Automatic segmentation of the spine by means of a probabilistic atlas with a special focus on ribs suppression

[EN] Purpose: The development of automatic and reliable algorithms for the detection and segmentation of the vertebrae are of great importance prior to any diagnostic task. However, an important problem found to accurately segment the vertebrae is the presence of the ribs in the thoracic region. To overcome this problem, a probabilistic atlas of the spine has been developed dealing with the proximity of other structures, with a special focus on ribs suppression. Methods: The data sets used consist of Computed Tomography images corresponding to 21 patients suffering from spinal metastases. Two methods have been combined to obtain the final result: firstly, an initial segmentation is performed using a fully automatic level-set method; secondly, to refine the initial segmentation, a 3D volume indicating the probability of each voxel of belonging to the spine has been developed. In this way, a probability map is generated and deformed to be adapted to each testing case. Results: To validate the improvement obtained after applying the atlas, the Dice coefficient (DSC), the Hausdorff distance (HD), and the mean surface-to-surface distance (MSD) were used. The results showed up an average of 10 mm of improvement accuracy in terms of HD, obtaining an overall final average of 15.51 2.74 mm. Also, a global value of 91.01 3.18% in terms of DSC and a MSD of 0.66 0.25 mm were obtained. The major improvement using the atlas was achieved in the thoracic region, as ribs were almost perfectly suppressed. Conclusion: The study demonstrated that the atlas is able to detect and appropriately eliminate the ribs while improving the segmentation accuracy.The authors thank the financial support of the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds under Grants TEC2012-33778 and BFU2015-64380-C2-2-R (D.M.) and DPI2013-4572-R (J.D., E.D.)Ruiz-España, S.; Domingo, J.; Díaz-Parra, A.; Dura, E.; D'ocon-Alcaniz, V.; Arana, E.; Moratal, D. (2017). 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In vivo lumbar spine biomechanics : vertebral kinematics, intervertebral disc deformation, and disc loads

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references.Knowledge of lumbar spine biomechanics in living human subjects is fundamental for understanding mechanisms of spinal injury and pathology, for improvement of corresponding clinical treatments, and for design of spinal prosthesis. However, due to the complicated spine anatomy and loading conditions as well as high risks in these direct measurements, it has been a challenge to determine the in vivo biomechanics of the lumbar spine. To address this problem, the overall objective of this thesis was to develop and implement a dual fluoroscopic imaging system to non-invasively study human lumbar spine biomechanics. In line with this objective, the first goal was to quantify the ability of the dual fluoroscopic imaging system to determine vertebral kinematics. The second goal was to implement this technique to investigate spinal motion in both healthy subjects and patients with pathology. The third goal was to explore the feasibility of using kinematic data obtained from this system as boundary conditions in finite element analysis to calculate the physiological loads on the intervertebral disc. The system was shown to be accurate and repeatable in determining the vertebral kinematics in all degrees of freedom. For the first time, six degree-of-freedom motion of different structures of the spine, such as the vertebral body, intervertebral disc, facet joint and spinous process were measured in vivo in both healthy subjects and subjects with pathology during functional activities. In general, the group of subjects with pathology showed a significantly abnormal kinematic response during various physiological functional activities. Preliminary studies have shown the applicability and high accuracy of finite element modeling to calculate disc loads using in vivo vertebral kinematics as displacement boundary conditions.by Shaobai Wang.Ph.D

Discogenic low back pain : lumbar spondylodesis revisited

Neurosurgeon deals with chronic low back pain patients almost daily. Most of these patients still have complaints of low back pain despite many different previous therapies. Surgical treatment is only to be considered in few cases of chronic low back pain sufferers. From this large group of chronic low back pain patients we have tried to select a small group of patients who might benefit fiom spondylodesis. This thesis is about the selection and treatment of this patient group. Their assumed source of pain and the results of surgical treatment will also be discussed. ... Zie: Summary

Development of ultrasound to measure deformation of functional spinal units in cervical spine

Neck pain is a pervasive problem in the general population, especially in those working in vibrating environments, e.g. military troops and truck drivers. Previous studies showed neck pain was strongly associated with the degeneration of intervertebral disc, which is commonly caused by repetitive loading in the work place. Currently, there is no existing method to measure the in-vivo displacement and loading condition of cervical spine on the site. Therefore, there is little knowledge about the alternation of cervical spine functionality and biomechanics in dynamic environments. In this thesis, a portable ultrasound system was explored as a tool to measure the vertebral motion and functional spinal unit deformation. It is hypothesized that the time sequences of ultrasound imaging signals can be used to characterize the deformation of cervical spine functional spinal units in response to applied displacements and loading. Specifically, a multi-frame tracking algorithm is developed to measure the dynamic movement of vertebrae, which is validated in ex-vivo models. The planar kinematics of the functional spinal units is derived from a dual ultrasound system, which applies two ultrasound systems to image C-spine anteriorly and posteriorly. The kinematics is reconstructed from the results of the multi-frame movement tracking algorithm and a method to co-register ultrasound vertebrae images to MRI scan. Using the dual ultrasound, it is shown that the dynamic deformation of functional spinal unit is affected by the biomechanics properties of intervertebral disc ex-vivo and different applied loading in activities in-vivo. It is concluded that ultrasound is capable of measuring functional spinal units motion, which allows rapid in-vivo evaluation of C-spine in dynamic environments where X-Ray, CT or MRI cannot be used.2020-02-20T00:00:00

Short and Long Term Immobilization on the Lumbar Spinal Joints: An Experimental Study Using Large Animal Model

Low back pain (LBP) is a common, widespread social and economic problem. Degenerative disc disease has been considered as a main risk factor for the LBP. In order to develop safe, effective and cost-efficient treatments, it is important to explore the pathomechanisms of this disease. In vivo animal models have an irreplaceable role in detecting long-term reactions to environmental factors, biology or biomechanical risk factors, and preclinical evaluation of therapeutics. Large animal models, due to their similarity in cellular populations, anatomy and biomechanics, are more closely comparable to the human intervertebral disc than smaller animal models. The major goal of current thesis was characterizing the effect of short and long term immobilization on the magnetic resonance imaging, radiological, histological and biomechanical characteristics of the in vivo ovine lumbar spine joints. To achieve this target, four experimental projects were performed. In the first experimental portion, a three-dimension motion capture system was set up and validated. A reliable method of the spinal kinematic analysis was established. The second experimental portion evaluated the biomechanical aspect of a synthetic biomimetic spine model with a validated spinal biomechanical test system combined with the motion capture system set up in the first study. This established the whole system applicability to the specific goal of examining spinal biomechanics. The third experimental chapter is an in vitro ovine biomechanical study. The purpose of this study was to characterize the effect of loading and soaking conditions on the spinal segment biomechanical property. Results indicated the biomechanics of spinal samples with hydration and dehydration discs differ considerably. Thus, the suitable pretest conditions need to be considered during in vitro spinal biomechanical test. The fourth experimental portion was the in vivo ovine model study. The aim of this chapter was evaluate the effect of the short and long term immobilization on the ovine lumbar spinal joints. The posterior pedicle screw instrumentation was applied on skeletally mature sheep lumbar spine. The immobilized level and adjacent levels spinal joints were evaluated at 0, 6 and 26 weeks. Results demonstrated the both short and long term immobilization can induce spinal joint degeneration on sheep model. This work presents a novel degenerative disc model without the need for annulus violation or chemical treatmen

An Evaluation of passive recumbent quantitative fluoroscopy to measure mid-lumber intervertebral motion in patients with chronic non-specific low back pain and healthy volunteers.

Introduction: The biomechanical model of back pain has failed to find distinct relationships between intervertebral movement and pain due to limitations and variation in methods, and errors in measurement. Quantitative fluoroscopy (QF) reduces variation and error and measures dynamic intervertebral motion in vivo. This thesis used recumbent QF to examine continuous mid-lumbar intervertebral motion (L2 to L5) in patients with assumed mechanical chronic non-specific low back pain (CNSLBP) that had been clinically diagnosed. It aimed to develop kinematic parameters from the continuous data and determine whether these could detect subtle mechanical differences by comparing this to data obtained from healthy volunteers. Methods: This was a prospective cross sectional study. Forty patients with CNSLBP (age 21 to 51 years), and 40 healthy volunteers matched for gender, age and body mass index underwent passive recumbent QF in the coronal and sagittal planes. The patient group completed questionnaires for pain and disability. Four kinematic parameters were developed and compared for differences and diagnostic accuracy. Reference intervals were developed for three of the parameters and reproducibility of two were assessed. The radiation dose was compared to lumbar spine radiographs and diagnostic reference levels were established. Finally, relationships between patient’s pain and disability and one of the kinematic parameters (continuous proportional motion CPM) were explored. Results: Reproducibility was high. There were some differences in the coronal plane and flexion for each kinematic parameter, but no consistency across segments and none had high diagnostic accuracy. Radiation dose for QF is of the same magnitude as radiographs, and there were no associations between patient characteristics of pain and disability and CPM. Conclusion: Although the kinematic differences were weak, they indicate that biomechanics may be partly responsible for clinically diagnosed mechanical CNSLBP, but this is not detectable by any one kinematic parameter. It is likely that other factors such as loading, central sensitisation and motor control may also be responsible for back pain that is considered mechanical. QF is easily adapted to clinical practice and is recommended to replace functional radiography, but further work is needed to determine which kinematic parameters are clinically useful

Subject-Specific Computational Musculoskeletal Modeling of Human Trunk in Lifting : Role of Age, Sex, Body Weight and Body Height

Résumé Les troubles musculosquelettiques sont parmi les problèmes de santé les plus fréquents et les plus coûteux au monde. Les maux de dos figurent en deuxième position sur la liste des états chroniques les plus répandus au Canada et quatre adultes sur cinq souffriront de lombalgie un jour ou l’autre de leur vie. Les efforts excessifs sur la colonne vertébrale constituent l’un des facteurs de risque potentiels de lombalgie et peuvent initier ou générer de la douleur et de la dégénérescence des disques. À cet effet, plusieurs études s’accordent pour affirmer qu’une estimation juste des charges vertébrales est utile pour une prévention efficace des blessures et pour des programmes de réadaptation appropriés. Toutefois, il n’existe pas de méthodes directes pour mesurer les charges vertébrales et de plus, toutes les méthodes indirectes (comme la mesure de la pression intradiscale – PID – et l’estimation au moyen de prothèse discale instrumentée) sont invasives et limitées. Les modèles musculosquelettiques (MS) offrent toutefois une alternative intéressante en estimant de manière non invasive, économique et précise les forces musculaires, les charges vertébrales ainsi que la stabilité de la colonne vertébrale en tenant compte des différences individuelles. Dans cette thèse, un modèle MS du tronc par éléments finis (EF) guidé par la cinématique a été mis à niveau. L’architecture des origines et insertions musculaires a été améliorée, une unité vertébrale comprenant un disque déformable a été ajoutée (T11-T12) et un nouvel algorithme de mise à l’échelle a été introduit afin d’explorer les effets du sexe, de l’âge, du poids et de la taille sur la biomécanique et les charges appliquées sur la colonne vertébrale. Au moyen de données issues d’imageries médicales et à partir de principes biomécaniques, l’algorithme de mise à l’échelle a permis d’ajuster l’architecture musculaire (les bras de levier des muscles et les aires transverses), la géométrie et les propriétés passives ligamentaires de la colonne vertébrale ainsi que la charge gravitationnelle, le tout en fonction du sexe, de l’âge, du poids et de la taille. Une analyse de sensibilité a été effectuée au moyen d’une analyse factorielle multiple. Les données d’entrées du modèle (sexe, âge, poids et taille) ont été modifiées à l’intérieur de plages physiologiques (sexe : femme et homme ; âge : 35 à 60 ans ; poids : 50 à 120 kg ; taille : 150 à 190 cm) tandis que le modèle personnalisé par EF était guidé par une cinématique spécifique à l’âge et au sexe lors de différentes tâches de flexion avant avec ou sans charges manuelles. Des graphiques illustrant les effets principaux et des analyses de variance ont été utilisés pour évaluer les effets des données d’entrées sur le chargement au dos. Le poids du corps a été le facteur le plus influent, en expliquant 99 % du chargement lombaire en compression et 96 % de celui en cisaillement, alors que les effets de la taille, du sexe et de l’âge (<5 %) étaient minimes. Aussi, pour des poids et des tailles similaires aux hommes, les femmes supportaient généralement des charges plus importantes au dos (5 % en compression, 9 % en cisaillement) La prévalence de l’obésité, dont l’indice de masse corporelle (IMC) dépasse les 30 kg/m2, est en croissance constante dans les pays développés comme dans les pays en voie de développement et a atteint un seuil critique « d’épidémie mondiale ». Bien que l’obésité soit associée à plusieurs problèmes au dos (ex. : dégénération discale, fractures vertébrales, maux de dos), le rôle de la biomécanique dans les problèmes liés à l’obésité demeure inconnu. La distribution du tissu adipeux varie considérablement d’un individu obèse à un autre, et ce, même dans les cas d’IMC et de poids identiques. On retrouve différentes formes d’obésité, dont celle « en pomme » et celle « en poire » (androïde et gynoïde respectivement). Le rôle de l’obésité et des formes d’obésité sur les charges supportées par la colonne vertébrale et sur les fractures de compression vertébrale a été étudié à l’aide du modèle personnalisé mis à jour. Trois formes distinctes d’obésité (correspondant à une taille de circonférence minimale, moyenne et maximale) pour un poids et un IMC identiques ont été simulées au moyen de mensurations anthropométriques obtenues à partir de 5852 individus obèses et d’une analyse par composantes principales. L’obésité a des conséquences significatives sur le chargement lombaire : la compression sur L4-L5 a bondi de 16 % (2820 N vs 3350 N) pour une flexion avant sans charges lorsque l’IMC a augmenté de 31 kg/m2 à 39 kg/m2. Dans une comparaison entre une taille de circonférence minimale (obésité en forme de poire) et celle d’une circonférence maximale (obésité en forme de pomme), le chargement lombaire a subi une augmentation similaire à celle d’ajouter 20 kg de poids supplémentaire, ainsi qu’un risque de fracture de fatigue vertébrale sept fois plus élevé. En somme, l’obésité et les formes d’obésité ont une influence considérable sur la biomécanique de la colonne vertébrale, et donc, devraient être prises en compte lors d’une modélisation spécifique aux sujets. En plus de servir à l’évaluation de la force maximale du tronc et à la normalisation de l’électromyographie (EMG), les contractions musculaires volontaires maximales (CVM) peuvent être utilisées pour calibrer et valider les modèles MS. La performance du modèle MS personnalisé a été étudiée en comparant les activités musculaires estimées avec les EMG durant diverses tâches de CVM. Le stress musculaire maximal des muscles du tronc a également été calculé pour chaque sujet. Ce dernier a varié considérablement entre différents sujets et groupes musculaires. Le muscle grand droit et le muscle oblique externe de l’abdomen ont eu, respectivement, le plus petite (0,40 ±0,22 MPa) et la plus grande valeur (0,99 ±0,29 MPa) de stress musculaire maximal parmi les groupes de muscles. Pour les CVM en flexion et en extension, les activités musculaires estimées correspondaient adéquatement avec les EMG. Cependant, cette correspondance était faible pour les CVM en flexion latérale et rotations axiales. Le chargement lombaire des femmes était en général plus faible que celui des hommes. Les charges vertébrales maximales lors des CVM ont été obtenues lors des efforts en extension (compression d’environ 6000 N à L5-S1) tandis que les plus faibles ont été enregistrées en flexion avant (compression d’environ 3000 N à L5-S1) ; les participants ont subi des chargements lombaires assez importants durant des CVM en flexion latérale et rotation axiale. (5500 N en compression et 1700 N en cisaillement). La prédiction exacte du stress musculaire maximal et l’évaluation complète de la performance d’un modèle MS nécessitent la prise en compte des tâches de CVM dans toutes les directions et l’application des moments dans les plans principaux et couplés du modèle. Une simulation adéquate des ligaments passifs de la colonne vertébrale, l’une des composantes majeures d’un modèle MS du tronc, est d’une importance capitale. Les modèles détaillés d’EF peuvent capturer avec précision les réactions non linéaires et temporelles de la colonne vertébrale. Toutefois, en raison des coûts de calcul importants des modèles détaillés d’éléments finis, des modèles simplifiés (c.-à-d. à partir de joints sphériques et de poutres ayant des propriétés passives linéaires ou non linéaires) sont couramment utilisés dans les principaux modèles MS. Par conséquent, la précision et la validité de l’utilisation de modèles simplifiés et de leur positionnement antéro-postérieur dans l’estimation de la cinématique de la colonne vertébrale ligamentaire, des forces musculaires et des charges spinales ont été étudiées. Contrairement aux poutres, les articulations de type sphérique négligeaient les degrés de liberté en translation et n’ont pas réussi à prédire la cinématique de la colonne lombaire avec précision, surtout dans la direction craniocaudale. Les poutres et les joints sphériques non linéaires ont prédit de manière satisfaisante la PID en comparaison avec les mesures in vivo d’activités physiques variées. En revanche, l’utilisation des poutres ou des joints sphériques aux propriétés linéaires passives n’a donné que des résultats valides que pour des angles de flexion d’amplitude faible ou modérée (<40 o). En négligeant les propriétés passives des articulations (joints sphériques sans frottement), on a considérablement augmenté le chargement lombaire en compression et en cisaillement, de 32 % et 63 % respectivement. Le déplacement postérieur (de 8 mm) d’une articulation simplifiée a augmenté les charges lombaires (en compression et en cisaillement) d’environ 20 %, tandis qu’un déplacement vers l’avant (2 mm) a diminué de 10 % la compression et de 18 % la force de cisaillement. De plus, un déplacement postérieur du modèle simplifié a réduit la force passive des muscles agonistes, et ce, tout en augmentant leurs composantes actives. Les modèles d’articulation simplifiés avec des propriétés passives non linéaires devraient se situer entre -2 à +4 mm (+ : postérieur) du centre du disque pour des prédictions justes des forces sur la colonne vertébrale et des forces musculaires actives/passives. L’obtention de résultats valides à l’aide des modèles MS exige des moyens considérables comme une collecte complète de données (ex. : cinématiques, EMG), un laboratoire bien équipé et une formation suffisante. Par ailleurs, des équations de régression faciles à utiliser ont précédemment été mises au point pour estimer le chargement lombaire. Cependant, ces équations ne tiennent pas compte de l’anthropométrie des participants (ex. : poids et taille) fondée sur une approche physiologique, et elles négligent souvent l’asymétrie de la tâche. Dans cette partie de l’étude, des équations de régression spécifiques aux sujets ont été développées pour prédire le chargement lombaire (à L4-L5 et L5-S1) en utilisant un modèle d’EF guidé par la cinématique. L’exactitude de ce modèle et des équations de régression ont été évaluées en comparant les activités musculaires estimées par le modèle avec ceux obtenus au moyen de l’EMG et des PDI calculées avec ceux de la littérature existante. Les valeurs estimées de la PDI spécifiques aux sujets présentaient des corrélations élevées avec les résultats d’études in vivo lors de tâches symétriques et asymétriques (R2=0.82). Dans le cas des tâches symétriques, les estimations d’activité musculaire étaient raisonnablement comparables avec les résultats d’EMG. Toutefois, dans les tâches asymétriques, les estimations étaient moyennement (muscles du dos) ou faiblement (muscles de l’abdomen) en accord avec les EMG. En somme, les équations de régression développées peuvent être utilisées dans le but d’estimer le chargement lombaire dans des tâches de levage symétriques et asymétriques. Ces équations personnalisées pourraient servir à l’évaluation des risques de blessure au dos lors d’activités de manutention. En résumé, un modèle MS d’EF guidé par la cinématique, mis à jour par une architecture musculaire améliorée, un disque déformable additionnel (T11-T12) et un nouvel algorithme de mise à l’échelle a été utilisé pour examiner la biomécanique personnalisée de la colonne vertébrale. En personnalisant tous les paramètres du modèle MS (les bras de levier des muscles, les aires transverses musculaires, le chargement gravitationnel, la géométrie de la colonne, les propriétés passives et la cinématique de la colonne vertébrale), et en effectuant une analyse de sensibilité sur les données d’entrées du modèle (sexe, âge, taille et poids), il a été démontré que le poids d’une personne influence nettement les forces de chargement subies par la colonne vertébrale, alors que l’influence des autres facteurs était plutôt faible. Deux formes distinctes d’obésité ont été reconstituées à partir d’un ensemble de données anthropométriques disponibles dans la littérature. Les résultats ont établi que l’obésité et les formes d’obésité (formes en pomme ou en poire) affectent, toutes les deux, les forces sur la colonne vertébrale ainsi que le risque de fracture de fatigue vertébrale. Lors de tâches de CVM (en extension, en flexion, en flexion latérale et en rotation axiale), les grandeurs du stress musculaire variaient substantiellement parmi les sujets et différents groupes musculaires. Dans le cas des CVM en flexion et en extension, les valeurs prédites d’activité musculaire par le modèle personnalisé étaient près des EMG enregistrés, alors que les prédictions concernant les CVM en rotation axiale et en flexion latérale n’avaient pas la même exactitude. Des poutres et des joints sphériques ayant des propriétés non linéaires (d’une position variant de -2 à +4 mm [+ : postérieur] du centre des disques) prédisait avec exactitudes les cinématiques de la colonne vertébrale, le chargement lombaire et les activités musculaires. Par contre, les modèles articulaires qui avaient des propriétés linéaires ou qui n’avaient pas de degrés de liberté en translation détérioraient l’exactitude des prédictions. Enfin, des équations de régression faciles à utiliser ont été mises au point dans le but de prédire les forces de compression et de cisaillement subies par la colonne vertébrale (aux niveaux L4-L5 et L5-S1) lors de tâches symétriques et asymétriques. Les équations personnalisées ont correctement estimé les valeurs de PID en comparant les valeurs calculées avec les résultats mesurés in vivo retrouvés dans la littérature. Lors de plusieurs tâches symétriques et asymétriques, les valeurs estimées des activités musculaires étaient moyennement (pour les muscles du dos) à faiblement (pour les muscles abdominaux) comparables avec les EMG enregistrés des participants. Par conséquent, les équations de régression proposées peuvent être utilisées pour évaluer les risques de blessures lors d’activités de manutention. ---------- Abstract Musculoskeletal disorders are one the most frequent and costly disabilities in the world. Back problems are the second most common chronic condition in Canada. Four out of five adults experience low back pain in their lifetime. As one of the potential risk factors of back pain, excessive loads on the spine can initiate and promote disc degeneration and pain, so accurate estimation of spinal loads are helpful in designing effective prevention, evaluation, and treatment programs. There is no direct method to measure spinal loads, and all indirect methods (intradiscal pressure – IDP – and instrumented vertebral replacement) are invasive and scarce. Alternatively, musculoskeletal (MS) models with physiological scaling algorithms economically and accurately estimate muscle forces, spinal loads and spinal stability margin by taking into account individual differences. An existing kinematics driven (KD) finite element (FE) MS musculoskeletal model of the trunk has been upgraded in this work by refining the muscle architecture, by adding a new deformable disc level (T11-T12), and by introducing a novel scaling algorithm to explore likely effects of sex, age, body weight (BW) and body height (BH) on spine biomechanics and spinal loads. By using imaging datasets and biomechanical principles, the scaling algorithm adjusted the muscle architecture (muscle moment arms and cross-sectional areas), spine geometry, passive properties of the ligamentous spine and gravity loads based on subject’s sex, age, BH and BW. To perform a sensitivity analysis in a full-factorial design, model inputs (i.e., sex, age, BH and BW) were altered within physiological ranges (sex: female and male; age: 35-60 years; BH: 150-190 cm; BW:50-120 kg) while the personalized KD-FE model of the trunk was driven with sex- and age-specific kinematics during different forward flexion tasks with and without a hand-load. Main effect plots and the analysis of variance were employed to investigate effects of inputs on spinal loads. As the most influential factor, BW contributed 99% to compression and 96% to shear spinal loads while effects of BH, sex and age (<5%) remained much smaller. At identical BH, BW and waist circumference, females had slightly greater spinal loads (5% in compression; 9% in shear). The prevalence of obesity (body mass index; BMI>30 kg/m2) is rising in both developed and developing countries, and has reached “global epidemic” proportions. Although obesity has been associated with various back problems (e.g., disc degeneration, vertebral fracture and back pain),the likely role of biomechanics in obesity-related back problems is still unknown. At identical BMI and BW, fat distribution varies substantially from one obese individual to another. Different obesity types have qualitatively been described as apple- and pear-shaped (or android and gynoid). Therefore, effects of obesity and obesity shapes on spinal loads and vertebral compression fracture were investigated by using the upgraded subject-specific model. At identical BW and BH, three distinct obesity shapes (corresponding to minimum, average and maximum waist circumferences) were reconstructed by using available anthropometric measurements of 5852 obese individuals and principal component analysis. Obesity markedly affected spinal loads; L4-L5 compression increased by 16% (2820 N vs 3350 N) in forward flexion without a hand-load when BMI increased from 31 kg/m2 to 39 kg/m2. Greater waist circumferences (apple-shaped obesity) in comparison with smaller waist circumferences (pear-shaped obesity) increased spinal loads to the extent of gaining 20 kg additional BW and the risk of vertebral fatigue fracture by up to ~7 times. Therefore, both obesity and obesity shapes substantially affected spine biomechanics and should be taken into account in subject-specific modeling of the spine. Apart from serving in the trunk strength quantification and electromyography (EMG) normalization, maximum voluntary exertions (MVEs) can be used to calibrate and validate MS models. The performance of the current upgraded subject-specific MS model was investigated by comparing estimated muscle activities with reported EMGs during various MVE tasks. Maximum muscle stresses of trunk muscles were also calculated for each subject individually. Estimated maximum muscle stresses varied substantially among subjects and different muscle groups; rectus abdominis and external oblique had the smallest (0.40±0.22 MPa) and largest (0.99±0.29 MPa) maximum muscle stresses, respectively. In sagittal symmetric MVEs (extension and flexion), estimated muscle activities were found in satisfactory agreement with measured reported EMGs while in lateral and axial MVEs, the agreement was rather weak. Females in general had smaller spinal loads. Peak spinal loads were obtained in extension MVE (~6000 N compression at L5-S1) while flexion MVE yielded the smallest spinal loads (~3000 N compression at L5-S1); subjects experienced rather large spinal loads (5500 N in compression and 1700 N in shear) under lateral and axial MVEs. Accurate prediction of maximum muscle stresses and comprehensive evaluation of the performance of a MS model require the consideration of MVE tasks in all directions with the application of both primary and coupled moments to the model. Accurate simulation of the passive ligamentous spine, as one of the integral components of a trunk MS model, is of great importance. Detailed FE models can accurately capture nonlinear and time-dependent responses of the spine; however, due to the significant computational costs of detailed FE models, simplified models (i.e., spherical joints/beams with linear/nonlinear passive properties) are commonly used in the trunk MS models. Therefore, the accuracy and validity of using simplified models and their anterior-posterior positioning in estimating kinematics of the ligamentous spine, muscle forces and spinal loads were investigated. Unlike beam elements, spherical joints overlooked translational degrees of freedom and failed to accurately predict kinematics of the lumbar spine particularly in the cranial-caudal direction. Nonlinear shear deformable beams and spherical joints were found to satisfactorily predict IDPs in comparison with in vivo measurements during various activities. In contrast, using beams or spherical joints with linear passive properties yielded valid results only in small to moderate flexion angles (<40o). Neglecting passive properties of joints (frictionless spherical joints) substantially increased compression and shear spinal loads by 32% and 63%. Shifting a simplified joint posteriorly (by 8 mm) increased spinal loads (compression and shear) by ~20% while an anterior shift (by 2 mm) decreased spinal loads by 10% and 18% in compression and shear directions. Moving simplified joint models posteriorly reduced also passive muscle forces of agonist muscles while increasing their active components. Simplified joint models with nonlinear passive properties should be located in -2 to +4 mm (+: posterior) range from the disc center for accurate predictions of spinal loads and active/passive muscle forces. Obtaining reasonably accurate results by MS models requires comprehensive data collection (e.g., kinematics, EMG), equipped laboratory, and sufficient training. Alternatively, easy to use regression equations have previously been developed to estimate spinal loads, but they do not take account of personalized anthropometric factors (e.g., BW and BH) based on a physiological approach and often overlook task asymmetry. Thus, in this work, subjects-specific regression equations were developed to predict spinal loads at lower spinal levels (L4-L5 and L5-S1) by using the upgraded KD-FE model, and the Accuracy of the model and regression equations were subseq

IMAGE ANALYSIS FOR SPINE SURGERY: DATA-DRIVEN DETECTION OF SPINE INSTRUMENTATION & AUTOMATIC ANALYSIS OF GLOBAL SPINAL ALIGNMENT

Spine surgery is a therapeutic modality for treatment of spine disorders, including spinal deformity, degeneration, and trauma. Such procedures benefit from accurate localization of surgical targets, precise delivery of instrumentation, and reliable validation of surgical objectives – for example, confirming that the surgical implants are delivered as planned and desired changes to the global spinal alignment (GSA) are achieved. Recent advances in surgical navigation have helped to improve the accuracy and precision of spine surgery, including intraoperative imaging integrated with real-time tracking and surgical robotics. This thesis aims to develop two methods for improved image-guided surgery using image analytic techniques. The first provides a means for automatic detection of pedicle screws in intraoperative radiographs – for example, to streamline intraoperative assessment of implant placement. The algorithm achieves a precision and recall of 0.89 and 0.91, respectively, with localization accuracy within ~10 mm. The second develops two algorithms for automatic assessment of GSA in computed tomography (CT) or cone-beam CT (CBCT) images, providing a means to quantify changes in spinal curvature and reduce the variability in GSA measurement associated with manual methods. The algorithms demonstrate GSA estimates with 93.8% of measurements within a 95% confidence interval of manually defined truth. Such methods support the goals of safe, effective spine surgery and provide a means for more quantitative intraoperative quality assurance. In turn, the ability to quantitatively assess instrument placement and changes in GSA could represent important elements of retrospective analysis of large image datasets, improved clinical decision support, and improved patient outcomes

Combined numerical and morphological study of the lumbar spine: parametric finite element model and evaluation of dynamic implants

Low back pain is a major cause of disability and requires the development of new devices to treat pathologies and improve prognosis following surgery. Finite Element (FE) Methods represent an appealing solution to provide mechanical evaluations of new devices speeding up the design process, as well as evaluating several anatomical scenarios. The aim of this thesis was to develop an accurate FE of the lumbar spine and the evaluation of the variability introduced by morphological and material parameters. The generation of the geometrical model were implemented in a toolbox, the LMG (Lumbar Model Generator), with dimensions based on correlation analyses or subject-specific measurements. It allows the automatic preparation of the FE model, performing the mesh generation and evaluation, assigning material properties, boundary conditions and analysing the results. The FE model of a functional unit (L1-L2) was evaluated and the FE results were in agreement with studies available in literature. Sensitivity analyses on the material properties and morphological parameters were performed and the most influential parameters identified. Moreover, the mechanical behaviour of two devices, the BDyn (S14 Implants (Pessac, France)) and the GsDyn (a device for the paediatric scoliosis developed as part of the Spinal Implant Design project) were evaluated

Development of an Intervertebral Disc Mechanobiological System

Intervertebral disc degeneration is a leading cause of low back pain, a significant socioeconomic burden with a broad array of costly treatment options. Motion-based therapy has shown modest efficacy in treating LBP. Basic science research has begun to identify thresholds of beneficial and detrimental mechanical loading of the intervertebral disc. Ex-vivo mechanobiological systems are important experimental models for determining the effect of loading parameters on disc biology and matrix homeostasis. A novel experimental platform has been developed to facilitate in-situ loading of a rabbit functional spinal unit (FSU) with outcome measures relevant to disc matrix homeostasis and cell behavior. First, the system was designed for multi-axis motion outside of an incubator and validated for rigid fixation and stable, physiologic environmental conditions that maintained adequate cell viability. Following system development and validation, experimental testing on rabbit FSUs proceeded with cyclic compression and four-hour constant compression compared. Disc tissue was analyzed for cell viability using a colorimetric absorbance assay or relative gene expression. Conditioned media was assayed for matrix metalloproteinase activity, type-II collagen degradation fragments, prostaglandins, and an aggrecan epitope implicated in aggrecan synthesis. Cell viability remains high (>90%) regardless of loading. Relative gene expression shows small increases in anabolism and larger, variable increases in catabolic and inflammatory markers. These trends are more reliable in AF than NP. Interestingly, matrix metalloproteinase activity trends toward a decrease in media in loaded specimen culture. Although type-II collagen fragment concentrations do not correlate with loading, the aggrecan synthesis marker concentrations do. Results indicate increased catabolism and aggrecan turnover in response to loading, though the net effect on matrix homeostasis at later time points is unclear. Future work will explore applying other loading patterns, rotational loading, and coupling local inflammatory stimuli with loading. This novel experimental platform will explore the effect of physiologic motion simulations on disc homeostasis, helping to improve motion-based therapies