Pedicle screw breakage and loosening remain as clinical complications of short segment instrumentation procedures for spinal stabilization. This study has directly visualized and measured elastic, plastic and total vertebral pedicle trabecular bone full-field strains in the regions immediately surrounding the pedicle screw during pedicle screw insertion by utilizing functional microCT imaging and digital volume correlation. Human, porcine and polyurethane foam samples were analyzed and compared. Analysis showed that when osteoporotic human, normal human and porcine pedicle trabecular bone samples were compared, osteoporotic samples showed higher peak plastic strains and greater variability of these strains from their means. This suggests that osteoporotic human samples are non-uniformly elastic and plastic, while normal human and porcine samples are more uniformly elastic and plastic throughout the trabecular structure. PU-foams are not appropriate as models for pedicle trabecular bone in the in vivo environment since strain results showed dissimilar plastic and elastic strain magnitudes than human and porcine pedicle trabecular bone. This study may aid in the development of performance criteria for new PU-foams and improved pedicle screw designs. / Graduation date: 2004

Introduction: The purpose of this study was to determine the effect of spinal manipulation therapy (SMT) duration and amplitude on spinal stiffness. Methods: Simulated SMTs were performed at the L6 spinous process in twenty-two felines. SMTs ranging from 25 to 250 ms duration were performed. Groups 1 and 2 received maximal displacements of 1.0mm to 3.0mm. Groups 3 and 4 received maximal loads of 25% to 85% body weight. Local stiffness was quantified by applying an indentation to the vertebra. Results: Repeated SMTs caused minimal changes in stiffness. The interaction effect of duration X displacement in Groups 1 and 2, and the effect of duration in Group 3 were significant. Conclusion: Repeated SMTs cause minimal changes in stiffness thought to be due to a viscoelastic response. Some of the changes following select SMT conditions may be the result of an interaction effect between SMT duration and amplitude. No specific threshold condition was identified as causing a greater stiffness change. / Physical Therapy

Injuries to the neck, or cervical region, are very importantsince there is a potential risk of damage to the spinal cord.Any neck injury can have devastating if not life threateningconsequences. High-speed transportation as well as leisure-timeadventures have increased the number of serious neck injuriesand made us increasingly aware of its consequences.Surveillance systems and epidemiological studies are importantprerequisites in defining the scope of the problem. Thedevelopment of mechanical and clinical tools is important forprimary prevention of neck injuries. Thus, the main objectives of the present doctoral thesisare:- To illustrate the dimension of cervical injuries inSweden,- To develop a Finite Element (FE) model of the uppercervical spine, and- To study spinal stability for cervical injuries. The incidence studies were undertaken with data from theinjury surveillance program at the Swedish National Board ofHealth and Welfare. All in-patient data from Swedish hospitals,ranging over thirteen years from 1987 to 1999, were analyzed.During this period 14,310 nonfatal and 782 fatal cervicalinjuries occurred. The lower cervical spine is the mostfrequent location for spinal trauma, although, this changeswith age so that the upper cervical spine is the most frequentlocation for the population over 65 years of age. The incidencefor cervical fractures for the Swedish population decreased forall age groups, except for those older than 65 years of age.The male population, in all age groups, has a higher incidencefor neck fractures than females. Transportation relatedcervical fractures have dropped since 1991, leaving fallaccidents as the sole largest cause of cervical trauma. An anatomically detailed FE model of the human uppercervical spine was developed. The model was validated to ensurerealistic motions of the joints, with significant correlationfor flexion, extension, lateral bending, axial rotation, andtension. It was shown that an FE-model could simulate thecomplex anatomy and mechanism of the upper cervical spine withgood correlation to experimental data. Three studies wereconducted with the FE model. Firstly, the model of the uppercervical spine was combined with an FE model of the lowercervical spine and a head model. The complete model was used toinvestigate a new car roof structure. Secondly, the FE modelwas used for a parameter study of the ligament materialcharacteristics. The kinematics of the upper cervical spine iscontrolled by the ligamentous structures. The ligaments have tomaintain spinal stability while enabling for large rotations ofthe joints. Thirdly, the FE-model was used to study spinalinjuries and their effect on cervical spinal stability inflexion, extension, and lateral bending. To do this, the intactupper cervical spine FE model was modified to implementruptures of the various spinal ligaments. Transection of theposterior atlantooccipital membrane, the ligametum flavum andthe capsular ligament had the most impact on flexion, while theanterior longitudinal ligament and the apical ligamentinfluenced extension. It is concluded that neck injuries in Sweden is a problemthat needs to be address with new preventive strategies. It isespecially important that results from the research on fallaccidents among the elderly are implemented in preventiveprograms. Secondly, it is concluded that an FE model of thecervical region is a powerful tool for development andevaluation of preventive systems. Such models will be importantin defining preventive strategies for the future. Lastly, it isconcluded that the FE model of the cervical spine can increasethe biomechanical understanding of the spine and contribute inanalyses of spinal stability.

Qualitative studies investigating the sexual activity of people with low back pain found a substantial reduction in the frequency of coitus and have shown that pain during coitus due to mechanical factors (i.e., movements and postures) are the primary reason for this decreased frequency. However, a biomechanical analysis of coitus has never been done. The main objective of this study was to describe male and female lumbar spine and hip motion and muscle activation patterns during coitus and compare these motions and muscle activity across five common coital positions. Specifically, lumbar spine and hip motion in the sagittal plane and electromyography signal amplitudes of selected trunk, hip, and thigh muscles were described and compared. A secondary objective was to determine if simulated coitus could be used in place of real coitus for future coitus biomechanics research. Ten healthy males (29.3 ± 6.9 years, 176.5 ± 8.6 centimeters, 84.9 ± 14.5 kilograms) and ten healthy females (29.8 ± 8.0 years, 164.9 ± 3.0 centimeters, 64.2 ± 7.2 kilograms) were included for analysis in this study. These couples had approximately 4.7 ± 3.9 years of sexual experience with each other. This study was a repeated-measures design, where the independent variables, coital position and condition, were varied five (i.e., QUADRUPED1, QUADRUPED2, MISSIONARY1, MISSIONARY2, and SIDELYING) and two (i.e., real and simulated) times, respectively. Recruited participants engaged in coitus in five pre-selected positions (presented in random order) for 20 seconds per position first in a simulated condition, and again in a real condition. Three-dimensional (3D) lumbar spine and hip kinematic data were continuously collected for the duration of each trial by optoelectronic and electromagnetic motion capture systems. Electromyography (EMG) signals were also continuously collected for the duration of each trial. The kinematic data and EMG signals were collected simultaneously for both participants. Five sexual positions were chosen for this study based on the findings of previous literature and a biomechanical rationale. QUADRUPED – rear-entry, female quadruped, male kneeling behind – had two variations; in QUADRUPED1 the female was supporting her upper body with her elbows and in QUADRUPED2 the female was supporting her upper body with her hands. MISSIONARY – front-entry, female supine, male prone on top – also had two variations; in MISSIONARY1 the female was not flexing her hips or knees and the male was supporting his upper body with his hands, but in MISSIONARY2, the female was flexing her hips and knees and the male was supporting his upper body with his elbows. SIDELYING – rear-entry, female side-lying on her left side, male side-lying behind – did not have any variations. To determine if each coital position had distinct spine and hip kinematic and muscle activation profiles, separate univariate general linear models (GLM) (factor: coital position = five levels, α=0.05) followed by Tukey’s honestly significant difference (HSD) post hoc analysis were used. To determine if simulated coitus was representative of real coitus across all spine and hip kinematic and muscle activation outcome variables, paired-sample t-tests (α=0.05) were performed on all outcome variables for the real condition and their respective simulated values. In general, the coital positions studied showed that, for both males and females, coitus is mainly a flexion-extension movement of the lumbar spine and hips. Males used a greater range of their spine and hip motion in comparison to females. As expected, differences were found between coital positions for males and females and simulated coitus was not representative of real coitus, in particular the spine and hip kinematic profiles. The results found in this biomechanical analysis of common coital positions may be useful in a clinical context. It is recommended that during the acute stage of a low back injury resulting in flexion-, extension-, or motion-intolerance that coitus be avoided. If the LBP is a more chronic issue, particular common coital positions should be avoided. For the flexion-intolerant male patient, avoid SIDELYING and MISSIONARY2 as they were shown to require the most flexion. Both variations of QUADRUPED are the more spine-sparing of coital positions followed by, MISSIONARY1. Coaching the male patient on proper hip-hinging technique while thrusting – an easy technique to incorporate in both variations of QUADRUPED – will likely decrease spine movement and increase the spine-sparing quality of QUADRUPED. For the flexion-intolerant female patient, avoid both variations of MISSIONARY, especially with hip and knee flexion, as they were shown to elicit the most spine flexion. QUADRUPED2 and SIDELYING are the more spine-sparing coital positions, followed by QUADRUPED1. Subtle posture changes for a coital position should not be considered lightly; seemingly subtle differences in posture can change the spine kinematic profile significantly, resulting in a coital position that was considered spine-sparing becoming a position that should be avoided. Thus, spine-sparing coitus appears to be possible for the flexion-, extension-, and motion-intolerant patient. Health care practitioners may recommend appropriate coital positions and coach coital movement patterns, such as speed control and hip-hinging. With respect to future research in the area of sex biomechanics, using simulated coitus in replace of real coitus is not justifiable according to the data of this study. However, including a simulated condition did prove beneficial for increasing the comfort level of the couples and allowing time to practice the experimental protocol. Future directions may address female-centric positions (e.g., ‘reverse missionary’ with male supine and female seated on top), and back-pained patients with and without an intervention (e.g., movement pattern coaching or aides, such as a lumbar support).

Spinal fusion is the process by which two or more vertebral levels are joined into a single, solid bone mass in order to restore stability to a spine that has been compromised by trauma, degeneracy or metastasis. Fusion is accomplished through internal hardware positioned anteriorly, posteriorly, or with combined anterior-posterior instrumentation. Since the 1990s the frequency of spinal fusions has been rising, and this trend is expected to continue. Posterior approaches to fusion are most common, primarily consisting of pedicle screw and rod constructs. Despite the high success rate for bony fusion with pedicle screw fixation, this technique poses risks to delicate neurological and vascular structures and is heavily dependent on surgeon expertise. In this thesis, a novel and less invasive posterior spinal hardware system was designed and evaluated, which solely utilizes the spinous processes and laminae of the vertebrae as the point of the bone-implant interface. Morphological and biomechanical studies of the posterior spine were undertaken in order to define important geometric information to guide the design of the proposed hardware and to determine the strength of the posterior elements throughout the spine to assess their ability to support posterior element plating. Utilizing this information, a modular dual plate fusion system was developed for single or multi-level fusion. The system accounts for the native curvature of the spine and can be extended to additional vertebral levels at the time of insertion, or at any later time. Prototypes were manufactured in titanium. Positive biomechanical results were found when the proposed hardware was used as a supplement to anterior instrumentation. Additionally, work focused on 2D-3D registration of neutral CT data with flexion extension x-ray images, was undertaken and shown to yield improved accuracy of important vertebral metrics utilized for clinical assessment of spine stability. This technique is applicable to the evaluation of pathology and kinematics at any level of the spine, including post-fusion adjacent level degeneration. The culmination of this work has resulted in a novel, patent pending posterior element spinal fusion system.

Background: No spine-specific educational tool has been developed using input from all relevant stakeholders, including patients. Purpose: The objective of this study was to determine the information needs of lumbar microdiscectomy patients. Methods: Qualitative methods with thematic analysis was used. Focus groups were conducted with: 1) preoperative microdiscectomy patients; 2) postoperative microdiscectomy patients; 3) spine surgeons; 4) spine fellows; 5) orthopaedic surgery residents; 6) anesthesiologists; 7) surgeons’ administrative assistants; and, 8) preoperative assessment team. Results: Major information needs were related to: anesthesia, surgical procedure details and postoperative course. Patients desire information on postoperative course much more than surgeons perceive. Desired attributes of information tools as well as patient factors that influence the extent of information shared by surgeons were determined. Information resources should be given to patients as soon as they are deemed surgical candidates. Conclusions: Microdiscectomy patients desire more information than currently provided to them – in particular postoperative-related information.

Background: No spine-specific educational tool has been developed using input from all relevant stakeholders, including patients. Purpose: The objective of this study was to determine the information needs of lumbar microdiscectomy patients. Methods: Qualitative methods with thematic analysis was used. Focus groups were conducted with: 1) preoperative microdiscectomy patients; 2) postoperative microdiscectomy patients; 3) spine surgeons; 4) spine fellows; 5) orthopaedic surgery residents; 6) anesthesiologists; 7) surgeons’ administrative assistants; and, 8) preoperative assessment team. Results: Major information needs were related to: anesthesia, surgical procedure details and postoperative course. Patients desire information on postoperative course much more than surgeons perceive. Desired attributes of information tools as well as patient factors that influence the extent of information shared by surgeons were determined. Information resources should be given to patients as soon as they are deemed surgical candidates. Conclusions: Microdiscectomy patients desire more information than currently provided to them – in particular postoperative-related information.

Spinal fusion is the process by which two or more vertebral levels are joined into a single, solid bone mass in order to restore stability to a spine that has been compromised by trauma, degeneracy or metastasis. Fusion is accomplished through internal hardware positioned anteriorly, posteriorly, or with combined anterior-posterior instrumentation. Since the 1990s the frequency of spinal fusions has been rising, and this trend is expected to continue. Posterior approaches to fusion are most common, primarily consisting of pedicle screw and rod constructs. Despite the high success rate for bony fusion with pedicle screw fixation, this technique poses risks to delicate neurological and vascular structures and is heavily dependent on surgeon expertise. In this thesis, a novel and less invasive posterior spinal hardware system was designed and evaluated, which solely utilizes the spinous processes and laminae of the vertebrae as the point of the bone-implant interface. Morphological and biomechanical studies of the posterior spine were undertaken in order to define important geometric information to guide the design of the proposed hardware and to determine the strength of the posterior elements throughout the spine to assess their ability to support posterior element plating. Utilizing this information, a modular dual plate fusion system was developed for single or multi-level fusion. The system accounts for the native curvature of the spine and can be extended to additional vertebral levels at the time of insertion, or at any later time. Prototypes were manufactured in titanium. Positive biomechanical results were found when the proposed hardware was used as a supplement to anterior instrumentation. Additionally, work focused on 2D-3D registration of neutral CT data with flexion extension x-ray images, was undertaken and shown to yield improved accuracy of important vertebral metrics utilized for clinical assessment of spine stability. This technique is applicable to the evaluation of pathology and kinematics at any level of the spine, including post-fusion adjacent level degeneration. The culmination of this work has resulted in a novel, patent pending posterior element spinal fusion system.

Motor vehicle accidents continue to be a leading cause of cervical spine injury despite a conscientious effort to improve occupant safety. Accurately predicting occupant head and neck response in numerical crash simulations is an essential part of the process for developing better safety solutions. <br /><br /> A biofidelic model of the human cervical spine was developed with a focus on accurate representation of the cervical spine at the local tissue level. These tissues were assembled to create a single segment model that was representative of <em>in vitro</em> spine in quasi-static loading. Finally, the single segment models were assembled to create a full cervical spine model that was simulated in dynamic loading and compared to human volunteer response. <br /><br /> Models of each segment were constructed from the basic building blocks of the cervical spine: the intervertebral disc, the vertebrae, the ligaments, and the facet joints. Each model was simulated in all modes of loading and at different levels of load. The results of the study indicate that the cervical spine segments performed very well in flexion, compression, and tension. Segment response to lateral bending and axial rotation was also good, while response in extension often proved too compliant compared to the experimental data. Furthermore, the single segment models did not fully agree with the experimental shear response, again being more compliant. <br /><br/> The full cervical spine model was assembled from the single segment models incorporating neck musculature. The model was simulated dynamically using a 15 G frontal impact test. Active muscles were used to simulate the response of the human volunteers used in the study. The response of the model was in reasonable agreement with the experimental data, and compared better than current finite element cervical spine models. Higher frequency oscillation caused most of the disagreement between the model and the experimental data, which was attributed to a lack of appropriate dynamic material properties of the soft tissues of the spine. In addition, a study into the active properties of muscle indicated that muscle response has a significant influence on the response of the head. <br /><br /> A number of recommendations were proposed that would improve the biofidelity of the model. Furthermore, it was recommended that the future goal of this model would be to implement injury-predicting capabilities through the development of advance material models.

Abstract Background: The process that involves the migration of the nucleus pulposus from the innermost annular layers and culminates with the final extrusion of the nucleus has been limited to a few studies. This investigation was directed towards a better understanding of the herniation process. The architecture of the annulus fibrosus and the mechanism of progressive disc herniation were analyzed, using a controlled porcine model. Microscopic and histochemical techniques were employed. <br /><br /> Methodology: Two studies were performed. In the first stage, the macroscopic and microscopic structures of twelve cervical intervertebral discs were compared with young human disc data from studies reported in the literature. Important structural features were studied such as annulus fibrosus thickness, number of lamellae, lamellae thickness, orientation of the lamellae fibers and blood supply. In the second study, sixteen fresh-frozen functional spine units were submitted to repetitive flexion?extension motions combined with a low compressive load in a servo-hydraulic dynamic testing system. Discograms, dissections and histochemical techniques were applied to characterize the cumulative damage. The experiment produced eight complete herniations, four partial herniations and four specimens without any microscopic detectable annular damage. <br /><br /> Results and Discussion: The structure of the cervical porcine disc resembles the lumbar human disc. Some differences are evident. The size of the annulus is smaller, the thickness of the lamellae is narrower and the number of layers is fewer in the pig. It is hypothesized that the flexion-extension motion combined with a low-level load produced an increased hydraulic pressure in the inner wall of the posterior annulus. This pressure and repetitive motion first produced a small cleft, spreading the collagen bundles inside the first layer. The nuclear material was "pumped" through the small cleft to the first layer filling the layer creating a fluid-filled pocket between the collagen fibers. Once the "pocket" acquired enough pressure a new cleft was produced in the weakest part of the layer allowing the nuclear material to create a new "pocket" in the second layer. This was the first stage of damage and disc herniation production. This mechanism was repeated until the nucleus traveled along the annulus reaching the posterior longitudinal ligament. At this point a complete extrusion herniation was produced. <br /><br /> Conclusion: The porcine model appears to be suitable as a model to understand the mechanism of disc herniation when the spine is subjected to flexion-extension motions combined with a low-level load. The first cumulative injury appears to be a cleft between the lamellae bundles produced by the nuclear hydraulic pressure. A cumulative load/cumulative injury model approach was used to create the damage that was quantified in the study.