The treatment of pediatric femur fractures continues to evolve. In the past, many of these fractu... more The treatment of pediatric femur fractures continues to evolve. In the past, many of these fractures required prolonged hospitalization in traction. More recently, flexible elastic nails have gained popularity. However, length unstable and comminuted fractures can present some unique challenges. To avoid common complications of elastic nailing in the setting of unstable fractures we describe a technique of augmenting this treatment with external fixation for cases requiring additional rotational or longitudinal stability. A series of two patients are described who underwent intramedullary flexible nails and external fixation for a closed unstable midshaft femur fracture: An 8-year-old male that sustained a left periprosthetic femur fracture after a fall on his scooter, and a 5-year-old female that sustained a right femur fracture after a fall from a wet decking. Both patients had their external fixator removed after 4 weeks and achieved radiographic and clinical fracture union at 8-...
Magnetic intramedullary nails (IMNs) are fully implantable lengthening devices that became availa... more Magnetic intramedullary nails (IMNs) are fully implantable lengthening devices that became available in the United States in 2011 for the correction of limb length discrepancies. This device represents a major advancement in the field of limb lengthening surgery as it is typically tolerated better than external fixation. Unlike traditional IMNs, surgeons recommend routine removal following limb lengthening. One such reason involves patient safety as it pertains to magnetic resonance imaging (MRI). Theoretical concerns with MRI exposure include implant migration, implant heating, and involuntary elongation of the lengthening mechanism. Our study seeks to investigate the effects of MRI on intramedullary magnetic lengthening nails. Twenty-five intramedullary magnetic nails were studied. One nail was placed within the magnetic field to measure maximum magnetic force. Nails were then scanned using standard knee MRI protocols, 12 in 3 T and 12 in 1.5 T MRI scanners. The following paramete...
We have performed eleven AMOS (Azimuthal Mode Simulator)[1] code runs with a simple, right circul... more We have performed eleven AMOS (Azimuthal Mode Simulator)[1] code runs with a simple, right circular cylindrical accelerating cavity inserted into a circular, cylindrical, lossless beam pipe to calculate the real part of the n = 1(dipole) transverse wakefield impedance of this structure. We have compared this wakefield impedance in units of ohms/m(Wm) over the frequency range of 0-1 GHz to
Journal of the National Comprehensive Cancer Network : JNCCN, 2015
A 47-year-old woman, initially diagnosed in 1996 with Cowden syndrome (CS), PTEN-mutant bilateral... more A 47-year-old woman, initially diagnosed in 1996 with Cowden syndrome (CS), PTEN-mutant bilateral breast cancer, a thyroid nodule, and uterine fibroids, presented to UCLA in 2013 with Ewing sarcoma of the pelvic bone. Her treatment course included mastectomies, hysterectomy/oophorectomy, and total thyroid resection, and chemotherapy, radiation, and hemipelvectomy for Ewing sarcoma. This case report illustrates the unusual presentation of Ewing sarcoma in a patient with PTEN-mutant CS, the probable underlying molecular pathogenesis, long-term management, and therapeutic considerations.
Vacuum insulators composed of alternating layers of metal and dielectric, known as high-gradient ... more Vacuum insulators composed of alternating layers of metal and dielectric, known as high-gradient insulators (HGIs), have been shown to withstand higher electric fields than conventional insulators. Primary or secondary electrons (emitted from the insulator surface) can be deflected by magnetic fields from external sources, the high-current electron beam, the conduction current in the transmission line, or the displacement current in the insulator. These electrons are deflected either toward or away from the insulator surface and this affects the performance of the vacuum insulator. This paper shows the effects of displacement current from short voltage pulses on the performance of high gradient insulators. Generally, vacuum insulator failure is due to surface flashover, initiated by electrons emitted from a triple junction. These electrons strike the insulator surface thus producing secondary electrons, and can lead to a subsequent electron cascade along the surface. The displacemen...
We analyze the sheath helix model of the pulseline accelerator [1]. We find the dispersion relati... more We analyze the sheath helix model of the pulseline accelerator [1]. We find the dispersion relation for a shielded helix with a dielectric material between the shield and the helix and compare it against the results from 3-D electromagnetic simulations. Expressions for the fields near the beam axis are obtained. A scheme to taper the properties of the helix to maintain synchronism with the accelerated ions is described. An approximate circuit model of the system that includes beam loading is derived.
BACKGROUND Estimates of the excess length of stay (LOS) attributable to healthcare-associated inf... more BACKGROUND Estimates of the excess length of stay (LOS) attributable to healthcare-associated infections (HAIs) in which total LOS of patients with and without HAIs are biased because of failure to account for the timing of infection. Alternate methods that appropriately treat HAI as a time-varying exposure are multistate models and cohort studies, which match regarding the time of infection. We examined the magnitude of this time-dependent bias in published studies that compared different methodological approaches. METHODS We conducted a systematic review of the published literature to identify studies that report attributable LOS estimates using both total LOS (time-fixed) methods and either multistate models or matching patients with and without HAIs using the timing of infection. RESULTS Of the 7 studies that compared time-fixed methods to multistate models, conventional methods resulted in estimates of the LOS to HAIs that were, on average, 9.4 days longer or 238% greater than those generated using multistate models. Of the 5 studies that compared time-fixed methods to matching on timing of infection, conventional methods resulted in estimates of the LOS to HAIs that were, on average, 12.6 days longer or 139% greater than those generated by matching on timing of infection. CONCLUSION Our results suggest that estimates of the attributable LOS due to HAIs depend heavily on the methods used to generate those estimates. Overestimation of this effect can lead to incorrect assumptions of the likely cost savings from HAI prevention measures.
The treatment of pediatric femur fractures continues to evolve. In the past, many of these fractu... more The treatment of pediatric femur fractures continues to evolve. In the past, many of these fractures required prolonged hospitalization in traction. More recently, flexible elastic nails have gained popularity. However, length unstable and comminuted fractures can present some unique challenges. To avoid common complications of elastic nailing in the setting of unstable fractures we describe a technique of augmenting this treatment with external fixation for cases requiring additional rotational or longitudinal stability. A series of two patients are described who underwent intramedullary flexible nails and external fixation for a closed unstable midshaft femur fracture: An 8-year-old male that sustained a left periprosthetic femur fracture after a fall on his scooter, and a 5-year-old female that sustained a right femur fracture after a fall from a wet decking. Both patients had their external fixator removed after 4 weeks and achieved radiographic and clinical fracture union at 8-...
Magnetic intramedullary nails (IMNs) are fully implantable lengthening devices that became availa... more Magnetic intramedullary nails (IMNs) are fully implantable lengthening devices that became available in the United States in 2011 for the correction of limb length discrepancies. This device represents a major advancement in the field of limb lengthening surgery as it is typically tolerated better than external fixation. Unlike traditional IMNs, surgeons recommend routine removal following limb lengthening. One such reason involves patient safety as it pertains to magnetic resonance imaging (MRI). Theoretical concerns with MRI exposure include implant migration, implant heating, and involuntary elongation of the lengthening mechanism. Our study seeks to investigate the effects of MRI on intramedullary magnetic lengthening nails. Twenty-five intramedullary magnetic nails were studied. One nail was placed within the magnetic field to measure maximum magnetic force. Nails were then scanned using standard knee MRI protocols, 12 in 3 T and 12 in 1.5 T MRI scanners. The following paramete...
We have performed eleven AMOS (Azimuthal Mode Simulator)[1] code runs with a simple, right circul... more We have performed eleven AMOS (Azimuthal Mode Simulator)[1] code runs with a simple, right circular cylindrical accelerating cavity inserted into a circular, cylindrical, lossless beam pipe to calculate the real part of the n = 1(dipole) transverse wakefield impedance of this structure. We have compared this wakefield impedance in units of ohms/m(Wm) over the frequency range of 0-1 GHz to
Journal of the National Comprehensive Cancer Network : JNCCN, 2015
A 47-year-old woman, initially diagnosed in 1996 with Cowden syndrome (CS), PTEN-mutant bilateral... more A 47-year-old woman, initially diagnosed in 1996 with Cowden syndrome (CS), PTEN-mutant bilateral breast cancer, a thyroid nodule, and uterine fibroids, presented to UCLA in 2013 with Ewing sarcoma of the pelvic bone. Her treatment course included mastectomies, hysterectomy/oophorectomy, and total thyroid resection, and chemotherapy, radiation, and hemipelvectomy for Ewing sarcoma. This case report illustrates the unusual presentation of Ewing sarcoma in a patient with PTEN-mutant CS, the probable underlying molecular pathogenesis, long-term management, and therapeutic considerations.
Vacuum insulators composed of alternating layers of metal and dielectric, known as high-gradient ... more Vacuum insulators composed of alternating layers of metal and dielectric, known as high-gradient insulators (HGIs), have been shown to withstand higher electric fields than conventional insulators. Primary or secondary electrons (emitted from the insulator surface) can be deflected by magnetic fields from external sources, the high-current electron beam, the conduction current in the transmission line, or the displacement current in the insulator. These electrons are deflected either toward or away from the insulator surface and this affects the performance of the vacuum insulator. This paper shows the effects of displacement current from short voltage pulses on the performance of high gradient insulators. Generally, vacuum insulator failure is due to surface flashover, initiated by electrons emitted from a triple junction. These electrons strike the insulator surface thus producing secondary electrons, and can lead to a subsequent electron cascade along the surface. The displacemen...
We analyze the sheath helix model of the pulseline accelerator [1]. We find the dispersion relati... more We analyze the sheath helix model of the pulseline accelerator [1]. We find the dispersion relation for a shielded helix with a dielectric material between the shield and the helix and compare it against the results from 3-D electromagnetic simulations. Expressions for the fields near the beam axis are obtained. A scheme to taper the properties of the helix to maintain synchronism with the accelerated ions is described. An approximate circuit model of the system that includes beam loading is derived.
BACKGROUND Estimates of the excess length of stay (LOS) attributable to healthcare-associated inf... more BACKGROUND Estimates of the excess length of stay (LOS) attributable to healthcare-associated infections (HAIs) in which total LOS of patients with and without HAIs are biased because of failure to account for the timing of infection. Alternate methods that appropriately treat HAI as a time-varying exposure are multistate models and cohort studies, which match regarding the time of infection. We examined the magnitude of this time-dependent bias in published studies that compared different methodological approaches. METHODS We conducted a systematic review of the published literature to identify studies that report attributable LOS estimates using both total LOS (time-fixed) methods and either multistate models or matching patients with and without HAIs using the timing of infection. RESULTS Of the 7 studies that compared time-fixed methods to multistate models, conventional methods resulted in estimates of the LOS to HAIs that were, on average, 9.4 days longer or 238% greater than those generated using multistate models. Of the 5 studies that compared time-fixed methods to matching on timing of infection, conventional methods resulted in estimates of the LOS to HAIs that were, on average, 12.6 days longer or 139% greater than those generated by matching on timing of infection. CONCLUSION Our results suggest that estimates of the attributable LOS due to HAIs depend heavily on the methods used to generate those estimates. Overestimation of this effect can lead to incorrect assumptions of the likely cost savings from HAI prevention measures.
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Papers by Scott Nelson