Spatial regularity of InAs-GaAs quantum dots: quantifying the dependence of lateral ordering on growth rate

The lateral ordering of arrays of self-assembled InAs-GaAs quantum dots (QDs) has been quantified as a function of growth rate, using the Hopkins-Skellam index (HSI). Coherent QD arrays have a spatial distribution which is neither random nor ordered, but intermediate. The lateral ordering improves as the growth rate is increased and can be explained by more spatially regular nucleation as the QD density increases. By contrast, large and irregular 3D islands are distributed randomly on the surface. This is consistent with a random selection of the mature QDs relaxing by dislocation nucleation at a later stage in the growth, independently of each QD’s surroundings. In addition we explore the statistical variability of the HSI as a function of the number N of spatial points analysed, and we recommend N > 10³ to reliably distinguish random from ordered arrays.

Achieving regionalization through rural interhospital transfer

Regionalization of emergency medical care aims to provide consistent and efficient high-quality care leading to optimal clinical outcomes by matching patient needs with appropriate resources at a network of hospitals. Regionalized care has been shown to improve outcomes in trauma, myocardial infarction, stroke, cardiac arrest, and acute respiratory distress syndrome. In rural areas, effective regionalization often requires interhospital transfer. The decision to transfer is complex and includes such factors as capabilities of the presenting hospital; capacity at the receiving hospital; and financial, geographic, and patient-preference considerations. Although transfer to a comprehensive center has proven benefits for some conditions, the transfer process is not without risk. These risks include clinical deterioration, limited resource availability during transport, vehicular crashes, time delays for time-sensitive care, poor communication between providers, and neglect of patient preferences. This article reviews the transfer decision, financial implications, risks, and considerations for patients undergoing rural interhospital transfer. We identify several strategies that should be considered for development of the regionalized emergency health care system of the future and identify areas where further research is necessary.

Interaction of Mn with GaAs and InSb: incorporation, surface reconstruction and nano-cluster formation

The deposition of Mn on to reconstructed InSb and GaAs surfaces, without coincident As or Sb flux, has been studied by reflection high energy electron diffraction, atomic force microscopy and scanning tunnelling microscopy. On both Ga- and As-terminated GaAs(0 0 1), (2 × n) Mn-induced reconstruction domains arise with n = 2 for the most well ordered reconstructions. On the Ga-terminated (4 × 6), the Mn-induced (2 × 2) persists up to around 0.5 ML Mn followed by Mn nano-cluster formation. For deposition on initially β2(2 × 4)-reconstructed GaAs(0 0 1), the characteristic trench structure of the reconstruction is partially preserved even beyond 1 monolayer Mn coverage. On both the β2(2 × 4) and c(4 × 4) surfaces, MnAs-like nano-clusters form alongside the reconstruction changes. In contrast, there are no new Mn-induced surface reconstructions on InSb. Instead, the Sb-terminated surfaces of InSb (0 0 1), (1 1 1)A and (1 1 1)B revert to reconstructions characteristic of clean In-rich surfaces after well defined coverages of Mn proportional to the Sb content of the starting reconstruction. These surfaces are decorated with self-assembled MnSb nanoclusters. These results are discussed in terms of basic thermodynamic quantities and the generalized electron counting rule.

Depth-dependent magnetism in epitaxial MnSb thin films: effects of surface passivation and cleaning

Depth-dependent magnetism in MnSb(0001) epitaxial films has been studied by combining experimental methods with different surface specificities: polarized neutron reflectivity, x-ray magnetic circular dichroism (XMCD), x-ray resonant magnetic scattering and spin-polarized low energy electron microscopy (SPLEEM). A native oxide ∼4.5 nm thick covers air-exposed samples which increases the film's coercivity. HCl etching efficiently removes this oxide and in situ surface treatment of etched samples enables surface magnetic contrast to be observed in SPLEEM. A thin Sb capping layer prevents oxidation and preserves ferromagnetism throughout the MnSb film. The interpretation of Mn L(3,2) edge XMCD data is discussed.

Verifying and evaluating progressive addition lenses in clinical practice

BACKGROUND

Despite the fact that more than 50% of multifocal lenses dispensed in the United States are progressive addition lenses, adequate methods for clinical verification of these lenses have been lacking. Using automated lens meter techniques, the author describes a simplified method for verification of these complex lenses.

METHODS

Thirty pairs of progressive lenses were measured in a modified method using a Humphrey 330 Lens Analyzer. Fifteen pairs were "premium-quality" progressive lenses: fifteen pairs were "non-premium-quality" progressives. Five criteria were assessed on each lens: Distance Zone Width (DZW). Intermediate Zone Width (IZW), Near Zone Width (NZW), Drop Distance (DD), and Maximum Astigmatic Distortion (MAD).

RESULTS

"Premium-quality" progressive lenses failed to demonstrate clear-cut superiority over "non-premium-quality" progressive lenses in the five specified criteria. Individual measurements indicate considerable product inconsistency affected every brand tested.

CONCLUSIONS

Premium- and non-premium-quality progressive lenses demonstrated similar performance characteristics in this study. Zone size variation in these lenses was found to be considerable, a characteristic that seemed to cut across brand lines. The AO Compact lens seemed to demonstrate a shorter drop distance than other lenses, which does enhance its suitability for use with small frames. A comparison of the Essilor Natural PAL to the Younger Image lens showed little difference in the categories measured, although peripheral distortions seemed closer to the reading zone in the image. A comparison of the MAD of lenses in this study to lenses tested in 1986 indicates a considerable improvement has been made in that important characteristic.

Cranial nerve palsy as a complication of operative traction

STUDY DESIGN

Case report.

OBJECTIVE

This report documents one case of diplopia from abducens (sixth cranial) nerve palsy after spinal surgery using a Jackson table and cranial traction.

SUMMARY OF BACKGROUND DATA

Cranial nerve deficits have frequently been described in the orthopedic literature after trauma, halo pelvic traction, and halo skeletal fixation. The theorized mechanism of injury to the abducens nerve involves stretch or traction force, which causes localized ischemia or a change in nerve position. An extensive literature search failed to show this type of injury using Gardner-Wells tongs in conjunction with the Jackson table.

METHODS

This is a case report that included a chart review, examination of the patient, and a literature search.

RESULTS

The patient had complete spontaneous resolution of abducens nerve dysfunction within 6 months.

CONCLUSIONS

It is important for the surgeon to be aware of this potential complication and to inform patients who have diplopia that develops from abducens nerve palsy that most of these cranial nerve deficits spontaneously improve.

Spinal anesthesia for elective lumbar spine surgery

STUDY OBJECTIVE

To evaluate a large series of elective lumbar spine surgical procedures by a single surgeon whose patients were all offered spinal anesthesia.

DESIGN

Retrospective chart review.

SETTING

Tertiary-care teaching hospital.

MEASUREMENTS AND MAIN RESULTS

The records of all elective lumbar spine procedures between 1984 and 1995 performed by one surgeon (GRB) were obtained, and 803 were identified. Of those 803 patients, 611 accepted spinal anesthesia. Data collected included patient demographics, details of the spinal and general anesthesia, perioperative complications, and impact of the spinal anesthetic options on the outcome of spinal anesthesia. General and spinal anesthesia patients were comparable for age, gender, height, and ASA physical status. Patients who received spinal anesthesia were significantly heavier than the general anesthesia patients. Among perioperative complications, nausea and deep venous thrombosis occurred significantly more often in the general than spinal anesthesia patients. Mild hypotension and decreased heart rate (HR) were the most common hemodynamic changes with spinal anesthesia, whereas hypertension and increased HR were the result of general anesthesia. Among spinal anesthetic drugs, plain bupivacaine was associated with the lowest incidence of supplemental local anesthetic use intraoperatively compared to hyperbaric bupivacaine or hyperbaric tetracaine.

CONCLUSION

Spinal anesthesia is an effective alternative to general anesthesia for lumbar spine surgery and has a reduced rate of minor complications.

Newer management options in patients with spinal metastasis

For some patients with spinal metastasis and spinal cord compression, newer surgical techniques are better than laminectomy or radiotherapy alone in relieving pain and restoring function. While radiotherapy remains the standard for spinal metastases due to myeloma, lymphoma, and many types of adenocarcinoma, proper surgical treatment can significantly improve function and outcome in selected patients.

Ischaemic optic neuropathy after spinal fusion

PURPOSE

We report a case of ischaemic optic neuropathy which occurred after prolonged spine surgery in the prone position in an obese, diabetic patient.

CLINICAL FEATURES

The patient was a 44-yr-old, 123 kg, 183 cm man for decompressive laminectomy and instrumented fusion of the lumbar spine. Anaesthesia was induced with thiopentone, fentanyl and succinylcholine and maintained with nitrous oxide, oxygen, isoflurane and a fentanyl infusion. He was positioned prone on the Relton-Hall frame and had an uneventful intraoperative course. Estimated blood loss was 3,000 ml. He was taken to the surgical intensive care unit (SICU) and the trachea was extubated 3.5 hr later. He had no pulmonary or haemodynamic problems and went to a regular nursing floor in the morning. He was discharged home on postoperative day #5. He telephoned his surgeon on postoperative day #7 to say that his vision had been blurry since surgery. His visual acuity was decreased, and on examination, he had a bilateral papillary defect, optic swelling and a splinter haemorrhage in the right eye. Magnetic resonance imaging (MRI) scan of the head and orbits detected no other abnormality. Based on this examination, he was felt to have bilateral ischaemic optic neuropathy and treated conservatively. By postoperative day #47, his visual acuity was greatly improved and near normal. Careful review of possible contributing factors suggests that the cause of the ischaemic optic neuropathy was venous engorgement.

CONCLUSION

This patient developed ischaemic optic neuropathy from a prolonged interval in the prone position of the Relton-Hall frame, which may be related to venous engorgement.

The surgical management of patients with rheumatoid cervical spine disease

Rheumatoid arthritis is an inflammatory disease that commonly affects the cervical spine. This article reviews the incidence of spinal involvement, the clinical manifestations of spinal disease, and the types of instability patterns that may occur and their radiographic diagnosis. Appropriate guidelines for obtaining imaging studies and for surgical referral is also described. Finally, the role of surgical stabilization is discussed.

Surgical treatment of spinal tumors

The surgical treatment of spinal tumors depends on a host of factors that include: the type of tumor and its location within the spine, the presence or absence of neural compression, the portion of the vertebrae involved, the anticipated mode of spinal failure, the biology of the tumor, the anticipated life expectancy of the patient, and the type of prior or subsequent adjuvant treatment. Two thirds of all spinal tumors arise from the vertebral body and only 1/3 originate from the posterior elements. Malignant tumors more commonly involve the vertebral body and benign lesions usually are located posteriorly. Malignant tumors, because of their aggressive nature and their propensity for anterior vertebral body involvement, are associated with a higher incidence of neurologic deficit than are benign lesions. The surgical treatment of spinal tumors is dictated largely by the location of the tumor within the spine; anterior vertebral body tumors generally should be approached anteriorly, whereas posterior lesions should be approached posteriorly. Because most malignant tumors, whether primary or secondary (metastatic), are located anteriorly within the vertebral body, most surgery for malignant tumors should be approached anteriorly. Anterior decompression should be accompanied by reconstruction with biologic materials such as autogenous bone graft unless life expectancy is certain to be very limited (<6 months).

Calcium pyrophosphate dihydrate crystal deposition disease as a cause of lumbar canal stenosis

STUDY DESIGN

This study measured the incidence of calcium pyrophosphate dihydrate crystal deposition in specimens of ligamenta flava in consecutive patients undergoing decompressive laminectomy between 1984 and 1991. The results were compared to determine the difference between calcium pyrophosphate dihydrate-negative patients with lumbar canal spinal stenosis.

OBJECTIVES

The results were compared with cadaver specimens and literature values to determine if calcium pyrophosphate dihydrate crystal deposition disease contributes to the thickening of the ligamentum flavum and thereby contributes to spinal stenosis.

SUMMARY OF BACKGROUND DATA

Calcium pyrophosphate dihydrate crystal deposition disease has been described in the axial skeleton. Hypertrophy of the ligamentum flavum has been suggested to contribute to stenosis. The association of calcium pyrophosphate dihydrate disease and hypertrophied ligamenta flava has not been fully defined nor linked to neurologic symptoms and signs.

METHODS

The incidence of calcium pyrophosphate dihydrate crystal deposition in specimens of ligamenta flava obtained from four groups was measured: specimens obtained during surgery from 102 consecutive patients undergoing decompression laminectomy between 1984 and 1991, 47 additional pathologic specimens of ligamentum flavum tested between 1984 and 1991, 222 calcium pyrophosphate dihydrate-positive Pathology Department specimens collected between 1980 and 1991, and, as control specimens from 20 cadavers. The associated patient histories were reviewed for the first two groups; no histories were available for the cadaver group.

RESULTS

The incidence of calcium pyrophosphate dihydrate crystal deposition was 24.5% in the ligamentum flavum among the surgical patients, 31% among the Pathology Department specimens, 33.8% among the calcium pyrophosphate dihydrate-positive Pathology Department specimens, and 5% among the cadavers. No associated medical conditions with calcium pyrophosphate dihydrate crystal deposition were found among the medical histories. Patients with the symptoms of spinal stenosis who were also calcium pyrophosphate dihydrate-negative patients with symptoms of less than 6 months' and less than 24 months' duration (P < 0.001). Except for time to presentation, calcium pyrophosphate dihydrate-negative patients had similar signs and symptoms of lumbar canal spinal stenosis. Having previous spine surgery did not produce a statistically significant risk of having calcium pyrophosphate dihydrate crystal deposition. No specific laboratory tests were found to be of predictive value.

CONCLUSIONS

These findings suggest that calcium pyrophosphate dihydrate crystal deposition may indeed be associated with the thickening of the ligamentum flavum, if so, patients may benefit from medical treatment before undergoing surgical treatment of lumbar canal spinal stenosis.

Application of frameless stereotaxy to pedicle screw fixation of the spine

Interactive frameless stereotaxy has been successfully applied to intracranial surgery. It has contributed to the improved localization of deep-seated brain lesions and has demonstrated a potential for reducing both operative time and morbidity. However, it has not been as effectively applied to spinal surgery. The authors describe the application of frameless stereotactic techniques to spinal surgery, specifically pedicle screw fixation of the lumbosacral spine. Preoperative axial computerized tomography (CT) images of the appropriate spinal segments are obtained and loaded onto a high-speed graphics supercomputer workstation. Intraoperatively, these images can be linked to the appropriate spinal anatomy by a sonic localization digitizer device that is interfaced with the computer workstation. This permits the surgeon to place a pointing device (sonic wand) on any exposed spinal bone landmark in the operative field and obtain multiplanar reconstructed CT images projected in near-real time on the workstation screen. The images can be manipulated to assist the surgeon in determining the proper entry point for a pedicle screw as well as defining the appropriate trajectory in the axial and sagittal planes. It can also define the correct screw length and diameter for each pedicle to be instrumented. The authors applied this device to the insertion of 150 screws into the lumbosacral spines of 30 patients. One hundred forty-nine screws were assessed to be satisfactorily placed by postoperative CT and plain film radiography. In this report the authors discuss their use of this device in the clinical setting and review their preliminary results of frameless stereotaxy applied to spinal surgery. On the basis of their findings, the authors conclude that frameless stereotactic technology can be successfully applied to spinal surgery.

The anterior approach to the cervical spine

This article focuses on the indications for anterior cervical surgery, relevant surgical anatomy, a brief description of the technique of anterior surgery followed by a discussion of results and complications. It is hoped that the reader will achieve a better understanding for the clinical syndrome of cervical disc degeneration and be better able to put into proper perspective the role of diagnostic imaging in the overall evaluation of the patient.

Biomechanical considerations in high myopia: Part III--Therapy for high myopia

Clinical procedures for the treatment of high myopia are updated in this third part of a report on high myopia. After a discussion of testing techniques and refractive approaches for high myopia, an examination of therapeutic drug experiences shows their relative merits. The author believes that more investigation of beta blocker and epinephrine topical solutions is needed pertaining to the treatment of high myopia. Theoretically, such agents could improve deficient arterial perfusion of the highly myopic eye, and could be helpful in retarding scleral creep. Lifestyle recommendations include patient advice on accommodative reduction and proper exercise techniques. Low impact aerobics may have merit for highly myopic patients since the improved cardiovascular efficiency they can provide may improve the deficient arterial perfusion of their retinas. A summary of the three-part report on high myopia concludes the article. The physiological patterns of high myopia dovetail into the biomechanical considerations showing that a scleral pathogenesis hypothesis of myopic development is a viable working theory. The author's clinical procedures reflect the influence of that theory. If research were redirected from deprivation studies to investigating biomechanical considerations and pharmacological approaches to high myopia, the author contends that dramatically improved treatment regimens could result.

Biomechanical considerations of high myopia: Part II--Biomechanical forces affecting high myopia

Assuming the possibility of a scleral pathogenesis hypothesis for the development of high myopia, an examination of biomechanical forces affecting myopic eyes is presented. The biomechanical considerations include Laplace's law applied to the eye, balloon expansion dynamics, and the "porthole" effect derived from mechanical engineering principles. Other biomechanical considerations include Coleman's pressure head theory of accommodation, extraocular muscle stresses, and the role of uveoscleral outflow. Balloon expansion dynamics cast doubt on the common usage of Laplace's law governing fluid filled spheres for estimating coat stresses in myopia. Coleman's theory of accommodation, featuring an accommodation induced pressure head between the anterior and vitreous chambers is reanalyzed. Experimental testing of this hypothesis is still lacking. Uveoscleral outflow computations show that the vitreous chamber distension of high myopia may dramatically increase the importance of uveoscleral outflow in the pressure dynamics of high myopia. These biomechanical force phenomena clearly provide fertile ground for several areas of research that could illuminate the great puzzles of myopia.

Biomechanical considerations of high myopia: Part I--Physiological characteristics

Prior to a discussion of biomechanical considerations in high myopia, a review of anatomical and physiological patterns in high myopia is presented. A scleral pathogenesis or mesodermal hypothesis of the anomaly is presented with the inclusion of supporting evidence. Retinal, choroidal, and vitreous malformations in high myopia also are highlighted. Notable is a pattern consistent with the concept of gradual stretching of the vitreous chamber. The association of high myopia with other diseases is shown, with special attention being given to the concomitant features of high myopia and glaucoma. A discussion of animal deprivation studies examines their relevance to cases of clinical myopia. The dopamine deficit found in the retinas of visually deprived animals appears to be an area that will attract considerable future research. However, there may be no connection of these experimental findings in deprived animals to most cases of high myopia.

Diagnosis of nerve root compression. Myelography, computed tomography, and MRI

Current technology and published studies support the preferential use of MRI in the diagnosis of cervical myelopathy. In cervical radiculopathy, data support the use of either contrast-enhanced CT or MRI. We prefer MRI as the initial diagnostic test because of the obvious advantage of its noninvasive nature. Similar to myelography, MRI permits visualization of the entire cervical canal and spinal cord. Unlike routine CT, MRI visualizes the spinal cord and nerve roots in two planes and is better in detecting unsuspected pathology at other cervical segmental levels. Because the quality of MRI scans in the cervical spine is subject to more variation than in the lumbar spine, anticipated pathology is sometimes not clearly visualized by cervical MRI. Under such circumstances, we obtain a water-soluble myelogram followed by contrast-enhanced CT. Because inaccurate radiographic diagnosis is one of the identifiable causes of poor outcome in surgical therapy for cervical spondylosis, accurate visualization of pathology in terms of its location, nature, and extent is imperative before performing decompressive cervical spine surgery.

Flexion-extension MRI of the upper rheumatoid cervical spine

Seven rheumatoid arthritis patients with involvement of the upper cervical spine were evaluated with a dynamic MRI study. Lateral T1 weighted images of the upper C-spine were obtained in the flexion, extension, and neutral positions. The indications for performing the dynamic MRI were radiographic instability of the upper C-spine, myelopathy, superior migration of the odontoid process, obliteration of bony landmarks on plain radiographs, and to determine the contribution of pannus on cord configuration. The dynamic MRI clearly delineated the relationship between the odontoid, foramen magnum, and cervical spinal cord as the neck was moved through a range of motion. This aided in the selection of operative candidates in four cases, and was instrumental in determining fusion levels. In three cases with suspected myelopathy secondary to cord impingement, MRI showed no significant cord compression, and aided in the decision to treat the patients conservatively. Lateral flexion-extension MRI is the diagnostic study of choice in dynamically evaluating the upper rheumatoid C-spine.

Cervical spine injuries and their neurologic implications

This article presents the neurologic implications of cervical spine injuries by reviewing (1) cervical spine anatomy, (2) initial patient evaluation, (3) the type of neurologic injuries that can occur, (4) the treatment of athletes with these injuries, and (5) criteria for returning to activity.

Cervical spine fractures in athletes

This article presents (1) the on-field assessment of the athlete who has sustained a cervical injury, (2) the diagnostic modalities necessary to make an accurate diagnosis, (3) the specific fractures/dislocations seen in the cervical spine, and (4) the guidelines used to determine if the athlete may return to active competition.

The syndrome of inappropriate antidiuretic hormone secretion and its effect on blood indices following spinal fusion

Red blood cell indices in four adolescent and preadolescent patients with documented inappropriate antidiuretic hormone secretion (SIADH) following spinal fusion were examined for evidence of dilution. The blood indices in these preoperative patients demonstrated evidence of dilution on both the intracellular and extracellular levels. The major factors causing these dilutional effects were elevated ADH, intravenous fluid overloading, and mobilization of "third space" fluids. It appears that extracellular dilution secondary to these factors results in spuriously low blood indices (namely, hemoglobin, hematocrit, and red blood cells) during the postoperative period. These findings suggest that an awareness of SIADH and avoiding intravenous fluid overloads by accurately managing intraoperative and postoperative fluids will decrease the dilutional effects observed on blood indices and perhaps save patients from unwarranted transfusions.

Heparinized materials for control of the formation of the laminectomy membrane in experimental laminectomies in dogs

This study examined the efficacy of heparinized biodegradable materials in the prevention of post-laminectomy scar formation using a canine system. Six-level noncontiguous laminectomies were performed on five adult canines. Exposed dura at each level was covered with the following: (1) nothing (control); (2) fat; (3) fat and autogeneic bone; (4) heparinized Avitene; (5) heparinized Surgicel; or (6) heparinized collagen gel. Canines were killed 16 weeks postoperatively and histologic specimens examined. Fibrous adhesions were abundant at Site 1 (control). Free fat grafts were well preserved and did not permit adhesions at Sites 2 and 3. None of the heparinized materials was as effective as fat in controlling scar formation. Overlying bone at Site 3 did not alter the quality of a free fat graft placed over the dura, a point possibly significant for laminectomies followed by fusion.

Computed tomography scanning after chymopapain injection for herniated nucleus pulposus. A prospective study

Fifty consecutive patients treated with chymopapain injection for a clinical and radiographic diagnosis of herniated nucleus pulposus were evaluated prospectively. All patients had a prechymopapain computed tomography (CT) scan and a three-month postinjection CT scan. In addition, ten patients (20%) had a six-month postinjection CT scan. All scans were interpreted blindly. Only six patients (12%) had obvious changes in the size of the disc when preinjection and three-month postinjection CT scans were compared. By six months, however, seven of ten patients (70%) had obvious changes in their CT scan. Seven patients (14%) were considered chymopapain treatment failures and were later treated with surgical discectomy. Only two of these seven patients (30%) had obvious changes in their three-month CT scan. Chymopapain injection did not alter the size of the herniated portion of the disc during the first three months after chymopapain injection. A decision to operate for presumed chymopapain failure should therefore be based on clinical grounds, rather than on the three-month CT appearance of the herniated disc.

The use of computerized tomography in evaluating non-visualized vertebral levels caudad to a complete block on a lumbar myelogram. A review of thirty-two cases

In thirty-two patients who demonstrated a complete or almost complete block on a lumbar myelogram, computerized tomography of the non-visualized vertebral levels caudad to the block was performed prior to surgical intervention. The purpose of this study was to evaluate the clinical value of computerized tomography in detecting a lesion that is caudad to the level of a myelographic block. For twenty-three patients the cause of the myelographic block was stenosis of the spine; for five patients, a combination of stenosis of the spine and herniation of a disc; for one patient, herniation of a disc between the fourth and fifth lumbar vertebrae alone; for two patients, arachnoiditis; and for one patient, kyphosis secondary to fracture. A total of fifty vertebral levels that could not be visualized because of the block were evaluated. Thirty (60 per cent) of the non-visualized vertebral levels, in nineteen (59 per cent) of the thirty-two patients, demonstrated stenosis of the spine or a herniated disc that was confirmed at the time of surgical treatment. The value of computerized tomography for the evaluation of the vertebral levels caudad to the level of a complete or almost complete block on a lumbar myelogram was threefold. First, it provided visualization of the vertebral levels that could not be evaluated by the myelography. Second, the findings on computerized tomography provided information that was essential for preoperative planning and it removed the so-called exploratory element from the operative procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

The syndrome of inappropriate antidiuretic-hormone secretion following spinal fusion

Ten adolescent and preadolescent patients who underwent posterior spinal fusion for idiopathic scoliosis or spondylolisthesis were examined for the presence or absence of the postoperative syndrome of inappropriate antidiuretic-hormone secretion. For each patient, levels of serum sodium, serum osmolality, urine sodium, urine osmolality, and serum antidiuretic hormone were obtained preoperatively and postoperatively. The investigation clearly showed that the syndrome occurred in each patient, with the level of serum antidiuretic hormone being highest within a few hours postoperatively. This resulted in a reduction of urinary output, the reduction being maximum on the day of operation and the output gradually rising to normal over the next three days. This syndrome and its associated low postoperative urinary output is common after spinal fusion and should be treated with restriction of fluids rather than administration of increased amounts of fluid.

A study of computer-assisted tomography. II. Comparison of metrizamide myelography and computed tomography in the diagnosis of herniated lumbar disc and spinal stenosis

One hundred twenty-two patients with surgically confirmed pathology consisting of either herniated lumbar disc, spinal stenosis, or both were included in this investigation. For each of these patients, preoperative metrizamide myelography and computerized tomography were performed. Each myelogram and CT scan was read blindly so that the neuroradiologist interpreting the study had no knowledge of the patient's surgical pathology, clinical examination, nor any knowledge of the interpretation of the other preoperative test. A painstaking attempt was made to describe precisely both the exact nature of the preoperative myelogram and CT scan interpretations. The correlations between the preoperative interpretation of each test and the observed surgical findings then were analyzed statistically. Based upon this analysis, myelography was found to be more accurate than computed tomography in the diagnosis of herniated lumbar disc (83% vs. 72%). In the diagnosis of spinal stenosis, myelography was slightly more accurate than computed tomography (93% vs. 89%). Based upon the results of this study, the authors conclude that metrizamide myelography is more accurate than computed tomography in the diagnosis of both herniated lumbar disc and spinal stenosis and remains the diagnostic study of choice for these conditions. Furthermore, metrizamide myelography gives the added advantage of visualizing the thoracolumbar junction and, thus, affords the opportunity to diagnose occult spinal tumors.

The conservative treatment of sciatica

The mainstay of rational treatment of acute sciatica involves bed rest and antiinflammatory drugs. The authors recommended 2 weeks of complete bed rest with progressive gradual mobilization over the next 7-10 days. Buffered aspirin in a dosage of 10-15 grains every 4 hours is prescribed both for its analgesic effect as well as for its antiinflammatory properties. Through the low-back school, the patient is instructed in low-back hygiene. Physically capable patients are encouraged to begin an aerobic exercise program. In the absence of absolute indications for surgery (cauda equina syndrome or marked progressive muscle weakness) it seems reasonable to permit up to 3 months of conservative therapy before recommending surgery.

The Coleman theory of accommodation and its relevance to myopia

The Coleman theory of accommodation is reviewed in this paper, with the inclusion of subsequent experimental evidence to support the theory. Implications on the developmental characteristics of refractive error are presented. The scleral structure is hypothesized as an important refractive determinant, consistent with Coleman's accommodation theory. Additional concepts of refractive development are also explored.

Reactivity of Desulfovibrio gigas hydrogenase toward artificial and natural electron donors or acceptors

A purified preparation of hydrogenase from D. gigas was inactive toward ferredoxin, flavodoxin or rubredoxin in the absence of cytochrome c3 (M.W. 13,000), in an atmosphere of hydrogen, although direct reduction of benzyl viologen or FMN was possible. The hydrogen evolution reaction from dithionite was possible with methyl viologen. The same reaction also occured with cytochrome c3 (M.W. 13,000) or cytochrome c3 (M.W. 26,000). Addition of either ferredoxin or flavodoxin did not accelerate the reaction.

Evidence for the periplasmic location of hydrogenase in Desulfovibrio gigas

Hydrogenase has been found to be located in the periplasmic space of Desulfovibrio gigas, and it is proposed that hydrogenase plays an important and specific role in interspecies hydrogen transfer.