relating to the fracture site, contributes knowledge to this controversial decision between invasive and conservative treatment. References [1] Sekhon L.H., et al. Spine, 2001. [2] Wilcox R.K., et al. J-Biomechanics, 2001.
Transcript of Experimental and computational analysis of the spinal cord-fragment interactions during the burst...
$532 Journal of Biomechanics 2006, Vol. 39 (Suppl 1)
5640 We-Th, no. 6 (P59) Sternocleidomastoideus Muscle Activation Index; A promising tool for evaluating functional changes following whiplash associated disorders I. Ringheim, A. Indahl. Hospital for Rehabilitation, Rikshospitalet University Hospital, Stavem, Norway
Objective: To develop an objective measure for documentation of increased muscle activation in a group of patients suffering from head and neck pain following neck injury with whiplash mechanism. Subjects: Eight patients with whiplash associated disorders (grade 1-2) and eight age and gender matched healthy controls Method: During a period of three weeks, subjects were tested three times in the laboratory for movement analysis of the Hospital for Rehabilitation in Stavern, Norway. Kinematic data from the subjects was collected with 6 ProReflex MCU (Qualisys Medical AB) digital cameras. In addition sEMG from sternocleidomastoideus (SCM) was recorded bilaterally. In the analysis a model with two rigid bodies (head and trunk) was used. Angle of head rotation with respect to the trunk in the horizontal plane was calculated (Euler angles). The angles where SCM was activated and deactivated during head rotation was calculated bilaterally. From these angles the range of motion (RAM) in which SCM was activated was calculated and expressed as a Sternocleidomastoideus Muscle Activity Index (SMAI). Paired t-test was used to document differences between patients and healthy controls. Results: Considerable differences between patients and healthy controls were observed. The patients showed reduced RaM for head rotation compared to healthy subjects (910 vs. 132 °, p~< 0.05). At the same time, angular velocity was reduced (109°/s vs. 183°/s, p ~< 0.05) and SMAI was higher compared to healthy controls (64 vs. 32, p~< 0.1). Conclusion: The results indicate that patients with neck pain following neck injury with whiplash mechanism have activated mechanisms with increased muscular control for head rotation with respect to the trunk. Due to small sample size the SMAI only reached a level of significance of 0.1. Yet, SMAI may be a useful measure describing increased muscle activity objectively.
5.3. Spine Kinematics and Injury Biomechanics 4114 We-Th, no. 7 (P59) Experimental and computational analysis of the spinal cord-fragment interactions during the burst fracture process R.J. aakland 1, R.K. Wilcox 1, D.C. Barton 1, R.M. Hall 28. 1School of
UK, Muscoskeletal Services, Mechanical Engineering, University of Leeds, 2 School of Medicine, University of Leeds, UK
Introduction: Thoracolumbar burst fractures contribute to the large number of spinal cord injuries, imposing high costs to both individuals and society [1]. Although significant advances have been made in our understanding of the pathological cascade following the initial insult [2], little is known about the mechanical response of tissue within the spinal canal during the fracture process. The purpose of the study was to model the bone fragment and spinal cord interaction that occurs during a burst fracture. Methods: An in-vitro model was developed that reliably reproduced fragment- cord impact scenarios observed in a burst fracture study [3]. An analogue bone projectile was pneumatically propelled into explanted bovine cord at different velocities. The cord, instrumented with pressure transducers, was held in tension between a simulated posterior longitudinal ligament (PLL) and an anatomically correct surrogate of the posterior elements. The complete dynamic event was captured using high-speed video techniques. A finite element model of the fragment impingement was developed and validated against the experimental high-speed video images. Results: The status of the PLL played a key role in the fragment trajectory, whilst the dura mater was found to have no significant effect on the degree of cord contusion. Greater fragment velocities caused greater levels of occlusion and higher cord pressures. The finite element model gave a high level of agreement with experimentally observed cord compression and indicated that tension in the PLL affected the response of the cord. Conclusions: The combined study shows that the PLL is critical in reducing the occlusion of the fragment into the cord. Flexion or hyperextension would change the tension in the PLL and so would alter the degree of maximum cord compression as well as the final position. The same impact energy may therefore result in very different neurological outcomes depending on patient orientation at the time of fracture.
References [1] Sekhon L.H. et-al. Spine, 2001. [2] Fifford R.J. et-al. J-Neurotrauma, 2004. [3] Wilcox R.K. et-al. J-Biomechanics, 2002.
Poster Presentations
7487 We-Th, no. 8 (P59) Finite element simulation of chiropractic adjustment in the cervical spine J. Dahlkvist, K. Brolin, P. Halldin. Division of Neuronic Engineering, Royal Institute of Technology, Sweden
Introduction: The biomechanical effects of chiropractic treatments are unclear. To determine injury risk associated with different treatment techniques it is necessary to evaluate the transfer of loads and energy between spinal levels and tissues. Numerical simulations have becoming a useful technique in injury biomechanics. Therefore, the aim of this study is to simulate a chiropractic adjustment using the finite element (FE) technique Method: A previously developed FE-model of the human neck [1,2] was used to simulate a supine cervical adjustment, the index pillar push. A simple model of a finger was introduced in the FE-model as boundary condition to the movement. The FE-model was positioned by applying a prescribed motion of the skull that gave a rotation of 15 degrees. Secondly, flexion was compensated by axial rotation of the head to straighten the spinal curvature. Lastly, a force was introduced to simulate the application of pressure at the facet joints on the C4 to C5 level. The disc pressure and strain and ligament strain were studied for varied material properties of the surrounding ligaments and discs, and for varied magnitudes of the applied push-force. Results & Discussion: The FE-model was successfully positioned in accor- dance to filmed data, although there is a wide variation in head and spine position between different adjustments and practitioners. The finger-model was needed to obtain a realistic lordosis. The FE-model could distinguish between different push-forces in the strain responses of tissues. Also, the FE- model response differed depending on if the material data of the soft tissues represented young or elderly individuals. Hence, it is tempting to initiate further FE studies to determine when the injury risk for a specific patient motivates avoiding certain adjustments. Conclusion: The promising results of this study illustrated that the FE tech- nique can determine how the response to a chiropractic adjustment differs for degenerated patients and healthy individuals. Also, the effects of treatment implementation seem suitable to study with FE-models.
References [1] Brolin Halldin. Spine 2004; 29(4): 376-385. [2] Brolin et al. Traffic injury prevention 2005; 6(1): 67-76.
4703 We-Th, no. 9 (P59) Computational analysis of the spinal cord during the thoracolumbar burst fracture R.J. aakland -1, R.K. Wilcox -1 , D.C. Barton -1 , R.M. Hall -28. 1School ef Mechanical Engineering, University of Leeds, UK, 2Muscoskeletal Services, School of Medicine, University-of Leeds, UK
Introduction: Spinal cord injury (SCI) continues to challenge the healthcare and adjunct social welfare systems [1]. A significant cause of SCI is the propulsion of the bone fragment into the spinal canal during the thoracolumbar burst fracture. Although experimental studies have shown the fragments to recoil from a position of maximum occlusion [2], the short time-span of the fracture event and the need to preserve the structural integrity of the specimen limit the measurement techniques available. The purpose of the study was to develop a computational model to assess what effect the fragment propagation has on the tissue within the spinal canal during the fracture process. Methods: The computational model was constructed to accurately represent a series of in-vitro experimental tests, simulating the impact of a bone fragment on the spinal cord under a range of impact conditions. The dura mater and posterior longitudinal ligament (PLL) were also included in the model, located within a rigid body representation of the posterior elements of the spinal canal. Results: Increased tension in the PLL had significant effects on the fragment propagation, spreading the impact load and distributing the force and therefore the induced displacement more uniformly throughout the cord. The stress in the spinal cord was concentrated between the fragment and posterior elements during the initial fragment impingement, following by the propagation of perpendicular and longitudinal stress waves depending on the condition of the PLL. Deformations of the posterior surface of the cord according to the anatomical geometry of the posterior elements were noted. Conclusions: Although the cause and general patterns of injury for burst fractures have been established, the appropriate response to a stable fracture with canal occlusion is widely debated. Developing our understanding of the role the PLL plays in distributing the fragment impact force, and the associated cord displacement relating to the fracture site, contributes knowledge to this controversial decision between invasive and conservative treatment.
References [1] Sekhon L.H., et al. Spine, 2001. [2] Wilcox R.K., et al. J-Biomechanics, 2001.
