Caroline A. Grant

The assessment of regional lung mechanics with electrical impedance tomography: a pilot study during recruitment manoeuvres

ObjectiveThe purpose of lung recruitment manoeuvres is to open collapsed lung regions, improve gas exchange and optimise regional lung mechanics. This study investigates the efficacy of recruitment manoeuvres for improving regional ventilation distribution as characterised using electrical impedance tomography (EIT).Design, subjects, interventionsA ventilated ovine smoke inhalation lung injury model was used. Respiratory mechanics and regional filling capacity of the lung were measured using EIT pre- and post- recruitment and compared to a control group.MeasurementsEIT, expressed as the time course relation of the regional versus the global impedance change, measured the regional filling capacities of the lung.Main resultsAfter smoke inhalation injury, the dependent lung showed a significantly larger area of collapse and a reduced filling capacity compared to the non-dependent lung. After recruitment the ventilated volume increased and the dependent lung showed improved respiratory mechanics, whereas the non-dependent lung was more likely to be hyper-inflated during tidal breathing.ConclusionsLung recruitment manoeuvres have a significant impact on regional lung mechanics and individual measurement of ventilation distribution using EIT may assist to improve ventilatory management.

More is not necessarily better. A biomechanical study on distal screw numbers in volar locking distal radius plates.

INTRODUCTION Currently available volar locking plates for the treatment of distal radius fractures incorporate at least two distal screw rows for fixation of the metaphyseal fragment and have a variable-angle locking mechanism which allows placement of the screws in various directions There is, however no evidence that these plates translate into better outcomes or have superior biomechanical properties to first generation plates, which had a single distal screw row and fixed-angle locking. The aim of our biomechanical study was to compare fixed-angle single-row plates with variable-angle multi-row plates to clarify the optimal number of locking screws. MATERIALS AND METHODS Five different plate-screw combinations of three different manufacturers were tested, each group consisting of five synthetic fourth generation distal radius bones. An AO type C2 fracture was created and the fractures were plated according to each manufacturers recommendations. The specimens then underwent cyclic and load-to-failure testing. An optical motion analysis system was used to detect displacement of fragments. RESULTS No significant differences were detected after cyclic loading as well as after load-to-failure testing, neither in regard to axial deformation, implant rigidity or maximum displacement. The fixed-angle single-row plate showed the highest pre-test rigidity, least increase in post-testing rigidity and highest load-to-failure rigidity and least radial shortening. The radial shortening of plates with two distal screw rows was 3.1 and 4.3 times higher, respectively, than that of the fixed-angle single-row plate. CONCLUSION The results of our study indicate that two distal screw rows do not add to construct rigidity and resistance against loss of reduction. Well conducted clinical studies based on the findings of biomechanical studies are necessary to determine the optimal number of screws necessary to achieve reproducibly good results in the treatment of distal radius fractures.

Measurement of ventilation and cardiac related impedance changes with electrical impedance tomography

IntroductionElectrical impedance tomography (EIT) has been shown to be able to distinguish both ventilation and perfusion. With adequate filtering the regional distributions of both ventilation and perfusion and their relationships could be analysed. Several methods of separation have been suggested previously, including breath holding, electrocardiograph (ECG) gating and frequency filtering. Many of these methods require interventions inappropriate in a clinical setting. This study therefore aims to extend a previously reported frequency filtering technique to a spontaneously breathing cohort and assess the regional distributions of ventilation and perfusion and their relationship.MethodsTen healthy adults were measured during a breath hold and while spontaneously breathing in supine, prone, left and right lateral positions. EIT data were analysed with and without filtering at the respiratory and heart rate. Profiles of ventilation, perfusion and ventilation/perfusion related impedance change were generated and regions of ventilation and pulmonary perfusion were identified and compared.ResultsAnalysis of the filtration technique demonstrated its ability to separate the ventilation and cardiac related impedance signals without negative impact. It was, therefore, deemed suitable for use in this spontaneously breathing cohort.Regional distributions of ventilation, perfusion and the combined ΔZV/ΔZQ were calculated along the gravity axis and anatomically in each position. Along the gravity axis, gravity dependence was seen only in the lateral positions in ventilation distribution, with the dependent lung being better ventilated regardless of position. This gravity dependence was not seen in perfusion.When looking anatomically, differences were only apparent in the lateral positions. The lateral position ventilation distributions showed a difference in the left lung, with the right lung maintaining a similar distribution in both lateral positions. This is likely caused by more pronounced anatomical changes in the left lung when changing positions.ConclusionsThe modified filtration technique was demonstrated to be effective in separating the ventilation and perfusion signals in spontaneously breathing subjects. Gravity dependence was seen only in ventilation distribution in the left lung in lateral positions, suggesting gravity based shifts in anatomical structures. Gravity dependence was not seen in any perfusion distributions.

Lung recruitment and endotracheal suction in ventilated preterm infants measured with electrical impedance tomography.

Although suctioning is a standard airway maintenance procedure, there are significant associated risks, such as loss of lung volume due to high negative suction pressures. This study aims to assess the extent and duration of change in end‐expiratory level (EEL) resulting from endotracheal tube (ETT) suction and to examine the relationship between EEL and regional lung ventilation in ventilated preterm infants with respiratory distress syndrome.

Use of 3D printing in complex spinal surgery: historical perspectives, current usage and future directions

Three-dimensional (3D) printing has been used in complex spinal surgical planning since the 1990s and is now increasingly utilized to produce surgical guides, templates, and more recently customized implants. Surgeons report beneficial impacts using 3D-printed biomodels as a preoperative planning ai

Quantifying progressive anterior overgrowth in the thoracic vertebrae of adolescent idiopathic scoliosis patients a sequential magnetic resonance imaging study

Study Design. Anterior and posterior vertebral body heights were measured from sequential magnetic resonance imaging (MRI) scans of adolescent idiopathic scoliosis (AIS) patients and healthy controls. Objective. To measure changes in vertebral body height over time during scoliosis progression to assess how vertebral body height discrepancies change during growth. Summary of Background Data. Relative anterior overgrowth has been proposed as a potential driver for AIS initiation and progression. This theory proposes that the anterior column grows faster, and the posterior column slower, in AIS patients when compared with healthy controls. There is a disagreement in the literature as to whether the anterior vertebral body heights are proportionally greater than posterior vertebral body heights in AIS patients when compared with healthy controls. To some extent, these discrepancies may be attributed to methodological differences. Methods. MRI scans of the major curve of 21 AIS patients (mean age 12.5 ± 1.4 years, mean Cobb 32.2 ± 12.8 degrees) and between T4 and T12 of 21 healthy adolescents (mean age 12.1 ± 0.5 years) were captured for this study. Of the 21 AIS patients, 14 had a second scan on average 10.8 ± 4.7 months after the first. Anterior and posterior vertebral body heights were measured from the true sagittal plane of each vertebra such that anterior overgrowth could be quantified. Results. The difference between anterior and posterior vertebral body height in healthy, nonscoliotic children was significantly greater than in AIS patients with mild to moderate scoliosis. There was; however, no significant relationship between the overall anterior-posterior vertebral body height difference in AIS and either severity of the curve or its progression over time. Conclusion. Whilst AIS patients have a proportionally longer anterior column than nonscoliotic controls, the degree of anterior overgrowth was not related to the rate of progression or the severity of the scoliotic curve. Level of Evidence: 3

Is There Asymmetry Between the Concave and Convex Pedicles in Adolescent Idiopathic Scoliosis? A CT Investigation.

BackgroundAdolescent idiopathic scoliosis is a complex three-dimensional deformity of the spine characterized by deformities in the sagittal, coronal, and axial planes. Spinal fusion using pedicle screw instrumentation is a widely used method for surgical correction in severe (coronal deformity, Cobb angle > 45°) adolescent idiopathic scoliosis curves. Understanding the anatomic difference in the pedicles of patients with adolescent idiopathic scoliosis is essential to reduce the risk of neurovascular or visceral injury through pedicle screw misplacement.Questions/PurposesTo use CT scans (1) to analyze pedicle anatomy in the adolescent thoracic scoliotic spine comparing concave and convex pedicles and (2) to assess the intra- and interobserver reliability of these measurements to provide critical information to spine surgeons regarding size, length, and angle of projection.MethodsBetween 2007 and 2009, 27 patients with adolescent idiopathic scoliosis underwent thoracoscopic anterior correction surgery by two experienced spinal surgeons. Preoperatively, each patient underwent a CT scan as was their standard of care at that time. Twenty-two patients (mean age, 15.7 years; SD, 2.4 years; range, 11.6–22 years) (mean Cobb angle, 53°; SD, 5.3°; range, 42°–63°) were selected. Inclusion criteria were a clinical diagnosis of adolescent idiopathic scoliosis, female, and Lenke type 1 adolescent idiopathic scoliosis with the major curve confined to the thoracic spine. Using three-dimensional image analysis software, the pedicle width, inner cortical pedicle width, pedicle height, inner cortical pedicle height, pedicle length, chord length, transverse pedicle angle, and sagittal pedicle angles were measured. Randomly selected scans were remeasured by two of the authors and the reproducibility of the measurement definitions was validated through limit of agreement analysis.ResultsThe concave pedicle widths were smaller compared with the convex pedicle widths at T7, T8, and T9 by 37% (3.44 mm ± 1.16 mm vs 4.72 mm ± 1.02 mm; p < 0.001; mean difference, 1.27 mm; 95% CI, 0.92 mm–1.62 mm), 32% (3.66 mm ± 1.00 mm vs 4.82 mm ± 1.10 mm; p < 0.001; mean difference, 1.16 mm; 95% CI, 0.84 mm–1.49 mm), and 25% (4.10 mm ± 1.57 mm vs 5.12 mm ± 1.17 mm; p < 0.001; mean difference, 1.02 mm; 95% CI, 0.66 mm–1.39 mm), respectively. The concave pedicle heights were smaller than the convex at T5 (9.43 mm ± 0.98 vs 10.63 mm ± 1.10 mm; p = 0.002; mean difference, 1.02 mm; 95% CI, 0.59 mm–1.45 mm), T6 (8.87 mm ± 1.37 mm vs 10.88 mm ± 0.81 mm; p < 0.001; mean difference, 2.02 mm; 95% CI, 1.40 mm–2.63 mm), T7 (9.09 mm ± 1.24 mm vs 11.35 mm ± 0.84 mm; p < 0.001; mean difference, 2.26 mm; 95% CI, 1.81 mm–2.72 mm), and T8 (10.11 mm ± 1.05 mm vs 11.86 mm ± 0.88 mm; p < 0.001; mean difference, 1.75 mm; 95% CI, 1.30 mm–2.19 mm). Conversely, the concave transverse pedicle angle was larger than the convex at levels T6 (11.37° ± 4.48° vs 8.82° ± 4.31°; p = 0.004; mean difference, 2.54°; 95% CI, 1.10°–3.99°), T7 (12.69° ± 5.93° vs 8.65° ± 3.79°; p = 0.002; mean difference, 4.04°; 95% CI, 1.90°–6.17°), T8 (13.24° ± 5.28° vs 7.66° ± 4.87°; p < 0.001; mean difference, 5.58°; 95% CI, 2.99°–8.17°), and T9 (19.95° ± 5.69° vs 8.21° ± 4.02°; p < 0.001; mean difference, 4.74°; 95% CI, 2.68°–6.80°), indicating a more posterolateral to anteromedial pedicle orientation.ConclusionsThere is clinically important asymmetry in the morphologic features of pedicles in individuals with adolescent idiopathic scoliosis. The concave side of the curve compared with the convex side is smaller in height and width periapically. Furthermore, the trajectory of the pedicle is more acute on the convex side of the curve compared with the concave side around the apex of the curve. Knowledge of these anatomic variations is essential when performing scoliosis correction surgery to assist with selecting the correct pedicle screw size and trajectory of insertion to reduce the risk of pedicle wall perforation and neurovascular injury.

Apophyseal ossification of the iliac crest in forensic age estimation: computed tomography standards for modern Australian subadults

This study contrasts the ontogeny of the iliac crest apophysis using conventional radiography and multislice computed tomography (MSCT), providing probabilistic information for age estimation of modern Australian subadults. Retrospective abdominopelvic MSCT data acquired from 524 Australian individuals aged 7–25 and surveillance radiographs of adolescent idiopathic scoliosis patients included in the Paediatric Spine Research Group Progression Study (n = 531) were assessed. Ossification scoring of pseudo‐radiographs and three‐dimensional (3D) volume‐rendered reconstructions using Risser (1958) quantitative descriptors indicate discrepancies in age estimates, stage allocation, and conflicting morphological progression. To mitigate visualization limitations associated with two‐dimensional radiographs, we provide and validate a modified 3D‐MSCT scoring tier of ossification, demonstrating complete fusion between 17.3–19.2 and 17.1–20.1 years in males and females. Legal demarcation for doli incapax presumption and age of majority (18 years) can be achieved using probability estimates from a fitted cumulative probit model for apophyseal fusion using the recalibrated standards.

Mechanical testing of internal fixation devices: A theoretical and practical examination of current methods.

Successful healing of long bone fractures is dependent on the mechanical environment created within the fracture, which in turn is dependent on the fixation strategy. Recent literature reports have suggested that locked plating devices are too stiff to reliably promote healing. However, in vitro testing of these devices has been inconsistent in both method of constraint and reported outcomes, making comparisons between studies and the assessment of construct stiffness problematic. Each of the methods previously used in the literature were assessed for their effect on the bending of the sample and concordant stiffness. The choice of outcome measures used in in vitro fracture studies was also assessed. Mechanical testing was conducted on seven hole locked plated constructs in each method for comparison. Based on the assessment of each method the use of spherical bearings, ball joints or similar is suggested at both ends of the sample. The use of near and far cortex movement was found to be more comprehensive and more accurate than traditional centrally calculated interfragmentary movement values; stiffness was found to be highly susceptible to the accuracy of deformation measurements and constraint method, and should only be used as a within study comparison method. The reported stiffness values of locked plate constructs from in vitro mechanical testing is highly susceptible to testing constraints and output measures, with many standard techniques overestimating the stiffness of the construct. This raises the need for further investigation into the actual mechanical behaviour within the fracture gap of these devices.

Comparison of mechanical and ultrasound elastic modulus of ovine tibial cortical bone

Finite element models of bones can be created by deriving geometry from an X-ray CT scan. Material properties such as the elastic modulus can then be applied using either a single or set of homogeneous values, or individual elements can have local values mapped onto them. Values for the elastic modulus can be derived from the CT density values using an elasticity versus density relationship. Many elasticity-density relationships have been reported in the literature for human bone. However, while ovine in vivo models are common in orthopaedic research, no work has been done to date on creating FE models of ovine bones. To create these models and apply relevant material properties, an ovine elasticity-density relationship needs to be determined. Using fresh frozen ovine tibias the apparent density of regions of interest was determined from a clinical CT scan. The bones were the sectioned into cuboid samples of cortical bone from the regions of interest. Ultrasound was used to determine the elastic modulus in each of three directions - longitudinally, radially and tangentially. Samples then underwent traditional compression testing in each direction. The relationships between apparent density and both ultrasound, and compression modulus in each direction were determined. Ultrasound testing was found to be a highly repeatable non-destructive method of calculating the elastic modulus, particularly suited to samples of this size. The elasticity-density relationships determined in the longitudinal direction were very similar between the compression and ultrasound data over the density range examined. A clear difference was seen in the elastic modulus between the longitudinal and transverse directions of the bone samples, and a transverse elasticity-density relationship is also reported.