CT evaluation of torsional malalignment after intertrochanteric fracture fixation

INTRODUCTION

Trochanteric fractures are commonly stabilized either by intramedullary nailing or plate and screw fixation after reduction on the orthopaedic surgical table under radiological guidance.

HYPOTHESIS

Closed trochanteric fracture anatomic reduction is difficult in the transversal plane.

OBJECTIVES

The objective of this prospective study was to assess the rotational malalignment induced after reduction and osteosynthesis of trochanteric fractures.

PATIENTS AND METHODS

Prospective study including 40 patients (mean age, 78 years; range, 51-90 years) operated for a trochanteric fracture between January 2007 and September 2008. Fourteen fractures were treated using DHS™ (Synthes™) plate and screw fixation and 26 with intramedullary nailing (trochanteric nail™, Stryker™). All these patients underwent postoperative CT of the pelvis during their hospitalization with measurement of anteversion of the operated and healthy femoral necks at the posterior condyles. The evaluation criterion was whether or not there was malalignment greater than 15° on the operated side compared to the healthy side.

RESULTS

The mean anteversion was 14.2° for the healthy side and 23° for the operated side. The mean rotational malalignment was 15.3°. Forty percent of the rotational malalignments were greater than 15°, with a majority of cases showing excess internal rotation (35%) of the distal fragment.

CONCLUSION AND DISCUSSION

The rate of internal rotational malalignment of the distal fragment greater than 15° was high (40% of this series). This should encourage surgeons to reduce the excess internal rotation that tends to be attributed to the distal fragment during preoperative reduction of these fractures.

LEVEL OF EVIDENCE

Level III. Prospective diagnostic study with no control group.

Predictors of depression in multiple sclerosis patients

Depression is one of the major problems associated with multiple sclerosis (MS). Several physical and psychological factors tend to interact and make it difficult to pinpoint the predictors of the depression. It seemed particularly important to examine how anxiety and illness evolution (characterized by the functional status) influence the appearance of depression symptoms. Thus, the aim of this article was to clarify the relationship between depression and the factors associated with it. One hundred and fifteen participants living at home recruited through various associations and MS clinics answered socio demographic, medical and psychological questions and questionnaires (depression, anxiety, coping, social support, locus of control, alexithymia, self-esteem). Results show that functional status (EDSS), trait anxiety, alexithymia and satisfaction with social support system are the predicting factors of depression. Trait anxiety and functional status are two predictors that independently and simultaneously lead to the appearance of depression symptoms, with trait anxiety playing a predominant role. Alexithymia and social support indirectly influence the appearance of these symptoms.

Characterization of a major colon cancer susceptibility locus (Ccs3) on mouse chromosome 3

Treatment of mice with the carcinogen azoxymethane (AOM) induces a number of lesions in the colon, including hyperplastic lesions, as well adenomas and carcinomas in situ. Inbred strains of mice show different responses to AOM-induced carcinogenesis. A/J mice are highly susceptible and develop a greater number of hyperplastic lesions and tumors (15-70 tumors per mouse) than resistant C57BL/6J mice (0-6 tumors per mouse). Susceptibility to AOM-induced tumors segregates as a co-dominant trait in (A x B6)F1 hybrids. Using a set of 23 AcB and BcA recombinant congenic mouse strains derived from A/J (susceptible) and B6 (resistant) parents, we observed that the number of hyperplastic lesions and tumors induced by AOM was under different genetic controls in AcB/BcA strains. The multiplicity of AOM-induced tumors is controlled by a major locus that we have mapped on the distal portion of chromosome 3, to which we have given the temporary designation colon cancer susceptibility locus 3 (Ccs3). B6 and A/J alleles at Ccs3 are associated with resistance and susceptibility, respectively. Haplotype analysis in key informative AcB/BcA strains restricts the size of the Ccs3 locus to a 14 Mb segment that contains 94 annotated genes. The expression level of all these genes in normal colon has been established by transcript profiling with microarrays, and has led to the identification of a subset of positional candidates that are expressed at high levels in this tissue. The 4q and 1p human chromosomal segments sharing syntenic homology with the mouse Ccs3 segment are known to be associated with inflammatory bowel diseases and colorectal tumors in humans, suggesting that the study of the mouse Ccs3 locus may help further the pathogenesis of these human conditions.

Extending Cable Theory to Heterogeneous Dendrites

Dendrites may exhibit many types of electrical and morphological heterogeneities at the scale of a few micrometers. Models of neurons, even so-called detailed models, rarely consider such heterogeneities. Small-scale fluctuations in the membrane conductances and the diameter of dendrites are generally disregarded and spines merely incorporated into the dendritic shaft. Using the two-scales method known as homogenization, we establish explicit expressions for the small-scale fluctuations of the membrane voltage, and we derive the cable equation satisfied by the voltage when these fluctuations are averaged out. This allows us to rigorously establish under what conditions a heterogeneous dendrite can be approximated by a homogeneous cable. We consider different distributions of synapses, orderly or random, on a passive dendrite, and we investigate when replacing excitatory and inhibitory synaptic conductances by their local averages leads to a small error in the voltage. This indicates in which regimes the approximations made in compartmental models are justified. We extend these results to active membranes endowed with voltage-dependent conductances or NMDA receptors. Then we examine under which conditions a spiny dendrite behaves as a smooth dendrite. We discover a new regime where this holds true, namely, when the conductance of the spine neck is small compared to the conductance of the synapses impinging on the spine head. Spines can then be taken into account by an effective excitatory current, the capacitance of the dendrite remaining unchanged. In this regime, the synaptic current transmitted from a spine to the dendritic shaft is strongly attenuated by the weak coupling conductance, but the total current they deliver can be quite substantial. These results suggest that pedunculated spines and stubby spines might play complementary roles in synaptic integration. Finally, we analyze how varicosities affect voltage diffusion in dendrites and discuss their impact on the spatiotemporal integration of synaptic input.

The afterhyperpolarization conductance exerts the same control over the gain and variability of motoneurone firing in anaesthetized cats

Does the afterhyperpolarization current control the gain and discharge variability of motoneurones according to the same law? We investigated this issue in lumbar motoneurones of anaesthetized cats. Using dynamic clamp, we measured the conductance, time constant and driving force of the AHP current in a sample of motoneurones and studied how the gain was correlated to these quantities. To study the action of the AHP on the discharge variability and to compare it to its action on the gain, we injected an artificial AHP-like current in motoneurones. This increased the natural AHP. In three motoneurones, we abolished most of the natural AHP with the calcium chelator BAPTA to investigate the condition where the discharge was essentially controlled by the artificial AHP. Our results demonstrate that both the gain and the coefficient of variation of the firing rate are inversely proportional to the magnitude and to the time constant of the artificial AHP conductance. This indicates that the AHP exerts the same control over the gain and the variability. This mechanism ensures that the variability of the discharge is modulated with the gain. This guarantees a great regularity of the discharge when the motoneurone is in a low excitability state and hence good control of the force produced.

Comparison of epidemiological, clinical, and biological features of invasive aspergillosis in neutropenic and nonneutropenic patients: a 6-year survey

BACKGROUND

Invasive aspergillosis is an opportunistic infection that occurs mainly among patients with prolonged neutropenia. Few data are available on invasive aspergillosis in nonneutropenic patients.

METHODS

The aim of this survey was to compare neutropenic and nonneutropenic patients who had received a diagnosis of invasive aspergillosis at our institution during a 6-year period.

RESULTS

Among the 88 cases of invasive aspergillosis analyzed here, 12 were histologically proven, 52 were probable, and 24 were possible. Forty-seven percent of cases were diagnosed in the intensive care unit, and 40% were diagnosed in hematology units. Neutropenia was a risk factor for 52 patients (59%), most of whom had hematological or solid malignancies. Among the 36 nonneutropenic patients (41%), the main underlying conditions were steroid-treated chronic obstructive pulmonary disease, asthma, rheumatoid arthritis, giant-cell arteritis, and microvascular disorders; 10 patients were recipients of solid-organ transplants, and 1 patient was seropositive for human immunodeficiency virus. The distribution of proven and probable invasive aspergillosis was similar for neutropenic and nonneutropenic patients. The mortality rate was 71.5% overall and was significantly higher among nonneutropenic patients than among neutropenic patients (89% vs. 60%; P<.05). Compared with neutropenic patients, nonneutropenic patients were significantly less likely to have symptoms of invasive aspergillosis and more likely to have frequent intercurrent pneumonia due to another microorganism. The sensitivity of mycological examination of bronchoalveolar lavage fluid specimens was higher for nonneutropenic patients than for neutropenic patients (85% vs. 58%; P<.05), whereas the sensitivity of antigenemia was the same for the 2 populations (65% vs. 64%). Findings on thoracic computed tomographs were similar, except that segmental areas of consolidation occurred more frequently among neutropenic patients.

CONCLUSION

This survey at a whole institution underlines the high number of cases of invasive aspergillosis among nonneutropenic patients, with an overall mortality rate that was significantly higher than that for neutropenic patients.

How much afterhyperpolarization conductance is recruited by an action potential? A dynamic-clamp study in cat lumbar motoneurons

We accurately measured the conductance responsible for the afterhyperpolarization (medium AHP) that follows a single spike in spinal motoneurons of anesthetized cats. This was done by using the dynamic-clamp method. We injected an artificial current in the neurons that increased the AHP amplitude, and we made use of the fact that the intensity of the natural AHP current at the trough of the voltage trajectory was related linearly to the AHP amplitude. We determined at the same time the conductance and the reversal potential of the AHP current. This new method was validated by a simple theoretical model incorporating AHP and hyperpolarization-activated (Ih) currents and could be applied when the decay time constant of the AHP conductance was at least five times shorter than the estimated Ih activation time. This condition was fulfilled in 33 of 44 motoneurons. The AHP conductance varied from 0.3 to 1.4 microS in both slow- and fast-type motoneurons, which was approximately the same range as the input conductance of the entire population. However, AHP and input conductances were not correlated. The larger AHP in slow-type motoneurons was mainly attributable to their smaller input conductance compared with fast motoneurons. The likeness of the AHP conductance in both types of motoneurons is in sharp contrast to differences in AHP decay time and explains why slow- and fast-type motoneurons have similar gain.

Comparison between shell morphology and genetic diversity in two sympatric lymnaeid snails, vectors of fasciolosis

Species determination of freshwater snails is particularly important in the case of disease vectors. In central France, for example, it has been shown that Galba truncatula (Müller, 1774) and Omphiscola glabra (Müller, 1774), which can be found in sympatry, are intermediate hosts for fasciolosis. Although these two species are distinguishable based on their shell morphology, some snails present in sympatric zones possess shell characteristics that are common to both species, suggesting possible gene flow. To test this hypothesis, we carried out multilocus enzyme electrophoreses on individuals sampled in one zone of sympatry. Our results clearly show that all snails with shell characteristics common to both species are O. glabra. We also note an absence of hybridization between G. truncatula and O. glabra in the study area. Remarkably, we observe a total monomorphism at the six studied loci among individuals of G. truncatula. Similarly, we find a total lack of heterozygotes in the O. glabra sample (with classic or intermediate shell characteristics). These results suggest a predominance of selfing in the reproductive mode of both species. Our results suggest that conchological characteristics can provide information about the taxonomic position of lymnaeids. However, they are insufficient to confidently differentiate species.

How Membrane Properties Shape the Discharge of Motoneurons: A Detailed Analytical Study

Electrophysiological experiments and modeling studies have shown that after hyperpolarization regulates the discharge of lumbar motoneurons in anesthetized cats and is an important determinant of their firing properties. However, it is still unclear how firing properties depend on slow after hyperpolarization, input conductance, and the fast currents responsible for spike generation. We study a single-compartment integrate-andfire model with a slow potassium conductance that exponentially decays between spikes. We show that this model is analytically solvable, and we investigate how passive and active membrane properties control the discharge. We show that the model exhibits three distinct firing ranges (primary, secondary, and high frequency), and we explain the origin of these three ranges. Explicit expressions are established for the gain of the steady-state current-frequency (I− f) curve in the primary range and for the gain of the I− f curve for the first interspike interval. They show how the gain is controlled by the maximal conductance and the kinetic parameters of the after hyperpolarization conductance. The gain also depends on the spike voltage threshold, and we compute how it is decreased by threshold accommodation (i.e., the increase of the threshold with the injected current). In contrast, the gain is not very sensitive to the input conductance. This implies that tonic synaptic activity shifts the current-frequency curve in its primary range, in agreement with experiments. Taking into account the absolute refractory period associated with spikes somewhat reduces the gain in the primary range. More importantly, it accounts for the approximately linear and steep secondary range observed in many motoneurons. In the nonphysiological high-frequency range, the behavior of the I− f curve is determined by the fast voltage-dependent currents, via the amplitude of the fast repolarization afterspike, the duration of the refractory period, and voltage threshold accommodation, if present.

Intérêts et difficultés d’interprétation du coefficient de transfert du CO (TLCO/VA)

INTRODUCTION

Interpreting measurements of carbon monoxide can be problematic.

STATE OF THE ART

The transfer factor (TLCO) is usually calculated by multiplying the decrease in alveolar CO concentration between the beginning and the end of a 10 second breath hold (KCO) by the alveolar volume (VA). Thus a reduced TLCO may occur due to either a low KCO, a reduced VA, or a combination of both.

PERSPECTIVES

A careful examination of KCO and VA will usually suggest a specific explanation for a reduction in TLCO. In restrictive lung diseases from extrapulmonary origin, TLCO is low but TLCO/VA [[/INF 120% of the reference values. In interstitial lung disease, the value of TLCO/VA depends on whether the loss of lung units is diffuse or not, and probably also on the status of the microcirculation. In airflow obstruction, a low VA is caused by uneven distribution of inspired He/CO mixture within the breath-hold time.

CONCLUSIONS

The transfer factor for carbon monoxide is best interpreted in terms of its components, alveolar volume and carbon monoxide transfer coefficient.

Small effective population sizes in a widespread selfing species, Lymnaea truncatula (Gastropoda: Pulmonata)

We present here a spatial and temporal population genetic survey of a common freshwater snail, also a predominantly selfing species, Lymnaea truncatula. The rate of genetic diversity loss was quantified by estimating the effective size (Ne) of the snail populations, using two different methods. A temporal survey allowed estimation of a variance effective size of the populations, and a spatial survey allowed the estimation of an inbreeding effective size, from two-locus identity disequilibria estimates. Both methods were consistent and provided low Ne values. Drift due to (i) high amounts of selfing and (ii) fluctuations in population sizes because of temporary habitats, and also selection coupled to genome-wide linkage disequilibria, could explain such reductions in Ne. The loss of genetic diversity appears to be counterbalanced only very partially by low apparent rates of gene flow.

How shunting inhibition affects the discharge of lumbar motoneurones: a dynamic clamp study in anaesthetized cats

In the present work, dynamic clamp was used to inject a current that mimicked tonic synaptic activity in the soma of cat lumbar motoneurones with a microelectrode. The reversal potential of this current could be set at the resting potential so as to prevent membrane depolarization or hyperpolarization. The only effect of the dynamic clamp was then to elicit a constant and calibrated increase of the motoneurone input conductance. The effect of the resulting shunt was investigated on repetitive discharges elicited by current pulses. Shunting inhibition reduced very substantially the firing frequency in the primary range without changing the slope of the current-frequency curves. The shift of the I-f curve was proportional to the conductance increase imposed by the dynamic clamp and depended on an intrinsic property of the motoneurone that we called the shunt potential. The shunt potential ranged between 11 and 37 mV above the resting potential, indicating that the sensitivity of motoneurones to shunting inhibition was quite variable. The shunt potential was always near or above the action potential voltage threshold. A theoretical model allowed us to interpret these experimental results. The shunt potential was shown to be a weighted time average of membrane voltage. The weighting factor is the phase response function of the neurone that peaks at the end of the interspike interval. The shunt potential indicates whether mixed synaptic inputs have an excitatory or inhibitory effect on the ongoing discharge of the motoneurone.