michael wang

As minimally invasive approaches gain popularity in spine surgery, clinical outcomes and effectiveness of mini-open transforaminal lumbar interbody fusion (TLIF) compared with traditional open TLIF have yet to be established. The authors retrospectively compared the outcomes of patients who underwent mini-open TLIF with those who underwent open TLIF. Between 2003 and 2006, 42 patients underwent TLIF for degenerative disc disease or spondylolisthesis; 21 patients underwent mini-open TLIF and 21 patients underwent open TLIF. The mean age in each group was 53 years, and there was no statistically significant difference in age between the groups (p = 0.98). Data were collected perioperatively. In addition, complications, length of stay (LOS), fusion rate, and modified Prolo Scale (mPS) scores were recorded at routine intervals. No patient was lost to follow-up. The mean follow-up was 24 months for the mini-open group and 34 months for the open group. The mean estimated blood loss was 194 ml for the mini-open group and 505 ml for the open group (p < 0.01). The mean LOS was 3 days for the mini-open group and 5.5 days for the open group (p < 0.01). The mean mPS score improved from 11 to 19 in the mini-open group and from 10 to 18 in the open group; there was no statistically significant difference in mPS score improvement between the groups (p = 0.19). In the mini-open group there were 2 cases of transient L-5 sensory loss, 1 case of a misplaced screw that required revision, and 1 case of cage migration that required revision. In the open group there was 1 case of radiculitis as well as 1 case of a misplaced screw that required revision. One patient in the mini-open group developed a pseudarthrosis that required reoperation, and all patients in the open group exhibited fusion. Mini-open TLIF is a viable alternative to traditional open TLIF with significantly reduced estimated blood loss and LOS. However, the authors found a higher incidence of hardware-associated complications with the mini-open TLIF.

SUMMARY OF BACKGROUND DATA:: Percutaneous pedicle screws have become accepted as an effective method for segmental fixation in a variety of settings. However, fixation to the pelvis, which offers unique biomechanical advantages, had remained elusive from a minimally invasive approach. OBJECTIVE:: To ascertain the safety of percutaneous iliac screws implanted placement using fluoroscopic guidance. METHODS:: In an effort to verify the accuracy of a fluoroscopically-guided technique for safe iliosacral screw placement, we reviewed the imaging results from 24 consecutive patients undergoing this procedure. Percutaneous iliac screw placement was accomplished using primarily X-Ray guided screw insertion (obturator outlet view technique) without frameless image-guidance and with limited exposure of bony landmarks or tactile feedback. Indications for surgery included infection, neoplasia, trauma, and deformity. All patients underwent early postoperative CT scanning to determine the accuracy of screw positioning. RESULTS:: A total of 24 patients had 47 screws placed for fixation at the lumbosacral junction. No cases required abortion of the procedure or conversion to an open operation. All of the percutaneous screws were placed appropriately as verified by postoperative CT scanning with three-dimensional reconstruction. There were no hardware related complications. However, one 75 year-old patient suffering a sacral fracture died of medical co-morbidities on postoperative day 10. CONCLUSIONS:: A minimally invasive technique for iliac screw placement can be performed safely with a low likelihood of bony violation. This technique offers the unique biomechanical advantages of iliac fixation without the soft tissue exposure traditionally needed for safe hardware insertion. The technique relies on high quality intraoperative fluoroscopic imaging.

Minimally invasive spine (MIS) procedures are increasingly being recognized as equivalent to open procedures with regard to clinical and radiographic outcomes. These techniques are also believed to result in less pain and disability in the immediate postoperative period. There are, however, little data to assess whether these procedures produce their intended result and even fewer objective data to demonstrate that they are cost effective when compared with open surgery. The authors performed a retrospective analysis of hospital charges for 1- and 2-level MIS and open posterior interbody fusion for lumbar spondylotic disease, disc degeneration, and spondylolisthesis treated at a single academic medical center. Patients presenting with bilateral neurological symptoms were treated with open surgery, and those with unilateral symptoms were treated with MIS. Overall hospital charges and surgical episode-related charges, length of stay (LOS), and discharge status were obtained from the hospital finance department and adjusted for multi-/single-level surgeries. During a 14-month period, 74 patients (mean age 55 years) were treated. The series included 59 single-level operations (75% MIS and 25% open), and 15 2-level surgeries (53% MIS and 47% open). The demographic profile, including age and Charlson Comorbidity Index, were similar between the 4 groups. The mean LOS for patients undergoing single-level surgery was 3.9 and 4.8 days in the MIS and open cases, respectively (p = 0.017). For those undergoing 2-level surgery, the mean LOS was 5.1 for MIS versus 7.1 for open surgery (p = 0.259). With respect to hospital charges, single-level MIS procedures were associated with an average of $70,159 compared with $78,444 for open surgery (p = 0.027). For 2-level surgery, mean charges totalled $87,454 for MIS versus $108,843 for open surgery (p = 0.071). For single-level surgeries, 5 and 20% of patients undergoing MIS and open surgery, respectively, were discharged to inpatient rehabilitation. For 2-level surgeries, the rates were 13 and 29%, respectively. While hospital setting, treatment population, patient selection, and physician expectation play major roles in determining hospital charges and LOS, this pilot study at an academic teaching hospital shows trends for quicker discharge, reduced hospital charges, and lower transfer rates to inpatient rehabilitation with MIS. However, larger multicenter studies are necessary to validate these findings and their relevance across diverse US practice environments.

To assess the safety and stability of thoracic or thoracolumbar deformity correction from a solely posterior approach with placement of modular anterior cages and posterior segmental fixation in one operation. Twenty-eight patients who failed brace trial for 6 months or longer were included in the series. All patients had progressive neurological deficit and/or deformity progression at time of operation. All patients underwent a single operation in the prone position. Segmental fixation was accompanied by anterior column reconstruction using modular cages avoiding nerve root sacrifice. Stackable cages were used for high thoracic deformity. Deformity, Cobb angle, visual analog pain score, and x-ray evaluation of fusion ensued for mean follow-up period of 31 months. Patients achieved a mean sagittal deformity correction of 13.3 degrees +/- 7.4 standard deviation. Improved or maintained American Spinal Injury Association scores were noted in all patients. The mean time of operation was 334 minutes +/- 85 standard deviation, or 6 to 7 hours. At a mean follow-up of 31 months (range, 12-36 mo), the following complications were noted: subsidence greater than 2.5 mm (n = 3), cage migration requiring revision (n = 1), brachial plexopathy from malpositioning (n = 1), and intraoperative cerebrospinal fluid leak managed via lumbar drain (n = 2). Plain and dynamic radiographic evidence of maintained deformity correction was noted in 27 patients. Delayed kyphotic deformity correction of the thoracolumbar spine is achieved via a posterior-only approach. At a mean follow-up period of 31 months, sagittal angles remained acceptable. Improved fusion criteria and patient numbers will be required to determine fusion and loss of correction rates over time.

A major barrier to understanding facetogenic low back pain has been the lack of radiographic diagnostic criteria. This study investigates the correlation between radiographic findings on magnetic resonance imaging (MRI) scans and single photon emission computed tomographic (SPECT) scans in patients clinically found to have facetogenic axial back pain. Thirty-one patients with severe axial back pain underwent lumbar MRI and SPECT scans. Two hundred thirty facets were identified and were graded from 1 to 4 using synovial area, size, cartilaginous discontiguity, osteophytic overgrowth, and joint space obliteration. Twenty-nine "hot" joints were identified on SPECT scans. MRI features of 230 lumbar facets were correlated with SPECT results. Four basic morphological patterns were identified on the basis of synovial appearance on MRI scans, light, mottled, narrowed, and obliterated, and formed the basis for the grading 1 to 4, respectively (sensitivity for "hot facet", 0.93). The mottled group had 0.90 specificity (P = 0.0001). Osteophytic overgrowth demonstrated 0.94 specificity (P = 0.0004). Facet hypertrophy was not associated with increased tracer uptake. We identify four types of synovial architecture on T2-weighted MRI scans with overall high sensitivity for predicting SPECT positivity. These four grades likely represent a continuum of facet degeneration, from a normal to obliterated joint. One particular subtype, Grade 2, demonstrated a high specificity for SPECT and synovial fluid increase suggestive of inflammation. Facet hypertrophy was not predictive of bone scan positivity, perhaps suggesting the protective nature of a hypertrophied facet. Synovial abnormalities correlate with SPECT findings and a grading scale is proposed delineating the degeneration of a lumbar facet over time. A subtype of SPECT(+) inflamed joint is proposed. Further studies will be needed to improve our understanding of the natural history of the lumbar facet.

Numerous new posterior dynamic stabilization (PDS) devices have been developed for the treatment of disorders of the lumbar spine. In this report the authors provide a classification scheme for these devices and describe several clinical situations in which the instrumentation may be expected to play a role. By using this classification, the PDSs that are now available and those developed in the future can be uniformly categorized.

Background/Purpose: Falls are classified as low or high level for triage purposes. Because triage criteria dictate less urgency for low-level falls, this classification scheme has important implications for pediatric emergency care. Methods: Retrospective analysis was conducted of 729 (393 low-level and 336 high-level) pediatric patients treated for fall-related trauma (1992 through 1998). Falls were classified as low (<15 feet) or high-level (≥15 feet). All falls were reported as accidental or unintentional. Results: The overall mortality rate was 1.6% (2.4% for high-level falls compared with 1.0% for low-level falls). All 4 patients who died of a low-level fall had an abnormal head computed tomography (CT) scan and intracranial hypertension. Half of deaths from high-level falls were attributable to intracranial injuries, and half were caused by severe extracranial injuries. Common extracranial injuries were upper extremity fracture (6.2%), lower extremity fracture (5.6%), pulmonary contusion (1.8%), pneumothorax (1.1%), liver laceration (1.1%), bowel injury (1.0%), and splenic injury (2.1%). Orthopedic and thoracic injuries resulted more commonly from high-level falls, whereas abdominal injuries were as likely to occur after a low-level fall. Conclusions: Intracranial injury accounts for the majority of deaths from falls. Children suffering low-level falls were at similar risk for intracranial and abdominal injuries compared with those who fell from greater heights. Pediatric trauma triage criteria should account for these findings. J Pediatr Surg 36:1528-1534. Copyright © 2001 by W.B. Saunders Company.

The aim of the present study was to investigate the effect of polydatin on apoptosis induced by ischemia/reperfusion (I/R) in rat myocardium and to explore the underlying mechanism. Adult male Sprague-Dawley (SD) rats were randomly divided into control, I/R and polydatin (50 mumol/L) groups. On the Langendorff apparatus, isolated rat heart was subjected to 30-min global ischemia followed by 60-min reperfusion. TUNEL labeling and flow cytometric techniques were used for the measurement of apoptosis and the expression of Bcl-2 and Bax protein in cardiomyocytes of rat. The results showed: (1) Compared with those in the control group, the number of TUNEL-positive cells and apoptosis rate were increased in I/R group; (2) Compared with that in the I/R group, the number of TUNEL-positive cells was significantly decreased in the polydatin group [(18.1+/-4.0)% vs (35.1+/-5.4)%, P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.01]; (3) Apoptosis rate assayed by flow cytometry in I/R group was significantly higher than that in polydatin group [(15.43+/-4.55)% vs (8.66+/-3.18)%, P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.01]; (4) Expression level of Bax protein was higher in I/R group than that in polydatin group (P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05), while the level of Bcl-2 protein and Bcl-2/Bax ratio were higher in polydatin group than those in I/R group (P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05, P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.01), respectively. The results obtained suggest that polydatin exerts an inhibitory effect on I/R-induced apoptosis through increasing Bcl-2 protein expression and decreasing Bax protein expression in myocardium of the rat.

The clinical outcome and response to therapy of hepatitis B virus infection differ depending upon viral genotype. Most methods of determining the viral genotype are relatively time-consuming and costly. Moreover, the results of some methods are influenced by single nucleotide mutations. To develop a novel HBV genotyping process insensitive to single nucleotide mutations using an improved reverse dot blot method employing the principle of &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;flow-through hybridization&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;. The flow through reverse dot blot (FT-RDB) method was developed using DNA from different HBV genotypes. HBV sequences from Genebank were used to design primers and probes. Specificity and sensitivity of the method were evaluated with clinical samples in which the HBV viral load was quantified by real-time PCR. Results were compared to those of multiplex PCR and sequencing. Another 59 clinical samples were used to test the clinical applicability of the method. We showed that FT-RDB could be made insensitive to single nucleotide mismatch by adjusting the hybridization temperature. All HBV-negative samples showed no signals in the assay. The detection sensitivity of the method was found to be between 10(3) and 10(4) DNA copies/ml. The results of FT-RDB were 84% concordant with those of multiplex PCR, and 96% concordant with sequencing results in 101 cases. The genotype all 59 clinical samples was accurately identified. We demonstrated that the FT-RDB method was rapid, reliable, accurate and inexpensive. It appears to be useful for routine clinical HBV genotyping even in non-specialized hospital laboratories.

θ- to α-phase transformation of three different nano-sized θ-Al2O3 powders pre-treated with high uniaxial pressure (250–750 MPa) was examined. During phase transformation, the presence of critical crystallite sizes of θ- (dcθ=∼25 nm) and α-Al2O3 (dcα=∼17 nm) and the primary size of α-Al2O3 (dp=∼45 nm) is required. The high pressure induces a removal of the agglomerate state among the θ-Al2O3 crystallites and an increase in bulk density of the green compact. The former eventually creates homogeneity in the interspacing of the θ-particles (=crystallites) that results in a narrowed exothermic peak on the differential thermal analysis (DTA) profile while the latter brings the particles closer in distance, thus resulting in a reduction of the transformation temperature. And the de-agglomeration effect presumably abates the finger growth of α-Al2O3 crystallites.The estimated lowest temperature for the completion of θ- to α-Al2O3 phase transformation using θ-powders derived from boehmite is 1050°C at a heating rate of 10°C/min. And the process duration is about 3.5 min or 35°C on the DTA profile.

To label rat bone marrow mesenchymal stem cells (BMSCs) with superparamagnetic iron oxide (SPIO) in vitro, and to monitor the survival and location of these labeled BMSCs in a rat model of traumatic brain injury (TBI) by susceptibility weighted imaging (SWI) sequence. BMSCs were cultured in vitro and then labeled with SPIO. Totally 24 male Sprague Dawley (SD) rats weighing 200-250 g were randomly divided into 4 groups: Groups A-D (n equal to 6 for each group). Moderate TBI models of all the rats were developed in the left hemisphere following Feeney&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s method. Group A was the experimental group and stereotaxic transplantation of BMSCs labeled with SPIO into the region nearby the contusion was conducted in this group 24 hours after TBI modeling. The other three groups were control groups with transplantation of SPIO, unlabeled BMSCs and injection of nutrient solution respectively conducted in Groups B, C and D at the same time. Monitoring of these SPIO-labeled BMSCs by SWI was performed one day, one week and three weeks after implantation. Numerous BMSCs were successfully labeled with SPIO. They were positive for Prussian blue staining and intracytoplasm positive blue stained particles were found under a microscope (200). Scattered little iron particles were observed in the vesicles by electron microscopy (5000). MRI of the transplantation sites of the left hemisphere demonstrated a low signal intensity on magnitude images, phase images and SWI images for all the test rats in Group A, and the lesion in the left parietal cortex demonstrated a semicircular low intensity on SWI images, which clearly showed the distribution and migration of BMSCs in the first and third weeks. For Group B, a low signal intensity by MRI was only observed on the first day but undetected during the following examination. No signals were observed in Groups C and D at any time points. SWI sequence in vivo can consecutively and noninvasively trace and demonstrate the status and distribution of BMSCs labeled with SPIO in the brain of TBI model rats.

ABSTRACT Modern data centers deliver resources over the cloud for clients to run various applications and jobs with diverse requirements. Today&amp;#39;s cloud resource management is able to support certain Quality of Service (QoS) requirements including reliability and security. However, in many settings such as the military cloud where latency requirement is paramount, existing cloud resource management schemes fall short in providing a systematic framework to meet and balance disparate types of application deadlines, since they are primarily focused on speeding up job executions for timely processing. In this paper we present a self-adaptive, deadline-aware resource control framework that can be implemented in a fully distributed fashion, making it suitable for unreliable environments where a single point of failure is not acceptable. Relying on Nash Bargaining in non-cooperative game theory, our framework allocates cloud resources in an optimal way to maximize the Nash Bargaining Solutions (NBS) with respect to both job priority and deadline. Further, it also enables self-adaptive deadline-aware resource allocation and rebalancing under cyber or physical attacks that may diminish cloud capacity. We validate our technique by performing experiments on the Hadoop framework.

In this paper, a parameterization level set method is presented to simultaneously perform shape and topology optimization of compliant mechanisms. The structural shape boundary is implicitly embedded into a higher-dimensional scalar function as its zero level set, resultantly, establishing the level set model. By applying the compactly supported radial basis function with favorable smoothness and accuracy to interpolate the level set function, the temporal and spatial Hamilton–Jacobi equation from the conventional level set method is then discretized into a series of algebraic equations. Accordingly, the original shape and topology optimization is now fully transformed into a parameterization problem, namely, size optimization with the expansion coefficients of interpolants as a limited number of design variables.Design of compliant mechanisms is mathematically formulated as a general optimization problem with a nonconvex objective function and two additionally specified constraints. The structural shape boundary is then advanced as a process of renewing the level set function by iteratively finding the expansion coefficients of the size optimization with a sequential convex programming method. It is highlighted that the present method can not only inherit the merits of the implicit boundary representation, but also avoid some unfavorable features of the conventional discrete level set method, such as the CFL condition restriction, the re-initialization procedure and the velocity extension algorithm. Finally, an extensively investigated example is presented to demonstrate the benefits and advantages of the present method, especially, its capability of creating new holes inside the design domain.

Lateral mass screw fixation of the subaxial cervical spine has been a major advancement for spinal surgeons. This technique provides excellent three-dimensional fixation from C3 to C7. However, exposure of the dorsal spinal musculature can produce significant postoperative neck pain. The incorporation of a minimal access approach using tubular dilator retractors can potentially overcome the drawbacks associated with the extensive muscle stripping needed for traditional surgical exposures. A retrospective analysis was performed on the first 18 patients treated using lateral mass screws placed in a minimally invasive fashion. All patients, except 2 who were lost to follow-up, had a 2-year minimum clinical follow-up. All patients had a computed tomography (CT) scan in the immediate postoperative period to check the positioning of implanted hardware. Operative time, blood loss, and complications were ascertained. Fusion was assessed radiographically with dynamic radiographs and CT scans. Sixteen of the 18 patients underwent successful screw placement. Two patients had the minimal access procedure converted to an open surgery because radiographic visualization was not adequate in the lower cervical spine. Six cases involved unilateral instrumentation and 10 had bilateral screws. A total of 39 levels were instrumented. There were no intraoperative complications, and follow-up CT scans demonstrated no bony violations except in cases where bicortical purchase was achieved. All patients achieved bony fusion. A minimally invasive approach using tubular dilator retractors can be a safe and effective means for placing lateral mass screws in the subaxial cervical spine. Up to two levels can be treated in this manner. This approach preserves the integrity of the muscles and ligaments that maintain the posterior tension band of the cervical spine but requires adequate intraoperative imaging.

Over the course of the past few decades, it has become apparent that in contrast to previously held beliefs, the adult central nervous system (CNS) may have the capability of regeneration and repair. This greatly expands the possibilities for the future treatment of CNS disorders, with the potential strategies of treatment targeting the entire scope of neurological diseases. Indeed, there is now ample evidence that stem cells exist in the CNS throughout life, and the progeny of these stem cells may have the ability to assume the functional role of neural cells that have been lost. The existence of stem cells is no longer in dispute. In addition, once transplanted, stem cells have been shown to survive, migrate, and differentiate. Nevertheless, the clinical utility of stem cell therapy for neurorestoration remains elusive. Without question, the control of the behavior of stem cells for therapeutic advantage poses considerable challenges. In this paper, the authors discuss the cellular signaling processes that influence the behavior of stem cells. These signaling processes take place in the microenvironment of the stem cell known as the niche. Also considered are the implications attending the replication and manipulation of elements of the stem cell niche to restore function in the CNS by using stem cell therapy.

Cervical arthroplasty is a promising nonfusion alternative for the treatment of degenerative disc disease. After anterior cervical discectomy for neurological decompression, the intervertebral space is reconstructed by use of a metal and polymer prosthesis, allowing semiconstrained motion in multiple planes. This approach allows for preservation of cervical motion, potentially reducing the risk of transitional-level disease.

Atlantal lateral mass screws provide an alternative to C1/C2 transarticular screws and, in some cases, can obviate the need for extending a fusion to the occiput. For these reasons, C1 lateral mass screws are becoming increasingly popular. However, the critical local anatomy and unfamiliarity with this new technique can make C1 screw placement more challenging. Morphometric analysis was performed on 74 cadaveric spines obtained from the Department of Anatomy at the Keck School of Medicine, University of Southern California. Critical measurements were determined for screw entry points, trajectories, and lengths for application of the technique described by Harms and Melcher. The mean height and width for screw entry on the posterior surface of the lateral mass were 3.9 and 7.3 mm, respectively. The maximum medialized screw trajectory ranged from 25 to 45 degrees (mean, 33 degrees). The mean maximal screw length to obtain bicortical purchase was 22.5 mm, and the mean minimum screw depth was 14.4 mm. Screw depths varied on the basis of the entry point, trajectory, and vertebral morphology. The overhang of the posterior arch averaged 11.4 mm (range, 6.9-17 mm). All specimens could accommodate 3.5-mm lateral mass screws bilaterally with proper preparation of the entry site. Significant variations in the morphology of C1 exist. However, the large size of the atlantal lateral mass makes screw placement forgiving. Preoperative computed tomographic scans and intraoperative fluoroscopy are useful in guiding proper screw placement. Close attention should be paid to preparation of the screw entry site.

In this paper we present a new framework to approach the problem of structural shape and topology optimization. We use a level-set method as a region representation with a moving boundary model. As a boundary optimization problem, the structural boundary description is implicitly embedded in a scalar function as its “iso-surfaces.” Such level-set models are flexible in handling complex topological changes and are concise in describing the material regions of the structure. Furthermore, by using a simple Hamilton–Jacobi convection equation, the movement of the implicit moving boundaries of the structure is driven by a transformation of the objective and the constraints into a speed function that defines the level-set propagation. The result is a 3D structural optimization technique that demonstrates outstanding flexibility in handling topological changes, the fidelity of boundary representation, and the degree of automation, comparing favorably with other methods in the literature based on explicit boundary variation or homogenization. We present two numerical techniques of conjugate mapping and variational regularization for further enhancement of the level-set computation, in addition to the use of efficient up-wind schemes. The method is tested with several examples of a linear elastic structure that are widely reported in the topology optimization literature.

Spinal cord injury (SCI) is a catastrophic neurological event with no proven treatments that protect against its consequences. Potential benefits of hypothermia in preventing/limiting central nervous system injury are now well known. There has been an interest in its potential use after SCI. This article reviews the current experimental and clinical evidence on the use of therapeutic hypothermia in patients with SCI. Review of literature. There are various mechanisms by which hypothermia is known to protect the central nervous system. Modest hypothermia (32°C-34°C) can deliver the potential benefits of hypothermia without incurring the complications associated with deep hypothermia. Several recent experimental studies have repeatedly shown that the use of hypothermia provides the benefit of neuroprotection after SCI. Although older clinical studies were often focused on local cooling strategies and demonstrated mixed results, more recent data from systemic hypothermia use demonstrate its safety and its benefits. Endovascular cooling is a safe and reliable method of inducing hypothermia. There is robust experimental and some clinical evidence that hypothermia is beneficial in acute SCI. Larger, multicenter trials should be initiated to further study the usefulness of systemic hypothermia in SCI.

The technique of lateral mass screw and rod or plate fixation is a major advancement in the posterior instrumentation of the cervical spine. This technique provides rigid three-dimensional fixation, restores the dorsal tension band, and provides highly effective stabilization in patients with many types of traumatic injuries. Patient 1 was a 32-year-old man who had been in a motor vehicle accident. He presented with right C5 radiculopathy. X-ray findings included 45% anterolisthesis of C4 on C5, bilateral facet disruption, and right unilateral C4-C5 facet fracture and dislocation. The patient was placed in Gardner-Wells tongs, and the fracture was reduced with 25 pounds of traction. Patient 2 was a 56-year-old woman who had been in a motor vehicle accident that resulted in complete quadriplegia. Her initial imaging studies revealed a C3-C4 right unilateral facet fracture with subluxation. She was placed in traction, and her neurological status was reassessed. The findings of her neurological examination revealed improvement: she was found to have Brown-Séquard syndrome. Patient 3 was a 33-year-old man who was involved in a diving accident that resulted in bilaterally jumped facets at C3-C4. The patient was neurologically intact, and attempts at closed reduction were not successful. Patients 1 and 2 underwent anterior cervical discectomy with iliac crest autograft fusion and plating. They were then placed in the prone position, and a dilator tubular retractor system was used to access the facet joint at the level of interest. The facet joints were then denuded and packed with autograft. Lateral mass screws were then placed by means of the Magerl technique, and a rod was used to connect the top-loading screws. Patient 3 underwent posterior surgery that included only removal of the superior facet, intraoperative reduction, and bilateral lateral mass screw and rod placement. This technical note describes the successful placement of lateral mass screw and rod constructs with the use of a minimally invasive approach by means of a tubular dilator retractor system. This approach preserves the integrity of the muscles and ligaments that maintain the posterior tension band of the cervical spine.

Expansile laminoplasty has been successfully used to treat cervical myelopathy attributable to canal stenosis. However, detachment of the posterior cervical muscles is thought to contribute to postoperative axial neck pain and kyphosis. Minimizing the amount of muscular dissection might reduce the likelihood of these sequelae. Six human cadaveric spines were used to assess the feasibility of a minimally invasive laminoplasty technique. A 22-mm tubular dilator port was used to access the lamina-facet junctions from C2 to C7, through bilateral stab incisions at C4-C5 and C5-C6. Troughs at the lamina-facet junctions were drilled bilaterally, and the contiguous laminae were lifted en bloc from one side. Ten-millimeter rib allograft spacers were inserted to maintain a gap on the open side. Exposure of six cervical levels was easily accomplished with two small incisions on each side. Drilling was achieved without dural violations. The midsagittal spinal canal diameter was increased by a mean of 38% and the spinal canal area was increased by an average of 43% at the level of C5. A minimally invasive approach for cervical laminoplasty could be performed in human cadavers. The measured increases in spinal canal space approximated those demonstrated to be associated with stabilization or improvement of neurological status.

In this paper we address the problem of structural shape and topology optimization in a multi-material domain. A level-set method is employed as an alternative approach to the popular homogenization-based methods of rule of mixtures for multi-material modeling. A multi-phase level-set model is adapted for material and topology representation. This model eliminates the need for a material interpolation or phase mixing scheme. It only requires m level-set functions to represent a structure of n=2m different material phases, in a principle similar to combining colors from the three primary colors. Therefore, this multi-phase model may be referred to as a “color” level-set representation which has its unique benefits: it is flexible to handle complex topologies; it substantially reduces the number of model functions when n>3; it automatically avoids the problem of overlap between material phases of a conventional partitioning approach. We describe numerical techniques for efficient and robust implementation of the method, by embedding a rectilinear grid in a fixed finite element mesh defined on a reference design domain. This would separate the issues of accuracy in numerical calculations of the physical equation and in the level-set model propagation. A gradient projection method is described for incorporating multiple constraints in the problem. Finally, the benefits and the advantages of the developed method are illustrated with several 2D examples of mean compliance minimization of multi-material structures.

Thoracic and lumbar pedicle screws have become popular because of their biomechanical superiority over other methods of spinal fixation. However, the safety and efficacy of transpedicular screws depend on their proper placement. Recent advances in imaging have resulted in the ability to acquire three-dimensional (3-D) axial images of the spine during surgery, and this study was undertaken to assess the reliability of this technology to detect pedicle violations. Pedicle screws were placed in six human cadaver spines from T1 to S1 using standard techniques. Intentional pedicle violations were created in 74 of 216 pedicles, and violations were graded on a four-point scale (range, 0-3). Radiographic images were then obtained using a conventional spiral computed tomographic scanner and the Siremobil Iso-C 3D (Siemens Medical Solutions, Erlangen, Germany) 3-D fluoroscopy unit. An independent neuroradiologist then graded pedicle violations as ascertained by the two imaging modalities. Using direct inspection of the pedicles as the &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;gold standard,&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; the overall sensitivity and specificity for detecting pedicle violations were 0.716 and 0.789, respectively, with 3-D fluoroscopy. The overall sensitivity and specificity for detecting pedicle violations were 0.608 and 0.937, respectively, with conventional computed tomography. All Grade 2 pedicle violations were detected in the thoracic spine by both modalities, and all Grade 3 violations were detected by both modalities. Axial images obtained with 3-D fluoroscopy demonstrate a higher sensitivity but lower specificity than conventional computed tomographic scanning for assessing pedicle violations. By providing real-time intraoperative imaging, 3-D fluoroscopy may enhance the safety of thoracic transpedicular instrumentation.

Resorbable polylactic acid spinal implants have recently become commercially available. These spacers carry the advantages of allowing for clear visualization of new bone growth, eliminating the risk of pathogen transmission, and providing for consistent biomechanical quality. However, previously published reports on the use of these spacers have all utilized bone morphogenetic proteins to supplement the fusion. This report describes our early experience with the use of these devices for interbody reconstruction in anterior cervical discectomy with fusion. Twenty patients underwent an anterior cervical discectomy with fusion at 30 levels during an 18-month period. All patients were implanted with polylactic acid interbody spacers using the Smith-Robinson technique. Supplementary anterior cervical plating was applied using unicortical semiconstrained screws, and the spacers were filled with vertebral endplate autograft bone shavings. Seven of the patients were smokers, and three were diabetics. Radiographic fusion was determined with dynamic cervical spine x-rays, and clinical responses were determined using the Medical Outcomes Study Short-Form 36-Item Health Survey, Odom&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s criteria, Nurick scores, and functional outcome swallowing score dysphagia scores. Follow-up averaged 11.6 months. Of the 9 patients with myelopathy, all experienced clinical improvement, with the mean Nurick score improving from 2.7 to 1.3. Of the 14 patients who had radiculopathy, 9 had complete resolution of symptoms, 4 experienced some improvement, and 1 had no improvement. All 20 patients demonstrated radiographic fusion at last follow-up as demonstrated by bridging bone between the vertebral bodies and the absence of motion on dynamic x-rays. Resorbable polylactic acid interbody spacers are safe and effective for anterior cervical discectomy and fusion. Use of locally harvested vertebral endplate bone packed within the spacer is sufficient to promote fusion in anterior cervical discectomy with fusion.

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This paper presents a multiphase level set method of piecewise constants for shape and topology optimization of multi-material piezoelectric actuators with in-plane motion. First, an indicator function which takes level sets of piecewise constants is used to implicitly represent structural boundaries of the multiple phases in the design domain. Compared with standard level set methods using n scalar functions to represent 2n phases, each constant value in the present method denotes one material phase and 2n phases can be represented by 2n pre-defined constants. Thus, only one indicator function including different constant values is required to identify all structural boundaries between different material phases by making use of its discontinuities. In the context of designing smart actuators with in-plane motions, the optimization problem is defined mathematically as the minimization of a smooth energy functional under some specified constraints. Thus, the design optimization of the smart actuator is transferred into a numerical process by which the constant values of the indicator function are updated via a semi-implicit scheme with additive operator splitting (AOS) algorithm. In such a way, the different material phases are distributed simultaneously in the design domain until both the passive compliant host structure and embedded piezoelectric actuators are optimized. The compliant structure serves as a mechanical amplifier to enlarge the small strain stroke generated by piezoelectric actuators. The major advantage of the present method is to remove numerical difficulties associated with the solution of the Hamilton–Jacobi equations in most conventional level set methods, such as the CFL condition, the regularization procedure to retain a signed distance level set function and the non-differentiability related to the Heaviside and the Delta functions. Two widely studied examples are chosen to demonstrate the effectiveness of the present method.

This paper proposes a new level set method for structural shape and topology optimization using a semi-implicit scheme. Structural boundary is represented implicitly as the zero level set of a higher-dimensional scalar function and an appropriate time-marching scheme is included to enable the discrete level set processing. In the present study, the Hamilton–Jacobi partial differential equation (PDE) is solved numerically using a semi-implicit additive operator splitting (AOS) scheme rather than explicit schemes in conventional level set methods. The main feature of the present method is it does not suffer from any time step size restriction, as all terms relevant to stability are discretized in an implicit manner. The semi-implicit scheme with additive operator splitting treats all coordinate axes equally in arbitrary dimensions with good rotational invariance. Hence, the present scheme for the level set equations is stable for any practical time steps and numerically easy to implement with high efficiency. Resultantly, it allows enhanced relaxation on the time step size originally limited by the Courant–Friedrichs–Lewy (CFL) condition of the explicit schemes. The stability and computational efficiency can therefore be greatly improved in advancing the level set evolvements. Furthermore, the present method avoids additional cost to globally reinitialize the level set function for regularization purpose. It is noted that the periodically applied reinitializations are time-consuming procedures. In particular, the proposed method is capable of creating new holes freely inside the design domain via boundary incorporating, splitting and merging processes, which makes the final design independent of initial guess, and helps reduce the probability of converging to a local minimum. The availability of the present method is demonstrated with two widely studied examples in the framework of the structural stiffness designs.

Abstract: This paper addresses the problem of struc-tural shape and topology optimization. A level set method is adopted as an alternative approach to the pop-ular homogenization based methods. The paper focuses on four areas of discussion: (1) The level-set model of the ...

We present a level set based shape and topology optimization method for maximizing the simple or repeated first eigenvalue of structure vibration. Considering that a simple eigenvalue is Fréchet differentiable with respect to the boundary of a structure but a repeated eigenvalue is only Gateaux or directionally differentiable, we take different approaches to derive the boundary variation that maximizes the first eigenvalue. In the case of simple eigenvalue, material derivative is obtained via adjoint method, and variation of boundary shape is specified according to the steepest descent method. In the case of N-fold repeated eigenvalue, variation of boundary shape is obtained as a result of a N-dimensional algebraic eigenvalue problem. Constraint of a structure’s volume is dealt with via the augmented Lagrange multiplier method. Boundary variation is treated as an advection velocity in the Hamilton–Jacobi equation of the level set method for changing the shape and topology of a structure. The finite element analysis of eigenvalues of structure vibration is accomplished by using an Eulerian method that employs a fixed mesh and ersatz material. Application of the method is demonstrated by several numerical examples of optimizing 2D structures.

Parting direction is one of the main parameters that significantly affect mouldability and manufacturing costs of a cast part. In conventional optimal design of cast part, a parting direction is pre-selected by a designer and fixed throughout the optimization. However, when the optimization is performed with a different parting direction, the resulting design will also be different, and more importantly it will end up with different working performance. Therefore, we take the parting direction as a design variable in the optimization of a cast part so that the working performance can be optimized as much as possible. With these goals, a level set based method is proposed for the simultaneous optimization of cast part and parting direction. In each iteration, an optimal parting direction is first computed for the current structure, then the boundary of the current structure is updated by a design velocity that guarantees the design be moldable with the optimal parting direction. Therefore, although the parting direction may be changed during the optimization, the structure will always be moldable in the current parting direction. Numerical examples are provided in 3D.