Integrated implementation system for pseudodynamic testing

The pseudodynamic test method is a tool for obtaining the non-linear response of structures to transient ground acceleration. The modelling technique relies on representing the inertial and viscous damping components of the equation of motion computationally, while obtaining a measure of the non-linear elastic restoring forces experimentally. A pseudodynamic implementation system is presented, displaying innovations within both the computational and experimental domains. A SDOF pseudodynamic test facility has been designed and manufactured employing a computer controlled servo-hydraulic actuator system. The experimental facility enables displacements of up to 50mm under forces of up to 50kN with all required instrumentation. The experimental apparatus is controlled by algorithms running in the LabView environment, fully integrated within the execution system, rendering the requirement for a hardware controller obsolete. The execution system allows interactive control of the experiments, and offers a large range options with respect to both control and time integration. The execution routine incorporates both the time integration and control algorithms, and combines these such that they effectively execute as an integrated system. This enables semi-continuous implementation of the pseudodynamic tests with very limited resources. A novel, integral form time stepping scheme is proposed, based on an explicit integral form algorithm (Chang et al. 1998) and the Newmark Implicit scheme. The proposed formulation offers an implicit, and thus unconditionally stable alternative to Chang's algorithm without introducing further approximations. This yields improved dissipation and accuracy properties in addition to enabling combination of the integral form schemes' advantages of representing non-linear force variations during a time step with an unlimited time step size. The improvements have been shown both through analytical analyses and numerical examples in linear and non-linear systems. Implementation of the implicit integral form algorithm has been enabled by coding parts of the algorithm directly into the digital controller

Temporary Prosthetic Shunt to Permanent Aortic Prosthesis in a Patient with an Infected Thoracoabdominal Aneurysm to Shorten Ischemia Time

High operative mortality of infected thoracoabdominal aortic aneurysms (ITAA) is partly attributable to ischemic injury during aortic clamping. We report a 62-year-old man with biliary cirrhosis, who developed a rapidly enlarging ITAA secondary to thoracolumbar osteomyelitis. Additional infectious foci were found in the pubic and ischial bones and in the left lung. Blood cultures gave growth of streptococcus pneumoniae. The aneurysm was repaired through a thoracoabdominal incision with a Dacron prosthesis. Prior to aneurysm repair, a prosthetic shunt was anastomosed end – to- side to the aortic prosthesis and to the descending aorta using a side-biting clamp. The shunt allowed perfusion of the lower body and of renal and visceral vessels after 45 minutes, the time needed to resect infected tissue and complete the distal anastomosis. The proximal anastomosis and orthopedic treatment of the spinal osteomyelitis could be performed, while the lower body and visceral organs were perfused. Postoperatively, the patient developed hypotension and increasing lactacidosis. Laparotomy revealed intestinal infarction, and gut resection was performed. Following a temporary improvement, he developed multiorgan failure and candida sepsis and died after 32 days. No atheroemboli were found in arteries of resected intestines. Portal hypertension most likely was present and it could be calculated that minimum intestinal perfusion pressure the night after the operation could have been in the range of 30-37 mm Hg, which probably was not enough to maintain aerobic metabolism. In the presence of aortic atheromas it may be advisable to divert blood to the shunt from an axillary artery.publishedVersio

Temporary Prosthetic Shunt to Permanent Aortic Prosthesis in a Patient with an Infected Thoracoabdominal Aneurysm to Shorten Ischemia Time

High operative mortality of infected thoracoabdominal aortic aneurysms (ITAA) is partly attributable to ischemic injury during aortic clamping. We report a 62-year-old man with biliary cirrhosis, who developed a rapidly enlarging ITAA secondary to thoracolumbar osteomyelitis. Additional infectious foci were found in the pubic and ischial bones and in the left lung. Blood cultures gave growth of streptococcus pneumoniae. The aneurysm was repaired through a thoracoabdominal incision with a Dacron prosthesis. Prior to aneurysm repair, a prosthetic shunt was anastomosed end – to- side to the aortic prosthesis and to the descending aorta using a side-biting clamp. The shunt allowed perfusion of the lower body and of renal and visceral vessels after 45 minutes, the time needed to resect infected tissue and complete the distal anastomosis. The proximal anastomosis and orthopedic treatment of the spinal osteomyelitis could be performed, while the lower body and visceral organs were perfused. Postoperatively, the patient developed hypotension and increasing lactacidosis. Laparotomy revealed intestinal infarction, and gut resection was performed. Following a temporary improvement, he developed multiorgan failure and candida sepsis and died after 32 days. No atheroemboli were found in arteries of resected intestines. Portal hypertension most likely was present and it could be calculated that minimum intestinal perfusion pressure the night after the operation could have been in the range of 30-37 mm Hg, which probably was not enough to maintain aerobic metabolism. In the presence of aortic atheromas it may be advisable to divert blood to the shunt from an axillary artery

Surgery in Degenerative Spondylolisthesis: Does fusion improve outcome in subgroups? A secondary analysis from a randomized trial (NORDSTEN trial)

BACKGROUND CONTEXT Patients with spinal stenosis and degenerative spondylolisthesis are treated surgically with decompression alone or decompression with fusion. However, there is debate regarding which subgroups of patients may benefit from additional fusion. PURPOSE To investigate possible treatment effect modifiers and prognostic variables among patients operated for spinal stenosis and degenerative spondylolisthesis. DESIGN A secondary exploratory study using data from the Norwegian Degenerative Spondylolisthesis and Spinal Stenosis (NORDSTEN-DS) trial. Patients were randomized to decompression alone or decompression with instrumented fusion. PATIENT SAMPLE The sample in this study consists of 267 patients from a randomized multicenter trial involving 16 hospitals in Norway. Patients were enrolled from February 12, 2014, to December 18, 2017. The study did not include patients with degenerative scoliosis, severe foraminal stenosis, multilevel spondylolisthesis, or previous surgery. OUTCOME MEASURES The primary outcome was an improvement of ≥ 30% on the Oswestry Disability Index score (ODI) from baseline to 2-year follow-up. METHODS When investigating possible variables that could modify the treatment effect, we analyzed the treatment arms separately. When testing for prognostic factors we analyzed the whole cohort (both treatment groups). We used univariate and multiple regression analyses. The selection of variables was done a priori, according to the published trial protocol. RESULTS Of the 267 patients included in the trial (183 female [67%]; mean [SD] age, 66 [7.6] years), complete baseline data for the variables required for the present analysis were available for 205 of the 267 individuals. We did not find any clinical or radiological variables at baseline that modified the treatment effect. Thus, none of the commonly used criteria for selecting patients for fusion surgery influenced the chosen primary outcome in the two treatment arms. For the whole cohort, less comorbidity (American Society of Anesthesiologists Classification [ASA], OR = 4.35; 95% confidence interval (CI [1.16–16.67]) and more preoperative leg pain (OR = 1.23; CI [1.02–1.50]) were significantly associated with an improved primary outcome. CONCLUSIONS In this study on patients with degenerative spondylolisthesis, neither previously defined instability criteria nor other pre-specified baseline variables were associated with better clinical outcome if fusion surgery was performed. None of the analyzed variables can be applied to guide the decision for fusion surgery in patients with degenerative spondylolisthesis. For both treatment groups, less comorbidity and more leg pain were associated with improved outcome 2 years after surgery.publishedVersio

Decompression with or without Fusion in Degenerative Lumbar Spondylolisthesis

BACKGROUND In patients with lumbar spinal stenosis and degenerative spondylolisthesis, it is uncertain whether decompression surgery alone is noninferior to decompression with instrumented fusion. METHODS We conducted an open-label, multicenter, noninferiority trial involving patients with symptomatic lumbar stenosis that had not responded to conservative management and who had single-level spondylolisthesis of 3 mm or more. Patients were randomly assigned in a 1:1 ratio to undergo decompression surgery (decompressionalone group) or decompression surgery with instrumented fusion (fusion group). The primary outcome was a reduction of at least 30% in the score on the Oswestry Disability Index (ODI; range, 0 to 100, with higher scores indicating more impairment) during the 2 years after surgery, with a noninferiority margin of −15 percentage points. Secondary outcomes included the mean change in the ODI score as well as scores on the Zurich Claudication Questionnaire, leg and back pain, the duration of surgery and length of hospital stay, and reoperation within 2 years. RESULTS The mean age of patients was approximately 66 years. Approximately 75% of the patients had leg pain for more than a year, and more than 80% had back pain for more than a year. The mean change from baseline to 2 years in the ODI score was −20.6 in the decompression-alone group and −21.3 in the fusion group (mean difference, 0.7; 95% confidence interval [CI], −2.8 to 4.3). In the modified intentionto- treat analysis, 95 of 133 patients (71.4%) in the decompression-alone group and 94 of 129 patients (72.9%) in the fusion group had a reduction of at least 30% in the ODI score (difference, −1.4 percentage points; 95% CI, −12.2 to 9.4), showing the noninferiority of decompression alone. In the per-protocol analysis, 80 of 106 patients (75.5%) and 83 of 110 patients (75.5%), respectively, had a reduction of at least 30% in the ODI score (difference, 0.0 percentage points; 95% CI, −11.4 to 11.4), showing noninferiority. The results for the secondary outcomes were generally in the same direction as those for the primary outcome. Successful fusion was achieved with certainty in 86 of 100 patients (86.0%) who had imaging available at 2 years. Reoperation was performed in 15 of 120 patients (12.5%) in the decompression- alone group and in 11 of 121 patients (9.1%) in the fusion group. CONCLUSIONS In this trial involving patients who underwent surgery for degenerative lumbar spondylolisthesis, most of whom had symptoms for more than a year, decompression alone was noninferior to decompression with instrumented fusion over a period of 2 years. Reoperation occurred somewhat more often in the decompressionalone group than in the fusion group. (NORDSTEN-DS ClinicalTrials.gov number, NCT02051374.