Spinal ligaments may be a significant source of chronic back pain, yet they are often disregarded by the clinical community due to a lack of information with regards to their material response, and innervation characteristics. The purpose of this dissertation was to characterize the material response of spinal ligaments and to review their innervation characteristics. Review of relevant literature revealed that all of the major spinal ligaments are innervated. They cause painful sensations when irritated and provide reflexive control of the deep spinal musculature. As such, including the neurologic implications of iatrogenic ligament damage in the evaluation of surgical procedures aimed at relieving back pain will likely result in more effective long-term solutions. The material response of spinal ligaments has not previously been fully quantified due to limitations associated with standard soft tissue testing techniques. The present work presents and validates a novel testing methodology capable of overcoming these limitations. In particular, the anisotropic, inhomogeneous material constitutive properties of the human supraspinous ligament are quantified and methods for determining the response of the other spinal ligaments are presented. In addition, a method for determining the anisotropic, inhomogeneous pre-strain distribution of the spinal ligaments is presented. The multi-axial pre-strain distributions of the human anterior longitudinal ligament, ligamentum flavum and supraspinous ligament were determined using this methodology. Results from this work clearly demonstrate that spinal ligaments are not uniaxial structures, and that finite element models which account for pre-strain and incorporate ligament’s complex material properties may provide increased fidelity to the in vivo condition.

Autism spectrum disorder (ASD) affects about 1.5 million individuals in the US alone. The consequences of ASD affect families, caregivers, and social structures. This thesis adds to a growing group of people performing research on mitigating the effects of autism through robotics. Children with ASD tend to interact with robots more easily than with other humans. The goal of robotic therapy is not to help children interact with robots, but to generalize the behavior to humans. An articulated spine is a key to human emotional expression through shaping, weight shifting, and flow. Despite this importance, this feature is all but lacking in robots. The primary contribution of this work is a novel 3-link planar spine with compliant, partial-gravity-compensating springs, capable of reproducing simple emotion-conveying poses for use in robot-based therapy for children with ASD. The design was based on the movements of expression experts using motion tracking markers. This information was used to optimize the number of links in the spine and their corresponding lengths. It is the goal of this research to make robotic therapy more effective for the children, raising the potential for life-changing results.

The increasing incidence of disc degeneration and its correlation with lower back pain is an alarming trend in modern society. The research of intervertebral disc degeneration and low back pain would greatly benefit from additional methods to study its etiology and possible treatment methods. A large animal model that maintains the biological and mechanical environment that is most similar to the human lumbar spine could provide substantial improvements in understanding and resolving the problem of intervertebral disc related low back pain.This dissertation presents my doctoral work of investigating the potential for the camelid cervical spine to serve as a suitable animal model for advancing biomechanical research of low back pain and intervertebral disc degeneration in the human lumbar spine. Specifically, this work identifies the cellular, morphological and biomechanical characteristics of the camelid cervical spine and intervertebral disc as compared to the human lumbar spine. My results demonstrate that there are remarkable similarities in all aspects. Many of the similarities with respect to the cellular environment of the intervertebral disc are a consequence of the camelid status as a large mammal. Additional testing of the cellular makeup of the camelid intervertebral disc cells revealed that many human qRT-PCR primers associated with disc degeneration are suitable for use in alpacas without modification. From a biomechanics standpoint, the camelid cervical spine also has a vertically oriented spinal posture and is unsupported near the end in an open kinetic chain, providing a mechanical parallel with the human lumbar spine. The camelid cervical intervertebral disc size is closer to the human lumbar intervertebral disc than all other currently used animal models available for comparison in the literature. Average flexibility (range of motion) of a camelid spinal motion segment showed similarities in all modes of loading. Based on magnetic resonance imaging and radiologic grading of the intervertebral disc, almost 90% of elderly camelids exhibited advanced degeneration (Pfirrmann grade 3 or higher) in their cervical spine, and about half of aged camelids have developed severe degeneration (Pfirrmann grade 4 or higher) in at least one or more of their cervical segments, most commonly within the two lowest cervical segments (e.g. c6c7 and/or c7t1). Thus, while there remain differences, the remarkable similarities between the camelid and human spine strengthen the case for using camelids as a model for human disc degeneration, normal and pathological biomechanics and fluid transport, and potentially as a pre-clinical model for investigating the efficacy of novel spinal devices.

There is a need for spinal implants that have nonlinear stiffness to provide stabilization if the spine loses stiffness through injury, degeneration, or surgery. There is also a need for spinal implants to be customizable for individual needs, and to be small enough to be unobtrusive once implanted. Past and ongoing work that defines the effects of degeneration on the torque rotation curve of a functional spinal unit (FSU) were used to produce a spinal implant which could meet these requirements. This thesis proposes contact-aided inserts to be used with the FlexSuRe™ spinal implant to create a nonlinear stiffness. Moreover, different inserts can be used to create customized behaviors. An analytical model is introduced for insert design, and the model is verified using a finite element model and tests of physical prototypes both on a tensile tester and cadaveric testing on an in-house spine tester. Testing showed the inserts are capable of creating a non-linear force-deflection curve and it was observed that the device provided increased stiffness to a spinal segment in flexion-extension and lateral-bending. This thesis further proposes that the FlexSuRe™ spinal implant can be reduced in size by joining LET joint geometries in series in a serpentine nature. An optimization procedure was performed on the new geometry and feasible designs were identified. Moreover, due to maintaining LET joint geometry, the contact-aided insert could be implemented in conjunction with this new device geometry.

The primary objective of this research is to associate lumbar segmental mechanical response with intervertebral disc degeneration under physiologic testing conditions. Because no mathematical model exists for lumbar spine segmental rotations, a portion of this thesis evaluates potential methods for curve fitting the torque-rotation curves. The Dual Inflection Point (DIP) Boltzmann equation was developed during the course of this research and is presented here as a method for fitting spinal motion data wherein a physical meaning can be assigned to each of the model coefficients. This model can tell us more about the effects of degeneration, testing conditions, and other factors that are expressed in the change in spinal motion. Previous studies have investigated the relationship between the degeneration grade and flexibility of the intervertebral disc, but were completed without the presence of a compressive follower load. This study builds on past work by performing the testing under a compressive follower load. Segmental stiffness, range of motion (ROM), hysteresis area, and normalized hysteresis (hysteresis area/ROM) were evaluated and the effect of degeneration, segment level, temperature, and follower load were analyzed. Twenty-one functional spinal units (FSUs) were tested in the three primary modes of loading at both body temperature and room temperature in a near 100% humidity environment. A compressive follower load of 440 N was applied to simulate physiologic conditions. Fifteen of the twenty-one segments were also tested without the follower load to determine the effects of the load on segmental biomechanics. The grade of degeneration for each segment was determined using the Thompson scale and the torque-rotation curves were fit with the DIP-Boltzmann sigmoid curve.The effect of degeneration was statistically significant (α = 0.05) for stiffness, ROM, and hysteresis area in axial rotation (AR) and lateral bending (LB); it was also statistically significant for ROM and normalized hystersis in flexion-extension (FE). The lumbosacral joint (L5-S1) was significantly stiffer in AR and LB; the decrease in ROM and hysteresis area in AR and LB were also statistically significant for the lumbosacral joint compared to L1-L2 and L3-L4. Temperature had a significant effect on stiffness and hysteresis area in AR and on hysteresis area in LB. The follower load increased stiffness in all three modes of loading, but was significant only in AR and LB; it also reduced ROM and increased normalized hysteresis in all three modes of loading.

The purpose of this work was to determine the possible effects of isolated spinal ligament transection on the biomechanics of the lumbar spine. A finite element model of a lumbar spine was developed and validated against experimental data. The model was tested in the primary modes of spinal motion in the intact condition, followed by comparative analysis of isolated removal of each spinal ligament. Results showed that stress increased in the remaining ligaments once a ligament was removed, potentially leading to ligament damage. Results also showed changes in bone remodeling "stimulus" which could lead to changes in bone density. Isolated ligament transection had little effect on intervertebral disc pressures. All major biomechanical changes occurred at the same spinal level as the transected ligament, with minor changes at adjacent levels. The results of this work demonstrate that iatrogenic damage of spinal ligaments disturbs the load sharing within spinal-ligament complex and may induce significant clinical changes in the spinal motion segment.

The purpose of this research was to investigate the influence of applying an intrinsic decompressive pre-load to a particular dynamic stabilization device on the biomechanical response of the lumbar spine. The FlexSPAR, which supports this ability, was used as a test case. A finite element model of a full lumbar spine was developed and validated against experimental data, and tested in the primary modes of spinal motion. The model was used to compare five lumbar spine test cases: healthy, degenerate, implanted with a pre-loaded device, implanted with a device without a pre-load, and implanted with rigid fixators. Results indicated that a pre-loaded FlexSPAR led to improved disc height restoration and segmental biomechanics. Results also showed that a pre-loaded FlexSPAR led to less change in bone remodeling stimulus in comparison to the device without a pre-load and rigid fixators. This work shows that there is a potential to improve the performance of posterior dynamic stabilization devices by incorporating a pre-load in the device.

The purpose of this work was to analyze the biomechanics of degeneration, damage, and failure in biological soft tissues both experimentally and computationally to provide insight into tendon or ligament tearing, tendo-achilles lengthening and lumbar spine dysfunction. For soft tissue tearing, experimental studies for calculating fracture toughness were performed and determined that tendons and ligaments are able to completely resist tear propagation. For tendo-achilles lengthening, a damage model was developed to mimic the behavior of the lengthening that occurs as a result of the percutaneous triple hemisection technique. The model provided insight for predicting the amount of lengthening that occurs during the procedure. For lumbar spine dysfunction, a finite element model was validated against experimental testing and simulated using boundary conditions representing physiological loading. The model was able to predict how biomechanical changes can lead to pain and how the prevalence of Schmorl's nodes can be predicted. For each of the situations, the best verification and validation methods were selected and are presented throughout the research to demonstrate the predictive capabilities and limitations of the work. Results of these studies are presented along with how those results influence the clinical endeavors associated with the degeneration, damage and failure of soft tissues.

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Currently, forensic scientists are only able to determine time since death (or postmortem interval) up to the first 60 hours. This is based largely on insect activity. Herein, it is proposed to use the degradation of the intervertebral disc (IVD) after death to determine a relationship between the mechanical properties of cadaveric tissue and time since death in order to extend the 60-hour window. To that end, 1 fresh human spine and 6 pig spines were each separated into sections (6 human and 48 pig), with each section having one intact disc. The sections were buried, unearthed, and cleaned, leaving only the disc and bone. To determine the mechanical properties, each disc underwent three different tests: cyclic conditioning, compression, and stress relaxation testing. The Schapery collocation method was used to create a theoretical curve from the data for the experimental curve. Observations were made involving the corresponding k values of the curve. Although there are trends in the data for k values that approximate the experimental stress relaxation curve, a correlation could not be determined.