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Adjacent Segment Disease (ASD) is a postoperative drawback of spinal fusion surgery which yields an increase in the range of motion in the adjacent spinal level. Therefore, the main aim of this study is to investigate the optimum mechanical properties of the spinal rod allowing a reduced rigidity in the spinal fixation level for decreasing the displacement of the adjacent segment. In this study, the spinal fixation system was modelled and attached to L3-L4 level. The elasticity modulus of the rods and the follower load were parametrically defined in order to investigate their optimum values under physiological loading conditions of extension. The maximum displacement value determined for the upper adjacent intervertebral disc was defined as the output parameter. Thereafter, the biomechanical response of the spinal bone-implant complex was simulated using Finite Element Analysis (FEA). Using the parametric FEA results, a polynomial mathematical model was constructed and Response Surface Method (RSM) was used to plot the relationship between input and output parameters. According to the results of the study, the optimum elasticity modulus of the rods and the suggested follower load have been determined as 80.8 GPa and 303.84 N, respectively. The maximum principal strain values obtained in the pedicle screws were 746 µℇ, 1563 µℇ, 3037 µℇ and 2937 µℇ, respectively. However, since the results are strongly associated with anatomical and biomechanical differences, the proposed patient-specific approach may enhance the accuracy for a more successful spinal fusion surgery operation in terms of minimizing the risk of ASD.

Background: Surgical treatment for erosive pyogenic spondylodiscitis of the lumbar spine is challenging as, following debridement of the intervertebral and bony abscess, a large and irregular defect is created. Sufficient defect reconstruction with conventional implants using a posterior approach is often impossible. Therefore, we developed the “Cement-PLIF”, a single-stage posterior lumbar procedure, combining posterior lumbar interbody fusion (PLIF) with defect-filling using antibiotic-loaded polymethylmethacrylate (PMMA). This study first describes and evaluates the procedure’s efficacy, safety, and infection eradication rate. Radiological implant stability, bone-regeneration, sagittal profile reconstruction, procedure-related complications, and pre-existing comorbidities were further analyzed. Methods: A retrospective cohort study analyzing 73 consecutive patients with a minimum of a one-year follow-up from 2000–2017. Patient-reported pain levels and improvement in infectious serological parameters evaluated the clinical outcome. Sagittal profile reconstruction, anterior bone-regeneration, and posterior fusion were analyzed in a.p. and lateral radiographs. A Kaplan–Meier analysis was used to determine the impact of pre-existing comorbidities on mortality. Pre-existing comorbidities were quantified using the Charlson-Comorbidity Index (CCI). Results: Mean follow-up was 3.3 (range: 1–16; ±3.2) years. There was no evidence of infection persistence in all patients at the one-year follow-up. One patient underwent revision surgery for early local infection recurrence (1.4%). Five (6.9%) patients required an early secondary intervention at the same level due to minor complications. Radiological follow-up revealed implant stability in 70/73 (95.9%) cases. Successful sagittal reconstruction was demonstrated in all patients (p < 0.001). There was a significant correlation between Kaplan–Meier survival and the number of pre-existing comorbidities (24-months-survival: CCI ≤ 3: 100%; CCI ≥ 3: 84.6%; p = 0.005). Conclusions: The Cement-PLIF procedure for pyogenic erosive spondylodiscitis is an effective and safe treatment as evaluated by infection elimination, clinical outcome, restoration, and maintenance of stability and sagittal alignment.

Die vorliegende Arbeit befasst sich mit der Behandlung der Skoliose mithilfe von Wirbelsäulenimplantaten. Im Vordergrund stehen die Komponenten sowie verschiedenen Systeme. Zu diesen Komponenten zählen: Pedikelschrauben, Haken, Stangen und Drähte. Mithilfe dieser Bestandteile ist die Zusammenstellung verschiedener Systeme möglich, die in fusionslose Technik und Fusion unterteilt werden. Zur fusionslosen Technik zählen: Traditional growing rods, Vertical expandable prosthetic titanium rip TM, Magnetic controlled growing rods, Luqué trolley systems und Shilla. Jedes dieser Systeme soll das Wachstum der Wirbelsäule, ohne Fusion derer, präservieren, um das Wachstum des Brustkorbes nicht einzuschränken. Als Fusion wird eine vollständige Versteifung der Wirbelsäule oder bestimmter Wirbelsäulensegmente bezeichnet. Hierfür können verschiedene Zusammensetzungen oben genannter Komponente zur Anwendung kommen. Die gemeinsamen Charakteristika Komponenten sind die Erfüllung der Biofunktionalität und Biokompatibilität, um im menschlichen Körper Anwendung zu finden. Biofunktionalität betrifft die mechanischen Anforderungen an ein Produkt, welches die Erfüllung seines Zwecks ermöglichen. Biokompatibilität deskribiert die Fähigkeit eines Materials die Funktion mit einer angemessenen biologischen Reaktion zu vollführen. Diese Wesensmerkmale werden für die Determinierung möglicher Risikopotentiale einer Komponente genutzt. The following bachelor thesis describes the treatment of scoliosis with the usage of spinal implants. The priority of this paper is it to explain the components of spinal implants and the different systems that can be composed with these components. In general, spinal implants include: pedicle screws, hooks, rods and wires. With these components, it is possible to assemble a variety of systems that can be used for fusionless and fusion techniques in spinal surgery. The fusionless techniques consist of: Traditional growing rods, Vertical expandable prosthetic titanium rip TM, Magnetic controlled growing rods, Luqué trolley systems and Shilla. Each of these systems is designed to preserve the growth of the spine without restricting the growth of the rib cage. A fusion limits the motion of the spine or spine segments, which leads to a complete immobilisation of the spine. An immobilisation involves different compositions of above-mentioned components. The common characteristics of spinal implants are the fulfillment of biofunctionality and biocompatibility to find application in the human body. Biofunctionality defines the mechanical requirements of a product to fulfill its purpose. Biocompatibility describes the ability of a material to perform the function with an appropriate biological response. These characteristics are used to determine the potential risks of a component.

INTRODUCTION: Surgical instrumentation in children with adolescent idiopathic scoliosis (AIS) is performed early in life and the implants are left in situ for the rest of the patient's life. Concern has been raised regarding persistent elevated levels of serum metal ions, but only a few studies on the topic have been published. The aim of this study was to compare the levels of serum metal ions in patients with AIS treated with either Harrington rod instrumentation or bracing.MATERIALS AND METHODS: AIS patients treated with Boston brace (BB) or posterior spinal fusion with Harrington rod instrumentation (HR) from 1983 to 1990 were requested to return to clinic. One hundred fifty-nine (73%) of 219 patients were available for follow-up of whom 115 agreed to have a blood draw.RESULTS: The proportion of patients who agreed to have a blood draw were similar in the BB (48 of 100, 48%) and HR (67 of 115, 60%, p = 0.085) groups. None of the surgical patients had their implants removed; mean age at follow-up (BB: 43.2 years vs HR: 43.5 years, p = 0.566) and mean length of follow-up (BB: 26.5 years vs HR: 24.5 years). Mean chromium serum levels were similar between the BB (2.7 nmol/L) and the HR (2.9 nmol/L, p = 0.827). Mean Cobalt serum levels were also similar between the BB (2.6 nmol/L) and the HR (2.8 nmol/L, p = 0.200).CONCLUSION: Serum metal ions were similar in AIS patients treated with bracing or Harrington rod instrumentation 25 years after initiation of treatment.

The aim of this experimental study was to assess the biomechanical performance of a novel C1 posterior arch (C1PA) clamp compared with C1 lateral mass (C1LM) screws in constructs used to treat atlantoaxial instability. These constructs had either C2 pedicle (C2P) screws or C2 translaminar (C2TL) screws. Eight fresh-frozen human cadaveric ligamentous spine specimens (C0-C3) were tested under six conditions: the intact state, the destabilized state after a simulated odontoid fracture, and when instrumented with four constructs (C1LM-C2P, C1LM-C2TL, C1PA-C2P, C1PA-C2TL). Each specimen was tested in a spinal loading simulator that separately applied axial rotation, flexion-extension and lateral bending. In each test condition, displacement controlled angular motion was applied in both directions at a speed of 2 deg/s until a resulting moment of 1.5 Nm was achieved. The measured ranges of motion (ROM) of the C1-C2 segments were compared for each test condition using nonparametric Friedman tests. The destabilized state had significantly more C1-C2 motion ( p

Introduction The use of spinal implants for the treatment of back disorders is largely affected by the insurgence of infections at the implantation site. Antibacterial coatings have been proposed as a viable solution to limit such infections. However, despite being effective at short-term, conventional coatings lack the ability to prevent infections at medium and long-term. Hydrogel-based drug delivery systems may represent a solution controlling the release of the loaded antibacterial agents while improving cell integration. Agarose, in particular, is a biocompatible natural polysaccharide known to improve cell growth and already used in drug delivery system formulations. In this study, an agarose hydrogel-based coating has been developed for the controlled release of gentamicin (GS). Methods Sand blasted Ti6Al4V discs were grafted with dopamine (DOPA) solution. After, GS loaded agarose hydrogels have been produced and additioned with tannic acid (TA) and calcium chloride (CaCl2) as crosslinkers. The different GS-loaded hydrogel formulations were deposited on Ti6Al4V-DOPA surfaces, and allowed to react under UV irradiation. Surface topography, wettability and composition have been analyzed with profilometry, static contact angle measurement, XPS and FTIR spectroscopy analyses. GS release was performed under pseudo-physiological conditions up to 28 days and the released GS was quantified using a specific ELISA test. The cytotoxicity of the produced coatings against human cells have been tested, along with their antibacterial activity against S. aureus bacteria. Results A homogeneous coating was obtained with all the hydrogel formulations. Moreover, the coatings presented a hydrophilic behavior and micro-scale surface roughness. The addition of TA in the hydrogel formulations showed an increase in the release time compared to the normal GS-agarose hydrogels. Moreover, the GS released from these gels was able to significantly inhibit S. aureus growth compared to the GS-agarose hydrogels. The addition of CaCl2 to the gel formulation was able to significantly decrease cytotoxicity of the TA-modified hydrogels. Conclusions Due to their surface properties, low cytotoxicity and high antibacterial effects, the hereby proposed gentamicin-loaded agarose-hydrogels provide new insight, and represent a promising approach for the surface modification of spinal implants, greatly impacting their application in the orthopedic surgical scenario., Natural Science and Engineering Research Council of Canada; Scientific and Technological Research Council of Turkey (TUBITAK) [1059B141700535]; Ege University BAP [16FBE025], This research was partially supported by the Natural Science and Engineering Research Council of Canada (Discovery program, Strategic and INNOV-I2I, CUI projects), by the Scientific and Technological Research Council of Turkey (TUBITAK) (Project Number: 1059B141700535), and by Ege University BAP (Project Number: 16FBE025).

This topical review describes the salient results of recent research on silicon nitride, a ceramic material with unique properties. The outcome of this ongoing research strongly encourages the use of monolithic silicon nitride and coatings as contemporary and future biomaterial for a variety of medical applications. Crystallographic structure, the synthesis and processing of monolithic structures and coatings, as well as examples of their medical applications that relate to spinal, orthopedic and dental implants, bone grafts and scaffolds, platforms for intelligent synthetic neural circuits, antibacterial and antiviral particles and coatings, optical biosensors, and nano-photonic waveguides for sophisticated medical diagnostic devices are all covered in the research reviewed herein. The examples provided convincingly show that silicon nitride is destined to become a leader to replace titanium and other entrenched biomaterials in many fields of medicine.

A cirurgia de artrodese da coluna vertebral é o tratamento padrão para quando o disco intervertebral está degenerado e métodos não cirúrgicos falharam. Neste tratamento, um dispositivo intervertebral ou espaçador intersomático é introduzido no lugar do disco, dando sustentação e tentando promover a fusão das vértebras adjacentes. O encaixe apropriado do implante com as vértebras é essencial para a recuperação do paciente. Tecnologias de imagem médica como a tomografia computadorizada (CT) já permitem que se faça uma reconstrução virtual da anatomia interna do paciente a ser tratado. No outro lado, a manufatura aditiva (AM) por extrusão de material permite que um modelo virtual seja facilmente materializado. A recente introdução do polímero biocompatível PEEK na tecnologia de extrusão possibilita o desenvolvimento de implantes personalizados, ou paciente-específico (PSI). PEEK já é usado em implantes de coluna e mostra algumas vantagens como radiotransparência e propriedades mecânicas próximas ao osso humano. O presente trabalho de pesquisa propõe e aplica uma metodologia para o desenvolvimento de implantes personalizados de coluna do tipo espaçador intersomático que alia as tecnologias de CT e AM por extrusão de PEEK. O intuito do estudo é mostrar evidências da viabilidade do uso do material e método para a produção de implantes personalizados. Implantes de coluna foram projetados e modelados de acordo com a geometria e necessidades de cinco casos de estudo. Protótipos dos implantes personalizados foram fabricados em PEEK via AM por extrusão de material e, então, passaram por um recozimento e esterilização. As propriedades dimensionais dos protótipos foram coletadas entre cada etapa. Os protótipos de implantes se mostraram precisos, sem alterações geométricas significativas. A metodologia, design do implante e tecnologias empregadas mostraram-se viáveis para a produção de implantes personalizados. Spinal fusion surgery is the standard treatment for when the intervertebral disc is degenerated and non-surgical methods have failed. In this treatment, an intervertebral device or spinal cage is introduced in the place of the disc, giving support and trying to promote the fusion of the adjacent vertebrae. Proper fitting of the implant with the vertebrae is essential for the patient’s recovery. Medical imaging technologies such as computed tomography (CT) already allow a virtual reconstruction of the internal anatomy of the patient to be treated. On the other hand, additive manufacturing (AM) by material extrusion allows a virtual model to be easily materialized. The recent introduction of the biocompatible PEEK polymer in material extrusion technology makes it possible to develop patient-specific implants (PSI). PEEK is already used in spine implants and shows some advantages such as radiolucency and mechanical properties close to human bone. The present research work proposes and applies a methodology in the development of custom spinal implants of the interbody spacer type that combines CT and AM technologies by PEEK extrusion. The purpose of the study is to show evidence of the feasibility of using this material and method for producing custom implants. Spine implants were designed and modeled according to the geometry and needs of five case studies. Prototypes of the custom implants were manufactured in PEEK via material extrusion AM and then underwent annealing and sterilization. The dimensional properties of the prototypes were collected between each stage. The implant prototypes proved to be accurate, without significant geometric changes. The methodology, implant design and technologies used proved to be viable for the production of personalized implants.

Neurosurgical patients with titanium spinal implant hypersensitivity can be difficult to diagnosis due to its rarity. Suspicion for titanium allergy is generally localized to the hardware site and may initially be thought to be an infectious process. Patients who report anorexia and fatigue over a long duration after the initial post-operative period may be diagnosed with depression rather than a systemic response to spinal metallic instrumentation. To our knowledge, a systemic titanium hypersensitivity reaction to spinal fixation devices has not been reported in the literature. We offer this report to give spine surgeons additional insight into suspected systemic titanium hypersensitivity symptoms which, if remain unidentified, can severely impair patient outcomes. A 67-year-old female with an unreported nickel allergy developed severe debilitating anorexia and fatigue one month post operatively, secondary to minimally invasive thoracic spinal fixation for T11 burst fracture with disruption of posterior elements. Over a two year period, weight loss reached approximately 25 kilograms with loss of muscle mass and subcutaneous tissue surrounding the spinal implants. The screws and rods were removed to avoid skin erosion. Upon hardware removal, the patient had rapid weight gain, improved stamina and generalized sense of well-being. We recommend the removal of spinal hardware in patients with suspected systemic titanium hypersensitivity reaction.

Additive Manufacturing (AM) is rapidly finding application in the manufacturing of spinal implants. The flexibility of manufacturing complex freeform structures combined with lattice structures has opened an era of newer types of spinal implants with better osseointegration surfaces and lesser stress shielding. AM is being utilized not only for off-the-shelf spinal implants but also for customized spinal implants also, manufactured using CT-scan/MRI data of patients. In the present study, efforts have been made to summarize work published in the field of metallic AM applications for spinal implants.

The goal of the work was to develop materials dedicated to spine surgery that minimized the potential for infection originating from the transfer of bacteria during long surgeries. The bacteria form biofilms, causing implant loosening, pain and finally, a risk of paralysis for patients. Our strategy focused both on improvement of antibacterial properties against bacteria adhesion and on wear and corrosion resistance of tools for spine surgery. Further, a ~35% decrease in implant and tool dimensions was expected by introducing ultrahigh-strength titanium alloys for less-invasive surgeries. The tested materials, in the form of thin, multi-layered coatings, showed nanocrystalline microstructures. Performed direct-cytotoxicity studies (including lactate dehydrogenase activity measurement) showed that there was a low probability of adverse effects on surrounding SAOS-2 (Homo sapiens bone osteosarcoma) cells. The microbiological studies (e.g., ISO 22196 contact tests) showed that implanting Ag nanoparticles into Ti/TixN coatings inhibited the growth of E. coli and S. aureus cells and reduced their adhesion to the material surface. These findings suggest that Ag-nanoparticles present in implant coatings may potentially minimize infection risk and lower inherent stress.

Radiation therapy, in conjunction with surgical implant fixation, is a common combined treatment in cases of bone metastases. However, metal implants generally used in orthopedic implants perturb radiation dose distributions. Carbon‐Fiber Reinforced Polyetheretherketone (CFR‐PEEK) material has been recently introduced for production of intramedullary nails and plates. The purpose of this work was to investigate the perturbation effects of the new CFR‐PEEK screws on radiotherapy dose distributions and to evaluate these effects in comparison with traditional titanium screws. The investigation was performed by means of Monte Carlo (MC) simulations for a 6 MV photon beam. The project consisted of two main stages. First, a comparison of measured and MC calculated doses was performed to verify the validity of the MC simulation results for different materials. For this purpose, stainless steel, titanium, and CFR‐PEEK plates of various thicknesses were used for attenuation and backscatter measurements in a solid water phantom. For the same setup, MC dose calculations were performed. Next, MC dose calculations for titanium, CFR‐PEEK screws, and CFR‐PEEK screws with ultrathin titanium coating were performed. For the plates, the results of our MC calculations for all materials were found to be in good agreement with the measurements. This indicates that the MC model can be used for calculation of dose perturbation effects caused by the screws. For the CFR‐PEEK screws, the maximum dose perturbation was less than 5%, compared to more than 30% perturbation for the titanium screws. Ultrathin titanium coating had a negligible effect on the dose distribution. CFR‐PEEK implants have good prospects for use in radiotherapy because of minimal dose alteration and the potential for more accurate treatment planning. This could favorably influence treatment efficiency and decrease possible over‐ and underdose of adjacent tissues. The use of such implants has potential clinical advantages in the treatment of bone metastases.

Implanted treatments aim to alleviate pain and restore the natural body. Currently, surgical procedures focus on a modular system, shaping patients to the nearest generically sized implant rather than tailoring to fit patient anatomies. Improper implant sizing or positioning can result in abnormal biomechanics, consequently leading to early failure. The rise in additive manufacturing has presented unique opportunities for patient specific implants. Custom devices have often been associated with shorter operative times, faster recoveries and lower rates of infection. Despite these inherent benefits, key remaining challenges facing its commercial viability include cost, delivery timeframe and quality assurance. This research details the design, development and validation of a system to fabricate patient specific implants through merging traditional and modern manufacturing techniques with patient adaptability. The templating system was explored in two applications, spine and skull reconstruction, with particular focus on the development of a regenerative, biomimetic intervertebral disc replacement. The functional and commercial feasibility of the templating system and resultant implants were examined. The templating system successfully generated a regenerative disc replacement that met geometrical, mechanical and biological requirements. Novel materials were developed into a custom disc implant that supported cell proliferation and biomechanical loads comparable with the native spine. The templating system was also applied clinically, providing superior aesthetic results when surgically used for cranioplasty. The findings of this thesis indicated the rapid templating system may overcome significant logistical limitations in shifting toward individualised treatments. Overall, the presented system exhibited strong functional and commercial potential toward integrating implants that were patient specific anatomically and mechanically into the healthcare domain.

Background: In radiotherapy, the presence of metallic implants affects the dose distribution, depending on beam energy and type, size, material and position of the implant. In this study, the effect of spinal implants on dose distribution was evaluated by Monte Carlo simulation. Methods: Oncor accelerator and water phantom, Plexiglas phantom containing spine and Plexiglas phantom containing spine and rod implants were simulated using BEAMnrc and DOSXYZnrc user codes and were validated. The effect of the implant presence, its size material, and location on dose distribution was investigated. Findings: Comparison of dose distributions with and without implants showed an increase of 5.5% in dose up to 4 mm from metal surface, due to the back scattering of electrons. Maximum attenuation in titanium rods was 9%. When the rods were positioned closer to each other, an increase in attenuation was observed. However, dose in spine was increased, when the distance between rods and spine was reduced. Rods with smaller cross section had less effect on dose. Attenuation in vitallium and stainless steel implants were 2 times greater than titanium implants. Conclusion: Depending on the location of implant with respect to spine, dose perturbation due to implants can either increase or decrease the dose in spine. The effect of size and material of implant was more important when spine was located under the implant. Generally, the effect of spinal implant on dose distribution is a function of size, material and position of the implant. Therefore, it is recommended to evaluate the dose distribution for such patients individually.

Summary Background Metal spinal rods are used as fixation devices in spinal surgery. The attenuation effect of these rods has not been completely studied for patients with spinal rods and requiring spinal radiotherapy. Aim The purpose of the current study was to investigate the dosimetric perturbation effect of metallic spinal rods in different photon beams. Materials/Methods Three photon beams of 6, 9 and 15MV were modelled using MCNP4C Monte Carlo (MC) code. The geometry consisted of two spinal rods at a depth of 4cm and a water phantom was used for MC calculations. The beam profiles at depths of 5.5, 6.5 and 7.5cm were calculated. Results Dose reductions of 10.2–11.2% and 5–6.2% were observed for steel and titanium rods respectively. The insertion of metallic rods into the photon beams did not change the spinal cord received dose but the effect of both types of rods on the target region behind the rods cannot be ignored, especially for steel rods. Conclusions Our results suggest that for reliable spinal radiotherapy the dose attenuation effect of spinal rods must be taken into account in treatment planning calculations.

Background Traditionally, spine societies and journals have set guidelines requiring a minimum 24-month follow-up for reporting results of surgical implant studies. However, the basis for this particular time period is not clear. The purpose of this study was to analyze prospective spinal implant studies reporting data at multiple specific follow-up periods to determine if there were significant changes in the clinical outcome throughout the 24-month follow-up period. Methods A comprehensive literature search was conducted using PubMed as well as searching the FDA web page. Studies were evaluated to identify those meeting the inclusion criteria: involved at least 100 patients receiving a spinal implant with data reported at multiple pre-defined time periods post-operatively for at least 24-months. Data recorded from each study included, number of patients, diagnoses, implant used, outcome measures used, and the results reported. The primary outcome data were analyzed in the current study to determine the amount of change in scores, with particular focus on the six and 24-month follow-up periods. Results Only 7 studies met the inclusion criteria. All seven studies were FDA-regulated trials published since 1997. Six addressed the treatment of symptomatic disc degeneration and 1 involved patients with neurogenic claudication due to stenosis. The outcome measures in the studies varied but pain and function were frequently assessed. In none of the studies was there a significant deterioration in results between the 6 and 24-month follow-up periods. In fact, the only changes during the follow-up periods were slight, not statistically significant, improvements, with the exception of 1 scale in 1 study where a slight, not statistically significant, decrease in the extent of improvement on a physical function assessment was noted between 6 and 24 months. These results suggest a great deal of stability in the mean scores for various outcome measures between the 6 and 24 months in patients receiving spinal implants. Conclusions Although long-term follow-up is certainly desirable for any clinical outcome study, there appears to be no significant change in outcome measures between the 6-month and 24-month follow-ups. These results support that earlier dissemination of results may be appropriate without producing overly-optimistic reports.

Congenital scoliosis represents a spinal malformation due to defects of formation, segmentation or mixed ones. It is characterized by a longitudinal and rotational imbalance. 54 patients were analyzed and 39 out of them were operated by various approaches with anterior and posterior instrumentations during 2000 and 2012. The impossibility to appoint some patients encountered in the daily practice into the known classifications, allowed us to purpose two categories of congenital scoliosis related to the predominance of spinal deviances in the coronal and transversal views. No certain etiology of congenital scoliosis has been identified until today. The susceptibility of some polygenic defects is obvious due to the presence of a sum of defects associated to most of the congenital scoliosis cases and the rarity of the presence of a unique defect. The diagnosis requires a thorough clinical and imaging examination in order to establish an individualized therapeutic strategy. The treatment of congenital scoliosis is different from the adolescent idiopathic one. Therapeutic criteria are significantly different. It is essential to assess the difference in growth of the concavity related to the convexity when choosing a particular procedure. The magnitude of the curve and the progressive rate are fundamental issues to the surgeon.

Using the unilateral pedicle screw fixation was thought to decrease the stiffness of the fixed segments. Various prospective, randomized studies were performed to determine whether unilateral pedicle screw fixation provides the necessities of bilateral fixation in one- or two-segment lumbar spinal fusion. In this study, four different unilateral pedicle screw fixation systems were evaluated to determine which one best approximated an intact spine with respect to biomechanics and kinematics. The four groups included an intact group, a unilateral facetectomy group with no fixation, a unilateral semi-rigid pedicle screw fixation group with a poly-ether-ether-ketone rod, and a unilateral dynamic pedicle screw fixation group. The bone mineral densities of all specimens were measured and specimens were matched with groups randomly. Flexion, lateral bending, and axial rotation tests were performed to compare the groups. For the flexion, lateral bending, and axial rotation tests, the best biomechanical outcomes were in the control group. The unilateral facetectomy group had the poorest performance and was not stable enough, compared with the control group. The dynamic and semi-rigid groups showed performance closer to that of the control group. The biomechanical responses of these two groups were also in good agreement, showing no significant statistical differences. Based on these test results, it is concluded that the unilateral dynamic and semi-rigid pedicle screw fixations can be used to provide stability to the vertebrae., The authors would like to acknowledge Turkish Science Foundation (TUBITAK) with the project #111M583 and #113S101 for the financial support for the study.

Background: The predilection of the cervical spine to a wide array of traumatic, degenerative and neoplastic diseases necessitates frequent surgical interventions. For successful surgical management of these conditions, a detailed anatomical knowledge of the cervical spine is required but variability in vertebral dimensions exists amongst different races and prevents the standardization of measurements. Aim: The aim of this study was to present a morphometric reference database for cervical vertebrae of the Indian population and enable comparisons with other populations. Materials and Methods: The study was conducted on 203 typical (C3-C6) cervical vertebrae. Linear measurements of the vertebrae were taken with the help of digital Vernier caliper and angular measurements were determined with software Image J. Statistical Analysis: Mean and standard deviation of the morphometric parameters taken into account were analysed. The comparison of morphometric dimensions of the right and left sides was performed using Student’s t-test and p-value was calculated. Results: The morphometric analysis of the cervical vertebrae demonstrated that when compared with other races, the mean height (11.39 ± 1.08 mm) and transverse diameters (22.18 ± 2.52 mm) of the vertebral body were larger but antero-posterior diameter was less, making the vertebral bodies in Indians transversely longer. The dimensions of the pedicle, laminae, articular processes and spinous process were smaller when compared to other populations. There existed a highly significant difference (p=0.002) between the widths of the right and left superior & inferior articular processes. A great disparity of the pedicle transverse angle was noted in different populations but in Indians the angle was 44.47 ± 2.81. Conclusion: The present morphometric study in Indian population would be valuable for the successful instrumentation of the cervical spine as smaller dimensions of the cervical vertebrae pose a challenge to the surgeons during application of plates and screws. The data would be helpful in designing spinal implants and permit identification of osteological remains.

International audience; Simulating compressive action of muscles, a follower load attends to reproduce a more physiological biomechanical behaviour of the cervical spine. Only few experimental studies reported its influence on kinematics and intradiscal pressure in the cervical spine.STUDY DESIGN:In vitro human cadaveric and numerical simulating evaluation of a compressive preload in the cervical spine.OBJECTIVES:To analyse the influence of a compressive follower preload on the biomechanical behaviour of the cervical spine.METHODS:The present study was divided into two parts: part 1: in vitro investigation; part 2: numerical simulating analysis. Part 1: Twelve human cadaveric spines from C2 to T2 were evaluated intact and after application of a 50-N follower load. All tests were performed under load control by applying pure moments loading of 2 Nm in flexion/extension (FE), axial rotation (AR) and lateral bending (LB). Three-dimensional displacements were measured using an optoelectronic system, and intradiscal pressures were measured at two levels. Part 2: Using a 3D finite element model, we evaluated the influence of a 50- and 100-N compressive preload on intradiscal loads, facets forces and ranges of motion. Different positions of the follower load along the anteroposterior axis (±5 mm) were also simulated.RESULTS:Part 1: Mean variation of cervical lordosis was 5° ± 3°. The ROM slightly increased in FE, whereas it consistently decreased in AR and LB. Coupled lateral bending during AR was also reduced. Increase in hysteresis was observed on load-displacement curves only for AR and LB. Intradiscal pressures increased, but the aspect of load-pressure curves was altered in AR and LB. Part 2: Using the FE model, only minimal changes in ROM were noted following the simulation of a 50-N compressive load for the three loading conditions. Compared to intact condition

The main objective of this thesis is to compare bony decompression with implantation of interspinous process devices (IPDs) in patients with intermittent neurogenic claudication (INC) caused by lumbar spinal stenosis (LSS). A national survey among Dutch spine surgeons is presented about the usual care of patients with intermittent neurogenic claudication caused by lumbar spinal stenosis. Surgeons' expectations of different treatment options are presented. The existing evidence on interspinous implant surgery will be systematically reviewed. Results of treatment with IPDs are compared with other (conservative) treatment options. The Foraminal Enlargement Lumbar Interspinosus distraXion (FELIX) trial is described. This double-blind, multicenter, randomized (cost)effectiveness study was designed to answer the question whether treatment with IPDs would be more (cost) effective compared with conventional bony decompression. Short-term results (eight weeks), long-term results (one and two year) and results in different subgroups are described in this thesis. The analysis based on total direct and indirect costs of both procedures (treatment with IPD and bony decompression) are also presented. INC suitable for surgical treatment. The compression on MR images was evaluated and correlated with baseline complaints and long-term clinical outcome.

Background The incidence of wound infections associated with instrumented spine surgery ranges from 2 to 20%. These complications may lead to poor outcomes. Knowing the risk factors associated with surgical site infections (SSI) after utilizing spinal implants is essential to avoid these complications, including hardware removal. Methods We reviewed retrospectively 550 patients who underwent spinal fusion surgery from 2011 to 2015; 16 developed SSI after spinal instrumentation. The diagnosis of SSI was established based on positive wound swab or blood cultures, and various clinical, laboratory, and radiological findings. Additional preoperative and intraoperative risk factors were analyzed. Results The incidence of SSI after spinal instrumentation surgery was 2.9%. Obesity was a statistically significant parameter (P = 0.013) that contributed to SSI along with the alcoholism and/or drug abuse (P = 0.034); use of a Foley catheter nearly reached significance levels. Conclusions There is an increased risk of SSI in patients who are obese or use drugs and/or alcohol. Clear preoperative identification of these risk factors prior to implanting spinal instrumentation should help prevent SSI in the future.

Background context In the 1980s, a new implant was developed to treat patients with intermittent neurogenic claudication caused by lumbar spinal stenosis (LSS). This implant is now widely used. Purpose The objective of this study is to determine whether a favorable cost-effectiveness for interspinous process devices (IPDs) compared with conventional bony decompression is attained. Study design/setting Cost-utility analysis was performed alongside a double-blind randomized controlled trial. Five neurosurgical centers (including one academic and four secondary level care centers) included participants for this study. Patient sample One hundred fifty-nine patients with LSS were treated with the implantation of IPD and with bony decompression. Eighty participants received an IPD, and seventy-nine participants underwent spinal bony decompression. Outcome measures Outcome measures were quality-adjusted life-years (QALYs) and societal costs in the first year (estimated per quarter), estimated from patient-reported utilities (US and The Netherlands EuroQol 5D [EQ-5D] and EuroQol visual analog scale) and diaries on costs (health-care costs, patient costs, and productivity costs). Methods All analyses followed the intention-to-treat principle. Given the statistical uncertainty of differences between costs and QALYs, cost-effectiveness acceptability curves graph the probability that a strategy is cost effective, as a function of willingness to pay. Paradigm Spine funded this trial but did not have any part in data analysis or the design and preparation of this article. Results According to the EQ-5D, the valuation of quality of life after IPD and decompression was not different. Mean utilities during all four quarters were, not significantly, less favorable after IPD according to the EQ-5D with a decrease in QALYs according to the US EQ-5D of 0.024 (95% confidence interval, −0.031 to 0.079). From a health-care perspective, the costs of IPD treatment were higher (difference €3,030 per patient, 95% confidence interval, €561–€5,498). This significant difference is mainly because of additional cost of implants of €2,350 apiece. From a societal perspective, a nonsignificant difference of €2,762 (95% confidence interval, −€1,572 to €7,095) in favor of conventional bony decompression was found. Conclusions Implantation of IPD as indirect decompressing device is highly unlikely to be cost effective compared with bony decompression for patients with intermittent neurogenic claudication caused by LSS. Trial registration Dutch Trial Register Number: NTR1307.

M.Ing. (Mechanical Engineering) A stand-alone anterior lumbar interbody fusion device is used to stabilise the spine and restore the disc space height without any other instrumentation. The stand-alone anterior lumbar interbody device is fixed to the adjacent vertebrae using titanium screws. In this research an experimental and numerical investigation on the structural strength of the SASCATM stand-alone anterior lumbar interbody fusion device are presented. The outcome of the investigation will be used as part of the device validation documentation necessary for market approval. The SASCATM device is manufactured from PEEK (a high strength polymer). Tensile and compressive testing was conducted to determine the appropriate mechanical properties of PEEK. The structural integrity of the SASCA device was evaluated by conducting full scale compression testing on a limited number of different design revisions. Comparisons as regards to their loaddisplacement behaviour were made. All specimens were visually inspected. The Finite Element Analysis (FEA) method was used in the numerical investigation of the SASCATM stand-alone anterior lumbar interbody device. Three studies were conducted. The first study aimed at comparing the full scale experimental compressive testing results with the FEA simulation. Although the desired results weren’t achieved, the model gave a fair representation of the initial region of the experimental setup in the sense that it had a similar slope. It was concluded that the nominal stress (4.1 MPa) fell within the proportional limit (35 MPa) as measured during the materials testing. The second study was aimed at determining the displacement at a worst-case load determined from the literature (2.7 kN). The study showed that the maximum Von Mises stress does not exceed the yield strength of the material. The third and final (parametric) study aimed at geometric optimisation of the cages. The motivation for the changes was based on the literature and customer suggestions for improvement. The geometric optimisation intended to show whether a desired increase in graft hole size would have an effect on the structural integrity of the device. The suggestion to move the screw holes of the threehole version closer to the center of the cage was also assessed. It was shown that enlarging the two graft holes does have an effect on the compressive strength. Higher stresses were presented in all but one case. Combining the holes also had an effect on the compressive strength. Movement of the screw holes more medially did have an impact on the compressive strength of the cages. The effect was significant. The closer the holes were to the center of the cage, the higher the Von Mises stress was. This change should therefore be considered before implementation. The results showed that different shapes and sizes of the graft holes do have an impact on the stress of this particular cage. None of the models exceeded the compressive yield strength of the material. The proposed graft hole opening design changes are therefore not warranted for the current SASCATM stand-alone anterior lumbar interbody device.

El proceso de fusión intervertebral depende de factores relacionados con la edad, enfermedades y calidad del hueso receptor, también se ve afectado por algunos parámetros del implante tales como tamaño de la jaula, diámetro externo e interno, grado de porosidad, tamaño del poro e interconectividad de los poros. La mayor parte de los estudios que se han documentado del crecimiento del hueso trabecular en vertebras con implante, son estudios experimentales en los cuales no se pueden controlar todas las variables que tienen efecto sobre el proceso de fusión y para obtener los resultados se necesita más tiempo que incrementa los costos. El objetivo de esta investigación es determinar el efecto de las variables de diseño (porosidad y tamaño del poro) de una jaula de fusión intersomática, en el proceso de fusión ósea implementando un modelo de optimización. Los resultados obtenidos presentan una distribución de densidad ósea y un incremento en la rigidez del nuevo tejido dependiendo de los parámetros del implante y las cargas impuestas, confirmando que el hueso se considera como un material de auto-optimización. Abstract. The process of intervertebral fusion depends on factors related to age, diseases and the quality of the bone receptor, as well as it is affected by various implant parameters such as the size of the cage, internal and external diameter, grade of porosity, pore size and the interconnectivity of the pores. The major part of documented studies regarding trabecular bone growth in vertebrae with an implant are experimental studies in which all of the variables that effect bone growth cannot be controlled and in order to obtain the results they need more time is required which raises the cost of studies. The objective of this investigation is to determine the effect of the design variables (porosity and pore size) of an interbody fusion cage in the bone fusion process implementing an optimization model. The results obtained present a distribution of bone density and an increase in rigidity of the new tissue depending of the parameters of the implant and the loads imposed, confirming that the bone is considered a self-optimizing material. Maestría

Background Reporting financial disclosures has become standard practice in both journal publications and during oral forum at scientific meetings. Despite this, the effect of reporting a financial disclosure of any member of an authorgroup, on the tone of the conclusion of an article has gained little attention. This study was performed to determine what effect reporting a financial disclosure has on the conclusion of an article. Methods A literature search for all articles on interspinous devices and cervical disc prostheses, published from January 1st, 2008 until December 1st, 2010 was performed. Financial disclosures were reported, as were funding by commercially active parties. The tone of the conclusions was graded as positive, neutral or negative. Results The odds ratio (OR) for a positive conclusion in cases where a financial disclosure was reported was 16.5 (95% CI: 4.7–58.1). Effect modification occurs with the presence of funding by a commercially active party. In cases where a financial disclosure was reported and funding was available for the study, the OR was 1.0 (95% CI: 0.08–12.6), whilst the OR was 33.3 (95%CI: 4.2–262.3) if funding was not provided. This discrepancy is mainly due to the large number of articles with a neutral/negative conclusion if the authors failed to report any financial disclosure and were not funded by a commercially active party. Conclusions Reporting a financial disclosure is a potential source of bias. Authors with disclosed financial relationships less often publish articles with a neutral/negative conclusion. This source of bias should certainly be taken into account during the critical appraisal of articles, particularly when the quality of the literature is being assessed. Electronic supplementary material The online version of this article (doi:10.1007/s00586-011-2086-x) contains supplementary material, which is available to authorized users.

Corrosion affects spinal instrumentations and may cause local and systemic complications. Diagnosis of corrosion is difficult, and nowadays it is performed almost exclusively by the examination of retrieved instrumentations. We conducted this study to determine whether it is possible to detect corrosion by measuring metal levels on patients with posterior instrumented spinal fusion. Eleven asymptomatic patients, with radiological signs of corrosion of their stainless steel spinal instrumentations, were studied by performing determinations of nickel and chromium in serum and urine. Those levels were compared with the levels of 22 patients with the same kind of instrumentation but without evidence of corrosion and to a control group of 22 volunteers without any metallic implants. Statistical analysis of our results revealed that the patients with spinal implants without radiological signs of corrosion have increased levels of chromium in serum and urine (P < 0.001) compared to volunteers without implants. Corrosion significantly raised metal levels, including nickel and chromium in serum and urine when compared to patients with no radiological signs of corrosion and to volunteers without metallic implants (P < 0.001). Metal levels measured in serum have high sensibility and specificity (area under the ROC curve of 0.981). By combining the levels of nickel and chromium in serum we were able to identify all the cases of corrosion in our series of patients. The results of our study confirm that metal levels in serum and urine are useful in the diagnosis of corrosion of spinal implants and may be helpful in defining the role of corrosion in recently described clinical entities such as late operative site pain or late infection of spinal implants.

Intervertebral disc degeneration has been reported as the underlying cause for 75% of cases of lower back pain and is marked by dehydration of the nucleus pulposus within the intervertebral disc. There have been many implant designs to replace the nucleus pulposus. Some researchers have proposed the replacement of the nucleus pulposus with hydrogel materials. The insertion of devices made from these materials further compromises the annulus of the disc. An ideal nucleus replacement could be injected into the disc space and form a solid in vivo. However, injectable replacements using curing elastomers and thermoplastic materials are not ideal because of the potentially harmful exothermic heat evolved from their reactions and the toxicity of the reactants used.We propose a hydrogel system that can be injected as a liquid at 25°C and solidified to yield a hydrogel within the intervertebral disc at 37ºC. In aqueous solutions, these polymers have Lower Critical Solution Temperatures (LCST) between 25-37°C, making them unique candidate materials for this application. Poly(Nisopropylacrylamide) (PNIPAAm) is the most widely studied LCST polymer due to its drastic transition near body temperature. However, by itself, pure PNIPAAm forms a hydrogel that has low water content and can readily undergo plastic deformation. To increase the water content and impart elasticity to PNIPAAm hydrogels, grafted and branched hydrogel systems were created that incorporated the thermogelling PNIPAAm and hydrophilic poly(ethylene glycol) (PEG).In this research, the effects of polymer composition and monomer to initiator ratio, which controls polymer MW, on the in vitro swelling properties (mass, chemical, and compressive mechanical stability) of hydrogels formed from aqueous solutions of these polymers were evaluated. Immersion studies were also conducted in solutions to simulate the osmotic environment of the nucleus pulposus. The effects of repeated compression and unloading cycles on the water content and dimensional recovery of hydrogels made from three candidate polymer formulations were also determined.Unlike PNIPAAm and PEG grafted PNIPAAm hydrogels, PEG branched hydrogels have covalently linked networks. Addition of 7 mol% PEG branches to PNIPAAm resulted in a hydrogel with a higher water content and better elastic recovery than hydrogels made from pure PNIPAAm. PEG branched PNIPAAm hydrogels were shown to have mass, chemical, and compressive mechanical stability in vitro. Furthermore, these hydrogels showed superior dimensional recovery after compressive cycling than pure PNIPAAm and PEG grafted PNIPAAm hydrogels. The 7 mol% PEG branched PNIPAAm hydrogels have suitable swelling and mechanical properties to potentially serve as a nucleus pulposus replacement.

The origin of the lower back pain is often the degenerated lumbar intervertebral disc (IVD). We are proposing replacement of the degenerated nucleus by a PVA/PVP polymeric hydrogel implant. We hypothesize that a polymeric hydrogel nucleus implant can restore the normal biomechanics of the denucleated IVD by mimicking the natural load transfer phenomenon as in case of the intact IVD.Lumbar IVDs (n=15) were harvested from human cadavers. In the first part, specimens were tested in four different conditions for compression: Intact, bone in plug, denucleated and Implanted. Hydrogel nucleus implants were chosen to have line-to-line fit in the created nuclear cavity. In the second part, nucleus implant material (modulus) and geometric (height and diameter) parameters were varied and specimens (n=9) were tested. Nucleus implants with line-to-line fit significantly restored (88%) the compressive stiffness of the denucleated IVD. The synergistic effect between the implant and the intact annulus resulted in the nonlinear increase in implanted IVD stiffness, where Poisson effect of the hydrogel played major role. Nucleus implant parameters were observed to have a significant effect on the compressive stiffness. All implants with modulus in the tested range restored the compressive stiffness. The undersize implants resulted in incomplete restoration while oversize implants resulted in complete restoration compared to the BI condition. Finite element models (FEM) were developed to simulate the actual test conditions and validated against the experimental results for all conditions. The annulus (defined as hyperelastic, isotropic) mainly determined the nonlinear response of the IVD. Validated FEMs predicted 120-3000 kPa as a feasible range for nucleus implant modulus. FEMs also predicted that overdiameter implant would be more effective than overheight implant in terms of stiffness restoration. Underdiameter implants, initially allowed inward deformation of the annulus and hence were less effective compared to underheight implants. This research successfully proved the feasibility of PVA/PVP polymeric hydrogel as a replacement for degenerated nucleus. This approach may reduce the abnormal stresses on the annulus and thus, prevent/postpone the degeneration of the annulus. A validated FEM can be used as a design tool for optimization of hydrogel nucleus implants design and related feasibility studies.

Study Design. In part 1 of the study, the morphometry of thoracic pedicles and bony landmarks for pedicle screw placement were evaluated. In part 2, pedicle screws were inserted in fresh cadavers, using a different entry point in the left and right pedicles. Objectives. To identify the safest entry point and screw orientation for pedicle screws in the thoracic spine. Summary of Background Data. A few morphometric investigations have been performed on thoracic vertebrae, but the safest technique for screw insertion in thoracic pedicles has not been analyzed. Methods. Mean, range, and standard deviations of pedicle transverse diameter and pedicle orientation were measured in 99 dried thoracic vertebrae. We evaluated the position of the bottom of the superior facet and that of the superior border of the transverse process in relation to the center of the pedicle. The relation between the pedicle axis and the superior facet in the frontal plane was also assessed. In part 2 of the study, pedicle screws were inserted in fresh cadavers at the intersection between the superior border of the transverse process and the middle of the superior facet (entry point A) and between the former and the lateral two thirds of the facet (entry point B). Results. The smallest transverse diameter was found at T6 (mean 4.3 mm) where pedicles measured less than 5 mm in 68% of the specimens. In the frontal plane, the pedicle axis intersected the middle of the superior facet in 15% of specimens, the lateral two-thirds in 62%, and the lateral border of the facet in 23%. Of the 126 screws inserted in fresh human cadavers, 15 (24%) of the screws inserted using entry point A and 10 (16%) of those inserted using entry point B violated the pedicle cortex (P > 0.05). Six (10%) of the screws inserted using entry point A compared with no screw inserted using entry point B penetrated the anterior vertebral cortex (P = 0.03). Conclusions. Pedicles between T4 and T8 may not be wide enough for screw fixation. An entry point for pedicle screws located at the intersection between the superior border of the transverse process and the lateral two thirds of the superior facet seems more likely to be in line with the pedicle axis than do other entry points. In the lower thoracic vertebrae this entry point, in combination with insertion of the screws more medially oriented than the pedicle axis, significantly reduces the risk of violating the anterior vertebral cortex.

Using the unilateral pedicle screw fixation was thought to decrease the stiffness of the fixed segments. Various prospective, randomized studies were performed to determine whether unilateral pedicle screw fixation provides the necessities of bilateral fixation in one- or two-segment lumbar spinal fusion. In this study, four different unilateral pedicle screw fixation systems were evaluated to determine which one best approximated an intact spine with respect to biomechanics and kinematics. The four groups included an intact group, a unilateral facetectomy group with no fixation, a unilateral semi-rigid pedicle screw fixation group with a poly-ether-ether-ketone rod, and a unilateral dynamic pedicle screw fixation group. The bone mineral densities of all specimens were measured and specimens were matched with groups randomly. Flexion, lateral bending, and axial rotation tests were performed to compare the groups. For the flexion, lateral bending, and axial rotation tests, the best biomechanical outcomes were in the control group. The unilateral facetectomy group had the poorest performance and was not stable enough, compared with the control group. The dynamic and semi-rigid groups showed performance closer to that of the control group. The biomechanical responses of these two groups were also in good agreement, showing no significant statistical differences. Based on these test results, it is concluded that the unilateral dynamic and semi-rigid pedicle screw fixations can be used to provide stability to the vertebrae.