Approximately 50% - 80% of the population will experience disabling low back pain at some point in their life. Assessing and developing interventions based on “lumbar stability” and/or joint stiffness to reduce low back pain has been a common research focus. Specific focus has been on identifying which muscles influence lumbar stability/stiffness, with one argument being between focusing training on the transverse abdominis and lumbar multifidus muscles versus broader training approaches involving the entire abdominal wall and erector spinae muscles. However, there has not been research on whether pain reduction was due to increased stability/stiffness or another mechanism. The main goals of this thesis were to determine the effect of individual muscles on stability/stiffness through a two phase process. In the first phase, a model sensitivity analysis was performed to assess the interactions of variables that influence the quantification of stability. Stability was quantified via the eigenvalues (EV) of the Hessian matrix of potential energies at each lumbar level and axis of rotation, for a total of 15 EVs (3 axes of rotation x 5 joints). In phase 2, assessment of clinical interventions on patients with low back pain designed to alter biomechanics was conducted to assess factors in stability/stiffness quantification and mechanisms of action in pain modulation. More detail of the study phases are described below, in order to test the following hypotheses: 1) It was hypothesized that individual muscles affect specific EVs, but no one muscle can be associated with one EV level. 2) It was hypothesized that specific muscles do affect specific planes of stability/stiffness. 3) It was hypothesized that EVs are affected by posture. 4) It was hypothesized that overactivating muscles by increasing muscle activation to 100% MVC negatively affects the EVs. 5) It was hypothesized that the relationship between muscles and specific EVs obtained during simulation remains with real subjects performing loaded tasks. 6) It was hypothesized that coaching and cueing specific movement patterns and motor patterns would alter pain in low back pain patients. 7) If hypothesis 6 is true, then it was hypothesized that changes in pain would be reflected in changes in EVs. Methods for Phase 1 The first phase involved a sensitivity analysis using an anatomically detailed spine model. Theoretical data including posture, motion and muscle activity were synthesized to include 23 static spine postures, including neutral, 0° - 50° flexion, 0° - 30° extension, 0° - 30° right and left lateral bend, and 0° - 40° right and left axial twist, all in increments of 10°. For each posture, all eleven muscles included in the model, some with several fascicles, were artificially activated to 50% MVC. A knockout approach ensued whereby activity in single muscles were systematically reduced to 0% MVC or increased to 100% MVC. The relationships between the 15 EVs and the changes in muscle activity and posture were assessed. This muscle knockout model was repeated with actual muscle activity values obtained from electromyographic (EMG) signals and postures obtained from four subjects who performed a walking task with a 15 kg load in each hand. Results for Phase 1 The sensitivity analysis showed that the abdominal muscles contribute a greater stabilizing effect on the L4 and L5 EVs, while the multifidus and erector spinae muscles contribute a greater effect on the L1, L2 and L3 EVs. When examining the effect of muscles on a specific plane in terms of influencing stability/stiffness, it was found that the abdominal muscles contribute a greater effect on the bend axis and twist axis EVs than the flexion axis EVs, while the erector spinae muscles contribute the greatest effect on the flexion axis EVs. Posture was found to have a biologically significant effect on EVs, with the 50° flexion and 30° extension postures having the most detrimental effect in terms of compromising stability/stiffness. In addition, when there was a 10° excursion in any axis, there was little change in the EVs, while postures at angles greater than this were often associated with decreases in stability/stiffness in some EVs. Increasing the muscle activation from 50% MVC to 100% MVC did not have a large effect on most EVs, but when there was a meaningful change, as defined by a change of 10% or greater in the EV, the 100% MVC activation level always resulted in more stability/stiffness at that particular EV. Finally, using actual EMG and lumbar angle patterns resulted in similar results as the theoretical data, as expected. Interpretation of these findings is limited by the following. Even though EVs changed, there is no guarantee that the magnitude of change in one EV could be interpreted to equal a similar magnitude of change in another EV, nor may it be assumed that EVs have a linear relationship with stability/stiffness. These results suggest that when the goal is to increase lumbar stability, a neutral spine should be maintained and activating the larger abdominal muscles is more important than activating the transverse abdominis or multifidus, as proposed by some clinical groups. Methods for Phase 2 Four case studies of individuals with chronic low back pain were recruited from whom kinematic, kinetic and EMG data were collected in addition to a measure of pain intensity using an 11-point verbal numerical rating scale. Pain provocation tests were performed by a clinician (professor Stuart McGill) to identify the motions, postures and loads that exacerbated their pain. Then these tasks were repeated while the motion and EMG data was collected. This was followed by interventions coached by the clinician that could include the abdominal brace (stiffening the abdominal wall), latissimus dorsi stiffening, incorporating a hip-hinge motion rather than spine bending, or any combination of these. The intention of the intervention was to immediately reduce pain intensity. These tasks arranged in a repeated measures design were assessed with the anatomically detailed spine model to calculate stability/stiffness from evaluation of the 15 EVs, lumbar compression and lumbar shear forces. Results for Phase 2 The results from phase 2 suggest that pain was sometimes reduced by altering motions, postures and load, but the mechanism of what proved effective and the degree of success was variable from patient to patient. In most situations, the EVs, lumbar compression forces and lumbar shear forces increased due to the intervention that was chosen. In addition, the lumbar flexion angle typically trended to a more neutral posture and in tasks where spine motion occurred, there was less spine motion when using the suggested intervention. Further, the biomechanical variable that would be expected to change based on clinical assessment did not always react in the expected way (i.e. a compression intolerant individual would be expected to have decreased compression linked with decreased pain, but this did not occur). While the stability/stiffness increased, the associated compression was tolerated suggesting that the increase in concomitant stiffness enhanced the compression load bearing tolerance. Overall Conclusions This thesis showed that careful examination of the EVs did not offer substantial insight into links between changes in individual EVs and individual muscles, as muscle activity was not reflected in the EVs. Specifically, single muscles contributions were not reflected in specific EVs as was hypothesized. Further, it was difficult to interpret the EVs collectively because of the inherent non-linearity between EV magnitude and changes in muscle activation/stiffness; it can only be said that there was more or less stability/stiffness with each change in an EV, not how much. In addition, pain reduction appeared to be due to a combination of altered motions, postures and loads, but this did not result in systematic EV changes. Globally, the present work provides evidence supporting the idea that maintaining a neutral posture and activating the abdominal muscles results in less pain and larger EVs, suggesting an increase in stability/stiffness. This work has potential for informing clinicians on possible options for immediate reduction in low back pain.

Thesis (Ph. D.)--Ohio State University, 2009. / Title from first page of PDF file. Includes bibliographical references (p. 232-256).

This thesis is concerned with the investigation, in vitro, of the mechanical properties of the intact and injured human lumbar spine under general loading conditions, by both experimentation and use of a numerical simulation. / For the experimental investigation, a three dimensional loading apparatus and displacement transducer were constructed. In order to standardize the experiment, the influence of several secondary variables was investigated. The load deflection properties of intact and injured joints were then studied. Eight states of injury were considered. As well, the effect of various types of preloading upon joint response was determined. / Using the data generated by the experimental study and measurements of the surface geometry of the vertebra, a numerical simulation was devised. This simulation allowed the interpretation of the experimental results in terms of strains in the soft tissue elements and facet interaction. As well, the locations of the instant center of rotation and the foraminal gap dimensions could be determined.

Introduction: Lumbar spine stability programs have been advocated to prevent and rehabilitate low back injury. Specifically, abdominal ‘drawing in’ has been used to train motor control deficits in individuals with low back pain. This technique requires differential activity within deep and superficial lumbar multifidus fibres, yet the ability of these fibres to act differentially has not been extensively examined. Deep fibres are hypothesized to act as spinal stabilizers while superficial fibres are hypothesized to act as global movers of the trunk. Objective: To investigate differential excitation of deep and superficial lumbar multifidus fibres during segmental indentation loads to the lumbar spine. Methods: Posterior-anterior indentation loads were applied to individual lumbar spinous processes of prone participants at three different velocities and three different indentation displacements. Indentations consisted of an initial downward displacement that was subsequently held for 500 milliseconds. Intramuscular electromyography (EMG) of deep and superficial lumbar multifidus fibres at L3, L4 and L5 was recorded. EMG was quantified by “average” root mean square (RMS), peak RMS of a sliding RMS window and time-to-peak RMS over the indentation phase and 500 millisecond hold phase. Results: Increased indentation displacement at the slowest velocity resulted in increased “average” RMS of only the L5 superficial multifidus fibres. Increased indentation velocity produced differential effects in deep and superficial multifidus fibres. “Average” RMS and peak RIVIS significantly increased with increasing indentation velocity in most deep fibre recording sites, yet superficial fibre excitation did not significantly increase. In most EMG recording sites, the time-to-peak RMS increased with increasing indentation displacement and decreased with increasing indentation velocity. Conclusion: Differential excitation of superficial and deep multifidus fibres was found with increasing indentation velocity; however, the result was opposite to that hypothesized. This result is clinically relevant because it suggests deep multifidus fibre excitation may increase in response to increased perturbation magnitude, possibly to restore vertebral body position. Differential excitation effects may also be related to different mechanical stimuli experienced by deep and superficial fibres due to vertebral body movement during indentation loads. 11

No description available.

Approximately 50% - 80% of the population will experience disabling low back pain at some point in their life. Assessing and developing interventions based on “lumbar stability” and/or joint stiffness to reduce low back pain has been a common research focus. Specific focus has been on identifying which muscles influence lumbar stability/stiffness, with one argument being between focusing training on the transverse abdominis and lumbar multifidus muscles versus broader training approaches involving the entire abdominal wall and erector spinae muscles. However, there has not been research on whether pain reduction was due to increased stability/stiffness or another mechanism. The main goals of this thesis were to determine the effect of individual muscles on stability/stiffness through a two phase process. In the first phase, a model sensitivity analysis was performed to assess the interactions of variables that influence the quantification of stability. Stability was quantified via the eigenvalues (EV) of the Hessian matrix of potential energies at each lumbar level and axis of rotation, for a total of 15 EVs (3 axes of rotation x 5 joints). In phase 2, assessment of clinical interventions on patients with low back pain designed to alter biomechanics was conducted to assess factors in stability/stiffness quantification and mechanisms of action in pain modulation. More detail of the study phases are described below, in order to test the following hypotheses: 1) It was hypothesized that individual muscles affect specific EVs, but no one muscle can be associated with one EV level. 2) It was hypothesized that specific muscles do affect specific planes of stability/stiffness. 3) It was hypothesized that EVs are affected by posture. 4) It was hypothesized that overactivating muscles by increasing muscle activation to 100% MVC negatively affects the EVs. 5) It was hypothesized that the relationship between muscles and specific EVs obtained during simulation remains with real subjects performing loaded tasks. 6) It was hypothesized that coaching and cueing specific movement patterns and motor patterns would alter pain in low back pain patients. 7) If hypothesis 6 is true, then it was hypothesized that changes in pain would be reflected in changes in EVs. Methods for Phase 1 The first phase involved a sensitivity analysis using an anatomically detailed spine model. Theoretical data including posture, motion and muscle activity were synthesized to include 23 static spine postures, including neutral, 0° - 50° flexion, 0° - 30° extension, 0° - 30° right and left lateral bend, and 0° - 40° right and left axial twist, all in increments of 10°. For each posture, all eleven muscles included in the model, some with several fascicles, were artificially activated to 50% MVC. A knockout approach ensued whereby activity in single muscles were systematically reduced to 0% MVC or increased to 100% MVC. The relationships between the 15 EVs and the changes in muscle activity and posture were assessed. This muscle knockout model was repeated with actual muscle activity values obtained from electromyographic (EMG) signals and postures obtained from four subjects who performed a walking task with a 15 kg load in each hand. Results for Phase 1 The sensitivity analysis showed that the abdominal muscles contribute a greater stabilizing effect on the L4 and L5 EVs, while the multifidus and erector spinae muscles contribute a greater effect on the L1, L2 and L3 EVs. When examining the effect of muscles on a specific plane in terms of influencing stability/stiffness, it was found that the abdominal muscles contribute a greater effect on the bend axis and twist axis EVs than the flexion axis EVs, while the erector spinae muscles contribute the greatest effect on the flexion axis EVs. Posture was found to have a biologically significant effect on EVs, with the 50° flexion and 30° extension postures having the most detrimental effect in terms of compromising stability/stiffness. In addition, when there was a 10° excursion in any axis, there was little change in the EVs, while postures at angles greater than this were often associated with decreases in stability/stiffness in some EVs. Increasing the muscle activation from 50% MVC to 100% MVC did not have a large effect on most EVs, but when there was a meaningful change, as defined by a change of 10% or greater in the EV, the 100% MVC activation level always resulted in more stability/stiffness at that particular EV. Finally, using actual EMG and lumbar angle patterns resulted in similar results as the theoretical data, as expected. Interpretation of these findings is limited by the following. Even though EVs changed, there is no guarantee that the magnitude of change in one EV could be interpreted to equal a similar magnitude of change in another EV, nor may it be assumed that EVs have a linear relationship with stability/stiffness. These results suggest that when the goal is to increase lumbar stability, a neutral spine should be maintained and activating the larger abdominal muscles is more important than activating the transverse abdominis or multifidus, as proposed by some clinical groups. Methods for Phase 2 Four case studies of individuals with chronic low back pain were recruited from whom kinematic, kinetic and EMG data were collected in addition to a measure of pain intensity using an 11-point verbal numerical rating scale. Pain provocation tests were performed by a clinician (professor Stuart McGill) to identify the motions, postures and loads that exacerbated their pain. Then these tasks were repeated while the motion and EMG data was collected. This was followed by interventions coached by the clinician that could include the abdominal brace (stiffening the abdominal wall), latissimus dorsi stiffening, incorporating a hip-hinge motion rather than spine bending, or any combination of these. The intention of the intervention was to immediately reduce pain intensity. These tasks arranged in a repeated measures design were assessed with the anatomically detailed spine model to calculate stability/stiffness from evaluation of the 15 EVs, lumbar compression and lumbar shear forces. Results for Phase 2 The results from phase 2 suggest that pain was sometimes reduced by altering motions, postures and load, but the mechanism of what proved effective and the degree of success was variable from patient to patient. In most situations, the EVs, lumbar compression forces and lumbar shear forces increased due to the intervention that was chosen. In addition, the lumbar flexion angle typically trended to a more neutral posture and in tasks where spine motion occurred, there was less spine motion when using the suggested intervention. Further, the biomechanical variable that would be expected to change based on clinical assessment did not always react in the expected way (i.e. a compression intolerant individual would be expected to have decreased compression linked with decreased pain, but this did not occur). While the stability/stiffness increased, the associated compression was tolerated suggesting that the increase in concomitant stiffness enhanced the compression load bearing tolerance. Overall Conclusions This thesis showed that careful examination of the EVs did not offer substantial insight into links between changes in individual EVs and individual muscles, as muscle activity was not reflected in the EVs. Specifically, single muscles contributions were not reflected in specific EVs as was hypothesized. Further, it was difficult to interpret the EVs collectively because of the inherent non-linearity between EV magnitude and changes in muscle activation/stiffness; it can only be said that there was more or less stability/stiffness with each change in an EV, not how much. In addition, pain reduction appeared to be due to a combination of altered motions, postures and loads, but this did not result in systematic EV changes. Globally, the present work provides evidence supporting the idea that maintaining a neutral posture and activating the abdominal muscles results in less pain and larger EVs, suggesting an increase in stability/stiffness. This work has potential for informing clinicians on possible options for immediate reduction in low back pain.

Thesis (MAppSc in Physiotherapy) -- University of South Australia

Nucleus replacement has recently come into favor as a possible treatment for Degenerative Disc Disease. Replacing degenerative nucleus tissue with a synthetic material that mimics healthy nucleus tissue may restore normal function and biomechanics to the disc and delay or obviate the need for more invasive procedures such as total disc replacement and fusion. This thesis evaluated a novel protein polymer hydrogel composed of silk and elastin as a nucleus replacement material. There are three experimental components; one in vivo and two in vitro portions. In the first experimental portion, a large animal model was developed to evaluate the biocompatibility of the material as well as the effect on surrounding boney and soft tissues. Three discs were evaluated in each animal; sham, discectomy and discectomy treated with hydrogel. Discs were evaluated at 4, 26 and 52 weeks. The hydrogel group showed a quiet cellular response, as well as decreased boney remodeling and fewer degenerative changes when compared to the discectomy group. The second experimental portion evaluated the biomechanics of 9 cadaveric motion segments loaded in axial rotation, lateral bending, flexion/extension (FE) and compression. Specimens were tested sequentially in the intact state, following annulotomy, discectomy and after hydrogel treatment. Range of Motion (ROM) in FE was shown to increase from the intact state (8.50+/-1.44˚) to the discectomy state (9.86+/-1.77˚) and decrease following hydrogel treatment (8.66+/-0.76˚) to be similar to the intact ROM. The third experimental portion investigates the effect of three commonly applied testing conditions on the mechanical properties of spinal segments. 27 motion segments were tested at 18˚C wrapped with Phosphate Buffered Saline (PBS), at 37˚C in a PBS bath, and at 37˚C and 100% humidity. Specimens were tested hourly for 6 hours. The heated conditions were shown to have lower stiffness and increased range of motion when compared 18 ˚C tests. Repeated testing with time increased neutral zone and ROM for all modes of bending. As tests are repeated over time, tissue properties change and may mask the ability of a nucleus replacement to restore biomechanics.

Diss. (sammanfattning) Uppsala : Univ., 2001. / Härtill 5 uppsatser.

Thesis (Ph. D., Computer Science)--University of Idaho, August 2007. / Major professor: Terence Soule. Includes bibliographical references (leaves 87-94). Also available online (PDF file) by subscription or by purchasing the individual file.