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Low back pain (LBP) is a substantial secondary disability among persons with lower-limb amputation (LLA). Abnormal mechanics of movement subsequent to LLA may increase the stability demands on the spinal column, and repetitive exposures to such abnormal movements may alter trunk passive properties and/or the coordination of surrounding trunk muscle responses. Further, preferential use of the sound limb may lead to asymmetries in these behaviors. Spine biomechanics (e.g., loading and stability) are substantially influenced by trunk passive properties and neuromuscular control, and alterations in these behaviors are associated with abnormal mechanics of the spinal column and an increased LBP risk. However, there is limited evidence regarding whether prolonged repeated exposures to abnormal gait and movement resulting from LLA and subsequent repeated use of a prosthetic device affect these trunk behaviors. Eight males with unilateral LLA and a matched sample of non-amputation controls completed three studies in which several measures of trunk passive properties, neuromuscular control, and spine biomechanics were quantified using laboratory experiments and biomechanical analyses. Each study involved a distinct task to investigate potential alterations and/or asymmetries in trunk passive properties and neuromuscular control. The first study used a seated balance task to assess trunk postural control and stability. The second study used multidirectional trunk perturbations to assess trunk mechanical and neuromuscular behaviors. Finally, the third study used controlled quasi-static trunk movements to assess load-sharing mechanisms between active and passive low back tissues. Significant alterations and asymmetries in trunk passive properties and trunk neuromuscular responses were present among participants with LLA, specifically reduced and asymmetric trunk stiffness and reflex response; decreased and asymmetric passive contributions to trunk movements; and increased trunk muscle activities. Significant increases in trunk postural sway and trunk muscle activities were also present during seated stability measures. Such alterations in these behaviors may be a result of repetitive exposures to abnormal gait and movement subsequent to LLA and the use of a prosthetic device, and could play a contributing role in the development of LBP in this population. Future work should investigate the temporal relationship between altered trunk behaviors and repeated exposure to abnormal gait and movement subsequent to LLA, to better identify critical years for rehabilitation and preventative care. / Ph. D.

Pathologic processes and surgical manipulations of the spinal column may result in alterations of the biomechanical properties of the spine through increases or decreases in the range of motion or stability of the spine. A decrease in range of motion between two adjacent vertebrae subsequent to arthrodesis or ankylosis appears, clinically, to be well tolerated without significant alterations to the functions of the spine; however, a decrease in spinal column stability as a result of pathologic changes or surgical alterations can result in catastrophic spinal cord injury. In order to determine the effect of various surgical procedures and trauma on the spinal column, in vitro biomechanical studies may be employed using a servohydraulic testing apparatus and cadaver vertebral motion units. The T₁₃ - L₁ vertebral motion units of 48 mix breed dogs were dissected free of surrounding musculature and prepared for biomechanical testing by mounting with cross pins and polymethylmethacrylate. Specimens were surgically altered by facetectomy, lateral fenestration, diskectomy, and combinations of these procedures. Specimens were subjected to lateral bending at a rate of 2.5 cm per minute to failure in a swing arm bending jig designed to simulate four point bending. The slopes of bending moment vs. angular displacement curves were compared and significance determined by the method of least squares. A statistical difference (p < 0.05) was found between the stiffness of all diskectomy groups when compared to any other group. Unilateral and bilateral facetectomies, and fenestration induced a non-significant decrease in stiffness in comparison to control specimens. This data may be combined with that of previous testing of the canine thoracolumbar spine in flexion-extension and rotation to determine the clinical effects of surgical manipulations and trauma on spinal stability. These results suggest that fenestrations and facetectomies do not appear to increase the risk of injury to the canine thoracolumbar spinal cord during lateral bending in the in vitro model; however, thoracolumbar spinal fractures involving the vertebral body as represented by the diskectomy in vitro model may significantly destabilize the spine in lateral bending. / Master of Science

Degeneration of the cervical spine is part of the normal aging process, usually occurring without clinical symptoms. Symptomatic degeneration most often occurs in the lower cervical spine, presenting as axial neck pain, radiculopathy, myelopathy, or any combination of the three. When conservative treatment does not adequately manage these symptoms, surgical intervention may be required. The longstanding surgical treatment for cervical degeneration is arthrodesis achieved through anterior cervical discectomy and fusion (ACDF). A relatively newer treatment is arthroplasty with a cervical total disc replacement (CTDR), a motion-sparing procedure designed to maintain adjacent-level loading. While literature exists comparing the effects of cervical arthrodesis and cervical arthroplasty on neck kinematics and loading, the vast majority of these studies applied only quasi-static, non-injurious loading conditions. This dissertation research used a state-of-the-art, full body human finite element (FE) model to investigate the effects of these surgical procedures on neck response during simulated dynamic impacts. A method was developed to measure cross-sectional forces and moments at each level of the neck in the FE model. Neck loading was captured during three automobile impact simulations: a frontal impact of a belted driver with airbag deployment, a frontal impact of a belted passenger without airbag deployment, and an unbelted side impact. The measured neck forces and moments were compared to existing injury threshold values and used to calculate injury criteria values. Four additional simulations of the frontal impact with the belted driver were conducted with neck modifications representative of either a fusion or arthroplasty of C5-6. While cross-sectional loading above and below the implants did not vary appreciably, key differences were noted in both the interbody and facet response. However, no neck injury thresholds were exceeded in any of the simulations. With cervical radiculopathy diagnosed in 24,742 active-duty U.S. military personnel between 2000 and 2009, interest in cervical arthroplasty as treatment for symptomatic cervical degeneration in this population has increased. This motion-sparing procedure has the potential to expedite post-operative recovery time, allowing for these highly trained individuals to return to active-duty sooner than with a fusion. Due to the physically demanding nature of the military environment, it is important to ensure that this surgical procedure does not increase the likelihood of a neck injury. An FE simulation environment was developed to investigate aviator head and neck response during a survivable, rotary-wing aircraft impact with the ground using both an anthropomorphic test device (ATD) and a human body model. The head and neck response of the ATD FE simulation was successfully validated against the results of a previously conducted experimental sled test. A more biofidelic head and neck response was produced with the human body model, including realistic changes in neck curvature. Additional simulations were conducted with the human body model to investigate the neck response after cervical arthroplasty of C5-6. While the adjacent-level, cross-sectional loading for the C5-6 segment was not appreciably altered by the CTDRs, the interbody range-of-motion was increased; subsequently altering both the interbody and cervical facet loading. Again, no neck injury thresholds were exceeded in these simulations. Overall, cervical arthroplasty did not appear to have a deleterious effect on the dynamic neck response during a simulated rotary-wing aircraft impact. / Ph. D.

The stability of the spine can be estimated from kinematic variability and nonlinear analyses of seated balance tasks. However, processing methods require sufficient signal duration and test-retest experiments require that the assessment must be reliable. Our goal was to characterize the reliability and establish the trial duration for spine stability assessment. Stationarity, kinematic variability and nonlinear dynamic stability were quantified from kinetic and kinematic data collected during balance performance. Stationarity results showed that a minimum 30 seconds test duration is necessary. Intra-session reliability was excellent, however inter-session reliability needed more test trials to achieve excellent reliability. Few studies have investigated the spinal stability during pushing and pulling exertions. Past studies suggest that the spine can be stabilized by paraspinal muscle stiffness as well as reflexes. We hypothesized that the stability of the spine decreases with exertion force and decreases during pushing more than during pulling exertion. Kinematic variability and nonlinear dynamic stability measurements were quantified from the balance performance during isometric pushing and pulling tasks. Results demonstrated that spinal stability decreased with exertion force and decreased a greater amount during pushing task than during pulling task. Stiffness alone may be insufficient to stabilize the trunk. Results may be able to be explained by slower reflex delay. The results suggested that pushing and pulling exertions have a potential risk of low-back disorders. / Master of Science

Few studies have investigated the neuromuscular recruitment and stabilizing control of the spine during pushing and pulling exertions. Past theoretical investigation suggest that co-contraction of the of the paraspinal muscles is necessary to stabilize the spine during pushing exertions. We hypothesized greater levels of co-contraction during pushing exertions. Co-contraction of trunk musculature was quantified during isometric pushing and pulling tasks. The mean value of co-contraction during pushing was two-fold greater (p < 0.01) than during extension. Co-contraction has been shown to increase the stiffness of the ankle but this effect has not been demonstrated in the trunk. Trunk stiffness was measured as a function of co-activation during extension exertions. Results demonstrate trunk stiffness was significantly (p < 0.01) greater with co-activation. Trunk stiffness was calculated during isometric pushing and pulling exertions. We hypothesized trunk stiffness would be greater during pushing tasks due to increased levels of co-contraction to maintain stability of the spine. Results demonstrate trunk stiffness was significantly (p < 0.05) greater during pushing compared to pulling exertions. Results suggest that trunk isometric pushing tasks require more co-contraction than pulling tasks enable to maintain spinal stability. Greater levels of co-contraction during pushing exertions caused trunk stiffness to be greater during pushing compared to pulling tasks. Results may indicate greater risk of spinal instability from motor control error during pushing tasks than pulling exertions. Future studies need to consider co-contraction and neuromuscular control of spinal stability when evaluating the biomechanical risks of pushing and pulling tasks. / Master of Science

Yes / The aim of this paper is to show how the spine of a PDE surface can be generated and how it can be used to efficiently parameterise a PDE surface. For the purpose of the work presented here an approximate analytic solution form for the chosen PDE is utilised. It is shown that the spine of the PDE surface is then computed as a by-product of this analytic solution. Furthermore, it is shown that a parameterisation can be introduced on the spine enabling intuitive manipulation of PDE surfaces.

Anterior cervical discectomy and fusion (ACDF) is one of the most common cervical spine surgery procedures performed worldwide. ACDF utilizes autologous bone graft (autograft) from the iliac crest to induce fusion between neighboring vertebrae following the procedure. The iliac crest is widely considered the gold-standard autograft for ACDF procedures due to its osteoinductive, osteoconductive, and osteointegrative properties. However, harvesting from a second surgical site, as seen with iliac crest autograft, is commonly associated with short- and long-term complications. To mitigate iliac crest harvest site complications, a novel autograft location must be identified. The adjacent cervical vertebral body has been identified as a potential alternative donor site to the iliac crest. Previous studies have shown that this novel autograft site does not biomechanically compromise the vertebral body harvest site and has demonstrated clinically successful fusion rates comparable to those of the iliac crest. Despite prior successful fusion, a direct morphological and mechanical comparison between autograft from the adjacent cervical vertebra and iliac crest has not been thoroughly investigated. The primary goal of this thesis was to morphologically and mechanically compare the cervical spine and iliac crest. It was hypothesized that the cervical spine and iliac crest would not significantly vary in their morphological properties; however, due to daily physiological loading at each graft location, it was hypothesized that the two graft locations would differ mechanically. A clinical model utilizing iliac crest and cervical vertebral bone from human donors was characterized at the meso- and microscale to quantify morphological properties and collagen organization using micro-computed tomography (microCT) and second-harmonic generation (SHG) imaging modalities, respectively. A pre-clinical large animal model was used to characterize the mechanical and material properties of lumbar spine tissue, under similar physiological loading as the cervical spine, relative to the iliac crest through uniaxial compression testing. No significant difference was identified in the morphological and collagen organization properties in tissue from a human clinical cohort; however, directionality and anatomical location significantly impacted the mechanical and material properties in a bovine comparative anatomy model. Here, trabecular bone from the lumbar vertebra was found to be transversely isotropic whereas iliac crest trabecular bone was nearly isotropic; thus, directionality and anatomical location should be considered and quantified when selecting autograft tissue for future ACDF surgeries. Further characterization of the mechanical properties of cervical vertebral tissue and determination of correlations between directionality, anatomical location, and morphology through microCT and compression testing should be completed before adopting the cervical vertebra as the gold standard autograft for ACDF procedures. / Master of Science / Anterior cervical discectomy and fusion (ACDF) is a common upper spine surgery that helps to stabilize the spine by fusing two or more vertebrae together. To achieve this fusion, surgeons often use bone grafts taken from the patient's own hip, specifically the iliac crest. While this method is effective, it can lead to complications at the hip bone harvest site. To avoid these complications, researchers are exploring the possibility of using bone from a nearby vertebra in the upper spine as an alternative graft source. Early studies suggest that using bone from the upper spine does not weaken the spine and achieves similar success rates in fusion as the hip bone. However, a detailed comparison between both graft sites has not been thoroughly investigated until now. The main goal of this thesis was to compare the bone from the upper spine and the hip in terms of structure and strength. It was expected that the two types of bone would be similar in structure but different in strength due to difference forces they experience in the body. The research involved examining human bone samples from both the upper spine and hip using advanced imaging techniques to analyze their structure and collagen organization. Additionally, a large animal comparative model was used to test the strength and material properties of bone from the lower spine and hip, which experience similar forces as the human upper spine and hip. The findings showed no significant difference in the structure and collagen organization of the human bone samples. However, in the animal model, the strength and material properties of the bone significantly varied depending on the direction and location. Bone from the lower spine was found to be significantly stronger in one direction in comparison to two other directions in the lower spine and all three directions in the hip. These results suggest that when choosing bone for fusion in ACDF surgeries, it is important to consider the direction and location of the graft. Further research is needed to fully understand the mechanical properties of upper spine bone and to confirm its suitability as a standard graft for ACDF procedures.

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