The cervical spine must provide structural support for the head, allow large range of motion and protect both the spinal cord and branching nerves. There are two types of spinal joints: the intervertebral discs which are flexible connections and the facets, which are articulating synovial joints. Both types degenerate with age. Current surgical treatments include spinal fusion and articulating disc replacement implants. If both disc and facet joints are degenerated, fusion is the only option. In spinal fusion, the disc is removed and the adjacent vertebrae are fused which causes abnormally high stress levels in adjacent discs. In disc replacement, an articulating device is inserted to restore intervertebral motion and mimic healthy spinal kinematics. Disc arthroplasty does not significantly increase adjacent level stress but the lack of rotational constraint causes increased facet contact pressures. Thus, there is a need for a cervical total level arthroplasty system (CTLAS) that has a disc implant specifically designed to preserve the facet joints and implants for facet arthroplasty that can act independently or in-unison with the disc replacement. The conceptual design of a CTLAS implant system was proposed that would replace the disc and the facet joints. To facilitate medical imaging, PEEK (polyetheretherkeytone) was selected as the structural and bearing material. In the present thesis, multi-station pin-on-plate wear testing was initiated for pairs of unfilled (OPT) and carbon-fiber-reinforced (CFR) PEEK. Wear is important in arthroplasty implant design because wear particles can cause osteolysis leading to loosening. A variety of experiments were performed to investigate the effects of load, contact geometry and lubricant composition on wear. CFR PEEK was found to have much lower and more predictable wear than OPT PEEK in the present experiments. The wear of OPT PEEK pairs showed sensitivity to lubricant protein concentration. The coefficient of friction during testing was found to be quite high (up to 0.5), which might have clinical implications. Also, some subsurface fatigue was found, exposing carbon fibers of CFR PEEK. This remains a concern for its long-term application. Further wear testing is recommended using actual implants in a spine wear simulator.

The cervical spine ligaments play an essential role in limiting the physiological ranges of motion in the neck; however, traumatic loading such as that experienced in automotive crash scenarios can lead to ligament damage and result in neck injury. The development of detailed finite element models for injury simulation requires accurate ligament mechanical properties at relevant loading rates. The objective of this research was to provide detailed mechanical properties for the cervical spine ligaments, by performing tensile tests at elongation rates relevant to automobile crash scenarios, using younger specimens (less than 50 years old), and to provide a comprehensive investigation of spinal level and gender effects. The five primary ligaments (present between C2-T1) investigated were: the anterior longitudinal ligament, posterior longitudinal ligament, capsular ligament, ligamentum flavum, and interspinous ligament. The craniovertebral ligaments (Skull/C0-C2) investigated were the tectorial membrane/vertical cruciate/apical/alar ligament complex, transverse ligament, anterior atlanto-occipital membrane, posterior atlanto-occipital membrane, anterior atlanto-axial membrane, and posterior atlanto-axial membrane. Tests were performed within an environmental chamber designed to mimic in vivo temperature and humidity conditions, and specimens were preconditioned for 20 cycles at 10% strain prior to testing to failure. Ligaments were tested at quasi-static (0.5s-1), medium (20s-1) and high (150-250s-1). These strain rates were predicted by an existing cervical spine finite element model under typical crash scenarios. Two hundred sixty-one total primary ligament tests were performed, with approximately even distribution within elongation rate, spinal level, and gender. Another forty-four craniovertebral ligaments were tested. Results were plotted as force-displacement curves and the response characteristics determined from the curves were: failure force, failure elongation, stiffness of the linear region, toe region elongation, failure stress, failure strain, modulus and toe region strain. The measured force-displacement data followed expected trends when compared with previous studies. The younger ligaments had less scatter, and were both stiffer and stronger than the older specimens that were reported in previous studies at both quasi-static and comparable higher elongation rates. Statistical analysis was performed on the results to establish significant effects. Strain rate effects were most significant whereas spinal level effects were not found. In general, gender effects were not found to be significantly different, but consistent trends were identified with male ligaments having a higher stiffness and failure force than female ligaments. The post-ultimate load region of the curves was reported to offer insight into the ligament failure mechanism. The characteristic values obtained were used to develop average curves for each ligament, with the intention to eventually be directly integrated into finite element models to better represent the ligament structures. Curves were developed to incorporate the strain rate, spinal level and gender effects for each ligament based on the statistical analyses. Post-failure response was incorporated into these curves because this region has been shown to have an effect on neck behaviour in mathematical models. Recommendations for future studies include measuring accurate cross sectional areas of ligaments during tensile testing to obtain true stress and true strain measurements to better understand if differences in mechanical properties are structural or material. Other possible improvements would be further testing of young cervical spine ligaments with larger sample sizes to further explore spinal level and gender effects. Additional testing performed under identical testing conditions as the current study would allow for pooling of the results effectively increasing the sample size.

No description available.

Im Rahmen der szintigraphischen Untersuchung der Halswirbelsäule gibt es unterschiedliche Aussagen zum physiologischen Speicherungsverhalten, insbesondere der kaudalen Facettengelenke. Eine Objektivierung der Szintigramme und Ermittlung von Normalbereichen der entsprechenden Speicherquotienten ist daher wichtig und stellt das Ziel dieser Arbeit dar. Zur Untersuchung kamen dafür 31 Pferde, bei denen es sich um Patienten der Chirurgischen Tierklinik in Leipzig aus dem Jahr 2008 handelte. Falls bei einem Pferd eine Lahmheit der Vordergliedmaße vorhanden war, wurde mit Hilfe der klinischen und szintigraphischen Untersuchung, sowie mittels diagnostischer Anästhesien als deren Ursache die Halswirbelsäule ausgeschlossen. Alle Pferde wiesen eine freie Beweglichkeit des Halses in alle Richtungen auf. Zur Bildung von Speicherquotienten wurden die als Interessenareale dienenden Facettengelenke C3/C4 bis C7/Th1, sowie der Wirbelkörper des sechsten Halswirbels zu verschiedenen Referenzarealen ins Verhältnis gesetzt. Als Referenzareale wurden dabei der Wirbelkörper des dritten und des vierten Halswirbels, sowie das auch als Interessenareal dienende Facettengelenk C3/C4 getestet. Anschließend wurden Normalbereiche für die Speicherquotienten ermittelt. Nach sonographischer Muskeldickenmessung über den Facettengelenken wurden deren Speicherquotienten mit Hilfe einer Formel auf einen Nullwert korrigiert, und für diese korrigierten Werte wurden ebenfalls Normalbereiche ermittelt. Es zeigte sich, dass die Speicherquotienten nach der Muskeldickenkorrektur gegenüber den nativen Speicherquotienten eine größere Streuung aufwiesen und somit größere und ungenauere Normalbereiche hervorbrachten. Dementsprechend sollten die nativen Speicherquotienten bevorzugt werden. Als das am besten geeignete Referenzareal für die Interessenareale C4/C5 bis C7/Th1 erweist sich hierbei die Isokontur-ROI auf dem Facettengelenk C3/C4. Für das Interessenareal C3/C4 eignet sich sowohl der Vergleich mit dem Referenzareal C3, als auch der mit dem Referenzareal C4. Das Interessenareal auf dem Wirbelkörper C6 wird am besten zum Referenzareal C4 ins Verhältnis gesetzt. Hervorzuheben sind die nativen Werte der Normalbereiche für die Gelenke C5/C6 und C6/C7, da hier am häufigsten röntgenologische Veränderungen zu finden sind. Sie betragen für das Gelenk C5/C6 auf der linken Halsseite 0,82-1,10 und auf der rechten Halsseite 0,86-1,10. Für das Gelenk C6/C7 beträgt der Normalbereich für die linke Halsseite 0,75-1,23 und für die rechte Halsseite 0,81-1,17. Zusammenfassend ist zu sagen, dass die quantitative Auswertung mittels der „Regions of Interest“-Technik an der Halswirbelsäule durchaus möglich ist und mit dieser Arbeit akzeptable Normalbereiche für die Facettengelenke C3/C4 bis C7/Th1 und für den Wirbelkörper C6 ermittelt werden konnten. Es fehlen nun noch Werte von Pferden mit einer klinischen Halswirbelsäulenproblematik, um die Aussagekraft der hier ermittelten Normalbereiche zu überprüfen.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1994. / Includes bibliographical references (leaves 146-162). / Microfiche. / xiii, 162 leaves, bound ill. 29 cm

The research described in this thesis focuses on the biomechanics of cervical spine injury diagnosis and rehabilitation management. This research is particularly relevant to the diagnosis of minor neck injuries that typically arise from motor vehicle accidents and are classified as "whiplash injuries". The diagnosis and treatment of these chronic neck problems has been particularly difficult and frustrating and these difficulties prompted calls for the objective evaluation of the techniques and procedures used in the measurement and assessment of neck dysfunction. The biomechanical aspects of the clinical diagnosis of minor cervical spine injuries were investigated in this work by reconfiguring an existing detailed biomechanical model of the human neck to simulate injuries to particular structures, and to model abnormal muscle activation. The investigation focused on the range of motion assessment and the methods of testing and rehabilitating the function of the deep neck muscles because the model could be applied to provide further insight into these facets of neck injury diagnosis and management. The de Jager detailed head-neck model, available as a research tool from TNO (The Netherlands), was chosen for this study because it incorporated sufficient anatomical detail, but the model required adaptation because it had been developed for impact and crash test dummy simulations. This adaptation significantly broadened the model's field of application to encompass the clinical domain. The facets of the clinical diagnosis of neck dysfunction investigated in this research were range of motion and deep muscle control testing. Range of motion testing was simulated by applying a force to the head to generate the primary motions of flexion/extension, lateral flexion and axial twisting and parametric changes were made to particular structures to determine the effect on the head-neck movement. The main finding from this study of cervical range of motion testing was that while motion can be accurately measured in three dimensions, consideration of the three dimensional nature of the motion can add little to the clinical diagnosis of neck dysfunctions. Given the non-discriminatory nature of range of motion testing, the scientific collection and interpretation of the three dimensional motion patterns cannot be justified clinically. The de Jager head-neck model was then further adapted to model the cranio-cervical flexion test, which is used clinically to test the function of the deep muscle groups of the neck. This simulation provided confirmation of the efficacy of using a pressure bio-feedback unit to provide visual indication of the activation of the deep flexor muscles in the neck. However, investigation of the properties of the pressure bio-feedback unit identified significant differences in the stiffness of the bag for the different levels of inflation that must be accounted for if comparisons are to be made between subjects. Following the identification of the calibration anomalies associated with the pressure bio-feedback unit, the motion of the point of pressure of the head on the headrest and the force at this point of contact during the activation of the deep flexor muscle group were investigated as an alternative source of feedback. This output, however, was found to be subject specific, depending on the posterior shape of the skull that determined the point of contact during the head rolling action. Clinically, an important outcome of the alternative feedback assessment was that the prescribed action to target the deep flexor muscle group will feel different for each individual, ranging from a slide to a roll of the head on the headrest, and this must be accounted for when explaining the action and during rehabilitation management.

Low back pain is an ailment that affects a significant portion of the community. However, due to the complexity of the spine, which is a series of interconnected joints, and the loading conditions applied to these joints the causes for back pain are not well understood. Investigations of damage or failure of the spinal structures from a mechanical viewpoint may be viewed as a way of providing valuable information for the causes of back pain. Low back pain is commonly associated with injury to, or degeneration of, the intervertebral discs and involves the presence of tears or lesions in the anular disc material. The aim of the study presented in this thesis was to investigate the biomechanical effect of anular lesions on disc function using a finite element model of the L4/5 lumbar intervertebral disc. The intervertebral disc consists of three main components - the anulus fibrosus, the nucleus pulposus and the cartilaginous endplates. The anulus fibrosus is comprised of collagen fibres embedded in a ground substance while the nucleus is a gelatinous material. The components of the intervertebral disc were represented in the model together with the longitudinal ligaments that are attached to the anterior and posterior surface of the disc. All other bony and ligamentous structures were simulated through the loading and boundary conditions. A high level of both geometric and material accuracy was required to produce a physically realistic finite element model. The geometry of the model was derived from images of cadaveric human discs and published data on the in vivo configuration of the L4/5 disc. Material properties for the components were extracted from the existing literature. The anulus ground substance was represented as a Mooney-Rivlin hyperelastic material, the nucleus pulposus was modelled as a hydrostatic fluid in the healthy disc models and the cartilaginous endplates, collagen fibres and longitudinal ligaments were represented as linear elastic materials. A preliminary model was developed to assess the accuracy of the geometry and material properties of the disc components. It was found that the material parameters defined for the anulus ground substance did not accurately describe the nonlinear shear behaviour of the tissue. Accurate representation this nonlinear behaviour was thought to be important in ensuring the deformations observed in the anulus fibrosus of the finite element model were correct. There was no information found in the literature on the mechanical properties of the anulus ground substance. Experimentation was, therefore, carried out on specimens of sheep anulus fibrosus in order to quantify the mechanical response of the ground substance. Two testing protocols were employed. The first series of tests were undertaken to provide information on the strain required to initiate permanent damage in the ground substance. The second series of tests resulted in the acquisition of data on the mechanical response of the tissue to repeated loading. The results of the experimentation carried out to determine the strain necessary to initiate permanent damage suggested that during daily loading some derangement might be caused in the anulus ground substance. The results for the mechanical response of the tissue were used to determine hyperelastic constants which were incorporated in the finite element model. A second order Polynomial and a third order Ogden strain energy equation were used to define the anulus ground substance. Both these strain energy equations incorporated the nonlinear mechanical response of the tissue during shear loading conditions. Using these geometric data and material properties a finite element model of a representative L4/5 intervertebral disc was developed. When the measured material parameters for the anulus ground substance were implemented in the finite element model, large deformations were observed in the anulus fibrosus and excessive nucleus pressures were found. This suggested that the material parameters defining the anulus ground substance were overly compliant and in turn, implied the possibility that the stiffness of the sheep anulus ground substance was lower than the stiffness of the human tissue. Even so, the mechanical properties of the sheep joints had been shown to be similar to those of the human joint and it was concluded that the results of analyses using these parameters would provide valuable qualitative information on the disc mechanics. To represent the degeneration of the anulus fibrosus, the models included simulations of anular lesions - rim, radial and circumferential lesions. Degeneration of the nucleus may be characterised by a significant reduction in the hydrostatic nucleus pressure and a loss of hydration. This was simulated by removal of the hydrostatic nucleus pressure. Analyses were carried out using rotational loading conditions that were comparable to the ranges of motion observed physiologically. The results of these analyses showed that the removal of the hydrostatic nucleus pressure from an otherwise healthy disc resulted in a significant reduction in the stiffness of the disc. This indicated that when the nucleus pulposus is extremely degenerate, it offers no resistance to the deformation of the anulus and the mechanics of the disc are significantly changed. Specifically, the resistance to rotation offered by the intervertebral disc is reduced, which may affect the stability of the joint. When anular lesions were simulated in the finite element model they caused minimal changes in the peak moments resisted by the disc under rotational loading. This suggested that the removal of the nucleus pressure had a greater effect on the mechanics of the disc than the simulation of anular lesions. The results of the finite element model reproduced trends observed in both the healthy and degenerate intervertebral disc in terms of variations in nucleus pressure with loading conditions, axial displacement of the superior surface and bulge of the peripheral anulus. It was hypothesised that the reduced rotational stiffness of the degenerate disc may result in overload of the surrounding innervated osseoligamentous anatomy which may in turn cause back pain. Similarly back pain may result from the abnormal deformation of the innervated peripheral anulus in the vicinity of anular lesions. Furthermore, it was hypothesised that biochemical changes may result in the degeneration of the nucleus, which in turn may cause excessive strains in the anulus ground substance and lead to the initiation of permanent damage in the form of anular lesions. With further refinement of the components of the model and the methods used to define the anular lesions it was considered that this model would provide a powerful analysis tool for the investigation of the mechanics of intervertebral discs with and without significant degeneration.

This project presented a biomechanical model of the lumbosacral spine and pelvis, including novel methodologies associated with the measurement of human mechanics. This research has, for the first time, produced accurate three-dimensional geometric models of the human skeleton from living subjects using magnetic resonance imaging technology, enabling the prediction of physiological muscle action within individuals. The model was used to examine changes in the mechanics of the lumbopelvic musculoskeletal system between the standing and seated postures due to the increasing prevalence of the seated posture in the work and home environment. The outcomes of this research included a novel bone wrapping algorithm used to describe the effect of muscle-bone interactions. a novel method for creating three-dimensional in vivo spinal reconstructions using MRI, three dimensional in vivo helical axis measurements and subject specific normalised moment data.

The pelvic floor muscles (PFM) form the base of the abdominal canister, and like the other muscle groups around the canister, the abdominal muscles and the diaphragm, they contribute to and are affected by pressures within the canister. But they also have a role in organ support and continence. In urinary incontinence, clinical rehabilitation has targeted the PFM in isolation. It aims to build up strength and endurance of these muscles, but without consideration of the influence of intra-abdominal pressure, and therefore the co-ordination of muscles that generate that pressure, on PFM activity. Strengthening of the PFM has not resolved incontinence for all women, and the benefits are not sustained in the long term. Thus consideration of factors beyond the pelvic floor (PF) may lead to better outcomes for rehabilitation in both the short and long term. Thus these studies aimed to investigate the influences of abdominal muscle activity and spinal posture on the recruitment of the PFM. The studies firstly investigated the association between the abdominal and PFM during voluntary tasks. Further studies examined the effect of automatic recruitment of the PFM and the abdominal muscles with postural disturbances and changes in spinal posture, and whether there was a difference in recruitment between layers of the PFM complex during function. Electromyographic (EMG) studies, using fine wire and/or surface electrodes, were performed to record patterns of muscle activity, while, in selected studies, this was accompanied by pressures recorded within the stomach, urethra, bladder, vagina, anus and rectum, to monitor the effects of the striated muscle activity on intra-abdominal pressure and urethral function. When the PFM were voluntarily contracted in healthy women, there was a co-ordinated response in all the abdominal muscles, which varied with the position of the lumbar spine. Conversely, when the lower abdominal muscles were drawn in towards the spine there was an increase in IAP, urethral pressure and PFM EMG activity. Relaxation of the abdominal muscles and bulging of the relaxed abdominal wall decreased PFM activity and urethral pressure below their resting baselines. Thus, voluntary activation of the abdominal or PFM influences activity in the other muscle group. Other studies investigated the automatic responses of abdominal and PFM during breathing, postural perturbation, sitting and coughing. Quiet breathing was associated with modulation of PFM EMG with greater activity during expiration than inspiration, in association with variations in abdominal muscle activity. Hypercapnoea accentuated these results. Postural perturbations generated co-activation of the PF and abdominal muscles before the onset of deltoid activity with sustained activity through out repeated arm movements. Changes in spinal posture also affected PFM activity. Like the abdominal muscles, PFM were less active when sitting in a slumped position. Similar changes occurred in women with stress urinary incontinence but with lower pelvic floor muscle activity levels. Women with stress urinary incontinence also had less lordosis of the lumbar spine in upright sitting and a trend for greater superficial abdominal muscle activity than continent women. Activity of the superficial, but not deep, PFM during coughing, was affected by different sitting postures, with greater activity during coughing in slumped than in upright postures. Different breathing patterns and changes in posture also affected IAP and abdominal muscle recruitment patterns during coughing. Investigation of PFM activity during functional tasks indicates that factors beyond the PF influence its activity. The findings from these studies indicate that PFM activity is inter-related with spinal posture and abdominal muscle activity. While most of these studies were conducted in healthy women, there are a number of different types of PF problems in women, in which the mechanics of the dysfunction differ from stress urinary incontinence. PFM activity has not been investigated in all types of PF dysfunction. The findings of co-ordinated recruitment of the abdominal and PFM and the effect of spinal posture on PFM function provide some evidence that PFM rehabilitation should not be undertaken in isolation, and that there is a likely advantage from exercising with a neutral lumbar spine. There is a need for further investigation of this co-ordinated muscle recruitment in subjects with different types of dysfunction, not just stress urinary incontinence. Findings from such investigations could then point the way forward to improved rehabilitation methods for people with problems, and more suitable methods of maintaining pelvic floor health.

Bibliography: leaves 102-116. / 116, [43] leaves, [51] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Analyses the characteristics and relative incidence of annular defects in the human lumbar spine and investigates their role in the pathogenesis of invertebral disc degeneration. / Thesis (Ph.D.)--University of Adelaide, Dept. of Pathology, 1992