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Using the largest three-dimensional particle-in-cell simulations to date, collisionless magnetic reconnection in large-scale electron-positron plasmas without a guide field is shown to involve complex interaction of tearing and kink modes. The reconnection onset is patchy and occurs at multiple sites which self-organize to form a single, large diffusion region. The diffusion region tends to elongate in the outflow direction and become unstable to secondary kinking and formation of "plasmoid-rope" structures with finite extent in the current direction. The secondary kink folds the reconnection current layer, while plasmoid ropes at times follow the folding of the current layer. The interplay between these secondary instabilities plays a key role in controlling the time-dependent reconnection rate in large-scale systems.

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Expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) subunit mRNAs were assayed in the ventral mesencephalon of rats that received either a unilateral microinjection of the dopamine neurotoxin 6-hydroxydopamine (6-OHDA; Experiment 1) or repeated treatment with amphetamine (Experiment 2). GluR2 levels were decreased 1 and 3 days after the lesion, and GluR1 and GluR3 levels also showed a transient decrease at 1 day after the lesion. Repeated amphetamine treatment did not significantly alter GluR1-4 levels measured 30 min after the third or tenth amphetamine injection, even though locomotor sensitization was obtained. Thus, while the present results indicate that AMPA receptor subunits are associated with dopamine-containing cell bodies in the ventral mesencephalon, these transcripts may not be responsible for the development of amphetamine sensitization.

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Current population studies characterize idiopathic scoliosis as a single-gene disorder that follows the patterns of mendelian genetics, including variable penetrance and heterogeneity. The role of melatonin and calmodulin in the development of idiopathic scoliosis is likely secondary, with indirect effects on growth mechanisms. Reported abnormalities of connective tissue, skeletal muscle, platelets, the spinal column, and the rib cage are all thought to be secondary to the deformity itself. Although no consistent neurological abnormalities have been identified in patients with idiopathic scoliosis, it is possible that a defect in processing by the central nervous system affects the growing spine. The true etiology of idiopathic scoliosis remains unknown; however, it appears to be multifactorial.

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Thrombolytic therapy with t-PA for acute ischemic stroke may provide benefit in long-term outcome. This retrospective study was undertaken to evaluate appropriateness of the National Institute of Neurological Disorders and Stroke (NINDS) protocol in the emergency department (ED). All patients with appropriate International Classification of Diseases, 9th revision (ICD-9) codes indicating stroke who presented to our 387-bed trauma-I community hospital during 1997 were included in the study. Of the nearly 35,000 patients screened, 201 patients satisfied our inclusion criteria. Mean age was 73.5 +/- 13.3 years. Men were evaluated and transported to computed tomography more rapidly and older patients more slowly. Nonwhites were more likely to arrive via emergency medical services (EMS). Average time from EMS arrival at scene to ED arrival was 22.7 minutes, and from ED arrival to triage was 8.4 minutes. The most common reason for exclusion from t-PA administration was delayed presentation (n = 188); this is the most serious barrier to use of t-PA for acute ischemic stroke. Extensive public education may combat this.

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The clinical outcome of posterolateral lumbar and lumbosacral fusions with facet screw fixation using the Boucher technique is reviewed retrospectively. The Boucher technique uses AO cortical screws that traverse the facet joint at an angle from the superior lamina, in a medial to lateral direction, to enter the respective inferior pedicle. The procedure was performed on 57 consecutive patients who had a degenerative disk disease. The pre-operative diagnosis was based on a physical examination and radiographs with myelography performed when deemed necessary. Surgery had been indicated and performed on patients with unresolved pain after 6 months of conservative therapy; radiographic signs of disk space narrowing, facet arthrosis, degenerative spondylolisthesis or instability on flexion and extension views. No prior history of spinal surgery, no involvement in any litigation or Workers Compensation process, and no detected psychiatric disturbances were also inclusion criteria for this study. Eighteen consecutive male and 39 consecutive female patients were included in the study. The average age at the time of surgery was 41.8 years. The mean active clinical follow-up (office visits) time was 5.06 months with the minimum follow-up time of 3 months. Two years after their surgery, all the patients were asked to fill out a questionnaire from which their progress was evaluated. All questionnaires were completed and returned. Postoperatively, patients were placed in either a lumbosacral corset, short rigid lumbosacral molded polypropylene brace or body cast. Overall clinical results for single level fusions showed that 91.2% of patients (31 of 34) had excellent results and 8.8% (3 of 34) had poor results. Of the multiple level fusions, 86.4% of patients (19 of 22) had excellent or good results and 9.1% (2 of 22) had poor results. Post-operative complications included only three wound infections at the iliac crest donor site. This study demonstrates that facet screw fixation using the Boucher technique has advantages. The technique not only is easy to implement by placing a small screw through a facet joint and it's respective pedicle, but produces excellent clinical results that are comparable to the other more bulky spinal instrumentation systems.

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The author presents the basic biomechanical concepts linked with spine implant testing. The paper also contains the methodology of in vitro and in vivo spine implant testing. The physical and biological properties of various materials and devices commonly used in spine surgery are discussed in relation to their role in spine surgery. The paper clearly shows how all these parameters influence surgical strategy for the spine and more importantly how the choice of methods and devices influences the long term results of spinal surgery. The author also presents the biomechanical repercussions of a failed spine and his own concept of an "ideal" fusion.

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During orthotopic liver transplantation (OLT) for fulminant hepatic failure (FHF), some patients develop cerebral injury secondary to intracranial hypertension. We monitored intracranial pressure (ICP) and cerebral perfusion pressure (CPP) before and during OLT in 12 FHF patients undergoing transplantation. All four patients who had normal ICP preoperatively maintained normal ICP/CPP throughout OLT. During OLT, four of the eight patients with pretransplant intracranial hypertension had six episodes of ICP increase. These episodes of intracranial hypertension occurred during failing liver dissection (n=3) and graft reperfusion (n=3). At the end of the anhepatic phase, the ICP was lower than the preoperative ICP in all patients, and was below 15 mmHg in all but one patient. These data suggest that in FHF patients who develop intracranial hypertension before OLT, dissection of the native liver and graft reperfusion are associated with a risk of brain injury resulting from intracranial hypertension and cerebral hypoperfusion.

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Appropriate levels for instrumentation and fusion in scoliosis have been a matter of debate among surgeons since the introduction of operative management of this deformity. We set out to examine the hypothesis that the amount of correction achieved in all planes during surgical instrumentation of a curve should be less than, or comparable to, the degree of correction attainable at any non-instrumented adjacent curve. An algorithm was designed to facilitate preoperative planning and intraoperative performance of spinal fusion procedures in the management of scoliosis. To test the validity of the hypothesis and the proposed algorithm, measurements were taken from the preoperative radiographs of 200 patients. The dimensions of the curves were obtained from an initial set of four X-ray films: (1) standing anteroposterior film of the whole spine, (2) standing lateral film of the whole spine, (3) two properly performed side-bending films including each curve of the spine. With this data, a plan was designed using the algorithm. The results of this plan were compared with the actual results of the surgery, which were revealed only at this stage. All patients in whom actual instrumentation levels fell within those predicted by the proposed algorithm had no imbalance at follow-up. All patients whose actual instrumentation levels were short of those recommended by the algorithm showed obvious imbalance on final postoperative standing radiograph.

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At times one pedicle screw cannot be used in a posterior construct because of morphometric reasons or when the pedicle is fractured intraoperatively. It is not clear from the literature whether and to what extent a construct's stability is compromised by substituting a hook claw for one pedicle screw. A synthetic vertebra model using a hook claw in lieu of a pedicle screw in a compressive and torsional mechanical study is evaluated. Isola screw-based constructs varying in the number of pedicle screws and hook claws were used. To recreate a realistic clinical scenario, transverse connectors and a Harms cage were used as well. In compression, substituting screws with claws did not substantially change the stiffness, whereas substituting one or two pedicle screws with one or two hook claws significantly reduced torsional stiffness. We conclude that using one or two hook claws is a viable alternative for pedicle screws when the latter cannot be used in a clinical situation, especially as an adjunct when the anterior column is reconstructed.

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To determine the net contribution of a spinal construct to stability, and whether extending the construct to another level in situations in which a defective pedicle cannot have a screw inserted, we performed biomechanical tests in which we evaluated three-, four-, and five-level synthetic spinal constructs in which the location and number of pedicle screws were varied above and below a vertebrectomy defect. We subjected all constructs to axial, compression, lateral bending, flexion, extension, and torsional forces with the use of an Instron biaxial machine. Left-right symmetrical constructs were more stable than asymmetrical ones. Three-level constructs were statistically stiffer than the longer ones in compression, left bending, and flexion. Torsional stability, however, was greater in the longer constructs. Five-level constructs with both end screws in place had greater torsional stiffness than when they were missing a screw. In vertebrectomy defects, if four screws cannot be placed across it, then the engagement of two screws is indicated. The stability provided by a single screw at a spinal level is minimal. Additional screws augment the purchase of the construct in the bone; however, they do not afford further protection to the defect.

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Biomechanical studies have shown hooks to be superior to pedicle screws in pull-out, especially in osteoporosis. This study evaluates the possible increase in stiffness of pedicle screws provided by laminar hooks while applying non-destructive forces to a vertebrectomy model assembled with Compact Cotrel Dubousset (CCD) instrumentation. Synthetic vertebrae were employed in a three-level vertebrectomy model. CCD screw-based three-level constructs with and without sublaminar hooks in the caudal element were tested in flexion, extension, compression, lateral bending, and torsion. There was no statistically significant advantage in adding inferior laminar hooks to a caudal end vertebra that had bilateral pedicle screws in any of the testing modes. Torsional stability, however, was augmented, but not significantly. Torsional instability and osteoporotic bone may be the clinical justifications for adding laminar hooks below screws in the caudal end vertebra.

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Familial dysautonomia (FD) is a rare autosomal recessive disease occurring in Jews of Ashkenazi descent, with only some 500 recognized cases. The causative gene was identified on chromosome 9. FD is of considerable orthopedic interest, because of the prevalence of skeletal deformity. About 90% of surviving dysautonomic children will develop a spinal curvature, commonly a scoliosis. The scoliotic curve is usually kyphotic rather than lordotic, and appears during the first decade of life. Fifty-one of the 90 reported cases of familial dysautonomia in Israel involved patients who were seen at the scoliosis clinic for assessment and treatment of their spinal deformities. Most of the patients presented with a scoliotic deformity associated in 37 cases with an increased thoracic kyphosis. In our series orthotic treatment and physiotherapy were found to be minimally successful at best. Surgical treatment of the spine was performed in 13 of 51 patients in this series. A retrospective review of these patients' charts and radiographs was carried out. Six years of follow-up are reported. The primary indication for surgery was progression of the spinal curve. Only posterior spinal fusions were performed. Anterior transthoracic procedures were avoided in spite of the significance of the kyphotic deformity, because of the frequency of pulmonary complications. Harrington distraction and compression instrumentation was used. Three-millimeter compression rods were used in a distraction mode in thin, young children. "Harri-Luque" segmental sublaminar wiring technique and Wisconsin spinous process segmental wiring was used in some. In all cases, the spine fusion was supplemented by bank bone only, to avoid the additional trauma of graft removal. We believe that surgical intervention is advantageous, if done early in the evolution of spinal deformity. Greater technical difficulties and a higher complication rate were encountered in this series relative to the problems usually seen after spinal deformity surgery in children; this is all the more important in a disease in which general anesthesia is an additional major complicating factor. It is hoped that the improved physical condition now seen after early gastrostomy and fundoplication will aid in reducing this high complication rate. Only a small degree (about 25%) of correction was achieved in the majority of patients. Some of this apparent rigidity derived from the inability to apply sufficient instrumental corrective force because of the friable osteoporotic bone. After surgery, there was a marked decrease in the frequency of pneumonia and an improvement in the degree of ataxia, for reasons not understood, which led to an obvious improvement in the quality of life.

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Single-site variants in the calmodulin-binding domain of RC3/neurogranin were heterologously expressed in Xenopus oocytes to examine their effects on serotonin-evoked currents. RC3 variants serine36 -->alanine (Ser36-->Ala), serine36-->glycine (Ser36-->Gly), and phenylalanine37-->tryptophan (Phe37-->Trp), which bind calmodulin but are deficient in protein kinase C (PKC) phosphorylation, display serotonin-evoked Ca(2+)-dependent Cl- currents in oocytes similar to control oocytes. A serine36-->aspartate (Ser36-->Asp) variant, which does not bind calmodulin and mimics the PKC-phosphorylated state of RC3, significantly enhances serotonin-evoked currents in a manner similar to wild-type. The results suggest that RC3 not only regulates the availability of free calmodulin in a dendritic spine but also, when phosphorylated, independently stimulates G-protein coupled second messenger pathways that generate inositol 1,4,5-trisphosphate (IP3), diacylglycerol (DAG) and intracellular Ca2+.

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Degenerative changes in the spine, specifically disc degeneration and facet arthrosis, and osteoporosis are conditions that primarily affect the elderly and may significantly impact the quality of life. The relationship between osteoporosis and degenerative changes in the hip joint has been studied, but their correlation in the spine is not entirely clear. Two hundred ninety-four subjects older than 50 years of age were retrospectively studied for the existence of lumbar spinal degeneration and osteoporosis through radiologic examination for 3 clinical manifestations: (1) disc degeneration, (2) facet joint arthrosis, and (3) lumbar osteoporosis. Peripheral osteoporosis in the distal radius of the nondominant hand was measured using a single-photon bone absorptiometer. Results indicated that subjects with severe osteoporosis in the distal radius also had severe degenerative changes in the discs and the facets; those with mild osteoporosis in the distal radius showed a tendency to have a lesser degree of degenerative changes than the subjects without osteoporosis.

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When introduced, the Wisconsin segmental spine instrumentation (WSSI) and the Cotrel Dubousset instrumentation (CDI) were promoted as technical advances for the correction of spinal deformities. Both systems provide acceptable correction and greatly reduce the need for postoperative immobilization. A retrospective study of a homogeneous group of 53 adolescent patients with idiopathic scoliosis with King Type II curves who had reached skeletal maturity at follow-up was conducted to compare and analyze the results of these two systems. Thirty-six of these patients had been operated on using WSSI and 17 had been operated on using CDI. CDI and WSSI were found to be equally effective in treating King Type II curves. No difference was found between the two groups in the fusion rates, spinal balance, time required for surgery, or amount of curve correction. The answer to the question of which system is "better" depends on the surgeon's experience and familiarity with the equipment.

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