The management and prognosis of aortic dissection (AD) is often challenging and the use of personalised computational models is being explored as a tool to improve clinical outcome. Including vessel ...wall motion in such simulations can provide more realistic and potentially accurate results, but requires significant additional computational resources, as well as expertise. With clinical translation as the final aim, trade-offs between complexity, speed and accuracy are inevitable. The present study explores whether modelling wall motion is worth the additional expense in the case of AD, by carrying out fluid-structure interaction (FSI) simulations based on a sample patient case.
Patient-specific anatomical details were extracted from computed tomography images to provide the fluid domain, from which the vessel wall was extrapolated. Two-way fluid-structure interaction simulations were performed, with coupled Windkessel boundary conditions and hyperelastic wall properties. The blood was modelled using the Carreau-Yasuda viscosity model and turbulence was accounted for via a shear stress transport model. A simulation without wall motion (rigid wall) was carried out for comparison purposes.
The displacement of the vessel wall was comparable to reports from imaging studies in terms of intimal flap motion and contraction of the true lumen. Analysis of the haemodynamics around the proximal and distal false lumen in the FSI model showed complex flow structures caused by the expansion and contraction of the vessel wall. These flow patterns led to significantly different predictions of wall shear stress, particularly its oscillatory component, which were not captured by the rigid wall model.
Through comparison with imaging data, the results of the present study indicate that the fluid-structure interaction methodology employed herein is appropriate for simulations of aortic dissection. Regions of high wall shear stress were not significantly altered by the wall motion, however, certain collocated regions of low and oscillatory wall shear stress which may be critical for disease progression were only identified in the FSI simulation. We conclude that, if patient-tailored simulations of aortic dissection are to be used as an interventional planning tool, then the additional complexity, expertise and computational expense required to model wall motion is indeed justified.
Abstract Background Context A variety of surgical approaches have been used for cage insertion in lumbar interbody fusion surgery. The direct anterior approach requires mobilization of the great ...vessels to access the intervertebral disc spaces cranial to L5/S1. With the lateral retroperitoneal transpsoas approach, it is difficult to access the L4/L5 intervertebral disc space due to the lumbar plexus and iliac crest, and L5/S1 is inaccessible. We describe a new anterolateral retroperitoneal approach, which is safe and reproducible to access the disc spaces from L1 to S1 inclusive, obviating the need for a separate direct anterior approach to access L5/S1. Purpose This paper had the following objectives: first, to report a reproducible novel single-incision, muscle-splitting, anterolateral pre-psoas surgical approach to the lumbar spine from L1 to S1; second, to highlight the technical challenges of this approach and highlight approach-related complications; and third, to evaluate clinical outcomes using this surgical technique in a prospective series of L1 to S1 anterior lumbar interbody fusions (ALIFs) performed as part of a 360-degree fusion for adult spinal deformity correction. Study Design This report used a prospective cohort study. Patient Sample A prospective series of patients (n=64) having ALIF using porous tantalum cages as part of a two-stage complex spinal reconstruction from L1 to S1 were studied. Outcome Measures Data collected included blood loss, operative time, incision size, technical challenges, perioperative complications, and secondary procedures. Clinical outcome measures used included visual analogue scale (VAS) Back Pain, VAS Leg Pain, EuroQoL-5 Dimensions (EQ-5D), EQ-5D VAS, Oswestry Disability Index (ODI), and Scoliosis Research Society-22 (SRS-22). Methods Pre- and postoperative radiographic parameters and clinical outcome measures were assessed. Mean follow-up time was 1.8 years. Results Mean blood loss was 68±9.6 mL. The mean VAS Back Pain score improved from 7.5±1.25 preoperatively to 2.5±1.7 at 3 months (p=.02), 1.2±0.5 at 6 months (p=.01), and 1.4±0.6 at 1 year (p=.02). The mean ODI improved from 64.3±31.8 preoperatively to 16.6±14.7 at 3 months (p>.05), 10.7±6.0 at 6 months (p=.02), and 6.7±6.1 at 1 year (p=.01). There were no permanent neurologic, vascular, or visceral injuries. One revision anterior procedure was required on a patient with rheumatoid arthritis and advanced systemic disease that sustained a sacral fracture and required revision ALIF at L5/S1. Conclusions The technique described is a safe, new, muscle-splitting, psoas-preserving, one-incision approach to provide access from L1 to S1 for multilevel anterior or oblique lumbar interbody fusion surgery.
Background Advances in endovascular technology have led to the successful treatment of complex abdominal aortic aneurysms. However, there is currently no consensus on what constitutes a juxtarenal, ...pararenal, or suprarenal aneurysm. There is emerging evidence that the extent of the aneurysm repair is associated with outcome. We compare the outcomes of 150 consecutive patients treated with a fenestrated or branched stent graft and present the data stratified according to the Society for Vascular Surgery classification based on proximal anatomic landing zones. Methods A prospectively collected database of consecutive patients undergoing fenestrated or branched stent graft insertion in a tertiary center between 2008 and 2013 was retrospectively analyzed. Aneurysms were subdivided into zones according to where the area of proximal seal could be achieved in relation to the visceral arteries. Zone 8 covers the renal arteries, zone 7 covers the superior mesenteric artery, and zone 6 covers the celiac axis. Patient demographics, operative variables, mortality, and major morbidity were analyzed by univariate and multivariate analysis to assess for differences between zones. Results During the study period, 150 patients were treated. There were 49 in zone 8, 76 in zone 7, and 25 in zone 6. Prior aortic surgery had been performed in 19 patients, which included 11 patients with previous endovascular aneurysm repairs. There was significantly increased blood loss ( P < .001), operative time ( P < .0001), total hospital stay ( P = .018), and intensive care unit stay ( P < .0001) as the zones ascended the aorta. There were 14 inpatient deaths recorded across all zones with a 30-day mortality rate of 8%. Logistic regression analysis for 30 day mortality showed a significant increase as the zones ascended ( P = .007). Kaplan-Meier analysis showed that 5-year survival significantly deteriorated as the zones ascended ( P = .039), with no significant difference in the freedom from reintervention curves between zones ( P = .37). Conclusions We have shown that the extent of the aneurysm repair as determined by the proximal sealing zone is associated with outcome. Mortality, operative duration, blood loss, and hospital stay all significantly increased as the zones ascended. These data also validate the use of the proposed new classification based on aortic anatomy.
Study Design:
Retrospective cohort study.
Objective:
To assess both implant performance and the amount of correction that can be achieved using multilevel anterior lumbar interbody fusion (ALIF).
...Methods:
Retrospective cohort study (n = 178) performed over a 4-year period. Surgical variables examined included blood loss, operative time, perioperative complications, and secondary/revision procedures. Follow-up radiographic assessment was performed to record implant-related problems. Radiographic parameters were examined pre- and postoperatively. Health-related quality of life (HRQOL) outcome measures were collected preoperatively and at 6 weeks, 6 months, 1 year, and 2 years postoperatively. Descriptive and comparative statistical analysis, using paired-sample t test and repeated-measures analysis of variance (rANOVA), was performed.
Results:
Lumbar lordosis increased from 42° ± 17° preoperatively to 55° ± 11° postoperatively (P < .001). The visual analog scale back pain mean score improved from 8.3 ± 1.5 preoperatively to 2.6 ± 2.4 at 2 years (P < .001). The mean Oswestry Disability Index improved from 69.5 ± 21.5 preoperatively to 19.9 ± 15.2 at 2 years (P < .001). The EQ-5D mean score improved from 0.2 ± 0.2 preoperatively to 0.8 ± 0.1 at 2 years (P = .02). There were no neurological, vascular, or visceral approach–related injuries reported. No rod breakages and no symptomatic nonunions occurred. There was one revision procedure performed for fracture.
Conclusions:
The use of porous tantalum cages as part of a 360-degree fusion to treat adult degenerative spinal deformity has been demonstrated to be a safe and effective strategy, leading to good clinical, functional, and radiographic outcomes in the short term.
Objective Fenestrated endovascular aortic aneurysm repair (f-EVAR) of juxtarenal aneurysms requiring cannulation of the superior mesenteric artery and renal arteries is technically challenging, has a ...long operating time, and requires bilateral large-caliber sheath insertion into the femoral arteries. Consequently, the risk of lower limb ischemia and subsequent reperfusion injury is increased. We describe the use of an adjunct temporary axillobifemoral bypass graft (TABFBG) for f-EVAR and propose that it be used as a strategy to avoid ischemia–reperfusion injury in patients anticipated as being at increased risk. Methods Consecutive patients from a tertiary referral center undergoing f-EVAR, between October 2008 and August 2011, were retrospectively analyzed. Patients with lower limb arterial occlusive disease and those with difficult anatomy had an adjunct TABFBG. Results All patients presenting with a juxtarenal aortic aneurysm were treated endovascularly, regardless of aneurysm anatomy and technical difficulties. There were 37 patients without TABFBG (group 1) and 27 with TABFBG (group 2). No patients required open conversion. Sex and age were not significantly different between the groups. The median ankle-brachial pressure index was significantly higher in group 1 ( P = .0001). The groups had similar median blood loss, percentage of target vessel cannulation, and median stay in the intensive therapy unit. Morbidities were similar in both groups. There were no significant differences in cardiac, renal, or respiratory complications between the groups. The 30-day mortality was 10.8% (n = 4) in group 1 and 0% in group 2 ( P = .046). Conclusions Our series has demonstrated a significant reduction in mortality (10.8% absolute risk reduction) and no increase in morbidity with the use of a TABFBG for fenestrated grafts. This is likely a result of the reduction in ischemia and ischemia–reperfusion injury in these patients. We therefore recommend the use of TABFBG in patients with proximal severe stenotic or occlusive disease and those in whom an operative time of >4 hours is predicted (typically those for whom three or more target fenestrations is planned).
Prolonged endovascular procedures requiring a large diameter sheath in each groin can be associated with significant intraoperative lower limb ischemia, particularly in those with pre-existing ...peripheral vascular disease. We report the case of a patient who suffered severe ischemia-reperfusion injury following endovascular repair of a pararenal aortic aneurysm using a fenestrated stent graft and describe the use of temporary axillobifemoral bypass in a patient with similar comorbidities undergoing the same procedure. We propose this adjunctive technique as a means of maintaining antegrade limb perfusion and avoiding the peripheral and central metabolic consequences of ischemia-reperfusion injury.
Objectives Comprehensive long-term outcome data after endovascular aneurysm repair (EVAR) are scarce, although anecdotes of endograft failure in the early 1990s abound. The objective of this report ...is to provide comprehensive outcomes after EVAR performed with the earliest available endograft components. These were a home-made endograft (pre-expanded polytetrafluoroethylene PTFE fixed with giant Palmaz stents) and first-generation Talent endografts (World Medical, Sunrise, Fla). Methods A prospectively recorded database of all cases undertaken at a tertiary referral center was retrospectively interrogated. Sex, age, types of endograft used, and fate of patient and endografts implanted between 10 and 15 years previously were studied. A literature search was undertaken to obtain data for long-term survival after EVAR and open surgery (OR). Results There were 50 patients in total operated on between 1994 and 1998 of whom 43 were male. The median age was 73 years (54-93) at time of EVAR and 85 years (67-100) in the survivors at a median of 12 years later. There were 26 home-made (PTFE fixed with Palmaz stents) and 24 Talent endografts (World Medical). Thirty-day mortality was 4%, one death in a ruptured abdominal aortic aneurysm. Twenty-one (42%) survived for 12 years to the time of reporting. Of these, 6 have functioning home-made endografts, 8 have Talent endografts, and 8 (5 home-made and 3 Talent) survive after conversion to OR. Secondary interventions took place in 9 further patients. Of 27 late deaths, 1 suffered endograft sepsis, 20 died of cardio-respiratory causes and 6 died of cancer. The only report of more than a 10-year survival after OR was found in an e-publication from Sweden. The projected survival after 10 years was 40% for unruptured aneurysms. However, survival in the general population was higher at 60%. Conclusions Ten-year survival after EVAR parallels that of elective OR but is less than the general population. Although the rate of eventual conversion to open repair was high using this earliest available endograft technology, the aneurysm-related mortality was low, and both endografts remain functional for more than 10 years after placement.
•A simplified method to account for wall motion in blood flow simulations is proposed.•An aortic dissection case is studied and results are compared against FSI.•Wall-motion effects on flow are ...accurately captured at less computational cost.•Patient-specific simulations tuned with imaging data (e.g. MRI) possible.•Proposed approach is a promising alternative to FSI for patient-specific models.
Aortic dissection (AD) is a complex and highly patient-specific vascular condition difficult to treat. Computational fluid dynamics (CFD) can aid the medical management of this pathology, yet its modelling and simulation are challenging. One aspect usually disregarded when modelling AD is the motion of the vessel wall, which has been shown to significantly impact simulation results. Fluid-structure interaction (FSI) methods are difficult to implement and are subject to assumptions regarding the mechanical properties of the vessel wall, which cannot be retrieved non-invasively. This paper presents a simplified ‘moving-boundary method’ (MBM) to account for the motion of the vessel wall in type-B AD CFD simulations, which can be tuned with non-invasive clinical images (e.g. 2D cine-MRI). The method is firstly validated against the 1D solution of flow through an elastic straight tube; it is then applied to a type-B AD case study and the results are compared to a state-of-the-art, full FSI simulation. Results show that the proposed method can capture the main effects due to the wall motion on the flow field: the average relative difference between flow and pressure waves obtained with the FSI and MBM simulations was less than 1.8% and 1.3%, respectively and the wall shear stress indices were found to have a similar distribution. Moreover, compared to FSI, MBM has the advantage to be less computationally expensive (requiring half of the time of an FSI simulation) and easier to implement, which are important requirements for clinical translation.
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