Rapid prototype patient-specific drill template for cervical pedicle screw placement.

OBJECTIVE: To assess the feasibility and accuracy of a drill template for the placement of a cervical pedicle screw in a single vertebral level. MATERIALS AND METHODS: A volumetric CT scan was performed on a cadaver cervical spine. Using computer software, a drill template with a predefined trajectory was constructed that was designed to match the posterior surface of the right side of the fifth cervical vertebra. A physical template was created from the computer model using a rapid prototyping machine. The drill template was used to guide drilling of a pilot hole, and a CT scan was performed to assess the accuracy of this hole. A 3.5-mm diameter pedicle screw was placed in the pilot hole. The spine was then dissected to separate the vertebrae and the trajectory of the screw was visually inspected. RESULTS: The feasibility of this patient-specific rapid prototyping technique was demonstrated. Imaging and visual inspection confirmed accurate placement of the pilot hole and cervical pedicle screw without cortical violation. CONCLUSIONS: The potential use of drill templates to place cervical pedicle screws is promising. Our initial methodology appears to provide an accurate technique and trajectory for pedicle screw placement in the cervical spine.     

In vitro effects of detergent sclerosants on coagulation, platelets and microparticles.

OBJECTIVES: To investigate the in vitro effects of Sodium Tetradecyl Sulphate (STS) and Polidocanol (POL) on clotting tests, clotting factors, platelets and microparticles. MATERIALS AND METHODS: Platelet rich (PRP) and platelet poor (PPP) plasmas were incubated with varying concentrations of STS and POL. Clotting tests, platelet/plasma turbidity, and microparticle studies were performed. Specimens were mixed with individual factor deficient plasmas and clotting factor activities were studied. RESULTS: STS at high concentrations (>0.3%) destroyed platelets, microparticles and the clotting factors V, VII and X. It prolonged all clotting tests including prothrombin time (PT), activated partial thromboplastin time (APTT), non-activated partial thromboplastin time (NAPTT), thrombin time (TT), factor Xa clotting time (XACT) and surface activated clotting time (SACT). Higher concentrations of POL were required to achieve some anticoagulant activity. Low sclerosant concentrations shortened XACT and SACT, and induced release of procoagulant platelet derived microparticles. Increased exposure time resulted in increased procoagulant activity. STS at concentrations higher than 0.5% precipitated a complex containing apolipoprotein b and fibrinogen. CONCLUSIONS: Detergent sclerosants affect the clotting mechanism by interfering with clotting factor activities, procoagulant phospholipids and platelet derived microparticles. STS has more anticoagulant activity than POL in high concentrations. Low concentration sclerosants demonstrate procoagulant activity.     

Performance of Residents and Anesthesiologists in a Simulation-based Skill Assessment

Background: Anesthesiologists and anesthesia residents are expected to acquire and maintain skills to manage a wide range of acute intraoperative anesthetic events. The purpose of this study was to determine whether an inventory of simulated intraoperative scenarios provided a reliable and valid measure of anesthesia residents' and anesthesiologists' skill.

Methods: Twelve simulated acute intraoperative scenarios were designed to assess the performance of 64 residents and 35 anesthesiologists. The participants were divided into four groups based on their training and experience. There were 31 new CA-1, 12 advanced CA-1, and 22 CA-2/CA-3 residents as well as a group of 35 experienced anesthesiologists who participated in the assessment. Each participant managed a set of simulated events. The advanced CA-1 residents, CA-2/CA-3 residents, and 35 anesthesiologists managed 8 of 12 intraoperative simulation exercises. The 31 CA-1 residents each managed 3 intraoperative scenarios.

Results: The new CA-1 residents received lower scores on the simulated intraoperative events than the other groups of participants. The advanced CA-1 residents, CA-2/CA-3 residents, and anesthesiologists performed similarly on the overall assessment. There was a wide range of scores obtained by individuals in each group. A number of the exercises were difficult for the majority of participants to recognize and treat, but most events effectively discriminated among participants who achieved higher and lower overall scores.     

Age-dependent Responses to Thermal Hyperalgesia and Mechanical Allodynia in a Rat Model of Acute Postoperative Pain

Background: Developmental differences in short- and long-term responses to pain, especially surgical pain, have received minimal attention. The purpose of the present study was to examine postoperative responses in rats of developmental ages paralleling the infant to young adult human.

Methods: The withdrawal threshold to von Frey filament testing and withdrawal latency to hind-paw radiant heating were determined before and for various times after hind-paw incision in rats 2, 4, and 16 weeks of age. Control rats of these ages were observed serially without surgery.

Results: In control animals, younger rats were more sensitive to mechanical stimulation and less sensitive to thermal stimulation. Paw incision resulted in similar changes to both types of stimulation in all age groups, peaking 4 h after surgery. However, the return to normal sensitivity to mechanical stimulation, as measured by return of threshold to 80% of normal, occurred more quickly in 2-week-old than in 4- and 16-week-old animals. In contrast, there was no age difference for time to return to normal sensitivity to thermal stimulation after surgery.     

Interobserver Agreement for the Diagnosis of Venous Thromboembolism on Computed Tomography Chest Angiography and Indirect Venography of the Lower Extremities in Emergency Department Patients

Objectives: To determine interobserver agreement between radiologists for computed tomography (CT) angiography and venography. CT venography of the lower extremities combined with standard CT angiography of the chest may result in an increased overall diagnosis rate of venous thromboembolism (pulmonary embolism or deep venous thrombosis).
Methods: The study had a retrospective cohort design. The population consisted of emergency department patients who were evaluated for suspected pulmonary embolism. A random sample of 50 patients diagnosed and treated for venous thromboembolism and 50 age- and gender-matched patients whose CT angiograms and venograms were read as negative were enrolled. The original reading (R1) was compared with readings of two study radiologists: R2, a general radiologist, and R3, a radiologist with fellowship training in cross-sectional imaging. All readers were blinded to each other.
Results: Both R2 and R3 found both CT angiogram and venogram components technically adequate in 95% (95% CI = 89% to 98%) and 86% (95% CI = 78% to 92%) of studies, respectively. The agreement was very good for CT angiography (lowest agreement = 92%; lowest κ = 0.83) and was good for CT venography (85%, κ = 0.65). In nine cases, R1 read the CT angiogram as negative but the venogram as positive for DVT, whereas both R2 and R3 read both components as negative in four of these nine, suggesting a false-positive isolated DVT rate of 44% (95% CI = 19% to 73%). In no case did R1 read both scan components as negative when R2 and R3 agreed on presence of pulmonary embolism or DVT.
Conclusions: Diagnosis of pulmonary embolism on CT angiography is more reliable than diagnosis of isolated DVT on CT venography.     

Generation of cell diversity and segmental pattern in the embryonic central nervous system of Drosophila.

Development of the central nervous system (CNS) involves the transformation of a two-dimensional epithelial sheet of uniform ectodermal cells, the neuroectoderm, into a highly complex three-dimensional structure consisting of a huge variety of different neural cell types. Characteristic numbers of each cell type become arranged in reproducible spatial patterns, which is a prerequisite for the establishment of specific functional contacts. The fruitfly Drosophila is a suitable model to approach the mechanisms controlling the generation of cell diversity and pattern in the developing CNS, as it allows linking of gene function to individually identifiable cells. This review addresses aspects of the formation and specification of neural stem cells (neuroblasts) in Drosophila in the light of recent studies on their segmental diversification.     

Distortion and size calibration of the scanning laser ophthalmoscope (SLO) laser-beam raster.

PURPOSE: The Rodenstock scanning laser ophthalmoscope (SLO) is useful for mapping retinal function and for developing and evaluating visual rehabilitation methods. It is essential to know the visual angle subtended by stimuli in the SLO laser-beam raster and to accurately measure angular distances between objects in the final SLO image. To accomplish this, the angular extent of the SLO laser-beam raster must be calibrated. METHODS: We developed a simple method and apparatus for calibrating the raster and used it for repeated calibrations during a 3-month period. RESULTS: The laser-beam raster is quite stable in shape and size, but it is trapezoidally distorted in the vertical direction. Consequently, SLO images are distorted. CONCLUSIONS: Trapezoidal distortion of the SLO laser-beam raster can cause stimulus size to change as much as 10% from the top to the bottom of the raster. Measurements of fixed horizontal retinal landmark distances in SLO images can also vary as much as 10%. We developed a straightforward mathematical method for correcting distortion in SLO image measurements.     

Motor and non-motor sequence learning in children and adolescents with cerebellar damage.

Cerebellar involvement in motor and non-motor sequence learning was examined with serial reaction time tasks (SRT). Our sample consisted of 8 children and adolescents who had undergone surgical removal of a benign posterior fossa tumor (PFT) during childhood. None of them had undergone chemotherapy or cranial radiation therapy (CRT). Ages ranged from 1-11 years at surgery and 9-17 years at testing. The children were tested not earlier than 2.5 years after surgery (M = 5.9 years), enabling brain plasticity and recovery of functions. Their performance was compared with a matched control sample. The PFT group was not impaired in the implicit learning of sequences, as reflected in their performance in blocks with a repeated sequence, both before and after a random block. However, in the perceptual task, their performance deteriorated more than that of the control group when a random block was introduced, suggesting that it was more difficult for the patients to respond flexibly or change their response set when encountering changing task demands. These results are in line with another study by our group on task switching with the same patients.