Virtual Reality Single-Port Sleeve Gastrectomy Training Decreases Physical and Mental Workload in Novice Surgeons: An Exploratory Study.

BACKGROUND: Novice surgeons experience high levels of physical and mental workload during the early stages of their curriculum and clinical practice. Laparoscopic sleeve gastrectomy is the first bariatric procedure worldwide. Feasibility and safety of single-port sleeve gastrectomy (SPSG) has been demonstrated. An immersive virtual reality (VR) simulation was developed to provide a repetitive exercise to learn this novel technique. The primary objective of this study was to evaluate the impact of the VR training tool on mental and physical workload in novice surgeons. The secondary objective included an evaluation of the VR simulator. METHODS: A monocentric-controlled trial was conducted. Ten participants were divided into two groups, the VR group and the control group (without VR training). Surgery residents participated in a first real case of SPSG and a second case 1 month later. The VR group underwent a VR training between the two surgeries. Mental and physical loads were assessed with self-assessment questionnaires: NASA-TLX, Borg scale, and manikin discomfort test. The VR simulator was evaluated through presence, cybersickness, and usability questionnaires. RESULTS: This study showed a decrease of the mental demand and effort dimensions of NASA-TLX between the first and the second surgery in the VR group (P < .05). During the second surgery, a marginally significant difference was shown concerning the mental demand between the two groups. Postural discomfort of the VR group decreased with practice (P < .01), mainly between the first and the second surgery (P < .05). Furthermore, participants characterized the VR simulator as realistic, usable, and very useful to learned surgery. CONCLUSION: This exploratory study showed an improvement in mental and physical workload when novice surgeons trained with VR (repetitive practice, gesture improvement, reduction of stress, etc.). Virtual reality appears to be a promising perspective for surgical training.

Comparison of Kriging and Moving Least Square Methods to Change the Geometry of Human Body Models.

Finite Element Human Body Models (HBM) have become powerful tools to study the response to impact. However, they are typically only developed for a limited number of sizes and ages. Various approaches driven by control points have been reported in the literature for the non-linear scaling of these HBM into models with different geometrical characteristics. The purpose of this study is to compare the performances of commonly used control points based interpolation methods in different usage scenarios. Performance metrics include the respect of target, the mesh quality and the runability. For this study, the Kriging and Moving Least square interpolation approaches were compared in three test cases. The first two cases correspond to changes of anthropometric dimensions of (1) a child model (from 6 to 1.5 years old) and (2) the GHBMC M50 model (Global Human Body Models Consortium, from 50th to 5th percentile female). For the third case, the GHBMC M50 ribcage was scaled to match the rib cage geometry derived from a CT-scan. In the first two test cases, all tested methods provided similar shapes with acceptable results in terms of time needed for the deformation (a few minutes at most), overall respect of the targets, element quality distribution and time step for explicit simulation. The personalization of rib cage proved to be much more challenging. None of the methods tested provided fully satisfactory results at the level of the rib trajectory and section. There were corrugated local deformations unless using a smooth regression through relaxation. Overall, the results highlight the importance of the target definition over the interpolation method.

Distribution and variability study of the femur cortical thickness from computer tomography.

In the context of patient-specific 3D bone reconstruction, enhancing the surface with cortical thickness (COT) opens a large field of applications for research and medicine. This functionality calls for database analysis for better knowledge of COT. Our study provides a new approach to reconstruct 3D internal and external cortical surfaces from computer tomography (CT) scans and analyses COT distribution and variability on a set of asymptomatic femurs. The reconstruction method relies on a short (∼5 min) initialisation phase based on 3D reconstruction from biplanar CT-based virtual X-rays and an automatic optimisation phase based on intensity-based cortical structure detection in the CT volume, the COT being the distance between internal and external cortical surfaces. Surfaces and COT show root mean square reconstruction errors below 1 and 1.3 mm. Descriptions of the COT distributions by anatomical regions are provided and principal component analysis has been applied. The first mode, 16-50% of the variance, corresponds to the variation of the mean COT around its averaged shape; the second mode, 9-28%, corresponds to a fine variation of its shape. A femur COT model can, therefore, be described as the averaged COT distribution in which the first parameter adjusts its mean value and a second parameter adjusts its shape.

CT-based semi-automatic quantification of vertebral fracture restoration.

Minimally invasive surgeries aiming to restore fractured vertebral body are increasing; therefore, our goals were to create a 3D vertebra reconstruction process and design clinical indices to assess the vertebral restoration in terms of heights, angles and volumes. Based on computed tomography (CT)-scan of the vertebral spine, a 3D reconstruction method as well as relevant clinical indices were developed. First, a vertebra initial solution requiring 5 min of manual adjustments is built. Then an image processing algorithm places this solution in the CT-scan images volume to adjust the model's nodes. On the vertebral body's anterior and posterior parts, nine robust heights, volume and endplate angle measurement methods were developed. These parameters were evaluated by reproducibility and accuracy studies. The vertebral body reconstruction accuracy was 1.0 mm; heights and volume accuracy were, respectively, 1.2 and 179 mm3. In conclusion, a 3D vertebra reconstruction process requiring little user time was proposed as well as 3D clinical indices assessing fractured and restored vertebra.

Prediction of the vertebral strength using a finite element model derived from low-dose biplanar imaging: benefits of subject-specific material properties.

STUDY DESIGN: A finite element analysis on osteoporotic vertebrae. OBJECTIVE: This study aims to validate subject-specific finite element models (FEMs) derived from a low-dose imaging system (EOS, Biospace Med, France) for the prediction of vertebral strength. The vertebrae are submitted to an eccentric compression force leading to compression and anterior bending. SUMMARY OF BACKGROUND DATA: Given the aging population, osteoporosis and vertebral fractures are a major public health issue. A low bone mineral density (BMD) does not always explain incident fractures, and multifactorial analyses are required. In this context, FEMs based on quantitative computed tomography (QCT) have been proposed to predict vertebral strength in vitro or quantify effects of treatments. However, the clinical use of such a model for the in vivo follow-up of the whole spine is limited by the high-radiation dose induced by QCT and the lying position, which does not allow postural assessment with the same modality. METHODS: Fourteen vertebrae were modeled using a parametric meshing method. The mesh was subject-specific using geometric parameters computed on the 3-dimensional (3D) reconstructions obtained from the EOS biplanar radiographs. The contribution of cortical bone was taken into account by modeling a cortico-cancellous shell whose properties were derived from experimental data. The effect of subject-specific bone Young's moduli derived from EOS vertebral areal BMD was quantified. The 3D position of the point-of-load application and the 3D orientation of the force was faithfully reproduced in the model to compare the predicted strength and experimental strength under the same loading conditions. RESULTS: The relative error of prediction decreased from 43% to 16% (2.5 times) when subject-specific mechanical properties, derived from EOS areal BMD, were implemented in the FEM compared with averaged material properties. The resulting subject-specific FEMs predicted vertebral strength with a level of significance close to the QCT-based models (r adjusted = 0.79, root mean square error = 367 N). CONCLUSION: This work underlines the potential of low-dose biplanar x-ray devices to make subject-specific FEMs for prediction of vertebral strength.

Fat content of hip muscles: an anteroposterior gradient.

BACKGROUND: Despite the importance of the hip muscles in protecting against hip fracture and in the outcome of hip arthroplasty, the variability in their fat content has not been previously studied. Our objectives were to evaluate the variability in the fat content of the hip muscles in a population without myopathy or a need for hip surgery with the use of computed tomography (CT), to study the relationship between hip muscle fat content and physical performance, and to identify medical conditions and lifestyle habits associated with an increase in hip muscle fat content. METHODS: Ten normal subjects without a relevant medical history and ninety-nine consecutive nonsurgical patients without myopathy (age, twenty-one to ninety-four years) underwent a nonenhanced CT scan of the pelvis. Patients were asked to perform physical tests (six-meter walk, repeated chair stands, and Trendelenburg test), and their level of physical activity and medical history were recorded. Evaluation of the fat content of the hip muscles was based on the analysis of four reproducible and representative CT slices with use of custom software. RESULTS: The fat content varied among the muscles, with an anteroposterior gradient from the hip flexors (mean, 2%) to the hip extensors (mean, 10%). This gradient increased after fifty years of age. Fat content also varied considerably among patients. Higher fat content was associated with poorer performance on physical tests, even after adjustment for the cross-sectional area of the muscle (p < 0.05). Higher fat content was also associated with greater age, higher body-mass index, and lower physical activity (p < 0.001). CONCLUSIONS: The observed variability in the fat content of individuals without myopathy or a need for hip surgery should be useful for comparison with future studies of specific populations of patients, such as those with muscle weakness secondary to hip fracture or hip surgery. Simple lifestyle changes such as dietary restriction, increased physical activity, and vitamin D supplementation may decrease muscle fat content and improve physical performance in the elderly.

Sensitivity of patient-specific vertebral finite element model from low dose imaging to material properties and loading conditions.

Patient-specific modeling could help in predicting vertebral osteoporotic fracture. The accuracy requirement for input data available in clinical routine is related to the model sensitivity. The objective of this study is to assess the relative impact of material properties and of loading conditions on vertebral strength using a finite element model. Fourteen subject-specific vertebral finite element models were used to investigate the effect of material properties and loading conditions. A design of experiment was set to study three parameters: Young's moduli of trabecular bone and cortico-trabecular bone (outer 3 mm of the vertebra), and load location. Cortico-trabecular bone modulus variation from 270 to 478 MPa made fracture load vary from 22 to 51%, depending on other parameters. Trabecular bone modulus variation from 115 to 258 MPa made fracture load vary from 11 to 43%. Displacing load location by 1 cm resulted in a mean decrease of 48-60% of the fracture load. Anterior bending induced strain concentration in vertebral anterior wall. Material properties of both type of bone have about the same effect. Load location is the most sensitive. Effort should be made to take into account patients' specific load distribution regarding its sagittal balance, in addition to bone properties.

New method for 3D reconstruction of the human cranial vault from CT-scan data.

This study presents a new method for the 3D reconstruction of the human cranial vault from routine Computed Tomography (CT) data. The reconstruction method was based on the conceptualization of the shape of the cranial vault with a parametric description. An initialization was first realized with the identification of anatomical landmarks and contours on Digitally Reconstructed Radiographs (DRR) in order to obtain a pre-personalized reconstruction. Then an optimization of the reconstruction was performed to segment the internal and external surfaces of the cranial vault for thickness computation. The method was validated by comparing final reconstructions issued from our approach and from a manual slice-by-slice segmentation method on ten CT-scans. Errors were comparable to the CT image resolution, and less than 2 min were dedicated to the operator-dependent marking step. The reconstruction of internal and external surfaces of the cranial vault allows quantifying and visualizing of thickness throughout the cranial vault. This thickness mapping is useful for clinical purposes as additional pre-surgical information. Moreover, this study constitutes a first step in the personalized characterization of skull resistance directly from routine exams.

Reliability of magnetic resonance imaging measurements of the cross-sectional area of the muscle contractile and non-contractile components.

BACKGROUND/PURPOSE: Magnetic resonance imaging (MRI) is increasingly used to study skeletal muscles patients with muscular disorders. We report an MRI technique for evaluating the trunk muscles. This technique takes both the component surface area (CSA) and the density of the muscles on MRI axial slices into account . Using a computer-based image analysis system, we combined MRI data measuring the muscle CSA, which was separated into the contractile component (CCSA) and the non-contractile component (NCCSA). The purpose of this study was to analyze the reliability of this method of measuring the CSA, CCSA and NCCSA in trunk muscles on MRI axial slices through L4 and T12. METHODS: Thirty volunteer subjects were enrolled in this study. Two acquisitions were performed. For the reliability analyses, each of the two slices (T12 and L4) from 30 subjects was measured by three raters trained in this technique, on two occasions 2 weeks apart. Each muscle was surrounded and its CSA, NCCSA and CCSA were recorded. For each muscle, the agreement between the two sets of 30 measurements performed by three observers was evaluated by calculating an intra-class correlation coefficient (ICC). RESULTS: Regarding the slice through L4 and T12, the reliabilities of the measurement of CSA, CCSA were very good for all the muscles except the parietal muscles. CONCLUSION: MRI measurements of the trunk muscle cross-sectional areas and of the CCSA and NCCSA are reliable.

Greater tissue mineralization heterogeneity in femoral neck cortex from hip-fractured females than controls. A microradiographic study.

In addition to bone quantity, bone quality affects bone strength. Bone quality depends in part on the degree of mineralization of bone tissue (DMB). The relationship between the DMB distribution and the risk of osteoporotic hip fractures remains incompletely investigated. Here, our aim was to compare DMB distribution in femoral neck cortex specimens from 23 women with hip fractures (age, 65-96 years) and 14 control women (age, 75-103 years). Mineralization was determined using quantitative microradiography. We evaluated the following parameters of DMB frequency histograms, for both osteons and interstitial tissue: mode (oDMB(Al)mode and intDMB(Al)mode, respectively); 25th (oDMB(Al)q25, intDMB(Al)q25), 50th (oDMB(Al)q50, intDMB(Al)q50), and 75th (oDMB(Al)q75, intDMB(Al)q75) percentiles; and interquartile range (oDMB(Al)iqr, intDMB(Al)iqr). For each specimen, we also calculated the variance of pixel mineral content for osteons and interstitial tissue (oDMB(Al)var and intDMB(Al)var). We used nonparametric tests to compare frequency histogram parameters between hip-fractured women and controls and Fisher's test to compare variances between groups. All frequency histogram parameters for osteons and interstitial tissue except the 25th percentile, and the variances of pixel mineral content in osteons and interstitial tissue, were significantly different between hip-fractured women and controls, indicating greater heterogeneity of mineralization in the hip-fracture patients than in the controls. These cross-sectional data suggest that bone fragility may be related to greater DMB heterogeneity in osteons and interstitial tissue.

Three-dimensional stereoradiographic modeling of rib cage before and after spinal growing rod procedures in early-onset scoliosis.

BACKGROUND: Early-onset scoliosis frequently leads to major thoracic deformity and pulmonary restrictive disease. Growing rods surgical techniques were developed to achieve a satisfactory correction of the spinal curves during growth. The effect on the rib cage deformity has not yet been documented. The purpose of this study was to analyze the changes of the thoracic geometry after implantation of a growing rod, and to evaluate a stereoradiographic reconstruction method among young scoliotic patients. METHODS: Four patients were enrolled in the study, and four additional patients in the reproducibility study. Three-dimensional spine and rib cage models were generated after low-dose stereoradiographic imaging (EOS). Three-dimensional parameters were computed before and after surgery. Intra and inter-observer reproducibility was calculated, and the accuracy was assessed in comparison to volumetric CT-scan. FINDINGS: The average Cobb angle was reduced from 50.8 degrees to 26 degrees . The surgery resulted in a complex 3D effect on the rib cage, combining frontal, lateral, and axial rotation. This effect was dependent of the side (concave or convex), and the position relative to the apical vertebra. Mean errors in comparison to CT-scan were 3.5mm. INTERPRETATION: The results on the spinal deformity are comparable to other series. The effect on the rib cage is of a smaller magnitude than in the case of a spinal arthrodesis. A longer follow-up is necessary to confirm the positive effect on the rib cage deformity. Further research should be performed to improve the reproducibility of 3D parameters.

Comparison of methods to assess quadriceps muscle volume using magnetic resonance imaging.

PURPOSE: To compare the precision of four methods to estimate the volume of quadriceps muscles using axial MRI. MATERIALS AND METHODS: Entire legs of 10 healthy young subjects were scanned using a 1.5 Tesla magnetic resonance imaging scanner and 4-mm-thick sections without any gaps. Quadriceps muscles were outlined on all of the slices to obtain the MRI reference standard measure of quadriceps muscle volume. This MRI reference standard was compared with the volume estimated using (i) the truncated cone formula, (ii) the Cavalieri method, (iii) a cubic spline interpolation of missing cross sectional areas, and, (iv) the deformation of a parametric specific object. For each method, 3 to 21 slices were used. RESULTS: The average volume error was significantly (P < 0.001) different in comparing the four methods (4.4%, 2.3%, 1.1%, and 1.2%, respectively). In addition, the number of slices required to reach a given volume error was significantly (P < 0.001) different across all methods (respectively, 12, 9, 5, and 7 slices required to reach a volume error of 1.1%). CONCLUSION: While methods based on interpolation and deformation of a parametric specific object have not been used in literature, these two methods are the most precise approaches to reach a given level of precision.

Cortical bone mineralization differences between hip-fractured females and controls. A microradiographic study.

The strength of bone depends on both bone quantity and bone quality. One determinant of bone quality is the degree of mineralization of bone tissue (DMB). To assess the role for DMB in osteoporotic hip fractures, we compared the degree of mineralization in femoral neck cortex from 23 women with hip fractures (age, 65-96 years) and 14 female controls (age, 75-103 years) using quantitative microradiography calibrated with an aluminum step wedge. Variables were DMB in osteons (oDMB(Al)mean) and interstitial tissue (exDMB(Al)mean). Wilcoxon signed-rank tests were used to compare oDMB(Al)mean to exDMB(Al)mean in each group, and Mann-Whitney tests to compare oDMB(Al)mean and exDMB(Al)mean between hip-fracture patients and controls. DMB was significantly lower in the osteons than in the interstitial tissue in both groups (hip-fracture group, P=0.000; control group, P=0.001). DMB values in osteons and interstitial tissue were significantly greater in the hip-fracture patients than in the controls (P=0.007 and P=0.005, respectively). These cross-sectional data suggest that bone fragility may be related to a higher degree of tissue mineralization.

Erector spinae muscle changes on magnetic resonance imaging following lumbar surgery through a posterior approach.

STUDY DESIGN: Prospective randomized study of patients undergoing lumbar arthrodesis. OBJECTIVES: To quantify MRI changes of the erector spinae following lumbar surgery through a posterior approach and the possible protection of these muscles during surgery by the use of cholinergic blockade. SUMMARY OF BACKGROUND DATA: It has been shown that lumbar spine surgery through a posterior approach can induce iatrogenic lesions in the erector spinae. We have shown in a previous study that histologic changes on muscular biopsy performed in the multifidus at the end of the surgical procedure were not modified by the use of cholinergic blockade during surgery. METHODS: Twenty patients scheduled to undergo pedicle-screw enhanced L4-L5 arthrodesis were enrolled in this study. Ten patients received curare during anesthesia and 10 patients did not. MRI was obtained the day before the operation and at 6 months of follow-up on the same MR scanner. T1-weighted images were obtained in the axial plane. The 2 slices immediately proximal and distal to the pedicle screw construct on the postoperative MRI were selected. The corresponding slices were selected on the preoperative MRI. Each erector spinae on the 4 slices was surrounded using a mouse-guided tool. The contractile component of the cross-sectional area (CCSA) was calculated from the number of pixels surrounded and the signal intensity of each pixel. RESULTS: There was only slight changes in the erector spinae CCSA proximal to a posterior lumbar arthrodesis. Erector spinae CCSA decreased by 27% distal to the arthrodesis. Curare showed no efficacy in preventing muscle damage. CONCLUSIONS: Erector spinae muscle alterations mainly occur distal to posterior lumbar surgical procedures.