The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Alan W Eberhardt - One of the best experts on this subject based on the ideXlab platform.
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biomechanical response of the pubic Symphysis in lateral pelvic impacts a finite element study
Journal of Biomechanics, 2007Co-Authors: Zuoping Li, James S Davidson, Brandon S Etheridge, Jorge E Alonso, Alan W EberhardtAbstract:Abstract Automotive side impacts are a leading cause of injuries to the pubic Symphysis, yet the mechanisms of those injuries have not been clearly established. Previous mechanical testing of isolated symphyses revealed increased joint laxity following drop tower lateral impacts to isolated pelvic bone structures, which suggested that the joints were damaged by excessive stresses and/or deformations during the impact tests. In the present study, a finite element (FE) model of a female pelvis including a previously validated Symphysis sub-model was developed from computed tomography data. The full pelvis model was validated against measured force–time impact responses from drop tower experiments and then used to study the biomechanical response of the Symphysis during the experimental impacts. The FE models predicted that the joint underwent a combination of lateral compression, posterior bending, anterior/posterior and superior/inferior shear that exceeded normal physiological levels prior to the onset of bony fractures. Large strains occurred concurrently within the pubic ligaments. Removal of the contralateral constraints to better approximate the boundary conditions of a seated motor vehicle occupant reduced cortical stresses and deformations of the pubic Symphysis; however, ligament strains, compressive and shear stresses in the interpubic disc, as well as posterior bending of the joint structure remained as potential sources of joint damage during automotive side impacts.
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three dimensional finite element models of the human pubic Symphysis with viscohyperelastic soft tissues
Annals of Biomedical Engineering, 2006Co-Authors: Zuoping Li, James S Davidson, Brandon S Etheridge, Jorge E Alonso, Alan W EberhardtAbstract:Three-dimensional finite element (FE) models of human pubic symphyses were constructed from computed tomography image data of one male and one female cadaver pelvis. The pubic bones, interpubic fibrocartilaginous disc and four pubic ligaments were segmented semi-automatically and meshed with hexahedral elements using automatic mesh generation schemes. A two-term viscoelastic Prony series, determined by curve fitting results of compressive creep experiments, was used to model the rate-dependent effects of the interpubic disc and the pubic ligaments. Three-parameter Mooney-Rivlin material coefficients were calculated for the discs using a heuristic FE approach based on average experimental joint compression data. Similarly, a transversely isotropic hyperelastic material model was applied to the ligaments to capture average tensile responses. Linear elastic isotropic properties were assigned to bone. The applicability of the resulting models was tested in bending simulations in four directions and in tensile tests of varying load rates. The model-predicted results correlated reasonably with the joint bending stiffnesses and rate-dependent tensile responses measured in experiments, supporting the validity of the estimated material coefficients and overall modeling approach. This study represents an important and necessary step in the eventual development of biofidelic pelvis models to investigate Symphysis response under high-energy impact conditions, such as motor vehicle collisions.
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elastic and viscoelastic properties of the human pubic Symphysis joint effects of lateral impact loading
Journal of Biomechanical Engineering-transactions of The Asme, 2001Co-Authors: Greg J Dakin, Jorge E Alonso, Raul A Arbelaez, Fred J Molz, Kenneth A Mann, Alan W EberhardtAbstract:The human pelvis is susceptible to severe injury in vehicle side impacts owing to its close proximity to the intruding door and unnatural loading through the greater trochanter. Whereas fractures of the pelvic bones are diagnosed with routine radiographs (x-rays) and computerized tomography (CT scans), non-displaced damage to the soft tissues of pubic Symphysis joints may go undetected. If present, trauma-induced joint laxity may cause pelvic instability, which has been associated with pelvic pain in non-traumatic cases. In this study, mechanical properties of cadaveric pubic Symphysis joints from twelve normal and eight laterally impacted pelves were compared, Axial stiffness and creep responses of these isolated symphyses were measured in tension and compression (perpendicular to the joint), Bending stiffness was determined in four primary directions followed by a tension-to-failure test. Loading rate and direction correlated significantly (p<0.05) with stiffness and tensile strength of the unimpacted joints, more so than donor age or gender. The impacted joints had significantly lower stiffness in tension (p <0.04), compression (p<0.003), and posterior bending (p<0.03), and more creep under a compressive step load (p<0.008) than the unimpacted specimens. Tensile strength was reduced following impact, however, not significantly. We concluded that the Symphysis joints from the impacted pelves had greater laxity, which may correlate with post-traumatic pelvic pain in some motor vehicle crash occupants.
Jason Gardosi - One of the best experts on this subject based on the ideXlab platform.
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Symphysis fundus height and pregnancy characteristics in ultrasound dated pregnancies
Obstetrics & Gynecology, 1999Co-Authors: M Mongelli, Jason GardosiAbstract:Abstract Objective: To investigate the relation between maternal and pregnancy characteristics and Symphysis-fundus height values at term in an obstetric population dated by sonography. Methods: Three hundred twenty-five women were recruited from the antenatal clinics of the Queen’s Medical Centre, Nottingham, United Kingdom for measurement of fundal height and for ultrasound scans. Symphysis-fundus height measurements were analyzed by multivariate regression analysis in relation to gestational age, maternal height and weight, ethnic group, and smoking. Results: Gestational age and maternal characteristics explained nearly half of the variability in Symphysis-fundus height. Gestational age was the most important determinant, followed by maternal weight, parity, and sex of the infant. The other variables were not significantly correlated. Conclusion: Maternal characteristics had statistically significant effects on the expected Symphysis-fundus height, which suggests that individually adjusted fundal height charts may improve the precision of clinical screening for fetal growth restriction.
Amar Rangan - One of the best experts on this subject based on the ideXlab platform.
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a case of postpartum pubic Symphysis diastasis
Injury-international Journal of The Care of The Injured, 2010Co-Authors: P D Cowling, Amar RanganAbstract:The Symphysis pubis is a secondary cartilaginous joint and in response to hormonal changes during pregnancy (especially the 3rd trimester), the joint widens to increase the saggital diameter of the outlet. Mild separation of the pubic Symphysis is therefore considered necessary for childbirth, with an average normal radiological distance between pubic bodies of 4 mmwidening by a further 3 mm during pregnancy. A widening of 10 mm has been defined as the upper limit of physiological separation. Pubic Symphysis diastasis is a recognised rare complication of pregnancy, with a variable reported incidence of 1 in 300 to 1 in 30,000 deliveries. Separation of over 1 cm can rarely occur, and is often symptomatic, leading to pain at delivery and during the postpartum period. We present a case of spontaneous Symphysis pubis diastasis in a healthy primigravida, after a vaginal delivery.
Zuoping Li - One of the best experts on this subject based on the ideXlab platform.
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biomechanical response of the pubic Symphysis in lateral pelvic impacts a finite element study
Journal of Biomechanics, 2007Co-Authors: Zuoping Li, James S Davidson, Brandon S Etheridge, Jorge E Alonso, Alan W EberhardtAbstract:Abstract Automotive side impacts are a leading cause of injuries to the pubic Symphysis, yet the mechanisms of those injuries have not been clearly established. Previous mechanical testing of isolated symphyses revealed increased joint laxity following drop tower lateral impacts to isolated pelvic bone structures, which suggested that the joints were damaged by excessive stresses and/or deformations during the impact tests. In the present study, a finite element (FE) model of a female pelvis including a previously validated Symphysis sub-model was developed from computed tomography data. The full pelvis model was validated against measured force–time impact responses from drop tower experiments and then used to study the biomechanical response of the Symphysis during the experimental impacts. The FE models predicted that the joint underwent a combination of lateral compression, posterior bending, anterior/posterior and superior/inferior shear that exceeded normal physiological levels prior to the onset of bony fractures. Large strains occurred concurrently within the pubic ligaments. Removal of the contralateral constraints to better approximate the boundary conditions of a seated motor vehicle occupant reduced cortical stresses and deformations of the pubic Symphysis; however, ligament strains, compressive and shear stresses in the interpubic disc, as well as posterior bending of the joint structure remained as potential sources of joint damage during automotive side impacts.
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three dimensional finite element models of the human pubic Symphysis with viscohyperelastic soft tissues
Annals of Biomedical Engineering, 2006Co-Authors: Zuoping Li, James S Davidson, Brandon S Etheridge, Jorge E Alonso, Alan W EberhardtAbstract:Three-dimensional finite element (FE) models of human pubic symphyses were constructed from computed tomography image data of one male and one female cadaver pelvis. The pubic bones, interpubic fibrocartilaginous disc and four pubic ligaments were segmented semi-automatically and meshed with hexahedral elements using automatic mesh generation schemes. A two-term viscoelastic Prony series, determined by curve fitting results of compressive creep experiments, was used to model the rate-dependent effects of the interpubic disc and the pubic ligaments. Three-parameter Mooney-Rivlin material coefficients were calculated for the discs using a heuristic FE approach based on average experimental joint compression data. Similarly, a transversely isotropic hyperelastic material model was applied to the ligaments to capture average tensile responses. Linear elastic isotropic properties were assigned to bone. The applicability of the resulting models was tested in bending simulations in four directions and in tensile tests of varying load rates. The model-predicted results correlated reasonably with the joint bending stiffnesses and rate-dependent tensile responses measured in experiments, supporting the validity of the estimated material coefficients and overall modeling approach. This study represents an important and necessary step in the eventual development of biofidelic pelvis models to investigate Symphysis response under high-energy impact conditions, such as motor vehicle collisions.
Jason W Nascone - One of the best experts on this subject based on the ideXlab platform.
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superior pubic ramus osteotomy to treat locked pubic Symphysis a case report
Journal of Bone and Joint Surgery American Volume, 2006Co-Authors: Robert V Otoole, Carlos Sagebien, Romney C Andersen, Jason W NasconeAbstract:Pelvic ring disruption that results in a locked pubic Symphysis is an unusual injury. A locked pubic Symphysis is defined as a compression of the pelvic ring, with the intact pubis becoming trapped against the contralateral pubis. Although the injury pattern is well recognized in clinical practice, to the best of our knowledge, only eight patients with this injury have been reported in the English-language literature1-8 since its original description by Eggers in 19523. A proposed mechanism for a locked Symphysis is forced hyperextension and adduction of the hip1 resulting from a lateral compression force to the pelvis. This injury causes a rupture of the ligaments that normally stabilize the Symphysis. The superior, anterior, and posterior ligaments are weak, while the arcuate (or inferior) ligament is thought to confer most of the stability to this fibrocartilaginous joint9. After rupture of these ligaments, the displaced pelvic bone may lie either anterior or posterior to the contralateral pubis. Because of the direction and magnitude of this pubic displacement, the injury pattern has been associated with urethral injury2,3,5,7. Although an initial attempt at closed reduction has been advocated6, there is otherwise only limited guidance in the literature regarding the treatment of a locked Symphysis. One technique for closed reduction involves using the femur as a lever by locking it in flexion, abduction, and external rotation. The iliofemoral ligaments are thought to hold the femoral head within the acetabulum and to allow reduction with a gentle abduction and rocking motion of the affected extremity3. Authors have cited a risk of femoral fracture in association with this reduction technique and therefore have advocated external rotation of the hemipelvis with a force applied mostly to the …
