This thesis was initiated by an awareness of the impact of low back pain in Western society in general and Australian society in particular. The studies and experiments in this thesis contribute towards an understanding of chiropractic as a professional entity in Victoria and the nature of its clinical practice. The issue of male adolescent LBP has been explored and in addition to an epidemiological description of this clinical entity, its anthropometric dimensions have been documented. The qualitative review of the literature provides ample justification for the management of patients with LBP by chiropractors, using manual or manipulative techniques. The observational study of the Victorian context in which chiropractors are educated, registered, and entitled to practice, demonstrates that Victorian chiropractors are appropriate providers of manipulative health care. They perform the role of primary contact, primary health care providers with diagnostic, treatment and management skills focussed mainly on musculoskeletal conditions, but with a small proportion of practice based in the health or preventive context, and are well placed to provide the manual and manipulative services required in the management of LBP patients. The profession is shown to have strategies in place to ensure continued legal and community acceptance. The strategies include those at entry level to the profession, such as the legislative provisions of government and the competencies required for registration as instilled during the professional education process, and those which are more of the nature to maintain the integrity of professional practice, such as the " standards of practice" concept. These are important characteristics given it is shown that the Victorian chiropractic profession is not homogenous with respect to educational standards, has a disparate gender balance, the presence of a few non-registered 'chiropractors', and a disparity in utilisation patterns with a significant tail to the right. However the chiropractic profession is shown to hold a position of strength and leadership in the Australian context with respect to the provision of manipulative health care. Indeed, it could be said that chiropractors are at the leading edge of the quality process with respect to the provision of manipulative health care in Australia. The description of chiropractic practice shows a patient base of all ages, including adolescents, presenting with a range of possible diagnoses, often funded by a third party, and with a high proportion of return visits suggestive of patient compliance and satisfaction. It is convincingly demonstrated that persons with work-related LBP attend to chiropractors in Victoria and are effectively managed with the aim being the restoration of optimal spinal function and, in the case of work-injured patients, an early return to work. This thesis includes utilisation data which suggest only a minority of Victorian chiropractors practice outside the responsible parameters described above. The case-mix data and patient profiles presented in this thesis are congruent and complement each other, suggesting a high level of patient satisfaction indicated by the high proportion of return visits by regular patients and a faster, return-to-work by work-injured claimants. The point and sample prevalence of LBP in a population of suburban male adolescents is described and shown to be similar to those found in comparable Western societies. The data for a sample of traditional Australian male adolescents describes the LBP experience for the first time in such a population and emphasises the wide variance between societies which is now being identified in the literature. The LBP experience of a typical suburban Australian male adolescent is identified and described in terms of chronicity, frequency and episode duration. Typically the male adolescent with LBP has a chronic (> 90 d) problem with frequent episodes of pain (from 2 or 3 times a month to 2 or 3 times week) which last a few hours. The pain is a little limiting but allows the performance of the Activities of Daily Living. While some limitation of general sporting activity due to pain is experienced, school attendance is generally not compromised. A particular clinical instrument, the Metrecom computerised electro-goniometer, is studied and found to be appropriate for use in gathering anthropometric dimensions to test hypotheses relating to an association between anthropometric dimensions and LBP in a male adolescent population. The applied level of uncertainty of the instrument is within acceptable limits for these dimensions. The anthropometric study tests the broad null hypothesis that the mean of specific anthropometric dimensions would be equal among samples of male adolescents drawn from the Australian population. The actual groups are a Melbourne 'Pain' group, a Melbourne 'No Pain' group, and a 'Traditional No Pain' group. The pain group reported either current LBP or a positive history of LBP, while the 'no pain' groups denied either current or historical LBP. The alternate hypothesis will be shown to be proven for the dimensions 'sitting height', 'upper body' length, 'pelvic height', and the ratio of the 'upper:lower' body segment in a population of male adolescents with idiopathic or mechanical LBP. This thesis meets its objectives of describing the chiropractic profession and its practise in the Victorian context, demonstrates the prevalence of LBP in a male adolescent population, and identifies particular anthropometric dimensions associated with those who report a LBP experience. The fact that a number of anthropometric dimensions are detectable in adolescence may allow the development of appropriate screening programs which in turn may lead to the design and introduction of suitable prophylactic interventional programs for persons found to be potentially prone to idiopathic or mechanical LBP, at the least reducing the severity and at most reducing the onset of this expensive problem in adulthood. The ratio of the upper body segment to the lower body segment would appear to be most appropriate indicator; it is robust in that it is a prime dimension, easily accessible, and with a low level of measurement uncertainty. Most importantly it would appear to hold validity throughout adolescence as it does not have a linear relationship with age.

Background: There is limited knowledge about leisure time physical activity and the body mass index (BMI) as prognostic factors for recovery from persistent back pain. The aim of this study was to assess the influence of leisure time physical activity and BMI on recovery from persistent back pain among men and women in a general population. Methods: The study population (n=1836) in this longitudinal cohort study consisted of participants reporting persistent back pain in the baseline questionnaire in 2002-2003. Data on leisure time physical activity, BMI and potential confounders were also collected at baseline. Information on recovery from persistent back pain (no back pain periods >= 7 days during the last 5 years) was obtained from the follow-up questionnaire in 2007. Log-binomial models were applied to calculate Risk Ratios with 95 percent Confidence Intervals (CI) comparing physically active and normal weight groups versus sedentary and overweight groups. Results: Compared to a sedentary leisure time, all measured levels of leisure time physical activity were associated with a greater chance of recovery from persistent back pain among women. The adjusted Risk Ratios was 1.46 (95% CI: 1.06, 2.01) for low leisure time physical activity, 1.51 (95% CI: 1.02, 2.23) for moderate leisure time physical activity, and 1.67 (95% CI: 1.08, 2.58) for high leisure time physical activity. There were no indications that leisure time physical activity influenced recovery among men, or that BMI was associated with recovery from persistent back pain either among men or among women. Conclusions: Regular leisure time physical activity seems to improve recovery from persistent back pain among women.

Background: The use of meta-analysis to combine the results of observational studies is controversial. Despite its common use, methodological work in this area is lacking. Because of the diversity of study designs, exposure and outcome measures, and differential adjustment for confounding variables, the identification of sources of heterogeneity among study effect estimates is particularly important when combining data from observational studies. This thesis presents the results of a study that examines the relative ability of individual participant data (IPD) meta-analysis (which was considered a “gold standard”) and traditional aggregate data (AD) meta-analysis to identify sources of heterogeneity among studies examining mechanical exposure and low back pain (LBP) in workers. Materials and Methods: A systematic literature search was conducted to identify relevant articles. The corresponding author of each article was contacted to request their individual-level data. Because the outcome definitions and exposure measures were not uniform across studies, two sub-studies were conducted 1) to identify sets of outcome definitions that could be combined in a meta-analysis and 2) to develop methods to translate mechanical exposure onto a common metric. IPD analyses were conducted using generalized estimating equation (GEE) regression to identify variables that acted as strong confounders and effect modifiers. Traditional AD meta-analysis was also conducted and potential sources of heterogeneity were tested using meta-regression. Key Findings: (1) Overall, we found an association between both forces and postures on LBP, although the magnitude varied depending on the exposure-outcome combination. Among the outcomes, the ORs tended to be highest for sick leave due to LBP. (2) There was very little evidence of strong confounders in the relationship between mechanical exposure and LBP; thus differential adjustment for confounders in studies would not likely be an important source of heterogeneity in an AD meta-analysis. (3) AD meta-analysis was able to identify the same study-level effect modifiers as IPD meta-analysis, but did not consistently identify individual-level effect modifiers. Both individual-level characteristics (older age and being male), and study-level characteristics (population-based studies and self-reported mechanical exposure), were associated with an increased OR for many of the LBP outcome and mechanical exposure combinations. Conclusion: AD meta-analysis is likely sufficient to detect heterogeneity for study-level factors but is not sufficient to identify individual-level effect modifiers. When the primary source of evidence in a research area is observational studies and when there is controversy despite several systematic reviews, IPD meta-analysis can be used to better understand sources of heterogeneity and provide context

Background: The use of meta-analysis to combine the results of observational studies is controversial. Despite its common use, methodological work in this area is lacking. Because of the diversity of study designs, exposure and outcome measures, and differential adjustment for confounding variables, the identification of sources of heterogeneity among study effect estimates is particularly important when combining data from observational studies. This thesis presents the results of a study that examines the relative ability of individual participant data (IPD) meta-analysis (which was considered a “gold standard”) and traditional aggregate data (AD) meta-analysis to identify sources of heterogeneity among studies examining mechanical exposure and low back pain (LBP) in workers. Materials and Methods: A systematic literature search was conducted to identify relevant articles. The corresponding author of each article was contacted to request their individual-level data. Because the outcome definitions and exposure measures were not uniform across studies, two sub-studies were conducted 1) to identify sets of outcome definitions that could be combined in a meta-analysis and 2) to develop methods to translate mechanical exposure onto a common metric. IPD analyses were conducted using generalized estimating equation (GEE) regression to identify variables that acted as strong confounders and effect modifiers. Traditional AD meta-analysis was also conducted and potential sources of heterogeneity were tested using meta-regression. Key Findings: (1) Overall, we found an association between both forces and postures on LBP, although the magnitude varied depending on the exposure-outcome combination. Among the outcomes, the ORs tended to be highest for sick leave due to LBP. (2) There was very little evidence of strong confounders in the relationship between mechanical exposure and LBP; thus differential adjustment for confounders in studies would not likely be an important source of heterogeneity in an AD meta-analysis. (3) AD meta-analysis was able to identify the same study-level effect modifiers as IPD meta-analysis, but did not consistently identify individual-level effect modifiers. Both individual-level characteristics (older age and being male), and study-level characteristics (population-based studies and self-reported mechanical exposure), were associated with an increased OR for many of the LBP outcome and mechanical exposure combinations. Conclusion: AD meta-analysis is likely sufficient to detect heterogeneity for study-level factors but is not sufficient to identify individual-level effect modifiers. When the primary source of evidence in a research area is observational studies and when there is controversy despite several systematic reviews, IPD meta-analysis can be used to better understand sources of heterogeneity and provide context

Introduction: Physical inactivity, related lifestyle diseases and back pain are severe problems in today’s society. One way to increase physical activity level is through Motivational Interviewing (MI).   Purpose: Comparing participants who were in need of MI for physical activity due to risk of heart- and coronary disease with participants not in need of MI, and to describe whether MI for physical activity and other factors can predict change of physical activity level.   Method: A cohort was followed during two years and measured on lifestyle factors, socioeconomic and psychological factors, general health, motivation to change lifestyle and back pain by questionnaires. Based on risk of heart and coronary disease, participants underwent an MI-session for increased physical activity (n=393) or no MI-session (n=380) at baseline.   Results: Besides having a deteriorated lifestyle, the majority of participants who received MI were females, had lower self-estimated economy, had lower health-related quality of life, scored lower on psychological factors and had comorbidity and back pain to a larger extent. Factors related to increase of physical activity level included being physically inactive at baseline, being a female, not having MI and not having disability due to back pain.   Conclusion: Participants in the MI-group had poorer health and more back pain. Having MI did not predict an increase of physical activity, but a low level of physical activity in the past and being a female did play a part in the prediction. More research is needed on MI for increase of physical activity level for an individual with risk of heart- and coronary disease and/or with back pain. / Introduktion: Fysisk inaktivitet, livsstilssjukdomar, och ryggsmärta är stora problem i dagens samhälle. Ett sätt att öka fysisk aktivitet är motiverande samtal (MI).   Syfte: Att jämföra deltagare som på grund av ökad risk för hjärt-/kärlsjukdom har behov för MI för ökad fysisk aktivitet med de som inte har behov, samt att beskriva om MI för ökad fysisk aktivitet och andra faktorer kan predicera en ökning i fysisk aktivitetsnivå efter två år.   Metod: En cohort följdes genom två år och mättes med enkäter beträffande livsstils-, socioekonomiska och psykologiska faktorer, hälsa, motivation till ändrad livsstilsbeteende samt ryggsmärta. Baserad på sin risk för hjärt-/kärlsjukdom fick deltagare ett MI-samtal syftat till att öka sin fysiska aktivitetsnivå (n=393) eller inget MI-samtal (n=380) vid baslinjen.   Resultat: Deltagare som fick MI för ökad fysisk aktivitet var oftare kvinnor, hade lägre själv-estimerad ekonomi, sämre hälsorelaterad livskvalitet, sämre psykologisk hälsa, mera komorbiditet och mera ryggsmärta. Faktorer relaterade till ökning av fysisk aktivitetsnivå var att vara inaktiv vid baslinjemätningen, att vara kvinna, att inte ha haft MI och att inte ha funktionsnedsättning på grund av ryggsmärta.   Konklusion: Deltagare i MI-gruppen hade sämre hälsa och mera ryggsmärta. MI predicerade inte en ökning av fysisk aktivitetsnivå. Däremot predicerade tidigare låg aktivitetsnivå och att vara kvinna en ökning. Mer forskning behövs avseende effekt av MI för ökning av fysisk aktivitetsnivå för individer med risk för hjärt-/kärlsjukdom och/eller ryggsmärta.

Approximately 80% of the population will experience low-back pain within their lifetime. Significant research efforts have focused on compressive loading as an injury mechanism that could lead to low-back pain and injury. However, the influence of shear loading, and its relationship to vertebral tissue tolerances as well as modulating factors for these tolerances have not been studied as extensively. The primary objective of this thesis was to produce a series of investigations that begin to determine the roles of different modulating factors such as posture, compression, bone density, bone morphology, and repetitive load magnitude on measured vertebral joint shear failure tolerances. The thesis comprises four independent studies using in vitro mechanical testing, imaging modalities, and finite element modeling. Each of the in vitro studies within this thesis used a validated porcine cervical model as a surrogate for the human lumbar spine. The first study employed in vitro mechanical testing to investigate the combined roles of flexion/extension postural deviation and compressive load on the measured ultimate shear failure tolerances. Peripheral quantitative computed tomography scans of the pars interarticularis and measurements of vertebral bone morphology were used in the second investigation along with in vitro mechanical testing to identify the morphological characteristics that can be used to predict ultimate shear failure tolerances. The influence of sub-maximal shear load magnitude on the cumulative shear load and number of loading cycles sustained prior to failure were investigated with in vitro mechanical testing in the third study. Finally, a finite element model of the porcine C3-C4 functional spinal unit was used to investigate the plausibility of hypotheses, developed from previous research and the findings of the first investigation for this thesis, surrounding alterations in measured ultimate shear failure tolerances as a function of changes in facet interaction. Results from the first investigation showed that there was no statistically significant interaction between postural deviation and compressive force on ultimate shear failure tolerance. However, ultimate shear failure tolerance was reduced (compared to neutral) by 13.2% with flexed postures, and increased (compared to neutral) by 12.8% with extended postures. Each 15% increment (up to a maximum of 60% of predicted compressive failure tolerance) in compressive force was met with an average 11.1% increase in ultimate shear failure tolerance. It was hypothesized that alterations in flexion/extension posture and/or compressive force altered the location for the force centroid of facet contact. These changes in the location of facet contact were hypothesized to produce subsequent changes in the bending moment at the pars interarticularis that altered the measured ultimate shear failure tolerance. The three leading factors for calculating of measured ultimate shear failure tolerance were the pars interarticularis length for the cranial vertebra, the average facet angle measured in the transverse plane, and cortical bone area through the pars interarticularis. A bi-variate linear regression model that used the cranial vertebra’s pars interarticularis length and average facet angle as inputs was developed to nondestructively calculate ultimate shear failure tolerances of the porcine cervical spine. Longer pars interarticularis lengths and facets oriented closer to the sagittal plane were associated with higher measured ultimate shear failure tolerances. Fractures observed in this investigation were similar to those reported for studies performed with human specimens and also similar to reported spondylolitic fractures associated with shear loading in humans. This provided additional evidence that the porcine cervical spine is a suitable surrogate in vitro model for studying human lumbar spine mechanics. Altered sub-maximal shear load magnitude create a non-linear decrease in both the number of cycles and the cumulative shear load sustained prior to failure. These findings suggested that estimates of cumulative shear load should assign greater importance to higher instantaneous shear loads. This was due to an increased injury potential at higher instantaneous shear loads. Cumulative load sustained prior to failure was used to develop a tissue-based weighting factor equation that would apply nonlinearly increased weight to higher shear load magnitudes in estimates of cumulative shear load. A finite element model of the porcine C3-C4 functional spinal unit was created, and simulations were performed using similar boundary conditions as the comparable in vitro tests, to assess the plausibility of the moment arm hypothesis offered within the first investigation of this thesis. Moment arm length between the force centroid of facet contact and the location of peak stress within the pars interarticularis was increased for flexed postures and decreased for extended postures. Alterations in moment arm length were larger for postural deviation than compressive force, suggesting a secondary mechanism to explain the observed increase in shear failure tolerance with higher compressive loads from the first investigation. One such possibility was the increase in the number of contacting nodes with higher compressive forces. Alterations in moment arm length were able to explain 50% of the variance in measured ultimate shear failure tolerances from the first study. Thus, the finite element model was successful in demonstrating the plausibility of moment arm length between the force centroid of facet contact and the pars interarticularis as a modulator of measured ultimate shear failure tolerance. This thesis has developed the basis for understanding how failure of the vertebral joint exposed to shear loading can be modulated. In particular, this thesis has developed novel equations to predict the ultimate shear failure tolerance measured during in vitro testing, and to determine appropriate weighting factors for sub-maximal shear forces in calculations of cumulative shear load. Evidence presented within this thesis also provides support for the long-standing moment arm hypothesis for modulation of shear injury potential.

Work conducted as part of this thesis evaluated the lifting techniques of paramedics using a novel link-segment model that was validated against a commercially available software package, 3D Static Strength Prediction Program (3DSSPP). Twenty-five paramedics visited the Biomechanics Lab at Queen’s University to participate in testing sessions mimicking the daily lifting and carrying tasks performed by paramedics on the job. Participants were outfitted with the Xsens Motion Tracking System and asked to lift and carry bags ranging from 5-20kg. Output from the Xsens system was used in a 3D-inverse dynamic model to estimate loading at the L5/S1 joint. The compressive and shear force estimates at this joint are of particular interest given their correlation with low back pain and injury. Across all conditions the greatest compressive forces were seen during bag pickup and bag release. Additionally, reaching forward 50 cm at pickup increased peak spinal compressive loads by nearly 300N and 500N for a 5kg and 10kg handbag respectively. Not surprisingly, at bag release greater trunk lean values were correlated with higher compressive force estimates. Single-shoulder backpack carries showed similar loading characteristics when compared to double-shoulder backpack carries. Shear force estimates remained well below acceptable levels across all conditions. Based on paramedic feedback, a supplementary testing session was performed with a single participant to evaluate multi-bag carries and stair climbing. The results of this testing session showed that loading was reduced at pickup and release when the load was distributed across two bags. This research led to the development of four recommendations that have been presented to the Association of Municipal Emergency Medical Services of Ontario. 1. Paramedics should not lift single bags or a combination of bags that exceed 20kg. 2. Prior to lifting, bags should be located as close to the paramedic as possible. 3. When placing bags on the ground and when picking bags up off of the ground, paramedics should use a squat lift technique to prevent forward and side bending. 4. When multiple bags are carried the load should be evenly distributed within bags and across sides of the body. / Thesis (Master, Kinesiology & Health Studies) -- Queen's University, 2011-09-30 19:26:18.28

Objective : Low back pain (LBP), and in particular sacroiliac joint syndrome, is a significant health concern for both patient and their chiropractor with regards to quality of life and work related musculoskeletal disorders. Therefore, chiropractors often utilise mechanical aids to reduce the impact on the chiropractor’s health. It is, however, important to establish whether these mechanical aids are indeed clinically effective, therefore, this study evaluated the Activator Adjusting Instrument (AAI) against an AAI placebo to determine whether this adjusting instrument is an effective aid for both the chiropractor and the patient. Method : This randomised, placebo controlled clinical trial consisted of 40 patients (20 per group), screened by stringent inclusion criteria assessed through a telephonic and clinical assessment screen. Post receipt of informed consent from the patients, measurements (NRS, Revised Oswestry Disability Questionnaire, algometer) were taken at baseline, prior to consultation three and at the follow consultation. This procedure occurred with four interventions over a two week period. Results: The AAI group showed clinical significance for all clinical measures as compared to the AAI placebo group which attained clinical significance only for the Revised Oswestry Disability Questionnaire. By comparison there was only a statistically significant difference between the groups in terms of the algometer readings (p= 0.037). Conclusion : Therefore, it is evident that the AAI seems to have clinical benefit beyond a placebo. However this is not reflected in the statistical analysis. It is, therefore, suggested that this study be repeated with a larger sample size in order to verify the effect on the statistical analysis outcomes.

Darbo tikslas: Įvertinti specializuotos treniruočių programos poveikį darbingo amžiaus žmonių, jautusių NAD skausmą, taisyklingo judesio atlikimo rodiklių pokyčiams.Uždaviniai: 1. Įvertinti specializuotų ir bendrojo lavinimo treniruočių ciklų poveikį juosmens – dubens srities stabilumui ir judesių valdymui bei liemens raumenų ištvermei. 2. Palyginti specializuotos ir bendro lavinimo treniruočių programų poveikio rezultatus juosmens – dubens srities stabilumui ir judesių valdymui bei liemens raumenų ištvermei. Tyrimui buvo pakviesta 60 asmenų jautusių NAD skausmą. Visiems buvo pateiktas NAD skausmo trukmės ir fizinio aktyvumo vertinimo klausimynai, atliktas pirminis diagnostinis testavimas. Juosmens – dubens stabilumas vertintas statinės atlikties testais, naudojant slėgio matavimo prietaisą su grįžtamuoju ryšiu ,,Stabilizer‘‘. Juosmens – dubens srities judesių valdymas vertintas 6 judesių valdymo testais (,,Movement control tests’’). Liemens raumenų jėgos ištvermė vertinta statinės atlikties testais. Duomenų vertinimui buvo naudojama video kameros medžiagos ekspertinė analizė. Pagal atsakymus į klausimynus ir atlikus pirminį tyrimą, atrinkta 30 asmenų, kurių juosmens - dubens srities judesių valdymas įvertintas kaip nepakankamas. Tiriamųjų amžiaus vidurkis – 21,37 ± 0,2 metai (±SEM, standartinė vidurkio įverčio paklaida). Kūno masės indeksas – 21,7 ± 0,5 kg/m². Atsitiktine tvarka tiriamieji suskirstyti į tiriamąją (n=15) ir kontrolinę (n=15) grupes. Taikytos... [toliau žr. visą tekstą] / The aim of the study: To evaluate the effect of a specialized training program to the changes in indicators of the lumbarpelvic region motion performance of the employble age persons with low back pain. Tasks: 1. Evaluate the effect of the specialized training program cycle and general training program cycle for the lumbar-pelvic region stability, motions control and trunk muscle strength endurance.2. Compare the results between a specialized training program and the results of the general training program to the the lumbar-pelvic stability, motions control and trunk muscle strength endurance. The study involved 60 subjects with low back pain. All were submitted to the low back pain duration and physical activity assessment questionnaires, performed the primary diagnostic testing. Lumbar - pelvic stability was evaluated with static tests carried out by using a pressure measuring device with feedback,'' Stabilizer”. Lumbar - pelvic motion control was evaluated by 6 motion control tests ("Movement control tests'') by Hannu Luomajoki. Back and abdominal muscle endurance rated static tests carried out. For evaluation of the study data was used video materials expert analysis. According to the answers to the questionnaires and the primary investigation, 30 people with inadequate lumbar - pelvic motion control were selected for further research. Average age - 21.37 ± 0.2 years (± SEM, standard error of the mean estimate. Body mass index - 21. 7 ± 0.5 kg / m². Patients were... [to full text]

Approximately 80% of the population will experience low-back pain within their lifetime. Significant research efforts have focused on compressive loading as an injury mechanism that could lead to low-back pain and injury. However, the influence of shear loading, and its relationship to vertebral tissue tolerances as well as modulating factors for these tolerances have not been studied as extensively. The primary objective of this thesis was to produce a series of investigations that begin to determine the roles of different modulating factors such as posture, compression, bone density, bone morphology, and repetitive load magnitude on measured vertebral joint shear failure tolerances. The thesis comprises four independent studies using in vitro mechanical testing, imaging modalities, and finite element modeling. Each of the in vitro studies within this thesis used a validated porcine cervical model as a surrogate for the human lumbar spine. The first study employed in vitro mechanical testing to investigate the combined roles of flexion/extension postural deviation and compressive load on the measured ultimate shear failure tolerances. Peripheral quantitative computed tomography scans of the pars interarticularis and measurements of vertebral bone morphology were used in the second investigation along with in vitro mechanical testing to identify the morphological characteristics that can be used to predict ultimate shear failure tolerances. The influence of sub-maximal shear load magnitude on the cumulative shear load and number of loading cycles sustained prior to failure were investigated with in vitro mechanical testing in the third study. Finally, a finite element model of the porcine C3-C4 functional spinal unit was used to investigate the plausibility of hypotheses, developed from previous research and the findings of the first investigation for this thesis, surrounding alterations in measured ultimate shear failure tolerances as a function of changes in facet interaction. Results from the first investigation showed that there was no statistically significant interaction between postural deviation and compressive force on ultimate shear failure tolerance. However, ultimate shear failure tolerance was reduced (compared to neutral) by 13.2% with flexed postures, and increased (compared to neutral) by 12.8% with extended postures. Each 15% increment (up to a maximum of 60% of predicted compressive failure tolerance) in compressive force was met with an average 11.1% increase in ultimate shear failure tolerance. It was hypothesized that alterations in flexion/extension posture and/or compressive force altered the location for the force centroid of facet contact. These changes in the location of facet contact were hypothesized to produce subsequent changes in the bending moment at the pars interarticularis that altered the measured ultimate shear failure tolerance. The three leading factors for calculating of measured ultimate shear failure tolerance were the pars interarticularis length for the cranial vertebra, the average facet angle measured in the transverse plane, and cortical bone area through the pars interarticularis. A bi-variate linear regression model that used the cranial vertebra’s pars interarticularis length and average facet angle as inputs was developed to nondestructively calculate ultimate shear failure tolerances of the porcine cervical spine. Longer pars interarticularis lengths and facets oriented closer to the sagittal plane were associated with higher measured ultimate shear failure tolerances. Fractures observed in this investigation were similar to those reported for studies performed with human specimens and also similar to reported spondylolitic fractures associated with shear loading in humans. This provided additional evidence that the porcine cervical spine is a suitable surrogate in vitro model for studying human lumbar spine mechanics. Altered sub-maximal shear load magnitude create a non-linear decrease in both the number of cycles and the cumulative shear load sustained prior to failure. These findings suggested that estimates of cumulative shear load should assign greater importance to higher instantaneous shear loads. This was due to an increased injury potential at higher instantaneous shear loads. Cumulative load sustained prior to failure was used to develop a tissue-based weighting factor equation that would apply nonlinearly increased weight to higher shear load magnitudes in estimates of cumulative shear load. A finite element model of the porcine C3-C4 functional spinal unit was created, and simulations were performed using similar boundary conditions as the comparable in vitro tests, to assess the plausibility of the moment arm hypothesis offered within the first investigation of this thesis. Moment arm length between the force centroid of facet contact and the location of peak stress within the pars interarticularis was increased for flexed postures and decreased for extended postures. Alterations in moment arm length were larger for postural deviation than compressive force, suggesting a secondary mechanism to explain the observed increase in shear failure tolerance with higher compressive loads from the first investigation. One such possibility was the increase in the number of contacting nodes with higher compressive forces. Alterations in moment arm length were able to explain 50% of the variance in measured ultimate shear failure tolerances from the first study. Thus, the finite element model was successful in demonstrating the plausibility of moment arm length between the force centroid of facet contact and the pars interarticularis as a modulator of measured ultimate shear failure tolerance. This thesis has developed the basis for understanding how failure of the vertebral joint exposed to shear loading can be modulated. In particular, this thesis has developed novel equations to predict the ultimate shear failure tolerance measured during in vitro testing, and to determine appropriate weighting factors for sub-maximal shear forces in calculations of cumulative shear load. Evidence presented within this thesis also provides support for the long-standing moment arm hypothesis for modulation of shear injury potential.