6,011 research outputs found
Risk factor analysis for early femoral failure in metal-on-metal hip resurfacing arthroplasty: the effect of bone density and body mass index
<p>Abstract</p> <p>Background</p> <p>The importance of appropriately selecting patients based on factors such as bone mineral density, body mass index, age, gender, and femoral component size has been demonstrated in many studies as an aid in decreasing the rate of revisions and improving the outcomes for patients after hip resurfacing arthroplasty (HRA); however, there are few published studies quantitatively specifying the potential risk factors that affect early femoral component failures. Therefore, the purpose of this study was to investigate the specific causes of early femoral component failures in hip resurfacing separately and more carefully in order to develop strategies to prevent these failures, rather than excluding groups of patients from this surgical procedure.</p> <p>Methods</p> <p>This retrospective study included 373 metal-on-metal HRAs performed by a single surgeon using the vascular sparing posterior minimally invasive surgical approach. The average length of follow-up was 30 ± 6 months. In order to understand the causes of early femoral failure rate, a multivariable logistic regression model was generated in order to analyze the effects of bone mineral density (T-score), gender, diagnosis, body mass index, femoral implant fixation type, age, and femoral component size.</p> <p>Results</p> <p>The average post-operative Harris hip score was 92 ± 11 points and the average post-operative UCLA score was 7 ± 2 points. There were three revisions due to femoral neck fracture and two for femoral component loosening. These occurred in two female and three male patients. In the multi-variable regression model, only T-score and body mass index showed significant effects on the failure rate of femoral components. Patients with a lower T-score and a higher body mass index had a significantly increased risk of early femoral component failure.</p> <p>Conclusion</p> <p>We recommend that dual energy x-ray absorptiometry scan T-score tests should be routinely performed on all hip resurfacing patients pre-operatively. If a patient has a low T-score (≤ -1.5), consideration should be given to additional precautions or treatments to alleviate his or her risk, especially when the patient has a higher body mass index (≥ 29 kg/m<sup>2</sup>).</p
Is there added risk in resurfacing a femoral head with cysts?
<p>Abstract</p> <p>Background</p> <p>Femoral head cysts have been identified as a risk factor for early femoral failures after metal-on-metal hip resurfacing arthroplasty (HRA) based on limited scientific data. However, we routinely performed HRA if less than 1/3 of the femoral head appeared destroyed by cysts on the preoperative radiograph. This study was undertaken to analyze whether there was an added risk of early femoral failures in HRA when femoral head cysts were present.</p> <p>Methods</p> <p>This retrospective case-control study included 939 MOM HRAs operated by a single surgeon with use of the posterior minimally invasive surgical (MIS) approach between November 2005 and January 2009. Patients with all diagnoses except osteonecrosis were included. Among them, 117 HRAs had femoral head cysts ≥ 1 cm identified in surgery. All cysts were treated with bone grafting using acetabular reamings packed into the cavitary defect (instead of filling the cysts with cement). The control group, which had no cyst observed at the time of surgery, was randomly selected from our database using computer algorithms to match those cases in the study group for the parameters of surgical date, age, gender, body mass index, diagnosis, femoral fixation method, and the size of the femoral component.</p> <p>Results</p> <p>The minimum follow-up was 24 months for both groups. The early femoral failure rate in the study group was 3/117 (2.6%) and 0/117 in the control group; there was no statistical difference between these two groups (<it>P </it>= 0.08). In the study group, there were two femoral neck fractures (revised): both occurred in patients having a cyst size of 1 cm<sup>3</sup>; and there was one femoral component loosening at 3-year follow up in a patient having a cyst size of 2 cm<sup>3</sup>.</p> <p>Conclusion</p> <p>Although the risk of early femoral failures among the group with cysts appeared higher than the group without cysts, we could not demonstrate a significant statistical difference between the two groups. It is possible that bone grafting cysts rather than cementing them may account for the low failure rate, and that this technique may minimize the risk of resurfacing a femoral head with cysts.</p
Mathematics and Morphogenesis of the City: A Geometrical Approach
Cities are living organisms. They are out of equilibrium, open systems that
never stop developing and sometimes die. The local geography can be compared to
a shell constraining its development. In brief, a city's current layout is a
step in a running morphogenesis process. Thus cities display a huge diversity
of shapes and none of traditional models from random graphs, complex networks
theory or stochastic geometry takes into account geometrical, functional and
dynamical aspects of a city in the same framework. We present here a global
mathematical model dedicated to cities that permits describing, manipulating
and explaining cities' overall shape and layout of their street systems. This
street-based framework conciliates the topological and geometrical sides of the
problem. From the static analysis of several French towns (topology of first
and second order, anisotropy, streets scaling) we make the hypothesis that the
development of a city follows a logic of division / extension of space. We
propose a dynamical model that mimics this logic and which from simple general
rules and a few parameters succeeds in generating a large diversity of cities
and in reproducing the general features the static analysis has pointed out.Comment: 13 pages, 13 figure
Circuit Electromechanics with a Non-Metallized Nanobeam
We have realized a nano-electromechanical hybrid system consisting of a
silicon nitride beam dielectrically coupled to a superconducting microwave
resonator. We characterize the sample by making use of the Duffing nonlinearity
of the strongly driven beam. In particular, we calibrate the amplitude spectrum
of the mechanical motion and determine the electromechanical vacuum coupling. A
high quality factor of 480,000 at a resonance frequency of 14 MHz is achieved
at 0.5 K. The experimentally determined electromechanical vacuum coupling of
11.5 mHz is quantitatively compared with finite element based model
calculations.Comment: Typos and one reference have been correcte
The role of clustering and gridlike ordering in epidemic spreading
The spreading of an epidemic is determined by the connectiviy patterns which
underlie the population. While it has been noted that a virus spreads more
easily on a network in which global distances are small, it remains a great
challenge to find approaches that unravel the precise role of local
interconnectedness. Such topological properties enter very naturally in the
framework of our two-timestep description, also providing a novel approach to
tract a probabilistic system. The method is elaborated for SIS-type epidemic
processes, leading to a quantitative interpretation of the role of loops up to
length 4 in the onset of an epidemic.Comment: Submitted to Phys. Rev. E; 15 pages, 11 figures, 5 table
Two-resonator circuit QED: Dissipative Theory
We present a theoretical treatment for the dissipative two-resonator circuit
quantum electrodynamics setup referred to as quantum switch. There, switchable
coupling between two superconducting resonators is mediated by a
superconducting qubit operating in the dispersive regime, where the qubit
transition frequency is far detuned from those of the resonators. We derive an
effective Hamiltonian for the quantum switch beyond the rotating wave
approximation and study the dissipative dynamics within a Bloch-Redfield
quantum master equation approach. We derive analytically how the qubit affects
the quantum switch even if the qubit has no dynamics, and we estimate the
strength of this influence. The analytical results are corroborated by
numerical calculations, where coherent oscillations between the resonators, the
decay of coherent and Fock states, and the decay of resonator-resonator
entanglement are studied. Finally, we suggest an experimental protocol for
extracting the damping constants of qubit and resonators by measuring the
quadratures of the resonator fields.Comment: 17 pages, 9 figure
Zero Modes in Electromagnetic Form Factors of the Nucleon in a Light-Cone Diquark Model
We use a diquark model of the nucleon to calculate the electromagnetic form
factors of the nucleon described as a scalar and axialvector diquark bound
state. We provide an analysis of the zero-mode contribution in the diquark
model. We find there are zero-mode contributions to the form factors arising
from the instantaneous part of the quark propagator, which cannot be neglected
compared with the valence contribution but can be removed by the choice of wave
function. We also find that the charge and magnetic radii and magnetic moment
of the proton can be reproduced, while the magnetic moment of the neutron is
too small. The dipole shape of the form factors, and
can be reproduced. The ratio decreases
with but too fast.Comment: 22 pages, 6 pages, accepted by J.Phys.
Child and Parent Report of Parenting as Predictors of Substance Use and Suspensions from School
This study examined how child and parent reports of parenting were related to early adolescent substance use and school suspensions. Data were from two time points six months apart on 321 families with an eighth grade student attending one of five schools in the Pacific Northwest. Child- and parent-report measures of family management practices were moderately correlated (r = .29). Child report, but not parent report, of more positive family management practices uniquely predicted a lower likelihood of adolescent substance use. Also, discrepancies between child and parent report of parenting predicted substance use, with child positive report of family management losing its protective association with adolescent substance use when parents had negative reports of their parenting. Parent report, but not child report, of better parenting predicted lower likelihood of suspensions, suggesting that the salience of child and parent report may depend on the type of behavioral outcome
Child and Parent Report of Parenting as Predictors of Substance Use and Suspensions from School
This study examined how child and parent reports of parenting were related to early adolescent substance use and school suspensions. Data were from two time points six months apart on 321 families with an eighth grade student attending one of five schools in the Pacific Northwest. Child- and parent-report measures of family management practices were moderately correlated (r = .29). Child report, but not parent report, of more positive family management practices uniquely predicted a lower likelihood of adolescent substance use. Also, discrepancies between child and parent report of parenting predicted substance use, with child positive report of family management losing its protective association with adolescent substance use when parents had negative reports of their parenting. Parent report, but not child report, of better parenting predicted lower likelihood of suspensions, suggesting that the salience of child and parent report may depend on the type of behavioral outcome
- …