Spinal Devices Research Articles

<em>In vivo</em> Imaging of the Mouse Spinal Cord Using Two-photon Microscopy

In vivo imaging using two-photon microscopy in mice that have been genetically engineered to express fluorescent proteins in specific cell types has significantly broadened our knowledge of physiological and pathological processes in numerous tissues in vivo. In studies of the central nervous system (CNS), there has been a broad application of in vivo imaging in the brain, which has produced a plethora of novel and often unexpected findings about the behavior of cells such as neurons, astrocytes, microglia, under physiological or pathological conditions. However, mostly technical complications have limited the implementation of in vivo imaging in studies of the living mouse spinal cord. In particular, the anatomical proximity of the spinal cord to the lungs and heart generates significant movement artifact that makes imaging the living spinal cord a challenging task. We developed a novel method that overcomes the inherent limitations of spinal cord imaging by stabilizing the spinal column, reducing respiratory-induced movements and thereby facilitating the use of two-photon microscopy to image the mouse spinal cord in vivo. This is achieved by combining a customized spinal stabilization device with a method of deep anesthesia, resulting in a significant reduction of respiratory-induced movements. This video protocol shows how to expose a small area of the living spinal cord that can be maintained under stable physiological conditions over extended periods of time by keeping tissue injury and bleeding to a minimum. Representative raw images acquired in vivo detail in high resolution the close relationship between microglia and the vasculature. A timelapse sequence shows the dynamic behavior of microglial processes in the living mouse spinal cord. Moreover, a continuous scan of the same z-frame demonstrates the outstanding stability that this method can achieve to generate stacks of images and/or timelapse movies that do not require image alignment post-acquisition. Finally, we show how this method can be used to revisit and reimage the same area of the spinal cord at later timepoints, allowing for longitudinal studies of ongoing physiological or pathological processes in vivo.

Development of New Titanium-Molybdenum Alloys with Changeable Young's Modulus for Spinal Fixture Devices

Development of New Titanium-Molybdenum Alloys with Changeable Young's Modulus for Spinal Fixture Devices

Spinal device cancer risk

Spinal device cancer risk

Postoperative Imaging of Spinal Disk Arthroplasty Devices

Cervical and lumbar arthroplasty is being increasingly used over the past decade for the management of degenerative spinal disease with multiple varied devices available worldwide. As more experience is obtained with the devices currently available, the need for postoperative imaging has heightened. Plain x-rays are still useful for the assessment of device positioning, determination of range of motion, and to rule out potential device migration. Computed tomography scanning can be combined with this, but incorporation of newer devices into bony endplates is difficult to visualize. In cases where neural structures need to be assessed at operated or adjacent levels, magnetic resonance (MR) scanning is suitable in most titanium-based or nonmetallic devices but produces significant artifact in cobalt-chromium alloy-based devices. In this latter group, computed tomography myelography, which is more invasive than MR scanning, will need to be used. In time, it would be envisioned that nonmetallic devices made of plastics should allow for acceptable postoperative MR imaging. As our experience with the devices and their imaging increases, these recommendations may change; however, material properties play a greater role in the decision making of type of modality used for postoperative imaging in scenarios where interbody fusion is performed.

Devices designed to avoid wrong route administration of drugs

In March 2007 and November 2009 the National Patient Safety Agency (NPSA) published safety alerts with regards to ‘promoting safer measurements and administration of liquid medicines via oral and other enteral routes’ and ‘safer spinal (intrathecal), epidural and regional devices’ [1–3]. These alerts were prompted by several serious incidents of wrong-route administration of drugs over the years. Several action plans have been suggested to reduce the risk of wrong-route administration of drugs. The main proposal is to create and implement a system of medical devices for each route that cannot physically connect to devices meant for another route. This means we have to stop using medical devices with the standard Luer connectors other than for one specific route (probably intravenous) [4]. The NPSA recommended that specific oral/enteral syringes should be in use by March 2008 and that spinal/epidural/regional needles and syringes with safe connectors should be in use by April 2012 [1–3]. But with several different companies producing a variety of medical devices, it is clear that there will be some connections overlooked. Cook et al. demonstrated this during their study to evaluate the usability of two alternative systems in 2010; following feedback the connectors have been modified [5]. However, this is still an ongoing issue: recently we discovered it is possible to connect an oral/enteral syringe to spinal devices with the Surety® connectors (Intervene Limited, Chesterfield, UK) and to connect a spinal/epidural/regional syringe with the Surety® connector to a paediatric nasogastric feeding tube. Both these situations can occur despite the devices’ having different connectors and without too much additional force (2, 3). The oral/enteral syringe connected to a spinal needle with the Surety® connector. The spinal/epidural/regional syringe with the Surety® connector connected to a paediatric nasogastric feeding tube. Although the possibility of having oral/enteral syringes within the clinical area whilst performing a spinal procedure and accidentally administering their contents is very remote, it is possible and has even been hinted at in the February 2011 Neuraxial Update [6]. We believe it is pointless to change from an existing system, with a rare but potentially catastrophic consequence, to another with a differing, rare but potentially catastrophic consequence. Thus, in the presence of the reverse Luer connectors of enteral feeding devices, the adoption of the Surety® non-Luer fittings cannot be recommended. The other issue in relation to the development of non-Luer connectors is the quality of the new devices. This has been highlighted in a Joint Statement published by our profession earlier this year, raising concerns that there will be an increased risk to patients undergoing anaesthesia due to the introduction of new neuraxial connectors into clinical practice in England and Scotland without formal testing [7]. Our opinion is that these issues rather defeat the whole idea behind the NPSA’s recommendation of a different fitting for devices meant for each different route. More time is needed to test the connectors thoroughly to ensure no cross-connectivity and to ensure a high quality product to deliver medications.

Effects of nonlinearity in the materials used for the semi-rigid pedicle screw systems on biomechanical behaviors of the lumbar spine after surgery**This work was presented at the 8th China–Korea Symposium on Biomaterials and Nano-Bio Technology (Pyeongchang, Korea, Dec. 13–17 2010).

Recently, various types of semi-rigid pedicle screw fixation systems have been developed for the surgical treatment of the lumbar spine. They were introduced to address the adverse issues commonly found in traditional rigid spinal fusion-–abnormally large motion at the adjacent level and subsequent degeneration. The semi-rigid system uses more compliant materials (nitinol or polymers) and/or changes in rod design (coiled or twisted rods) as compared to the conventional rigid straight rods made of Ti alloys (E = 114 GPa, υ = 0.32). However, biomechanical studies on the semi-rigid pedicle screw systems were usually limited to linear modeling of the implant and anatomic elements, which may not be capable of reflecting realistic post-operative motions of the spine. In this study, we evaluated the effects of nonlinearity in materials used for semi-rigid pedicle screw fixation systems to evaluate the changes in biomechanical behaviors using finite element analysis. Changes in range of motion (ROM) and center of rotation (COR) were assessed at the operated and adjacent levels. Actual load–displacement results of the semi-rigid rod from mechanical test were carried out to reflect the nonlinearity of the implant. In addition, nonlinear material properties of various spinal ligaments studies were used for the finite element modeling. The post-operative models were constructed by modifying the previously validated intact model of the L1-S1 spine. Eight different post-operative models were made to address the effects of nonlinearity—with a traditional stiffness modulus rod (with linear ligaments, case 1; with nonlinear ligaments, case 5), with a rigid rod (with linear ligaments, case 2; with nonlinear ligaments, case 6), with a soft rod (with linear ligaments, case 3; with nonlinear ligaments, case 7), and with a nonlinear rod (with linear ligaments, case 4; with nonlinear ligaments, case 8). To simulate the load on the lumbar spine in a neutral posture, follower load (400 N) was applied and then the hybrid loading condition was applied to measure the ROM and COR in the sagittal plane. The more the nonlinearity was included in the model the closer the motion behavior of the device was to that of the intact spine. Furthermore, our results showed that the nonlinearity of the semi-rigid rod was a more sensitive factor than the nonlinearity of the spinal ligaments on biomechanical behavior of the lumbar spine after surgery. Therefore, for better understanding of the surgical effectiveness of the spinal device, more realistic material properties such as nonlinearity of the device and anatomic elements should be considered. In particular, the nonlinear properties of the semi-rigid rod were considered more than the nonlinearity of spinal ligaments.

Preparation and Characterization of Bone-Like Apatite Coating on Ti6Al4V Spinal Fusion Devices

Sand-blasting treatment and chemically biomimetic growth are important methods improving the interface adhesion strength and formation of osteoconductive coatings for implants. In the present study, these methods were employed to generate bone-like apatite coating on Ti6Al4V spinal fusion devices. The surface morphology, elements and microstructure were analyzed using SEM, AFM, EDS, XRD and TEM. The results showed that bone-like apatite layer formed after sand blasting treatment and chemically biomimetic growth. Also the dimensional accuracy of device after the treatment could meet the implantation requirement of the device. The coating adhesion test suggests that rough surface after sand-blasting can improve the coating adhesion strength. The study will facilitate further the engineering application of chemically biomimetic growth in surface modification of Ti6Al4V implants and the medical application of spinal fusion device.

Evaluating the ability of posterior elements to support new instrumentation for spinal fusion

Posterior spinal plating devices have recently made a re-emergence as both stand-alone devices and for use in conjunction with anterior fusion. Yet, the structural integrity of the posterior elements to support loads throughout the spine and the impact of plating on posterior element strength has not been well characterized. This study aims to quantify the mechanical strength of the posterior elements (spinous processes/laminae) throughout the spine and to determine the effect of attaching posterior element plating systems on their ultimate load to failure. Vertebral levels from six cadaveric spines were grouped in pairs to account for varying geometries and sizes of the human posterior elements (a total of 59 levels in 5 groups). One sample from each pair was tested in its native state, and the complementary vertebra was tested via posterior plating. Posterior element plating caused moderate reductions in posterior element failure strength (15-24 percent) throughout the cervical, thoracic, and lumbar spine. Bone mineral density of the posterior elements had the most significant impact on ultimate load to failure (a decrease of 0.1 g/cm3, yields a 189N reduction in). The modest structural impact of posterior element plating motivates continued investigation into potential use of less invasive plating devices for posterior spinal fusion.

Financial Conflicts Cited in Investigation of Medtronic Spinal Fusion Device

Financial Conflicts Cited in Investigation of Medtronic Spinal Fusion Device

Bearing surfaces for total disc arthroplasty: metal-on-metal versus metal-on-polyethylene and other biomaterials

Concerns about the effect of metallic wear debris from metal-on-metal bearing surfaces in total hip arthroplasty have increased. Some spinal arthroplasty devices include metal-on-metal bearing surfaces. To review the literature for clinical reports of complications because of wear debris from metal-on-metal spinal arthroplasty devices. To review the biology of wear debris from metal-on-metal bearing surfaces drawn from the hip arthroplasty literature and place it in the context of global regulatory actions and clinical and laboratory studies. Literature review. To identify clinical reports, the PubMed database from the United States National Library of Medicine was queried using Medical Subject Headings terms and additional keyword terms. In addition, experts from academia and regulatory agencies were questioned regarding their knowledge of reports, including experts who attended the US Food and Drug Administration roundtable in September 2010. Three case reports and one case series including seven total cases were identified in which abnormal inflammatory reactions and soft-tissue masses after metal-on-metal disc replacements were consistent with pseudotumor and metal hypersensitivity. Spinal cases are present as pain and neurologic symptoms. On plain radiography, there is no clear periprosthetic osteolysis or loosening. On magnetic resonance imaging, there is increased magnetic susceptibility artifact because of metallic debris that renders images inadequate. Computed tomography myelography demonstrates a soft-tissue mass, which exhibits epidural extension surgically. Histologically, large areas of necrotic debris and exudates are interspersed with chronic inflammatory cells. Lymphocyte or macrophage predominance is determined by the rate of wear and the presence of gross, microscopic, or submicron metallic wear debris. The metallurgy of the involved devices is cobalt-chromium-molybdenum (CoCrMo) alloy, and the bearing surface is CoCrMo-on-CoCrMo. Metal-on-metal spinal arthroplasty devices are subject to postoperative complications because of metallic wear debris with similar clinical, radiographic, histologic, gross anatomic, and device-related features to those found in metal-on-metal bearing surfaces in total hip arthroplasty.

Halo-Gravity Traction Versus Surgical Release Before Implantation of Expandable Spinal Devices

Between 1997 and 2009, 124 children with severe early-onset spinal deformity were treated with the vertical expandable prosthetic titanium rib or growing rods. Before the implantation of the device, 12 underwent halo-gravity traction (HGT) and 13 had a spinal release (SR). This observational study is based on x-rays obtained before and after surgery and at the last follow-up and on medical records. To describe the indications and effectiveness of HGT and SR in young patients treated with expandable devices. Several studies have described the short-term effects of HGT and SR, in particular their safety and effectiveness on severe scoliosis, but none before the implantation of expandable spinal devices in severe early-onset spinal deformity. We measured the thoracic scoliosis and kyphosis, and the radiographic thoracic height and spinal length on x-rays. We also collected postoperative complications. Postoperatively, SR resulted in a better correction of the scoliosis (46 degrees) than HGT or no release (37 and 27 degrees, respectively) but HGT provided a better correction of the kyphosis (48 degrees) than SR or no-spinal release (27 and 9 degrees, respectively). At follow-up, all groups showed a loss of correction of the kyphosis. The postoperative increase in thoracic spine height, which was initially greater in the HGT group because of the traction, became higher in the SR group at follow-up. Device complications occurred in 54% of the participants in the HGT group, 75% in the SR group, and 28% in the control group, and had a negative impact on the final thoracic spine height. Neurologic complications occurred in 8% of the participants and were more frequent in the HGT group (25%). The surgical procedures had different short-term impacts on the curve, which did not necessary predict long-term outcomes (loss of correction, loss of height increase). The risk of device loosening was high in the HGT and SR groups, as was the risk of neurologic loss.

A novel synthetic material for spinal fusion: a prospective clinical trial of porous bioactive titanium metal for lumbar interbody fusion

The objective of this study was to establish the efficacy and safety of porous bioactive titanium metal for use in a spinal fusion device, based on a prospective human clinical trial. A high-strength spinal interbody fusion device was manufactured from porous titanium metal. A bioactive surface was produced by simple chemical and thermal treatment. Five patients with unstable lumbar spine disease were treated surgically using this device in a clinical trial approved by our Ethics Review Committee and the University Hospital Medical Information Network. Clinical and radiological results were reported at the minimum follow-up period of 1 year. The optimal mechanical strength and interconnected structure of the porous titanium metal were adjusted for the device. The whole surface of porous titanium metal was treated uniformly and its bioactive ability was confirmed before clinical use. Successful bony union was achieved in all cases within 6 months without the need for autologous iliac crest bone grafting. Two specific findings including an anchoring effect and gap filling were evident radiologically. All clinical parameters improved significantly after the operation and no adverse effects were encountered during the follow-up period. Although a larger and longer-term follow-up clinical study is mandatory to reach any firm conclusions, the study results show that this porous bioactive titanium metal is promising material for a spinal fusion device.

Clinical significance of different effects of static and pulsed electromagnetic fields on human osteoclast cultures

Electromagnetic fields are known to affect the bone metabolism by modifying some relevant physiologic cell parameters of cells, even though the underlying mechanisms are still unclear. The aim of our study was to evaluate the effect of both static magnetic fields (SMFs) of the same intensity of the one generated by spinal metal devices and pulsed electromagnetic fields (PEMFs) of the same intensity used for the management of nonunion on human osteoclasts cell culture. Primary osteoclast cells were isolated from primary human osteoclast precursors and were exposed to SMFs and to PEMFs. Morphology and tartrate-resistant acid phosphatase (TRAP) activity were evaluated in the osteoclast cultures after 7, 10, and 14 days of exposure. The SMF-exposed cells show a more differentiated phenotype and a significantly higher TRAP activity after 7 and 10 days of treatment with respect to a sham control. PEMF-exposed cells have a less-differentiated phenotype after 7 days of exposure compared with the relative sham control, while the TRAP activity shows no statistically significant differences between exposed and control cells at any observation time. Our results indicate that SMFs of the same intensity of the one generated around spinal devices can affect osteoclast differentiation and activity. Aseptic loosening around titanium implants might be due in part to an increased osteoclast activity and differentiation. PEMFs of the same intensity than the one used for the management of nonunions can affect osteoclasts phenotype after 7 days of exposure, while osteoclasts TRAP activity is not affected by this kind of electromagnetic fields.

Development of a multisegmental test body to calibrate and validate studies with spinal testing devices with follower load

Spinal testing devices need a tool for calibration and comparison of accomplished studies. The objective of this study was the development of a polysegmental test body, which simulates several functional spinal motion units and provides a standard calibration. The test body consists of aluminum moldings simulating the vertebral bodies, rubber discs simulating the intervertebral discs and cylindrical guide elements with ball joints simulating the vertebral joints. The test body was tested multidirectional with a moment of 7.5 Nm and follower loads up to 800 N. The results showed sigmoid load-deformation curves of the test body similar to a human lumbar cadaver spine, but with a higher range of motion (ROM). The follower load had no influence during extension-flexion, but an increasing follower load during lateral bending and rotation caused increased friction and restoring forces with a decrea-sed ROM. The polysegmental test body does not show the same mechanical behavior like a polysegmental human cadaver spine in all directions of motion, but it provides reproducible values without requiring preconditioning as proposed for human specimen. This test body could improve the comparability of cadaver studies performed with different spinal testing devices by standardization of the test set-ups.

OS07F043 Development of new titanium-molybdenum alloys with changeable Young's modulus for spinal fixture devices

Metallic implant rods that are used to design spinal fixtures should have a Young's modulus that is not only sufficiently low to prevent stress shielding for the patient but also sufficiently high to suppress springback for the surgeon. Therefore, there is a need for novel titanium alloys with good biocompatibility and a changeable Young's modulus. Molybdenum is non-toxic, and Ti-Mo alloys possess good biocompatibility. In metastable β-type Ti-Mo alloys, an ω phase can be introduced by deformation at room temperature. This study investigated the effects of deformation-induced phases on the mechanical properties of a metastable β-type Ti-16Mo alloy. The experimental results indicate that the Young's modulus, tensile strength, and Vickers hardness are increased remarkably by cold rolling. The microstructural observation result by transmission electron microscopy (TEM) shows that the deformation-induced ω phase transformation occurs during cold rolling in the Ti-16Mo alloy. Therefore, the increase in Young's modulus of the alloy after cold rolling at room temperature can be attributed to a deformation-induced ω phase.

OS07-2-2 Development of new Ti-Mo alloys with changeable Young's modulus for spinal fixture devices

OS07-2-2 Development of new Ti-Mo alloys with changeable Young's modulus for spinal fixture devices

Biomechanical effect of different interspinous devices on lumbar spinal range of motion under preload conditions

Interspinous devices are used as an alternative to the current gold standard treatment, decompressive surgery with or without fusion, for lumbar spinal stenosis. They are supposed to limit extension and expand the spinal canal and foramen at the symptomatic level, but still allow lateral bending and axial rotation in the motion segment. The aim of the present study is the biomechanical evaluation of the change in the range of motion of the affected and adjacent segments following implantation of different interspinous devices under load in all directions of motion. Eight fresh frozen human cadaver lumbar spines (L2-L5) were tested in a spinal testing device with a moment of 7.5 nm in flexion/extension, lateral bending and rotation with and without a preload (follower load of 400 N). The ROM was measured after implantation of Aperius (Kyphon, Mannheim), In-Space (Synthes, Umkirch), X-Stop (Tikom, Fürth) and Coflex (Paradigm Spine, Wurmlingen) into the segment L3/L4. All interspinous devices caused a significant reduction in extension of the instrumented segment without significantly affecting the other directions of motion. The flexion was reduced by all implants only when the follower load was applied. All devices caused a higher ROM of the whole spine during lateral bending and rotation. The actual evaluated interspinous devices led to a significant reduction in ROM during flexion-extension, but to a significant increase in ROM for the whole specimen (L2-L5) during lateral bending and rotation, which could increase the risk of adjacent segment degeneration.

Rigid and flexible spinal stabilization devices: A biomechanical comparison

The surgical devices for the treatment of degenerative disc disease are based on different concepts (rods for spine fusion, ROM-restricting or load-bearing devices for dynamic stabilization). In the present work, the effects of some stabilization systems on the biomechanics of the lumbar spine were investigated by means of a finite element model of the L2–L5 spine segment. Pedicular screws and stabilization devices were added at L4–L5. Different rods were considered: stainless steel, titanium, PEEK and the composite ostaPek. Two pedicular devices aimed at motion preservation were also considered: the FlexPLUS and the DSS. All models were loaded by using the hybrid protocol in flexion, extension, lateral bending and axial rotation. The spine biomechanics after implantation resulted significantly sensitive to the design and the materials of the device. The impact of all rods in reducing the ROM was found to be critical (>70% in flexion and extension). The dynamic devices were able to preserve the motion of the segment, but with different performances (ROM reduction from 30% (DSS) to 50% (FlexPLUS)). The shared load was more sensitive to the elastic modulus of the device material than the calculated ROMs (from 7% (PEEK) to 48% (stainless steel)). Regarding devices aimed at motion preservation, the authors suggest to distinguish “flexible” devices, which are able to preserve only a minor fraction (e.g. at most 50%) of the physiological ROM, from “dynamic” devices, which induce a smaller ROM restriction. However, the optimal characteristics of a stabilization device for the treatment of degenerative disc disease still need to be determined by means of basic science and clinical studies.

Electric Parameters Optimization in Spinal Cord Stimulation. Study in Conventional Nonrechargeable Systems

Spinal cord stimulation devices provide a means of creating an electric field. The parameters used to produce this electric field are: pulse amplitude, pulse width (Pw), and pulse frequency (F). The purpose is to document the effects that the various stimulus parameters have on patient perception of paresthesia and the relationship that this perception has on pain relief. Stimulus parameters were varied independently keeping the electrode polarity constant while recording stimulation thresholds. The Pw was varied from 195 to 300 µ sec while maintaining the frequency at 50 Hz. The F was varied from 10 to 100 Hz while maintaining the Pw at 300 µ sec. We also measured the paresthesia coverage percentage and the subjective perception of quality reported by the patients with each one of the parameter changes. There was a statistically significant correlation between Pw and all the stimulation thresholds. As for the therapeutic range, the differences observed also were statistically significant. Pw variation did not produce significant differences in coverage and subjective quality of the paresthesia. The perception threshold did not vary significantly with F changes. However, F significantly affected both coverage of the painful area and paresthesia perception quality. In the usual Pw ranges, it seems that its usefulness is limited to obtaining finer adjustments in the stimulation amplitude. Frequency management may be significantly useful to get a wider coverage of the stimulated area.

Computational analysis of bone remodeling during an anterior cervical fusion

The anterior cervical fusion is an established surgical procedure for spine stabilization after the removal of an intervertebral disc. However, it is not yet clear which bone graft represents the best choice and whether surgical devices can be efficient and beneficial for fusion. The aim of this work is to study the influence of the spine instrumentation on bone remodeling after a cervical spine surgery and, consequently, on the fusion process. A finite element model of the cervical spine was developed, having computed tomography images as input. Bone was modeled as a porous material characterized by the relative density at each point and the bone remodeling law was derived assuming that bone self-adapts in order to achieve the stiffest structure for the supported loads, with the total bone mass regulated by the metabolic cost of maintaining bone tissue. Apart from the analysis of healthy cervical spine, different surgical scenarios were tested: bone graft with or without a cage and the use of a stabilization plate system. Results showed that the anterior and posterior regions of the disc space are more important to stress transmission and that spinal devices reduce bone growth within bone grafts, being plate systems the most interfering elements. The material of the interbody cages plays a major role in fusion and, therefore, it should be carefully chosen.