Target Vertebra Research Articles

Optimizing Lumbar Pedicle Screw Trajectory Utilizing a 3D-Printed Drill Guide to Ensure Placement of Pedicle Screws Into Higher Density Bone May Improve Pedicle Screw Pullout Resistance

Lower preoperative Hounsfield Unit (HU) values of vertebral body are associated with pedicle screw (PS) loosening after implantation with traditional trans-pedicular trajectory. However, the relationship between trajectory HU value and PS fixation quality remains unknown. This study aimed to investigate if 3-dimensionally (3D)-printed guider directed accurate implantationof pedicle screw could increase the anti-pulling properties of screws. 3D models of cadaveric spines were reconstructed by using computed tomography image and PS trajectories were designed for both sides of vertebra. The designed trajectories were divided into high HU group and low HU group. PS implantation with 3D-printed screw guide can be in complementary shape with target vertebra. Throughout 3D finite element analysis and biomechanical tests, the pull-out strength of screws in high or low trajectoryHU groups were compared. The HU value was 132 ± 13 (mean ± standard deviation) in low HU group and 189 ± 17 in high HU group. The distance between planned trajectories and actual trajectories was 1.69 ± 0.4 mm. Biomechanical tests showed that in the high trajectory HU group the pull-out strength of screws was 750.41 ± 80.65 N; compared with 655.83 ± 74.31 N in the low trajectory HU group, the difference was statistically significant. When simulated with the finite element method, the pull-out strength of low HU trajectory pedicle screws was lower than that of high HU trajectory pedicle screws. Preoperative computer-assisted trajectory design using a 3D-printed screw guide may direct more accurate implantation with optimal implantation trajectory, and may provide a new way to improve pedicle screw fixation.

Reduction of inter-observer differences in the delineation of the target in spinal metastases SBRT using an automatic contouring dedicated system

BackgroundApproximately one third of cancer patients will develop spinal metastases, that can be associated with back pain, neurological symptoms and deterioration in performance status. Stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT) have been offered in clinical practice mainly for the management of oligometastatic and oligoprogressive patients, allowing the prescription of high total dose delivered in one or few sessions to small target volumes, minimizing the dose exposure of normal tissues. Due to the high delivered doses and the proximity of critical organs at risk (OAR) such as the spinal cord, the correct definition of the treatment volume becomes even more important in SBRT treatment, thus making it necessary to standardize the method of target definition and contouring, through the adoption of specific guidelines and specific automatic contouring tools. An automatic target contouring system for spine SBRT is useful to reduce inter-observer differences in target definition. In this study, an automatic contouring tool was evaluated.MethodsSimulation CT scans and MRI data of 20 patients with spinal metastases were evaluated. To evaluate the advantage of the automatic target contouring tool (Elements SmartBrush Spine), which uses the identification of different densities within the target vertebra, we evaluated the agreement of the contours of 20 spinal target (2 cervical, 9 dorsal and 9 lumbar column), outlined by three independent observers using the automatic tool compared to the contours obtained manually, and measured by DICE similarity coefficient.ResultsThe agreement of GTV contours outlined by independent operators was superior with the use of the automatic contour tool compared to manually outlined contours (mean DICE coefficient 0.75 vs 0.57, p = 0.048).ConclusionsThe dedicated contouring tool allows greater precision and reduction of inter-observer differences in the delineation of the target in SBRT spines. Thus, the evaluated system could be useful in the setting of spinal SBRT to reduce uncertainties of contouring increasing the level of precision on target delivered doses.

Three-Dimensional Printing Guide Template Assisted Percutaneous Vertebroplasty (PVP).

Percutaneous vertebroplasty (PVP) is considered an effective treatment for the back pain caused by osteoporotic vertebral compression fracture. The accuracy of PVP mainly depends on the surgeons' experience and multiple fluoroscopes during a traditional procedure. Puncture related complications were reported all over the world. To make the surgical procedure more precise and decrease the rate of puncture-related complications, our team applied a three-dimensional printing guide template to PVP to modify the traditional procedure. This protocol introduces how to model target vertebrae DICOM imaging data into three-dimensions in the software, how to simulate operation in this 3-D model, and how to use all of the surgical data to reconstruct a patient specific template for application. Using this template, surgeons can identify suitable puncture points accurately to improve the accuracy of the operation. The whole protocol includes: 1) diagnosis of the osteoporotic vertebral compression fracture; 2) acquisition of CT imaging of the target vertebra; 3) simulation of the operation in the software; 4) design and fabrication of the 3-D printing guide template; and 5) application of the template into an operation procedure.

Registration of MRI to intraoperative radiographs for target localization in spinal interventions

Decision support to assist in target vertebra localization could provide a useful aid to safe and effective spine surgery. Previous solutions have shown 3D–2D registration of preoperative CT to intraoperative radiographs to reliably annotate vertebral labels for assistance during level localization. We present an algorithm (referred to as MR-LevelCheck) to perform 3D–2D registration based on a preoperative MRI to accommodate the increasingly common clinical scenario in which MRI is used instead of CT for preoperative planning.Straightforward adaptation of gradient/intensity-based methods appropriate to CT-to-radiograph registration is confounded by large mismatch and noncorrespondence in image intensity between MRI and radiographs. The proposed method overcomes such challenges with a simple vertebrae segmentation step using vertebra centroids as seed points (automatically defined within existing workflow). Forwards projections are computed using segmented MRI and registered to radiographs via gradient orientation (GO) similarity and the CMA-ES (covariance-matrix-adaptation evolutionary-strategy) optimizer. The method was tested in an IRB-approved study involving 10 patients undergoing cervical, thoracic, or lumbar spine surgery following preoperative MRI.The method successfully registered each preoperative MRI to intraoperative radiographs and maintained desirable properties of robustness against image content mismatch and large capture range. Robust registration performance was achieved with projection distance error (PDE) (median ± IQR) = 4.3 ± 2.6 mm (median ± IQR) and 0% failure rate. Segmentation accuracy for the continuous max-flow method yielded dice coefficient = 88.1 ± 5.2, accuracy = 90.6 ± 5.7, RMSE = 1.8 ± 0.6 mm, and contour affinity ratio (CAR) = 0.82 ± 0.08. Registration performance was found to be robust for segmentation methods exhibiting RMSE <3 mm and CAR >0.50.The MR-LevelCheck method provides a potentially valuable extension to a previously developed decision support tool for spine surgery target localization by extending its utility to preoperative MRI while maintaining characteristics of accuracy and robustness.

The Accuracy of Locating Lumbar Vertebrae When Using Palpation Versus Ultrasonography

ObjectiveThe purpose of this study was to determine the accuracy of locating lumbar vertebrae using palpation vs ultrasonography. MethodsIn this study, ultrasonic imaging was used by 2 experienced clinicians to identify the third lumbar spinous process (target) of a female participant. The target was then located by 16 undergraduate chiropractic students using clinical palpation techniques learned in their academic program (with participant seated and prone) and ultrasonic imaging learned through a 5-minute training video. Presumed target locations identified by students were recorded by infrared motion capture equipment. The coordinates of the presumed target site were then compared statistically. ResultsThere was no significant difference between the presumed target position identified by the students using sitting and prone palpation (P = .346). These positions were significantly different from the target location identified by expert clinicians using ultrasonic imaging (P < .0001 in both cases). The vertebra identified by ultrasonic imaging by the students was the same vertebra identified by the expert clinicians using ultrasound. This position error in the vertebra identified by palpation resulted in the students mistakenly identifying the L4 spinous process as the target vertebra. ConclusionsThis study found that ultrasonography provided more accurate identification of a lumbar spinal landmark when compared with palpation. In addition, our data suggest that ultrasonic imaging to identify spinal landmarks can be learned easily and can improve accuracy of landmark detection. Although the time to use ultrasonic imaging was greater than with palpation, these results suggest that this procedure could potentially be used in clinical practice to identify spinal landmarks.

Long-term outcomes of vertebral column resection for kyphosis in patients with cured spinal tuberculosis: average 8-year follow-up.

OBJECTIVE The authors conducted a study to evaluate the long-term clinical and radiographic outcomes of vertebral column resection (VCR) for kyphosis in patients with cured spinal tuberculosis. METHODS This was a retrospective study. Between 2003 and 2009, 28 consecutive patients with cured spinal tuberculosis underwent VCR for kyphosis in which the target vertebra was removed completely. Autologous iliac crest bone graft or titanium mesh packed with autograft was placed into the osteotomy gap to reconstruct the spine for anterior column stability. Posterior pedicle screw fixation and fusion were typically performed. Radiographic parameters, including kyphosis angle and sagittal balance, were measured, and visual analog scale score, America Spinal Injury Association grade, Scoliosis Research Society outcome instrument (SRS-22) score, Oswestry Disability Index, patient satisfaction index, and long-term complications were evaluated. RESULTS This study included 12 males and 16 females, with an average age of 20.9 years at the time of surgery. The average follow-up was 96.9 months. No deaths occurred in this study. At the final follow-up, the kyphosis angle improved from the preoperative average of 70.7° to the final follow-up average of 30.2°, and the average kyphosis correction loss was 8.5°. The sagittal balance averaged 15.4 mm before surgery, 2.8 mm after surgery, and 5.4 mm at the final followup. Thirteen patients showed improvement of more than 1 America Spinal Injury Association grade. The visual analog scale, Oswestry Disability Index, and SRS-22 scores improved significantly, and the overall satisfaction rate was 92.9%. Adjacent-segment degeneration occurred in 3 patients. No severe instrumentation-related complications were observed. CONCLUSIONS The long-term safety and efficacy of the VCR technique for treating spinal tuberculosis-related kyphosis were favorable, and no severe late-stage complications appeared. Lumbar tubercular kyphosis showed a tendency for sagittal decompensation within the first 3 postoperative years. Cases of adjacent-segment degenerations were relatively few and mild without clinical symptoms.

Simple and Economical Method to Create Thoracolumbar Burst Fracture in a Calf Spine Model.

Study DesignCalf spine model study.PurposeTo describe a technique of creating thoracolumbar burst fractures in calf spine model by low weight drop weight.Overview of LiteratureBurst fractures are one of the commonest types of thoracolumbar fractures and their treatment is controversial. Biomechanical studies aid in the decision of treatment of these fractures. A simple method of creation of burst fractures would help these biomechanical studies.MethodsTen specimens of thoracolumbar spines harvested from 6–8 week old calves were weakened at the target vertebra by standardized osteotomy cuts. Burst fractures were created by dropping a 5-kg of weight from a height of 1.2 m using an in-house device. An accelerometer attached to the weight measured the acceleration at the point of impact.ResultsAverage weight and bone mineral density of the specimens was 390 g and 0.67 g/cm2, respectively. Computed tomography scan analysis of the fractures revealed McCormack grade 2 and grade 3 fractures in 5 and 3 specimens, respectively, Dennis type 2B in 4, type 2A burst fractures in 5 specimens and fracture dislocation in 1 specimen, AO type A3.1.1 in 4 specimens, type A3.2.2 in 4 and type A3.3.3 in 2 specimens. Vertical laminar split fracture was seen in 6 specimens. Average acceleration and energy at impact was 9.04 m/sec and 54.24 Nm, respectively.ConclusionsWe describe a technique to create thoracolumbar burst fractures in calf spine by a drop weight method using a device that is simple to operate and easy to construct. The method is consistent and produces fractures similar to those occurring naturally, and can be considered as an alternative method for creating burst fractures in biomechanical studies.

Discrete decreased activity in the lower thoracic spine on FDG PET/CT: another respiration-related artifact.

We observed that the diaphragmatic motion causing the well-known, so-called banana artifact on PET/CT images may additionally cause decreased FDG activity involving 1 or 2 lower thoracic vertebrae. The aim of this study was (1) to formally evaluate if this observation is indeed true and, if so, (2) to assess its frequency. One hundred fifty-four PET/CT scans (81 males and 73 females, age 61 ± 13 years) were analyzed. On the coronal CT images, the vertebra above where the hemi-diaphragmatic surfaces abut the vertebral column was defined as the target vertebra (TV). On sagittal PET images, FDG activity in TV was visually and quantitatively assessed. Then, the severity of banana artifact on coronal PET images was graded from 0 to 2: 0 if there was no artifact, 1 if a thin photopenic stripe, and 2 if a thick banana-shaped photopenic artifact in the vicinity of diaphragm. Visually decreased activity in TV was present in 0% (0/93), 3% (1/34), and 59% (16/27) of scans graded as 0, 1, and 2, respectively (grade 0 and/or 1 vs. grade 2, P < 0.001). The SUV ratio of TV to reference vertebrae were 0.99 ± 0.14, 0.99 ± 0.15, and 0.84 ± 0.19 in grade 0, 1, and 2 scans, respectively (P < 0.001). Error of attenuation correction from respiratory motion can lead to underestimation of FDG activity in the lower thoracic spine, and this should not be interpreted as possible marrow replacement process requiring further imaging if there is coexisting banana artifact.

Robotic system for cervical spine surgery

In contemporary surgical clinical practice, spinal instability is often treated with mechanical stabilization techniques in order to protect the spinal cord and nerve roots. These techniques involve placing screws in defined regions of the vertebrae, typically the pedicle, where the strongest bone is found. The challenge for the surgeon is the accurate placement of screws for good mechanical purchase and to avoid damage to surrounding vital anatomical structures. This is especially critical in the cervical region, where the target bone mass is smaller and the spinal cord, nerve roots and vertebral arteries are all at risk. A robotic system enabling the surgeon to precisely place implants into the vertebrae should enhance safety and may potentially improve surgical results. We describe such a system, which consists of a compact robot positioned using a passive structure, an optical tracking system, a surgical input device and planning and navigational software. The implant trajectory in each vertebra is planned preoperatively, using fine-cut computerized tomography (CT) scans. During surgery, registration matching between the CT scan and the patient's anatomy is achieved using point to point registration, refined with a surface merge technique. Approximate robot positioning is done passively by the surgeon. Final precise instrument positioning is performed by the robot according to the planned trajectory through the target vertebra. Implants (screws) are then placed through the robot-guided working channel. Six cadaver experiments, consisting of placing transarticular (i.e. crossing the joints between the vertebrae) screws in the upper two vertebrae of the human cervical spine, were performed. Implant placement accuracy was comparable with that achieved using freehand image-guided techniques by an experienced surgeon. These results confirm the utility and applicability of the system. It is currently in redesign to improve accuracy and to render it compatible with on-line planning.

The relation between the application angle of spinal manipulative therapy (SMT) and resultant vertebral accelerations in an in situ porcine model

It has been hypothesized that the posterior tissues of the spine are frictionless and therefore allow only the normal force component of spinal manipulative therapy (SMT) to pass to underlying vertebrae. Given this assumption, vertebrae could not be moved in practitioner-defined directions by altering the application angle of SMT. To investigate this possibility, porcine lumbar spines were excised and then SMT applied at 90° to the posterior tissues of the target vertebra. A standard curve was constructed of increasing SMT force versus vertebral acceleration. SMT forces were then applied at 60° and 120° and the resulting accelerations substituted into the standard curve to obtain the transmitted force. Results showed that vertebral accelerations were greatest at a 90° SMT application angle and decreased in all axes at application angles ≠ 90°. The average decrease in transmitted force using application angles of 60° and 120° was within 5% of the predicted absolute value. In this model, SMT applied at a non-normal angle does not increase vertebral acceleration in that same direction, but acts to reduce transmitted force. This work provides justification for future studies in less available human cadavers. It is not yet known if variations in SMT application angle have relevance to clinical outcomes or patient safety.

SU‐GG‐T‐462: Intra‐Fractional Motion of Bony Targets in the Spine and Pelvis During Extra‐Cranial SRS Treatment

Purpose: to quantify intra‐fractional motion of bony targets with respect to the immobilization cradle during extra‐cranial SRS treatments. Method and Materials: Pre and post treatment cone beam scans were acquired of 64 patients undergoing either single fraction or hypo‐fractionated therapy to tumors in the torso. The median dose delivered in a treatment session was 24 Gy. In the cone beam scans, both the target and the immobilization cradle are visible. Target shifts were determined by computing the difference in the target to target 3D registration, and the cradle to cradle 3D registration. Cradle to cradle registration was done manually. The registration target was either the involved vertebra, or the vertebra at the level of the actual target. Target registration was done automatically using a region of interest encompassing the target vertebra and extending midway into the adjacent vertebrae. Patients were monitored throughout treatment using a stereoscopic infra‐red tracking system. Results: The mean and standard deviation of the shift in target position in the left‐right, posterior‐anterior, and superior‐inferior directions were 0.0±1.4, 0.0±1.0, and 0.2±1.2 mm respectively. The rotations about the corresponding axes, determined from a separate 6D fit, were 0.0±0.7, 0.0±0.5, and 0.0±0.7 degrees, respectively. The length of time between the pre and post treatment scans was 48±15 minutes (mean±std.dev). No correlation was seen between the magnitude of the target shift and the length of time between scans, or between the magnitude of shift and the vertebral level. No indications of radiation induced myelopathy have been seen. Outliers (shifts &gt; 3mm in at least one direction) were seen in 8 patients. Conclusion: Although this form of immobilization works well for most patients, the existence of outliers indicates the importance of infra‐red surveillance.

Mesh-morphing algorithms for specimen-specific finite element modeling

Despite recent advances in software for meshing specimen-specific geometries, considerable effort is still often required to produce and analyze specimen-specific models suitable for biomechanical analysis through finite element modeling. We hypothesize that it is possible to obtain accurate models by adapting a pre-existing geometry to represent a target specimen using morphing techniques. Here we present two algorithms for morphing, automated wrapping (AW) and manual landmarks (ML), and demonstrate their use to prepare specimen-specific models of caudal rat vertebrae. We evaluate the algorithms by measuring the distance between target and morphed geometries and by comparing response to axial loading simulated with finite element (FE) methods. First a traditional reconstruction process based on μCT was used to obtain two natural specimen-specific FE models. Next, the two morphing algorithms were used to compute mappings from the surface of one model, the source, to the other, the target, and to use this mapping to morph the source mesh to produce a target mesh. The μCT images were then used to assign element-specific material properties. In AW the mappings were obtained by wrapping the source and target surfaces with an auxiliary triangulated surface. In ML, landmarks were manually placed on corresponding locations on the surfaces of both source and target. Both morphing algorithms were successful in reproducing the shape of the target vertebra with a median distance between natural and morphed models of 18.8 and 32.2 μm, respectively, for AW and ML. Whereas AW–morphing produced a surface more closely resembling that of the target, ML guaranteed correspondence of the landmark locations between source and target. Morphing preserved the quality of the mesh producing models suitable for FE simulation. Moreover, there were only minor differences between natural and morphed models in predictions of deformation, strain and stress. We therefore conclude that it is possible to use mesh-morphing techniques to produce accurate specimen-specific FE models of caudal rat vertebrae. Mesh morphing techniques provide advantages over conventional specimen-specific finite element modeling by reducing the effort required to generate multiple target specimen models, facilitating intermodel comparisons through correspondence of nodes and maintenance of connectivity, and lends itself to parametric evaluation of “artificial” geometries with a focus on optimizing reconstruction.

Real-time CT Fluoroscopy (CTF)-Guided Vertebroplasty in Osteoporotic Spine Fractures

The purpose of this study was to evaluate the clinical feasibility, benefits, and limitations of CT fluoroscopy (CTF)-guided percutaneous vertebroplasty (PVP). PVP under the guidance of CTF without additional guidance by conventional C-arm fluoroscopy was performed in a total of 29 vertebral bodies in 21 patients with vertebral compression fractures. While monitoring sectional CTF images, the needle was advanced from the skin to the target vertebra. Contrast media and polymethylmethacrylate (PMMA) were injected into the target vertebra with careful monitoring of their distribution. After the procedure, an evaluation was conducted to determine whether extraosseous leakage of PMMA occurred and whether sufficient filling of PMMA had been achieved. Needle placement into the target vertebra was easily achieved with both the transpedicular and posterolateral approaches. Injection of PMMA and venous leakage of contrast media were carefully monitored in all patients, and early detection of PMMA leaking was achieved in 5 patients. Extraosseous leakage that had not been detected during the procedure was not found upon postoperative evaluation. Pain scales were significantly decreased after the procedure, and no obvious complications occurred following the procedure. CTF-guided PVP without the combined use of C-arm fluoroscopy was feasible and showed definite benefits. We believe that, in spite of some limitations, CTF-guided PVP provides an alternative technique appropriate in certain situations.

Dynamic response of the cervical spine to posteroanterior mobilisation

Background. Posteroanterior mobilisation is a manual therapy technique that is commonly used in the examination and treatment of neck pain, but little is known about its biomechanical effect. The purpose of this study was to determine the intervertebral movements of the cervical spine produced by posteroanterior mobilisation. Methods. The cervical spines of nineteen healthy subjects were scanned using an open interventional magnetic resonance imaging scanner. Posteroanterior mobilisation forces were applied to the fifth cervical vertebra whilst they were in the prone position. Sagittal images of the spine were obtained before and during mobilisation. Findings. It was shown that posteroanterior mobilisation of the cervical spine generally produced extension of the upper motion segments and flexion of the lower segments. The middle segments were inconsistent in the direction of rotation. The cervical lordosis was found to increase with repeated PA loading cycles. Interpretation. The magnitude of intervertebral movement produced by mobilisation is small. Forces applied at one spinous process produced not only movements at the target vertebra but also movements of the entire cervical spine resulting in an increase in lordosis. Mobilisation should be interpreted as three-point bending of the entire cervical spine, rather than simple gliding of one vertebra upon another.

Surface-based registration accuracy of CT-based image-guided spine surgery.

Registration is a critical and important process in maintaining the accuracy of CT-based image-guided surgery. The aim of this study was to evaluate the effects of the area of intraoperative data sampling and number of sampling points on the accuracy of surface-based registration in a CT-based spinal-navigation system, using an optical three-dimensional localizer. A cadaveric dry-bone phantom of the lumbar spine was used. To evaluate registration accuracy, three alumina ceramic balls were attached to the anterior and lateral aspects of the vertebral body. CT images of the phantom were obtained (1-mm slice thickness, at1-mm intervals) using a helical CT scanner. Twenty surface points were digitized from five zones defined on the basis of anatomical classification on the posterior aspects of the target vertebra. A total of 20 sets of sampling data were obtained. Evaluation of registration accuracy accounted for positional and rotational errors. Of the five zones, the area that was the largest and easiest to expose surgically and to digitize surface points was the lamina. The lamina was defined as standard zone. On this zone, the effect of the number of sampling points on the positional and rotational accuracy of registration was evaluated. And the effects of the additional area selected for intraoperative data sampling on the registration accuracy were evaluated. Using 20 surface points on the posterior side of the lamina, positional error was 0.96 mm +/- 0.24 mm root-mean-square (RMS) and rotational error was 0.91 degrees +/- 0.38 degrees RMS. The use of 20 surface points on the lamina usually allows surgeons to carry out sufficiently accurate registration to conduct computer-aided spine surgery. In the case of severe spondylosis, however, it might be difficult to digitize the surface points from the lamina, due to a hypertrophic facet joint or the deformity of the lamina and noisy sampling data. In such cases, registration accuracy can be improved by combining use of the 20 surface points on the lamina with surface points on other zones, such as on the both sides of the spinous process.

Interruption of the bilateral segmental arteries at several levels: influence on vertebral blood flow.

The effect of ligation of the bilateral segmental arteries at the levels of T11, T12, and T13 on blood flow of the T12 vertebra was studied in a dog model. To determine the reduction of the vertebral blood flow resulting from interruption of bilateral segmental arteries at one to three vertebral levels. Intraoperative hemorrhage can be sometimes massive in patients with hypervascular spinal tumors, especially in radical resection such as total en bloc spondylectomy. The recent development of new embolization techniques ensures more aggressive, more extensive, and safer preoperative embolization for spinal tumors. The blood flow of the T12 vertebra of 12 female dogs was measured after ligation of the bilateral segmental arteries at one to three levels, including the T12. Spinal cord evoked potentials were recorded in this procedure. Spinal angiography using a silicon compound was performed on another 10 dogs after clipping and section of the bilateral segmental arteries. The blood flow of the T12 vertebra decreased to 70.13 +/- 6.37% of the control value after ligation of the bilateral segmental arteries of T12, to 46.48 +/- 8.97% after ligation of the bilateral segmental arteries of T12 and either T11 or T13, to 24.11 +/- 8.31% after ligation of T11, T12, and T13, respectively. The angiogram after ligation and section of T12 and the two levels including T12 showed thick and clear contrast medium in the cut distal ends of the T12 segmental arteries. After interruption at three levels (T11, T12, and T13), however, the cut distal ends of the T12 segmental arteries were seen thin and faint on the angiogram. No significant changes occurred in spinal cord evoked potentials after ligation of the segmental arteries at three levels in all six dogs. Interruption of the bilateral segmental arteries at three levels, one target vertebra and the two adjacent vertebrae, reduced the blood flow of the target vertebra to one fourth of the control value in the lower thoracic spine in dogs. This result suggests that preoperative embolization at three levels, the levels of the tumor vertebra and the adjacent vertebrae above and below it, may reduce intraoperative hemorrhage effectively during total en bloc spondylectomy for hypervascular spinal tumors.

Assessment of lumbar spine kinematics using dynamic MRI: a proposed mechanism of sagittal plane motion induced by manual posterior-to-anterior mobilization.

Descriptive study. The purpose of this study was to describe the segmental motion of the lumbar spine during a posterior-to-anterior (PA) mobilization procedure using dynamic magnetic resonance imaging and to propose a mechanism of the lumbar spine's motion as a result of a PA force to a lumbar spinous process. Studies reporting kinematic descriptions of PA mobilization are in agreement that motion takes place at all lumbar vertebrae. However, these studies differ in the reported direction of motion. Twenty asymptomatic subjects (mean age +/- SD, 31.1 +/- 7.0 years) participated in this study. For each subject, a PA mobilization force was manually applied at each lumbar spinous process while sagittal plane magnetic resonance images were simultaneously obtained. Intervertebral motion was defined as the change in the intervertebral angle between the resting and end range vertebral positions imparted by the PA pressure. PA force applied at 1 spinous process caused motion at the target vertebra and this motion was propagated caudally and cranially. Motion at the target segment was always into extension. A PA force applied at a single lumbar spinous process caused motion of the entire lumbar region. The magnitude and direction of intervertebral motions varied with the segment at which the PA force was applied. We postulated that the intervertebral motion induced by a PA force on a spinous process could be in part explained by the morphology of the lumbar spine.