Vacuum curette lumbar discectomy mechanics for use in spine surgical training simulators.

Simulation in surgical training is a growing field and this study aims to understand the force and torque experienced during lumbar spine surgery to design simulator haptic feedback. It was hypothesized that force and torque would differ among lumbar spine levels and the amount of tissue removed by ≥ 7%, which would be detectable to a user. Force and torque profiles were measured during vacuum curette insertion and torsion, respectively, in multiple spinal levels on two cadavers. Multiple tests per level were performed. Linear and torsional resistances of 2.1 ± 1.6 N/mm and 5.6 ± 4.3 N mm/°, respectively, were quantified. Statistically significant differences were found in linear and torsional resistances between all passes through disc tissue (both p = 0.001). Tool depth (p < 0.001) and lumbar level (p < 0.001) impacted torsional resistance while tool speed affected linear resistance (p = 0.022). Average differences in these statistically significant comparisons were ≥ 7% and therefore detectable to a surgeon. The aforementioned factors should be considered when developing haptic force and torque feedback, as they will add to the simulated lumbar discectomy realism. These data can additionally be used inform next generation tool design. Advances in training and tools may help improve future surgeon training.

Impact of calcification modeling to improve image fusion accuracy for endovascular aortic aneurysm repair.

Since the 1990s, endovascular aortic aneurysm repair (EVAR) has become a common alternative to open surgery for the treatment of abdominal aortic aneurysms (AAAs). To aid the deployment of stent-grafts, fluoroscopic image guidance can be enhanced using preoperative simulation and intraoperative image fusion techniques. However, the impact of calcification (Ca) presence on the guidance accuracy of such techniques is yet to be considered. In the present work, we introduce a guidance tool that accounts for patient-specific Ca presence. Numerical simulations of EVAR were developed for 12 elective AAA patients, both with (With-Ca) and without (No-Ca) Ca consideration. To assess the accuracy of the simulations, the image results were overlaid on corresponding intraoperative images and the overlay error was measured at selected anatomical landmarks. With this approach we gained insight into the impact of Ca presence on image fusion accuracy. Inclusion of Ca improved mean image fusion accuracy by 8.68 ± 4.59%. In addition, a positive correlation between the relative Ca presence and the image fusion accuracy was found (R = .753, p < .005). Our results suggest that considering Ca presence in patient-specific EVAR simulations increases the reliability of EVAR image guidance techniques that utilize numerical simulation, especially for patients with severe aortic Ca presence.

A manufacturing and annealing protocol to develop a cold-sprayed Fe-316L stainless steel biodegradable stenting material.

Biodegradable stents show promise to revolutionize coronary artery disease treatment. Its successful implementation in the global market remains limited due to the constraints of current generation biodegradable materials. Cold gas dynamic spraying (CGDS) has been proposed as a manufacturing approach to fabricate a metallic biodegradable amalgamate for stent application. Iron and 316L stainless steel powders are combined in a 4:1 ratio to create a novel biomaterial through cold spray. Cold spray processing however, produces a coating in a work hardened state, with limited ductility, which is a critical mechanical property in stent design. To this end, the influence of annealing temperature on the mechanical and corrosion performances of the proposed Fe-316L amalgamate is investigated. It was found that annealing at 1300 °C yielded a complex material microstructure, with an ultimate tensile strength of approximately 280 MPa and ductility of 23%. The static corrosion rate determined at this annealing temperature was equal to 0.22 mg cm-2 day-1, with multiple corrosion species identified within the degradation layers. Precipitates were observed throughout the microstructure, which appeared to accelerate the overall corrosion behaviour. It was shown that cold-sprayed Fe-316L has significant potential to be implemented in a clinical setting. STATEMENT OF SIGNIFICANCE: Biodegradable stents have potential to significantly improve treatment of coronary artery disease by decreasing or potentially eliminating late-term complications, including stent fracture and in-stent restenosis. Current generation polymer biodegradable stents have led to poorer patient outcomes in comparison to drug-eluting stents, however, and it is evident that metallic biomaterials are required, which have increased strength. To this end, a novel iron and stainless steel 316L biomaterial is proposed, fabricated through cold-gas dynamic spraying. This study analyses the effect of annealing on the Fe-316L biomaterial through corrosion, mechanical, and microstructural investigations. The quantitative data presented in this work suggests that Fe-316L, in its annealed condition, has the mechanical and corrosion properties necessary for biodegradable stent application.

Loss of mechanical directional dependency of the ascending aorta with severe medial degeneration.

Biomechanical characterization of the aortic wall may help risk stratify patients with aneurysms. We investigated the degree of anisotropy, the directional dependency of mechanical properties, in control and aneurysmal ascending aortic tissue. We hypothesized that medial degeneration and aortic wall remodeling as found in aneurysmal tissue alter energy loss in both the circumferential and longitudinal directions, thereby reducing anisotropy. Aneurysmal and control ascending aortic tissue excised during surgery was subjected to biaxial tensile testing. Stress-strain relationships were collected in the circumferential and longitudinal directions; from these data, the mechanical properties of energy loss and the apparent modulus of elasticity were derived, and the associated anisotropy indices were calculated. Movat pentachrome histological staining was performed, and aortic wall medial degeneration was quantified. Energy loss was greater in the circumferential than the longitudinal direction, demonstrating significant anisotropy in both normal and aneurysmal aortas (P<.0001). This directional dependency diminished in (a) larger aortas (r2=0.15, P=.01), especially when indexed to body surface area (r2=0.29, P=.002); (b) aortas with greater overall energy loss (r2=0.44, P<.0001); (3) aortas associated with tricuspid valves (P=.004); and (4) higher collagen-to-elastin ratio (r2=0.29, P=.001). Aortas with collagen-to-elastin ratios greater than 2 were uniformly isotropic. Furthermore, the greatest energy loss anisotropy was found on the inner curvature of the aorta (P=.01). Energy loss demonstrates the directional dependency of aortic tissue. Energy loss isotropy is associated with medial degeneration, indicating that microstructural changes can be captured by global biomechanics, thereby identifying it as a marker of disease severity.

The Ross procedure: biomechanical properties of the pulmonary artery according to aortic valve phenotype.

OBJECTIVES: The aim of this study is to determine whether patients undergoing the Ross procedure with bicuspid aortic valves have pulmonary artery biomechanical properties different from those with tricuspid valves. METHODS: Thirty-two pulmonary arteries and 20 aortas were obtained from patients undergoing the Ross procedure at the time of surgery, from a cohort of 32 patients. The aortic valve was tricuspid in 5 patients (16%), bicuspid in 18 patients (56%) and unicuspid in 9 patients (28%). Histological analysis and ex vivo equi-biaxial tensile testing completed within 8 hours of surgery were used to evaluate differences in patient groups and between the pulmonary artery and the ascending aorta. RESULTS: There was no difference in thickness among pulmonary arteries when compared according to aortic valve phenotype (P = 0.94). There was no difference in the tensile tissue properties among aortas and pulmonary arteries when compared according to aortic valve phenotype, in either the circumferential or longitudinal axis. When compared according to the main surgical indication, pulmonary artery walls from patients with pure aortic regurgitation were less stiff than their counterparts (aortic regurgitation: 0.055 ± 0.037 MPa, aortic stenosis: 0.103 ± 0.051 MPa, mixed disease: 0.110 ± 0.044 MPa and aortic valve endocarditis: 0.216 ± 0.033 MPa, P = 0.002). There was no difference in the number of elastic lamellae in pulmonary artery specimens from the three different aortic valve phenotypes, as well as in the aortic specimens. CONCLUSIONS: No significant differences were observed in the biomechanical properties of pulmonary arteries when compared according to aortic valve phenotype.

Biomechanics of the Ascending Thoracic Aorta: A Clinical Perspective on Engineering Data.

Aneurysms of the ascending thoracic aorta often require prophylactic surgical intervention to resect and replace the aortic wall with a synthetic graft to avoid the risk of dissection or rupture. The main criterion for surgical intervention is the size of the aneurysm, with elective surgery recommended with a maximal aortic diameter of 4.2-5.5 cm depending on valve type and other patient risk factors. Although the risk of dissection and rupture increases with the size of aneurysm, different pathologies, including aortic valve phenotype and connective tissue disorders uniquely influence the mechanical dysfunction of the aortic wall. Dissection and rupture are mechanical modes of failure caused by an inability of the tissue to withstand local tissue stresses. Tensile testing of aortic tissues, therefore, has been used to reveal the mechanical parameters of diseased and healthy tissues to better characterize the mechanical function of aortic tissues in different patient groups. In this review, we highlight the principles and methods of ex vivo tensile analysis as well as the composition and structural properties that contribute to the mechanical behaviour of the ascending aorta. We also present a clinically oriented description of mechanical testing along with insight into the characterization of aneurysm. Finally, we highlight recent advances in echocardiography, computer tomographic angiography, and magnetic resonance angiography that have the potential to measure biomechanical properties noninvasively and therefore help select aortas at risk.

Experimental validation of more realistic computer models for stent-graft repair of abdominal aortic aneurysms, including pre-load assessment.

Although the endovascular repair of abdominal aortic aneurysms is a less invasive alternative than classic open surgery, complications such as endoleak and kinking still need to be addressed. Numerical simulation of endovascular repair is becoming a valuable tool in stent-graft (SG) optimization, patient selection and surgical planning. The experimental and numerical forces required to produce SG deformations were compared in a range of in vivo conditions in the present study. The deformation modes investigated were: bending as well as axial, transversal and radial compressions. In particular, an original method was developed to efficiently account for radial pre-load because of the pre-compression of stents to match the graft dimensions during manufacturing. This is important in order to compute the radial force exerted on the vessel after deployment more accurately. Variations of displacement between the experimental and numerical results ranged from 1.39% for simple leg bending to 5.93% for three-point body bending. Finally, radial pre-load was modeled by increasing Young's modulus of each stent. On average, it was found that Young's modulus had to be augmented by a factor of 2. Copyright © 2016 John Wiley & Sons, Ltd.

Fracture Toughness of Vocal Fold Tissue: A Preliminary Study.

A customized mechanical tester that slices thin, soft samples was used to measure the fracture toughness of vocal fold tissue. Porcine vocal fold lamina propria was subjected to quasi-static, guillotine-like tests at three equally distanced regions along the anterior-posterior direction. The central one-third where high-velocity collisions between vocal folds occur was found to have the maximum fracture toughness. In contrast, the anterior one-third featured a lower toughness. Fracture toughness can be indicative of the risk of benign and malignant lesions in vocal fold tissue.

Effectiveness of low rate fluoroscopy at reducing operator and patient radiation dose during transradial coronary angiography and interventions.

OBJECTIVES: This study sought to determine the efficacy of low rate fluoroscopy at 7.5 frames/s (FPS) versus conventional 15 FPS for reduction of operator and patient radiation dose during diagnostic coronary angiography (DCA) and percutaneous coronary intervention (PCI) via the transradial approach (TRA). BACKGROUND: TRA for cardiac catheterization is potentially associated with increased radiation exposure. Low rate fluoroscopy has the potential to reduce radiation exposure. METHODS: Patients undergoing TRA diagnostic angiography ± ad-hoc PCI were randomized to fluoroscopy at 7.5 FPS versus 15 FPS prior to the procedure. Both 7.5 and 15 FPS fluoroscopy protocols were configured with a fixed dose per pulse of 40 nGy. Primary endpoints were operator radiation dose (measured with dosimeter attached to the left side of the thyroid shield in µSievert [µSv]), patient radiation dose (expressed as dose-area product in Gy·cm(2)), and fluoroscopy time. RESULTS: From October 1, 2012 to August 30, 2013, from a total of 363 patients, 184 underwent DCA and 179 underwent PCI. Overall, fluoroscopy at 7.5 FPS compared with 15 FPS was associated with a significant reduction in operator dose (30% relative reduction [RR], p < 0.0001); and in patient's dose-area product (19% RR; p = 0.022). When stratified by procedure type, 7.5 FPS compared with 15 FPS was associated with significant reduction in operator dose during both DCA (40% RR; p < 0.0001) and PCI (28% RR; p = 0.0011). Fluoroscopy at 7.5 FPS, compared with 15 FPS, was also associated with substantial reduction in patients' dose-area product during DCA (26% RR; p = 0.0018) and during PCI (19% RR; p = 0.13). Fluoroscopy time was similar in 7.5 FPS and 15 FPS groups for DCA (3.4 ± 2.0 min vs. 4.0 ± 4.7 min; p = 0.42) and PCI (11.9 ± 8.4 min vs. 13.3 ± 9.7 min; p = 0.57), respectively. CONCLUSIONS: Fluoroscopy at 7.5 FPS, compared with 15 FPS, is a simple and effective method in reducing operator and patient radiation dose during TRA DCA and PCI.

Neutrophil adhesion on endothelial cells in a novel asymmetric stenosis model: effect of wall shear stress gradients.

Leukocytes play a pivotal role in the progression of atherosclerosis. A novel three-dimensional in vitro asymmetric stenosis model was used to better investigate the role of local hemodynamics in the adhesion of leukocytes to an established plaque. The adhesion of a human promyelocytic cell line (NB4) on a human abdominal aortic endothelial cell (EC) monolayer was quantified. NB4 cells were circulated over TNF-alpha stimulated and nonstimulated ECs for 1 or 6 h at 1.25 or 6.25 dynes/cm(2) and compared to static conditions. Cytokine stimulation increased significantly EC expression of intercellular adhesion molecule and vascular cell adhesion molecule. Under static conditions, neutrophils adhered overall more than under flow, with decreased adhesion with increasing shear. Adhesion was significantly higher in the recirculation region distal to the stenosis than in the inlet. Preshearing the ECs decreased the expression of cell adhesion molecules in inflamed endothelium and significantly decreased adhesion. However, the ratio of adhesion between the recirculation zone and the inlet increased, hence exhibiting an increased regional difference. This work suggests an important role for neutrophil-EC interactions in the atherosclerotic process, especially in wall shear stress gradient regions. This is important clinically, potentially helping to explain plaque stability.

A comparison of mechanical properties of materials used in aortic arch reconstruction.

BACKGROUND: Differences in the mechanical properties of aortic tissues and replacement materials can have unwanted hemodynamic effects leading to graft failure. The aim of this experimental study was to compare the mechanical properties of different graft-patch materials used in aortic arch reconstruction with those of healthy and dilated human ascending aortas (AAs). METHODS: Four square samples were taken from 30 healthy (n = 120) and 14 dilated (n = 56) AA rings and from 34 human pericardial sections (fresh [n = 68] and Carpentiers solution fixed [n = 68]). In addition, square samples from commercial bovine pericardium (n = 14) were also compared with woven Dacron grafts (n = 24) and tested biaxially. Stress-strain curves (0% to 30%) were generated using a biaxial tensile tester to quantify the anisotropic properties and stiffness of the materials at 37 degrees C. RESULTS: We found significant differences in stiffness and anisotropy among all material types. Fresh and fixed human pericardia, bovine pericardium, and Dacron were 9.5, 7.1, 16.4, and 18.4 times stiffer than dilated AAs, which was 1.3 times stiffer than healthy AAs under physiologic stretch. Only dilated and healthy AAs showed an increase in anisotropic properties with increasing strain. CONCLUSIONS: The significant differences in the mechanical properties among all materials we found are intended to increase the awareness of these differences in materials used in aortic reconstruction surgery. This finding suggests that improvements are needed in prosthetic material design to better mimic native tissue.

Computational simulations of the aortic valve validated by imaging data: evaluation of valve-sparing techniques.

The goal of this study has been to develop a numerical model of the aortic valve, to validate it with in-vivo data and to computationally evaluate the effect of two types of aortic valve-sparing reconstructions on valve dynamics and hemodynamics. A model of the native aortic valve and two models of the valve after surgical reconstruction (reimplantation with a straight conduit and remodeling with a shaped conduit) were created. These models were transferred to a finite element analysis software where the interaction between valve structures and blood was taken into account in a dynamic manner. Leaflet and blood dynamics, as well as tissue compliance and stresses were evaluated. Leaflet dynamics and blood velocities were also assessed by magnetic resonance imaging in 15 healthy volunteers. Computational results in the native valve model correlated closely with the in-vivo imaging data. The creation of neo-sinuses was shown to restore leaflet opening and closing dynamics. Loss of compliance at the commissures led to altered stress distribution patterns. Preservation of sinus geometry was an important factor in end systolic vortex formation. This is the first study to have incorporated the effect of blood flow in the numerical evaluation of aortic reconstructions using a computational model validated by in-vivo data. Differences in valve dynamics after surgical reconstruction reported in this computational study match trends previously reported in other in-vivo studies. Numerical models such as this one can serve as increasingly sophisticated tools in the study of aortic valve pathologies and in the optimization of new surgical reconstruction techniques.

Aortic root reconstruction: from principles to numerical modeling.

Reconstructing the aortic root represents a formidable task for modern cardiac surgery. By the time an individual reaches 75 years of age his or her aortic apparatus has been submitted to more than three billion cardiac cycles, leaving no place for engineering flaws or misconception. The rules that have been established through millions of years of evolution are strict and demanding. During the past two decades, the cardiovascular community has manifested a growing interest in this topic, especially in patients with medial degenerative disease. However, the ideal reconstruction is still to be devised. To achieve a physiological root reconstruction that preserves the diastolic and systolic function of the valve as well as prevents premature degeneration, a few principles have to be respected. Neglecting any one of them has consequences on the normal functioning of the aortic valve. Current surgical techniques have limitations due to the limited availability of biomaterial and the lack of useful tools to assess pathophysiological conditions and assist surgeons in designing better custom-made reconstructions of the aortic root. The authors present a review of the principles behind the physiology of the reconstruction of the aortic root, and review the literature on computerized models exploring the biomechanics and kinetics of the ascending aorta.

Incidence of stent under-deployment as a cause of in-stent restenosis in long stents.

Although stent under-deployment (SU) has been associated with increased risk of in-stent restenosis, little data have been reported on the incidence of SU in patients presenting with clinical in-stent restenosis. In 59 patients referred for vascular brachytherapy and showing angiographic in-stent restenosis, we sought (1) to determine the incidence of SU using standard intravascular ultrasound (IVUS) criteria (2) to evaluate the effects of repeat angioplasty on further stent expansion. Stented length was 32+/-17 mm and diameter stenosis was 75+/-14%. Before re-intervention, the incidence of reduced absolute values of minimal stent cross-sectional area (MSCSA) varied from 69% (< or =8 mm2) to 15% (< or =5 mm2). After re-intervention, the incidence decreased to 24% (< or =8 mm2) (p = 0.0001) and 0% (< or =5 mm2) (p = 0.005). Before re-intervention, SU as assessed by relative criteria varied from 21% (80% mean reference lumen area or 90% minimum distal reference lumen area) to 28% (100% minimum reference lumen area). After re-intervention, the incidence of SU varied from 7% (90% minimum distal reference lumen area) (p = 0.0001 vs. pre) to 24% (55% mean reference EEM area) (p = ns). No change in strut apposition (97% pre vs. 100% post) nor in symmetry index (100% pre vs. post) was noted. From all criteria, the 90 and 100% minimum reference lumen area criteria were the most altered by repeat balloon dilatation, 21% pre vs. 7% post and 28% pre vs. 11% post, respectively. In conclusion, among patients presenting with severe angiographic in-stent restenosis, a significant number showed signs of SU whose incidence varied according to applied criteria. Significant stent re-expansion can be obtained following IVUS-guided repeat angioplasty irrespective of initial SU criteria.