A potential hidden layer of meteorites below the ice surface of Antarctica.

Antarctica contains some of the most productive regions on Earth for collecting meteorites. These small areas of glacial ice are known as meteorite stranding zones, where upward-flowing ice combines with high ablation rates to concentrate large numbers of englacially transported meteorites onto their surface. However, meteorite collection data shows that iron and stony-iron meteorites are significantly under-represented from these regions as compared with all other sites on Earth. Here we explain how this discrepancy may be due to englacial solar warming, whereby meteorites a few tens of centimetres below the ice surface can be warmed up enough to cause melting of their surrounding ice and sink downwards. We show that meteorites with a high-enough thermal conductivity (for example, iron meteorites) can sink at a rate sufficient to offset the total annual upward ice transport, which may therefore permanently trap them below the ice surface and explain their absence from collection data.

Factors determining the most efficient spray distribution for marine cloud brightening.

We investigate the sensitivity of marine cloud brightening to the properties of the added salt particle distribution using a cloud parcel model, with an aim to address the question of, 'what is the most efficient particle size distribution that will produce a desired cooling effect?' We examine the effect that altering the aerosol particle size distribution has on the activation and growth of drops, i.e. the Twomey effect alone, and do not consider macrophysical cloud responses that may enhance or mitigate the Twomey effect. For all four spray generation methods considered, Rayleigh jet; Taylor cone jet; supercritical fluid; and effervescent spray, salt particles within the median dry diameter range Dm=30-100 nm are the most effective range of sizes. The Rayleigh jet method is also the most energy efficient overall. We also find that care needs to be taken when using droplet activation parametrizations: for the concentrations considered, Aitken particles do not result in a decrease in the total albedo, as was found in a recent study, and such findings are likely to be a result of the parametrizations' inability to simulate the effect of swollen aerosol particles. Our findings suggest that interstitial aerosol particles play a role in controlling the albedo rather than just the activated cloud drops, which is an effect that the parametrization methods do not consider.

Injury of an aberrant vertebral artery during a routine corpectomy: a case report and literature review.

CASE REPORT: A case report of a 58-year-old man who sustained a laceration of his left vertebral artery during a routine corpectomy for cervical myelopathy is reported. OBJECTIVE: To report iatrogenic injury of a tortuous vertebral artery during anterior cervical spine surgery and discuss appropriate diagnosis and treatment options for this complication. SETTING: UMass Memorial Medical Center, Worcester, MA, USA. BACKGROUND DATA: Vertebral artery anomalies, although rare, are typically present with degenerative processes and great care must be taken to avoid damage during a corpectomy. Cross-sectional imaging coupled with intraoperative angiography is helpful for the urgent evaluation of the injury site and identification of the contralateral vertebral artery's status. METHODS: This is a single case of a patient sustaining a laceration of the left vertebral artery during surgery, which resulted in a lateral medullary stroke. RESULTS: After the left vertebral artery laceration, hemostasis was achieved. With the intent to better visualize and possibly embolize or stent the injury, an angiographic study was carried out. The angiogram revealed a laceration of the left vertebral artery within the vertebral foramina at vertebral body level C6, but intact distal flow. The patient underwent angiographic embolization and a subsequent magnetic resonance imaging (MRI) revealed a left lateral medullary stroke consistent with the lack of flow through the left vertebral artery from C6 to the basilar artery. CONCLUSION: If a tortuous vertebral artery is suspected, then meticulous review of preoperative cross-sectional imaging should be implemented along with angiographic examination. If anomalies are detected and the standard procedure cannot be safely carried out, then alterations, such as preoperative stent placement, need to be considered.

Electromagnetic field-based image-guided spine surgery part one: results of a cadaveric study evaluating lumbar pedicle screw placement.

STUDY DESIGN: Human cadaveric. OBJECTIVES: Compare the accuracy of electromagnetic field (EMF)-based image-guided lumbar pedicle screw insertion to conventional techniques using anatomic landmarks, and fluoroscopy. BACKGROUND: Image-guided surgical systems that aid in spinal instrumentation seek to minimize radiation exposure and improve accuracy. EMF tracking-based image-guidance was developed in the hopes of eliminating line-of-sight restrictions seen with other systems. MATERIALS AND METHODS: Sixteen fresh-frozen human cadavers were randomly allocated into three groups. Pedicle screws were inserted from L1 to L5 using only anatomic landmarks in group 1, fluoroscopy in group 2, and image-guidance in group 3. Insertion and total fluoroscopic time were recorded. Anatomic dissections were performed to assess screw placement. RESULTS: Accuracy was 83%, 78%, and 95% for groups 1, 2, and 3, respectively. However, image-guided pedicle screw placement resulted in a 5% critical perforation rate whereas anatomic and fluoroscopic placement resulted in a 15% and 22% critical perforation rate, respectively. The average degree of perforation was 1.5 mm with image guidance, and 3.8 mm with fluoroscopic guidance (P < 0.05). Fluoroscopy time and insertion time per screw were not improved using image guidance. CONCLUSIONS: Our study has shown that when EMF tracking was used for image-guided lumbar pedicle screw placement, accuracy was improved and the incidence and degree of cortical perforations that may place neurovascular structures at risk was also reduced. Current system requirements for set-up and image acquisition, however, do add time to the procedure, and when factored in, do not yet result in a decrease in the use of fluoroscopy or screw insertion time.

Electromagnetic field-based image-guided spine surgery part two: results of a cadaveric study evaluating thoracic pedicle screw placement.

STUDY DESIGN: Human cadaveric. OBJECTIVES: Compare the accuracy of electromagnetic field (EMF)-based image-guided thoracic pedicle screw insertion to conventional techniques using anatomic landmarks and fluoroscopy. BACKGROUND: Image-guided surgical systems that aid in spinal instrumentation seek to minimize radiation exposure and improve accuracy. EMF image guidance was developed as an alternative to optical tracking to eliminate potential line of sight issues. MATERIALS AND METHODS: Four fresh-frozen human cadavers were randomly allocated into two groups. Pedicle screws were inserted from T1 to T12 using anatomic landmarks and fluoroscopy in group 1 and image guidance in group 2. Insertion and fluoroscopy time were recorded. Anatomic dissections were performed to assess screw placement. RESULTS: Image guidance placed 92% of thoracic pedicle screws safely, and conventional fluoroscopy placed 90% safely. The average degree of perforation was 2.4 mm with conventional fluoroscopy and 1.7 mm with image guidance (P = 0.055). Fluoroscopic time per screw was 5.9 seconds for conventional fluoroscopy and 3.6 seconds for image guidance (P = 0.045). Insertion time per screw was 4.35 minutes for conventional fluoroscopy and 2.98 minutes for image guidance (P = 0.007). However, when set-up time and image capture time were taken into account, the total insertion time per screw was not significantly different between the two groups. CONCLUSIONS: Our study has shown that EMF image-guided thoracic pedicle screw placement results in a similar incidence of safely placed screws as does conventional fluoroscopy. When set-up time and image-capture time were factored in for image guidance, the average time to insert a pedicle screw was equal for both techniques. The use of EMF image guidance significantly reduced fluoroscopic time and thus radiation exposure per screw compared with conventional fluoroscopic techniques.

Cerebral venous thrombosis in children.

Cerebral venous thrombosis is an important cause of stroke in children. Understanding the natural history of the disease is essential for rational application of new interventions. We retrospectively identified 31 children with cerebral venous thrombosis confirmed by head computed tomography (4 patients) or by magnetic resonance imaging (27 patients). Risk factors, clinical and radiographic features, and neurologic outcomes were analyzed. There were 21 males and 10 females aged 1 day to 13 years (median 14 days). Nineteen (61%) were neonates. The most common risk factors included mastoiditis, persistent pulmonary hypertension, cardiac malformation, and dehydration. The chief clinical features were seizures, fever, respiratory distress, and lethargy. Fifteen patients had infarctions (8 hemorrhagic, 7 ischemic). Protein C and antithrombin III deficiency were the most common coagulopathies among 14 tested patients. On discharge, 11 patients were normal, 17 had residual deficits, and 2 patients died. Twenty-seven patients were followed from 1 month to 12 years (mean 22 months). At follow-up, 11 patients were normal, and 13 patients had development delay. One had residual hemiparesis and cortical visual impairment. Two had other deficits. Neonatal cerebral venous thrombosis is probably more common than previously thought, and outcomes are worse in this group. All children with cerebral venous thrombosis should be tested for coagulation disorders.

Return to play after cervical spine injury.

STUDY DESIGN: A questionnaire survey was mailed to members of the Cervical Spine Research Society, the Herodiuus Sports Medicine Society, and to members of the authors' Department of Orthopaedics. OBJECTIVES: The purpose of our study was to evaluate what influence, if any, factors such as published guidelines, type of sport of the patient, number of years in practice, subspecialty interest, and sports participation of the respondent held in the "return to play" decision-making process after a cervical spine injury. SUMMARY OF BACKGROUND DATA: The consequences of cervical spine injury are potentially catastrophic, and return to play decisions in athletes with a history of neck injury can be agonizing. Although recent publications have addressed some of the concerns regarding cervical spine injuries in the athletic population, many questions remain unanswered. Factors such as published guidelines, type of sport of the patient, number of years in practice, subspecialty interest, and sports participation of the respondent have all been suggested as having a possible role in return to play decisions. METHODS: Representative radiographs and case histories of 10 athletes who had sustained neck injury were mailed to 346 physicians. For each case physicians selected every type of play (of six categories) that they felt comfortable recommending. Type of play was divided into six categories: Type 1, collision sports; Type 2, contact sports; Type 3, noncontact, high velocity sports; Type 4, noncontact, repetitive load sports (e.g., running); Type 5, noncontact, low impact sports; Type 6, no sports. In addition, demographic data regarding board certification, subspecialty interest, number of years in practice, use of guidelines in return to play decisions, and personal participation in sports were queried from all respondents. Statistical analysis was completed with Statview (Berkeley, CA). Basic descriptive statistics, chi2, and ANOVA were used where appropriate. RESULTS: Three hundred forty-six questionnaires were mailed and 113 were returned (response rate 32.7%). One hundred ten (97%) of the respondents who completed the questionnaire were board certified. Seventy-five were subspecialists in spine, 22 were subspecialists in sportsmedicine, and 13 reported interests in both sports medicine and spine. Use of Published Guidelines. Although 49% of respondents reported using guidelines in decision-making, the use of guidelines was statistically significant in only one case (P = 0.04). Hierarchy of Risk. In general, those physicians who participated in the study followed the hierarchy of risk that we established in this study (Type 1 [collision sports; highest level of risk] through Type 6 [no sports; lowest level of risk]). Twelve (10.6%) respondents, however, deviated from it in one or more cases. Years in Practice. In three cases there was a statistically significant association between the number of years a physician was in practice and the type of play selected (P < 0.05). In each case a lower level of play tended to be recommended by more senior physicians. Subspecialty Interest. In three cases those respondents with a spine subspecialty interest recommended returned to a higher level of play (P < 0.05). CONCLUSIONS: There is no consensus on the postinjury management of many cervical spine-injured patients. Further research, education, and discussion on this topic are needed.

Recurrent laryngeal nerve injury with anterior cervical spine surgery risk with laterality of surgical approach.

STUDY DESIGN: A detailed review of anterior cervical fusion procedures from a university-based spine specialty service was completed. Noted were the laterality of approach, number of levels, discectomy or corpectomy, use of instrumentation, and cases of reoperation. OBJECTIVES: The primary purpose of the study is to determine whether there is in fact a greater risk of recurrent laryngeal nerve (RLN) injury with approach on the right or left side. Also evaluated is the risk with corpectomy, reoperative procedures, and instrumentation. BACKGROUND: Anatomic considerations have been used as justification to determine the side of surgical approach. However, few clinical studies have delineated the side of surgical approach in their results. METHODS: A total of 328 anterior cervical spine fusion procedures completed between 1989 and 1999 were reviewed. All speech changes reported were noted throughout follow-up. RESULTS: There were 187 anterior discectomy and 141 corpectomy procedures. There were 21 reoperative anterior fusions. There were 173 procedures completed from the right side and 155 from the left. There were nine patients documented to have dysphonia after surgery. Five had a left-sided approach and four had a right-sided approach. CONCLUSIONS: The incidence of RLN symptoms after surgery was 2.7% (9 of 328). The incidence of RLN symptoms was 2.1% with anterior cervical discectomy, 3.5% with corpectomy (5 of 141), 3% with instrumentation (8 of 237), and 9.5% with reoperative anterior surgery (2 of 21). There was a significant increase in the rate of injury with reoperative anterior fusion. There was no association between the side of approach and the incidence of RLN symptoms.

Mitomycin C reduces corneal light scattering after excimer keratectomy.

PURPOSE: To evaluate the effect of intraoperative mitomycin C (MMC) on corneal light scattering after excimer laser keratectomy. METHODS: Phototherapeutic keratectomy (PTK) was performed in 24 rabbit eyes. After 40-microm epithelial ablation, animals were divided into three groups. In group 1, filter paper discs soaked with MMC (group 1A, 0.5 mg/mL; group 1B, 0.25 mg/ml) were applied for 1 minute. In group 2, annular filter papers soaked with MMC (group 2A, 0.5 mg/mL; group 2B, 0.25 mg/mL) were applied for 1 minute. Controls received vehicle only (group 3). Six-millimeter diameter 100-microm deep PTK was performed. Corneal light scattering was measured weekly from 1 to 6 weeks, at 10 weeks, and at 8 and 13 months using a scatterometer. A corneal light scattering index (SI) ranging from 0 to 10 was calculated; SI of 1 represents normal scattering. RESULTS: A statistically significant decrease in mean SI was noted in group 2A (annular MMC 0.5 mg/mL; p<0.05) as compared with the control group at 2 weeks. At 10 weeks, SI approached baseline levels in group 2 and the control group but showed significant increase in group 1 (MMC disc; p < 0.05). At 8 and 13 months, SI showed no statistical differences between groups. CONCLUSIONS: Controlled application of 0.5 mg/mL MMC in the corneal midperiphery transiently reduces corneal light scattering after excimer keratectomy in this rabbit model.

Traumatic atlantoaxial distraction injury: a case report.

STUDY DESIGN: Case report. OBJECTIVES: Description of a rarely reported variant of traumatic C1-C2 dislocation and discussion of a favorable outcome in a nonsurgical treatment approach. SUMMARY OF BACKGROUND DATA: Atlantoaxial dislocation most commonly involves an anterior movement of C1 in relation to C2. Often, the integrity of the transverse ligament or odontoid process is compromised, and the atlantodental interval changed. The described patient sustained a purely craniocaudal atlantoaxial distractive lesion secondary to injury sustained in a high-speed motor vehicle accident. RESULTS: The initial treatment plan involved surgical stabilization subsequent to healing of a C1 ring fracture. After 12 weeks of external stabilization, ligamentous damage appeared well resolved. That there was no gross instability delayed using a surgical option. At periodic checkup, the patient was without symptoms. CONCLUSION: In this case, conservative management of a ligamentous C1-C2 injury was effective. At 5 years after trauma the patient was without sequelae. This outcome is in contrast to previous management of injuries of this type, all of which involved surgical intervention.

Synthesis and erythropoietin receptor binding affinities of N,N-disubstituted amino acids.

N,N-Dicinnamyl, N-benzyl-N-cinnamyl, and N,N-dibenzyl amino acids were prepared and evaluated in an EPO binding assay. Several derivatives of aspartic acid, glutamic acid, and lysine exhibited moderate (10-50 microM) affinity for EBP; 'dimerization' of the most potent analogues by coupling with linear diamines led to EPO competitors having 1-2 microM binding affinities.

Characteristics of unicortical and bicortical lateral mass screws in the cervical spine.

STUDY DESIGN: A biomechanical study evaluating the safety and efficacy of unicortical versus bicortical lateral mass screws in the cervical spine. OBJECTIVES: To analyze the safety, pullout strength and radiographic characteristics of unicortical and bicortical screws placed in cadaveric spines and to evaluate the influence of level of training on the positioning of these screws. SUMMARY OF BACKGROUND DATA: Lateral mass plating for posterior cervical spine fusion is an effective method for the treatment of traumatic and degenerative instability. The initial description of the technique included bicortical screw purchase. The added benefit of bicortical purchase must be weighed against the increased risk of injury to nerve roots and the vertebral artery. METHODS: In 21 cadaveric spines (mean age 78.9 years), 3.5-mm anterior oblique lateral mass screws were placed bilaterally from C3 to C6 (n = 168) using a modification of the Magerl technique. In the right side (unicortical) only 14-mm screws (effective length of 11 mm) were used, whereas on the left side, bicortical purchase was obtained. All screws were evaluated clinically and radiographically for safety and zone placement. Pullout force was determined for all screws. RESULTS: Most screws (92.8%) were rated satisfactory. There were no injuries to the spinal cord. On the right side (14 mm) 98.9% of the screws were satisfactory, and on the left side (bicortical) 68.1% were satisfactory. There was a 5.8% incidence of direct artery injury (compression of vessel wall) and a 17.4% incidence of direct nerve root injury by the bicortical screws. There were no direct injuries with the unicortical screws. Most of the direct-injury bicortical screws were placed by the surgeon with the least experience. The mean pullout force for all screws was 542.9 +/- 296.6 N. There was no statistically significant difference between the pullout force for unicortical (519.9 +/- 286.9 N) and bicortical (565.2 +/- 306 N) screws (P < 0.05). There were no significant differences in pullout strengths in association with zone placement. CONCLUSIONS: Fourteen-millimeter lateral mass screws (effective length, 11 mm) placed in a superolateral trajectory in the adult cervical spine provide an equivalent strength with a much lower risk of injury than the longer bicortical screws placed in a similar orientation.

Video-assisted thoracic diskectomy and anterior release: a biomechanical analysis of an endoscopic technique.

This study evaluates the residual biomechanical stability of the spine following multilevel anterior diskectomies and anterior longitudinal ligament release using video-assisted thoracoscopic surgery (VATS). Eighteen domestic pigs were randomly divided into three groups of six pigs. Group 1 underwent thoracic anterior release from T4-T9 using a left-sided VATS approach, group 2 underwent thoracic anterior release from T4-T9 via a traditional left thoracotomy (open), and group 3 did not undergo surgery and served as a control. After surgery, the animals were euthanized, and the thoracic spinal columns were harvested for biomechanical testing. Nondestructive testing was performed on all specimens in pure compression, flexion, extension, right lateral bending, and torsion. Specimens from group 1 had significantly lower stiffness values (P<.05) than the control group for all five test modes. These data demonstrate that adequate anterior release of the thoracic spine can be obtained with the VATS technique. Further prospective clinical studies on VATS are required before the widespread application of this technique.

The prevalence of cervical spondylolisthesis.

This study assessed the prevalence of cervical spondylolisthesis in patients undergoing radiographic studies for reasons unrelated to their cervical spine. Scout lateral cervical spine radiographs of 174 patients who had barium swallows were reviewed for the degree and level of cervical spondylolisthesis. Nine patients were found to have >2 mm of anterior subluxation of the cervical spine for a prevalence of 5.2%. Two patients had involvement at the C2-C3 level, one patient at C3-C4, four patients at C4-C5, one patient at C5-C6, and one patient at C7-T1. Subluxation ranged from 2 to 4 mm. Posterior subluxation (retrolisthesis) was not found in any patient. None of the nine patients with spondylolisthesis had complaints of neck pain or upper extremity symptoms, and none had a history of rheumatoid arthritis or cervical trauma.

N-hydroxyurea and hydroxamic acid inhibitors of cyclooxygenase and 5-lipoxygenase.

Two series of compounds (1 and 2) having structural features of the dual COX/5-LO inhibitor tepoxalin and the 5-LO inhibitor ABT-761 were prepared. Many of these hybrid compounds are potent COX and 5-LO inhibitors; two compounds (1a and 2t) inhibit eicosanoid biosynthesis in an ex vivo assay.

Artifacts in sensitivity-enhanced HSQC.

Proton-proton coupling can generate artifacts in sensitivity-enhanced HSQC spectra. These artifacts appear as cross-peaks involving remote protons. They are caused by relayed coherence transfer during the back-transfer portion of the pulse sequence. We present a product operator analysis of artifact formation and experimental results which demonstrate that the magnitude of these artifacts can exceed 10% of the main peak.

Structure, thermostability, and conformational flexibility of hen egg-white lysozyme dissolved in glycerol.

Hen egg-white lysozyme dissolved in glycerol containing 1% water was studied by using CD and amide proton exchange monitored by two-dimensional 1H NMR. The far- and near-UV CD spectra of the protein showed that the secondary and tertiary structures of lysozyme in glycerol were similar to those in water. Thermal melting of lysozyme in glycerol followed by CD spectral changes indicated unfolding of the tertiary structure with a Tm of 76.0 +/- 0.2 degreesC and no appreciable loss of the secondary structure up to 85 degreesC. This is in contrast to the coincident denaturation of both tertiary and secondary structures with Tm values of 74.8 +/- 0.4 degreesC and 74.3 +/- 0.7 degreesC, respectively, under analogous conditions in water. Quenched amide proton exchange experiments revealed a greater structural protection of amide protons in glycerol than in water for a majority of the slowly exchanging protons. The results point to a highly ordered, native-like structure of lysozyme in glycerol, with the stability exceeding that in water.

Bracing of patients after fusion for degenerative problems of the lumbar spine--yes or no?

The majority of spine fusions currently performed are for degenerative conditions. Controversy exists regarding whether to routinely brace patients during the postoperative period. The benefits of a rigid orthosis have yet to be documented in a scientific study, and the cost of a custom-molded orthosis can be quite high. An extensive literature search reveals few articles dealing with the subject, and none with an adequate study design to convincingly support or refute the use of external braces. In addition to the questions of whether an external brace is effective, the mechanism of action also remains unclear. It has been difficult to document mechanical effectiveness, so perhaps the effect is psychologic. In addition, it is possible that some, not all, fusion patients may benefit from a brace--yet our ability to select such a patient is poor. As a result, we have solicited the views of two experienced surgeons on the topic. Dr. Connolly argues that an external orthosis is advisable in many cases; Dr. Grob feels that the rigidity of internal fixation should be adequate to obviate the need for external bracing.