Utilization of Finite Element Analysis Techniques for Adolescent Idiopathic Scoliosis Surgical Planning

Adolescent Idiopathic Scoliosis, a three-dimensional deformity of the thoracolumbar spine, affects approximately 1-3% of patients ages 10-18. Surgical correction and treatment of the spinal column is a costly and high-risk task that is consistently complicated by factors such as patient-specific spinal deformities, curve flexibility, and surgeon experience. The following dissertation utilizes finite element analysis to develop a cost-effective, building-block approach by which surgical procedures and kinematic evaluations may be investigated. All studies conducted are based off a volumetric, thoracolumbar finite element (FE) model developed from computer-aided design (CAD) anatomy whose components are kinematically validated with in-vitro data. Spinal ligament stiffness properties derived from the literature are compared for kinematic assessment of a thoracic functional spinal unit (FSU) and benchmarked with available in-vitro kinematic data. Once ligament stiffness properties were selected, load sharing among soft tissues (e.g., ligaments and intervertebral disc) within the same FSU is then assessed during individual steps of a posterior correction procedure commonly used on scoliosis patients. Finally, the entire thoracolumbar spine is utilized to mechanically induce a mild scoliosis profile through an iterative preload and growth procedure described by the Hueter-Volkmann law. The mild scoliosis model is then kinematically compared with an asymptomatic counterpart. The thoracic deformation exhibited in the mild scoliosis model compared well with available CT datasets. Key findings of the studies confirm the importance of appropriately assigning spinal ligament properties with traditional toe and linear stiffness regimes to properly characterize thoracic spine FE models. Stiffness properties assigned within spinal FE models may also alter how intact ligaments and intervertebral discs respond to external loads during posterior correction procedures involving serial ligament removal, and thus can affect any desired post-surgical outcomes. Lastly, the thoracolumbar spine containing mild scoliosis experiences up to a 37% reduction in global range of motion compared to an asymptomatic spine, while also exhibiting larger decreases in segmental axial rotations at apical deformity levels. Future studies will address kinematic behavior of a severe scoliosis deformity and set the stage for column-based osseoligamentous load sharing assessments during surgical procedures

Biomechanical Comparison of Traditional Laminectomy and Minimally‑Invasive Facetectomies

The facet joints of the lumbar spine are one of the sources of low‑back pain that affects a great portion of the population. Minimally‑invasive (MI) procedures have been becoming more popular in the surgical decompression of the spine because they offer shorter recovery time and involve removal of smaller amounts of important structures. With these features, it is believed that MI procedures lead to less clinical instability, and the functionality of the segment is maintained. Another important factor is how the facet angle in the lumbar segments affects the biomechanical instability. In spite of all this interest in MI procedures, there is little biomechanical research to back these claims. Therefore, in this study two MI procedures were compared with the laminectomy, the gold‑standard for lumbar decompression. Eight lumbar cadaveric motion segment units were procured, mounted, and tested intact, and then following MI unilateral facetectomy (UF), MI bilateral facetectomy (BF), and a traditional laminectomy (TL) using three different loading scenarios. The three different loading scenarios utilized in this study were the pure moment (PM), combined loading and moment (CLM), and the coupled‑eccentric loading (CEL) protocols. The PM testing protocol is the standard form of biomechanical testing of the spine. The CLM testing protocol introduced compressive and shear forces to increase translation in the sagittal plane. The CEL protocol was used because it combined a sagittal bend with a forced axial rotation. Rotational values were analyzed at the end limit of 8 Nm for flexion and extension and at 6 Nm for left and right lateral bending. Translations under PM and CLM were calculated utilizing a simulation software Visual Nastran. The criterion for instability was used to see if UF, BF, and TL met this criterion as compared to what would be clinically seen radiographically. In addition to these biomechanical data, CT images were analyzed to determine the change in the facet angle, contact area of the facet, and length of the joint removed after the BF. Increased motion was seen in the BF and TL compared to the harvested spine condition in all protocols. A decrease in rotation was seen in the UF condition in all protocols, with the exceptions being in right lateral for PM. None of the PM and CLM data met the criteria for instability. A decrease in facet angle, contact area, and length of the facet after the BF was observed. The TL had the most number of significant biomechanical increases when compared to the harvested condition, making it a less favorable surgical procedure when compared to each of the MI procedures. No studies have used the multiple loading scenarios, have quantified the amount of instability, or have taken account the amount of resection and change in facet angle due to MI procedures. Further investigation of the biomechanical effects of the MI procedures is still needed to gain more insight on how MI procedures affect spine biomechanics

Development and application of methods for the biomechanical characterization of spine ligaments and intervertebral discs

The spine is one of the major organs subject to trauma or genetic problems. Today 30% of people suffer from back pain and every day a large number of surgical interventions on the spine are performed to treat those patients with severe spinal deformities (i.e. scoliosis or kyphosis). From a statistical analysis, the percentage of failures for this type of interventions is around 25-30%. The aim of my PhD thesis was the improvement of the knowledge of the strain distribution on biological tissues, in particular on ligaments and intervertebral discs of the human spine. The first part of this thesis aimed at improvement of the methodologies used to measure the strain distribution, simultaneously on hard (vertebrae) and soft tissues (ligaments and intervertebral discs), using Digital Image Correlation. The second part of my research studied the biomechanical behaviour of the intervertebral discs and of the different ligaments. The disc acts as a shock absorber for the spine, reducing shocks and impacts. The anterior longitudinal ligament (ALL), supraspinous and interspinous ligaments were studied analysing how they were deformed under different loading conditions. These ligaments limit the movement of the spine during flexion reducing the overload on the intervertebral disc. The ALL does not offer great mechanical strength during lateral bending and axial torsion. Summarizing, the study underlines the necessity of having a full-field strain analysis tool to enhance the knowledge of the biomechanics of the spine and the interaction between different types of tissue. Furthermore, the results reported in this thesis could be useful also to build better multibody spine models and to include more realistic properties in finite element models. These results could be a starting point for future works in which the effect of different surgical procedures and the use of new surgical devices could be investigated

Facteurs biomécaniques de risques de la cyphose jonctionnelle proximale

RÉSUMÉ Les déformations rachidiennes telles que la scoliose sont des pathologies du système musculo-squelettique qui nécessitent un traitement chirurgical d’instrumentation dans les cas de courbures pathologiques sévères (angle de Cobb > 40° pour les cas de scoliose) (Weinstein 2001; Morcuende and Weinstein 2003). Cette intervention d’instrumentation consiste à fixer des implants sur les vertèbres et redresser le rachis à l’aide de tiges métalliques, ce qui mène à la fusion permanente du rachis. Bien que ce traitement permette une correction efficace des courbures pathologiques du rachis (Weinstein 2001), la survenue de complications postopératoires peut parfois entraîner une révision de l’instrumentation. La première cause de révision est la cyphose jonctionnelle proximale (CJP) (Schairer, Carrer et al. 2013), avec une prévalence entre 20% et 43% (Yang and Chen 2003; Yagi, King et al. 2012). La CJP se manifeste comme une hypercyphose des vertèbres adjacentes au-dessus de l'instrumentation. Plusieurs études rétrospectives ont été réalisées afin d’en identifier les causes. Les facteurs de risque associés à la survenue et à la progression de la CJP incluent la dissection proximale des tissus mous postérieurs, la dégénérescence de la capsule articulaire, l’équilibre sagittal pré- et postopératoire, la thoracoplastie, la qualité osseuse, l'obésité et la raideur de l’instrumentation (Glattes, Bridwell et al. 2005; Kim, Bridwell et al. 2005; DeWald and Stanley 2006; Kim, Lenke et al. 2007; Yagi, King et al. 2012). Ainsi, on rapporte que la CJP pourrait être associée au nombre de vertèbres instrumentées, au type d’implant proximal ou de manière plus générale à la configuration de l'instrumentation au niveau de la vertèbre proximale instrumentée. Les pathomécanismes de la CJP demeurent toutefois encore controversés. En effet, les conclusions rapportées dans la littérature sont parfois contradictoires et n’arrivent pas à isoler l’effet spécifique d’une variable donnée par rapport à la CJP. En outre, aucune étude biomécanique n’a rapporté l'impact biomécanique de différentes variables de la chirurgie rachidienne sur les indices géométrico-mécaniques reliés à la CJP. L’objectif de ce projet de maîtrise a donc été de développer un modèle biomécanique de la chirurgie d’instrumentation afin d’analyser et comprendre les pathomécanismes postopératoires du segment jonctionnel proximal du rachis. Six variables chirurgicales pouvant augmenter potentiellement le risque de survenue de la CJP ont ainsi été analysées.----------ABSTRACT Spinal deformities such as scoliosis are a group of musculoskeletal disorders requiring surgical instrumentation in cases of severe pathological curvatures (e.g. Cobb angle > 40° for scoliosis) (Weinstein 2001; Morcuende and Weinstein 2003). Spinal instrumentation is a surgical procedure that stabilizes the spine and fuses vertebrae with implanted devices, such as metallic rods, screws and hooks. Although this treatment allows effective correction of pathological spinal curvatures (Weinstein 2001), the occurrence of postoperative complications can sometimes lead to a revision of the instrumentation. The first cause of revision surgery is the proximal junctional kyphosis (PJK) (Schairer, Carrer et al. 2013), having a prevalence between 20% and 43% (Yang and Chen 2003; Yagi, King et al. 2012). PJK appears as a hyperkyphosis of non instrumented proximal vertebrae. Several retrospective studies have been conducted to identify its causes. Risk factors related to PJK occurrence and progression include the proximal dissection of the posterior soft tissues, the joint capsule degeneration, the pre- and postoperative sagittal balance, the thoracoplasty, the bone quality, the obesity and the stiffness of the instrumentation (Glattes, Bridwell et al. 2005; Kim, Bridwell et al. 2005; DeWald and Stanley 2006; Kim, Lenke et al. 2007; Yagi, King et al. 2012). It is also reported that PJK could be associated to the number of instrumented vertebrae, the type of proximal implant or the construct configuration at upper instrumented vertebra. However, pathomechanisms of PJK are still controversial because findings reported in the literature are sometimes contradictory and not able to isolate the effect of a specific variable on PJK. In addition, no computational study has reported the impact of several surgical variables on biomechanical indices related to PJK. The objective of this Master project was therefore to develop a biomechanical model of spinal instrumentation in order to analyze and better understand the postoperative pathomechanisms of proximal junctional spinal segment. Six surgical variables potentially increasing the risk for PJK occurrence have been analyzed. In order to achieve this objective, a multibody model was developed and validated to computationally simulate surgical instrumentations of six adult patients affected by PJK. For each case, the spinal tridimensional geometry was reconstructed using two calibrated preoperative radiographs (postero-anterior and lateral). In these models, each vertebra wa

The safety and efficacy of mesenchymal stem cells for prevention or regeneration of intervertebral disc degeneration: a systematic review

General Posters: abstract no. GP86INTRODUCTION: Mesenchymal stem cells (MSCs) have been used to halt the progression or regenerate the disc with hopes to prevent or treat discogenic back pain. However, the safety and efficacy of the use of MSCs for such treatment in animal and human models at short and long term assessment (i.e. greater than 48 weeks) have not been systematically addressed. This study addressed a systematic review of comparative controlled studies addressing the use of MSCs to that of no treatment/saline for the treatment of disc degeneration. METHODS: Online databases were extensively searched. Controlled trials in animal models and humans were eligible for inclusion. Trial design, MSC characteristics, injection method, disc assessment, outcome intervals, and complication events were assessed. Validity of each study was assessed addressing trial design. Two individuals independently addressed the aforementioned. RESULTS: Twenty-two animal studies were included. No human comparative controlled trials were reported. All three types of MSCs (i.e. derived from bone marrow, synovial and adipose tissue) showed successful inhibition of disc degeneration progression. From three included studies, bone marrow derived MSC showed superior quality of disc repair when compared to other treatments, including TGF-β1, NP bilaminar co-culture and axial distraction regimen. However, osteophyte development was reported in two studies as potential complication of MSC transplantation. CONCLUSIONS: Based on animal models, the current evidence suggests that in the short-term MSC transplantation is safe and effective in halting disc degeneration; however, additional and larger studies are needed to assess the long-term regenerative effects and potential complications. Inconsistency in methodological design and outcome parameters prevent any robust conclusions. In addition, randomized controlled trials in humans are needed to assess the safety and efficacy of such therapy.published_or_final_versio

Development and Biodynamic Simulation of a Detailed Musculo-Skeletal Spine Model

Ph.DDOCTOR OF PHILOSOPH

Experimental biomechanics of vertebral fractures

Vertebral fractures are a severe cause of morbidity and disability. In particular, burst fractures are a common traumatic injury presenting neurological impairment in 47 % of cases. However, diagnosis and planning of the treatment is challenging as the injury originates in highly dynamic conditions. Short-segment pedicle instrumentation (SSPI) in combination with kyphoplasty (SSPI–KP) has been used to provide additional stabilisation of the fracture. However, there is a lack of understanding about the effectiveness SSPI–KP. The aim of this study was to follow the fracture pathway, from onset to the outcome of surgical treatment. The first part focused on the phenomena underlying fracture creation and the dynamics of interpedicular widening (IPW). Although associated with neurological deficit, no previous study has shown how IPW evolves at fracture initiation. Subsequently the performance of treatment was assessed to evaluate how KP can improve SSPI to a simulated early follow-up. Burst fractures were induced in 12 human three-adjacent-vertebrae segments. Following fracture investigation, SSPI and SSPI–KP were performed, and samples underwent fatigue loading. Image processing of high-resolution CT scans was performed to assess anatomical changes at consecutive experimental stages on the treated and adjacent vertebrae. Experiments proved that IPW reaches a maximum at fracture onset and then decreases to the value measured clinically. SSPI–KP marginally improved stability of the treated spine, whilst providing a significant restoration of the endplate geometry. Vertebral body underwent significant changes in height and endplate curvature throughout the fracture pathway. This study provided further insight on the biomechanics of vertebral fractures and the findings can be used to improve and/or develop novel treatments as well as validate numerical models for retrospective assessment of the injury. In addition, outcomes from the collaboration work on the development of a computational simulation may help better understand cancer related vertebral fractures

Spine Surgery

We are very excited to introduce this new book on spinal surgery, which follows the curriculum of the EUROSPINE basic and advanced diploma courses. The approach we take is a purely case-based one, in which each case illustrates the concepts surrounding the treatment of a given pathology, including the uncertainties and problems in decision-making. The readers will notice that in many instances a lack of evidence for a given treatment exists. So decisions taken are usually not a clearcut matter of black or white, but merely different shades of gray. Probably in a lot of cases, there is often more than one option to treat the patient. The authors were asked to convey this message to the reader, giving him a guidance as what would be accepted within the mainstream. In addition, the reader is provided with the most updated literature and evidence on the topic. Most of the authors are teachers in the courses of EUROSPINE or other national societies with often vast clinical experience and have given their own perspective and reasoning. We believe that the readers will profit very much from this variety and bandwidth of knowledge provided for them in the individual chapters. We have given the authors extensive liberty as to what they consider the best solution for their case. It is thus a representative picture of what is considered standard of care for spine pathologies in Europe. We hope that this book will be an ideal complement for trainees to the courses they take. Munich, Germany Bernhard Meyer Offenbach, Germany Michael Rauschman

'Clinical Triad' findings in Klippel-feil patients

E-Poster - Congenital Deformity: no. 530It has been propagated that Klippel-Feil Syndrome (KFS) is associated with the clinical triad findings (CTF) of short neck, low posterior hairline, and limited range of motion. This study noted that CTFs are not consistently noted in KFS patients. KFS patients with extensive congenitally fused cervical segments were more likely to exhibit one of the components of CTF.postprin