Distributed Voltage and Current Control of Multi-Terminal High-Voltage Direct Current Transmission Systems

High-voltage direct current (HVDC) is a commonly used technology for long-distance power transmission, due to its low resistive losses and low costs. In this paper, a novel distributed controller for multi-terminal HVDC (MTDC) systems is proposed. Under certain conditions on the controller gains, it is shown to stabilize the MTDC system. The controller is shown to always keep the voltages close to the nominal voltage, while assuring that the injected power is shared fairly among the converters. The theoretical results are validated by simulations, where the affect of communication time-delays is also studied

Is facet tropism associated with increased risk of disc herniation in the lumbar spine?

Study Design: Retrospective case control study. Purpose: In current study, we compared the incidence of facet tropism (FT) in patients with lumbar disc herniation and normal controls. Overview of Literature: It has been suggested that FT can be associated with increased risk of lumbar disc herniation. Methods: A total of 66 and 63 patients with L4/L5 and L5/S1 disc herniation, respectively, were evaluated in the present study. The control group comprised 61 normal subjects. Facet joint angle was measured using axial magnetic resonance images. The FT was defined as a difference of > 10° between the right and left facet joints. The incidence of FT was compared between patients and controls. We also investigated the relationship between facet orientation (sagittal or coronal) and side of disc herniation. Results: The incidence of FT at the L4/L5 level was significantly higher in patients with disc herniation (48.5 vs. 26.2, p =0.01), while it was found to be the same at the L5/S1 level in patients and controls (50.8 vs. 36, p =0.098). Among the 64 patients with FT, intervertebral disc herniation occurred significantly toward the more sagittally oriented facet joint in 41 patients (p < 0.05). Conclusions: FT is associated with increased risk of L4/L5 intervertebral disc herniation, but not at the L5/S1 level. In addition, disc herniation occurred toward the more sagittally oriented facet joint. © 2018 by Korean Society of Spine Surgery

Comparison of Harrington rod and Cotrel-Dubousset devices in surgical correction of adolescent idiopathic scoliosis

Background: Since the time of Paul Harrington numerous implants have been introduced for correction of scoliosis, but none are ideal. Newer devices are very expensive, and in our country some patients cannot afford them. Objectives: The aim of this study was to compare the results of the Harrington rod (HR) device and the newer Cotrel-Dubousset (CD) device in treatment of adolescent idiopathic scoliosis (AIS). Materials and Methods: A retrospective review assessed patients with AIS admitted for spinal curve correction treated with HR (n = 120) and CD devices (n = 138) between October 1988 to April 2001 at the Shafa Yahyaeian Hospital, Tehran, Iran. We extracted information from the patient's file and radiographs before, after and two years post-operation. Results: The mean age of patients was 16.7 ± 2.5 years. There was no statistically significant difference between the two groups regarding gender, age, curve before surgery, and percentage of flexibility. The mean curvature was 70 ± 20.7 in the HR and 64.81 ± 19.4 in the CD group before surgery (P = 0.09); and the mean curvature was 40 ± 16.3 and 26.58 ± 15.37 in HR and CD groups respectively after surgery (P = 0.156). The mean curvature was 47.2 ± 15.9 in HR and 31.2 ± 15.4 in CD groups at two years follow-up (P = 0.156). Conclusions: Results of many studies have shown no significant impairment in long-term quality of life and function in patients treated with Harrington rods. According to previously performed studies and the current study, surgical correction with Harrington rods seem to be comparable with the newer more expensive CD device. Although there is no doubt that the preference is to use newer devices in view of some disadvantages of HR, but this does not preclude using it for patients that cannot afford the newer devices. Copyright © 2013, Trauma Research Center; Published by Kowsar Corp

The role of spinopelvic parameters in clinical outcomes of spinal osteotomies in patients with sagittal imbalance

Background: Sagittal imbalance is known as the main radiographic driver of disability in adult spinal deformity (ASD). In this study, the association of radiological spinopelvic parameters and clinical outcomes was evaluated following the corrective surgery of sagittal imbalance, in order to explore the predictive ability of each parameter. Methods: A total of 23 patients, who underwent corrective osteotomy for restoration of sagittal balance, were included in this study. The mean follow-up period of the patients was 15.5±2.1, ranging from 12 to 18 months. Pre- and postoperative radiological parameters including pelvic tilt (PT), sagittal vertical axis (SVA) and pelvic incidence minus lumbar lordosis (PI-LL) were assessed for each patient. Clinical outcomes were evaluated using Oswestry disability Index (ODI). Results: The mean ODI improved 32 following the corrective osteotomy of sagittal imbalance. Postoperative ODI was significantly correlated with all preoperative radiological parameters (r=0.608, P=0.002 for PI-LL; r=0.483, P=0.01 for PT; and r=0.464, P=0.02 for SVA). ODI improvement was significantly correlated with PI-LL and SVA change (r=536, P=0.008 and r=416, P=0.04, respectively), but not with PT change (r=247, P=0.25). The outcome was better in pedicle subtraction osteotomy (PSO) compared to Smith-Petersen Osteotomy (SPO). Conclusion: Surgical correction of sagittal imbalance could limit the amount of disability caused by this misalignment. According to our results, while all the spinopelvic parameters could be used in the prediction of the outcomes of corrective surgery of sagittal imbalance, PI-LL was the most informative parameter and more attention should be devoted to this parameter. © 2018 By The Archives of Bone and Joint Surgery

Long-term outcome of posterior spinal fusion for the correction of adolescent idiopathic scoliosis

Background: Adolescent idiopathic scoliosis (AIS) is the most common form of idiopathic scoliosis, and surgery is considered as one of the therapeutic options. However, it is associated with a variety of irreversible complications, in spite of the benefits it provides. Here, we evaluated the long-term outcome of posterior spinal fusion (PSF) of AIS to shed more light on the consequences of this surgery. Methods: In a cross-sectional study, a total of 42 AIS patients who underwent PSF surgery were radiographically and clinically inspected for the potential post-operative complications. Radiographic assessments included the device failure, union status, and vertebral tilt below the site of fusion. Clinical outcomes were evaluated using the Oswestry disability index (ODI) and visual analogue scale (VAS). Results: The mean age of the surgery was 14.4 ± 5.1 years. The mean follow-up of the patients was 5.6 ± 3.2 years. Complete union was observed in all patients, and no device failure was noticed. Pre- and post-operative vertebral tilt below the site of fusion were 11.12° ± 7.92° and 6.21° ± 5.73°, respectively (p < 0.001). The mean post-operative ODI was 16.7 ± 9.8. The mean post-operative VAS was 2.1 ± 0.7. ODI value was positively correlated with follow-up periods (p = 0.04, r = 0.471). New degenerative disc disease (DDD) was observed in 6 out of 37 (16) patients. Conclusion: In spite of the efficacy and safety of PSF surgery of AIS, it might result in irreversible complications such as DDD. Moreover, the amount of post-operative disability might increase over the time and should be discussed with the patients. © 2018 The Author(s)

COVID-19 among patients with orthopedic surgery: our experience from the Middle East

Background: We report our experiences with COVID-19 in one of the largest referral orthopedic centers in the Middle East and aimed to describe the epidemiology and clinical characteristics of these patients. Methods: During February 20 and April 20, 2020, patients who underwent orthopedic surgery and healthcare staff who were in contact with these patients were screened for COVID-19. To identify patients who were in the incubation period of COVID-19 during their hospital stay, all patients were tested again for COVID-19 4 weeks after discharge. Results: Overall, 1244 patients underwent orthopedic surgery (1123 emergency and 121 elective) during the study period. Overall, 17 patients were diagnosed with COVID-19 during hospital admission and seven after discharge. Among the total 24 patients with COVID-19, 15 were (62.5) males with a mean (SD) age of 47.0±1.6 years old. Emergency surgeries were performed in 20 (83.3) patients, and elective surgery was done in the remaining 4 patients which included one case of posterior spinal fusion, spondylolisthesis, acromioclavicular joint dislocation, and one case of leg necrosis. A considerable number of infections occurred in patients with intertrochanteric fractures (n=7, 29.2), followed by pelvic fractures (n=2, 8.3), humerus fractures (n=2, 8.3), and tibial plateau fractures (n=2, 8.3). Fever (n=11, 45.8) and cough (n=10, 37.5) were the most common symptoms among patients. Laboratory examinations showed leukopenia in 2 patients (8.3) and lymphopenia in 4 (16.7) patients. One patient with a history of cancer died 2 weeks after discharge due to myocardial infarction. Among hospital staff, 26 individuals contracted COVID-19 during the study period, which included 13 (50) males. Physicians were the most commonly infected group (n = 11), followed by operation room technicians (n = 5), nurses (n = 4), and paramedics (n = 4). Conclusions: Patients who undergo surgical treatment for orthopedic problems, particularly lower limb fractures with limited ambulation, are at a higher risk of acquiring COVID-19 infections, although they may not be at higher risks for death compared to the general population. Orthopedic surgeons in particular and other hospital staff who are in close contact with these patients must be adequately trained and given appropriate personal protective equipment during the COVID-19 outbreak. © 2021, The Author(s)

Management of spine trauma in COVID-19 pandemic: A preliminary report

Background: COVID-19 was first identified in Iran in February 2020 and since then it spread rapidly through all over the country and soon after that it was reported as a pandemic. The current study presents a preliminary report of spine trauma management during COVID-19 pandemic. Methods: A cross sectional study was designed to evaluate patients admitted for vertebral fractures with diagnosis of COVID-19 infection on February and March 2020. Analysis was made based on clinical and laboratory data along with the imaging findings from chest HRCT. Results: Seven patients with spine trauma including five males and two females ranging from 14 to 59 years were diagnosed for COVID-19 infection through CT-scan findings. Except one, all other patients were asymptomatic for COVID-19 at the time of admission. In three cases the COVID diagnosis was made the day after arrival and in others after 10, 14 and 35 days. Five patients were treated surgically among whom four were admitted to ICU soon after the surgery. The mean ICU stay for operated patients were eight days and the mean hospital stay was 22.6 days. Conclusion: Proper diagnosis of COVID-19 is the keystone to protect both patients and health care providers. During the pandemic all admitted patients should be screened for COVID-19 infection. Unnecessary procedures for spine trauma patients should be avoided in order to reduce complications related to surgery and to preserve ICU beds. © 2020 BY THE ARCHIVES OF BONE AND JOINT SURGERY

Correlation between pelvic tilt and the sacro-femoral-pubic angle in patients with adolescent idiopathic scoliosis, patients with congenital scoliosis, and healthy individuals

Purpose: To examine whether the sacro-femoral-pubic (SFP) angle could estimate pelvic tilt (PT) in scoliotic and normal subjects. Methods: One hundred nine subjects including 38 patients with adolescent idiopathic scoliosis (AIS), 35 patients with congenital scoliosis (CS), and 36 healthy individuals were studied. PT, as the angle between the lines connecting the midpoint of the sacral plate to the centroid of one acetabulum and the vertical plane, and the SFP angle, as the angle between the midpoint of the upper sacral endplate, the centroid of one acetabulum, and the upper midpoint of the pubic symphysis, were calculated on full-length lateral and anteroposterior radiographs, respectively. Correlations between PT and the SFP angle were investigated in each group. Results: The three groups were comparable in terms of age, sex, and the mean SFP angle. The mean PT, however, was significantly lower in healthy subjects compared to that in patients with AIS and CS. Significant and reverse correlations were present between PT and the SFP angle in all three groups (AIS: r = �0.32, p = 0.04, PT = 82.5 � average SFP angle; CS: r = �0.48, p = 0.003, PT = 95.41 � average SFP angle; healthy: r = �0.33, p = 0.04, PT = 88.95 � average SFP angle). Conclusions: Unlike two previous reports, the SFP angle correlated poorly to PT in this study, limiting its use as a suitable surrogate for PT in scoliotic and healthy subjects. © 2015, Springer-Verlag Berlin Heidelberg

Vertebral, rib, and intraspinal anomalies in congenital scoliosis: a study on 202 Caucasians

Purpose: To investigate vertebral, rib and intraspinal anomalies in patients with congenital scoliosis and their association with each other Methods: Clinical data and preoperative imaging studies of 202 Caucasians with congenital scoliosis operated on at an educational hospital within 6 years were reviewed for vertebral, rib, and intraspinal anomalies. Results: Rib and intraspinal anomalies were present in 57.4 and 21.8 of patients, respectively. Most vertebral anomalies were located in the middle�lower thorax. Being the most common vertebral defect (53.5 ), failure of segmentation was significantly more common in males, whereas mixed defects were more frequent in females. Formation and mixed defects were associated with rib changes. Vertebral anomalies were more extensive in males than in females. The presence of multiple hemivertebrae was associated with rib deformity and intraspinal anomaly. Location of the vertebral anomalies varied with gender and rib involvement. Majority of rib changes were of simple type (70.7 ), significantly more common in males. Conversely, females had significantly more fused and bifid ribs. Two most common intraspinal anomalies were diastematomyelia (36.4 ) and syringomyelia (18.2 ). Intraspinal anomalies were located most frequently in the upper and lower thoracic regions. Syringomyelia and low conus were associated with female gender, and patients with rib changes suffered from intraspinal anomalies more frequently. No significant association was found between vertebral and intraspinal anomalies. Conclusions: The incidences of rib and intraspinal anomalies were 57.4 and 21.8 in surgical Caucasians with congenital scoliosis, respectively. Unlike vertebral and intraspinal anomalies, rib and intraspinal anomalies were significantly associated. Male gender and intraspinal anomaly were associated with some previously suggested risk factors of curve progression. © 2015, Springer-Verlag Berlin Heidelberg

Assessment of disability levels in patients with low back pain based on the type of lumbar spinal disorder

BACKGROUND: Low back pain (LBP) is a common health condition and the leading cause of activity limitation and absenteeism in most parts of the world. One-fifth of patients with LBP develop chronic pain disability. OBJECTIVE: This study investigated the disability levels in patients with different types of lumbar spinal disorders. METHODS: A total of 528 patients visiting spine clinics between June 2017 and February 2018 were enrolled in this study. A demographic checklist, the patients' medical records, the Oswestry Disability Questionnaire, and the Visual Analog Scale (VAS) were used to collect the data. RESULTS: Non-specific LBP (29.5) and discopathy (27) were the most common final diagnoses. The obtained Oswestry Disability Index (ODI) was significantly higher in older patients, those with higher body mass index, more work experience, and smokers. Lower ODI was found in individuals with a history of regular exercise. Most individuals in all diagnostic groups were categorized into the high ODI group (p⩽ 0.001). CONCLUSION: In patients with lumbar spine lesions, ODI is significantly correlated with age, BMI, work experience, smoking, and the type of disorder (discopathy, spondylolysis, and spondylolisthesis). Regular exercise is associated with lower levels of disability