Salt crystallization is a major cause of weathering of rocks, artworks and monuments. Damage can only occur if crystals continue to grow in confinement, i.e. within the pore space of these materials, thus generating mechanical stress. We report the direct measurement, at the microscale, of the force exerted by growing alkali halide salt crystals while visualizing their spontaneous nucleation and growth. The experiments reveal the crucial role of the wetting films between the growing crystal and the confining walls for the development of the pressure. Our results suggest that the measured force originates from repulsion between the similarly charged confining wall and the salt crystal separated by a ~1.5 nm liquid film. Indeed, if the walls are made hydrophobic, no film is observed and no repulsive forces are detected. We also show that the magnitude of the induced pressure is system specific explaining why different salts lead to different amounts of damage to porous materials. Salt weathering affects porous materials such as rock outcrops and minerals within the soil profile but also engineering structures monuments, and artworks . There i1Moreover, changes in humidity affect also the growth of microorganisms in stone and wood4567891011crystallization was approximated by the chemical potential difference between salt molecules in the crystal and in the supersaturated salt solution:m the molar volume of the solid phase, and S the supersaturation, which is the ratio of the solute concentrations in the solution c and in the saturated solution cs16171819Arguments explaining that growing crystals can generate stresses have been given for more than 150 years ago, since Lavalle and subsequently Becker reported that a crystal can grow under external pressure13151617More formally, this requires an activity product K[P] greater than the solubility product at atmospheric pressure K[0], as described by Freundlich equation for a crystal under pressure The direct measurement of the force exerted by a growing crystal in confinement is challenging, as illustrated by the small number of experimental results reported162324251523We report experimental results obtained with an innovative setup which permits to visualize the spontaneous primary nucleation and growth during the evaporation of the salt solution while directly measuring the force exerted by a crystal during its growth in confinement. Here, we do not impose a certain supersaturation, or impose a given load; we rather measure the force that the growing crystal exerts with its spontaneous precipitation. This should be contrasted with earlier attempts to measure the pressure exerted during a secondary nucleation process , for which only very modest supersaturations were consideredc/cs ~ 1.6 ± 0.2 at the onset of crystallization28Two alkali halides salts, sodium chloride (NaCl) and potassium chloride (KCl), are studied firstly because of their abundance and similar crystalline stucture . The second incentive for this choice of materials is that recently in experiments on the evaporation of NaCl solutions it became clear that primary nucleation results in very high supersaturations S = 0 ~ 0.2 μl) of the salt solution (NaCl or KCl) close to saturation 1 using a water bath thermostat. Once this air flow arrives in the chamber at the temperature T2 (21 °C), the partial vapor pressure Pw(T2) will be then equal to the saturated vapor pressure at T1 and consequently the relative humidity of the chamber will be fixed as:1, the relative humidity can be fixed to a desired value in the chamber very precisely (±2%).In our climatic chamber , the rel−3 ± 1.0 10−3 N) is detected; the measured force is in good agreement with the calculated theoretical value by considering the gap distance, the surface tension of the salt solution and its contact angle with the glass plateOnce the salt solution is entrapped between the two glass plates, an attractive (negative) capillary force  force develops, increasing in time. A steep increase of the force is detected when there is no more solution around the sides of the crystal : the remaining salt solution is in the liquid film that is observed between the glass plates and the crystal. Its subsequent evaporation induces the formation of steps on the confined face of the crystal322; the total area of one of the crystal face is much larger, on the order of ~2–3 105 μm2. This then gives a crystallization pressure deduced from the measured force and contact area of about 220 ± 50 MPa for experiment in Fig. 136In order to convert the measured force into a pressure, we measure the area of contact between the salt crystal and the glass plates using the rheometer see . The lat9 Pa for glass, the thickness of the glass slide is h = 0.9 mm and a crystal size b ~ 0.8 mm and a deformation S ~ 50 μm). These results obtained at the microscale confirm once again the arguments given at the beginning of the 20th century that a growing crystal in confinement can lift a load if the latter is in contact with a film of solution14At the end of each drying experiment, the precipitated microcrystal is gently removed and analysed by SEM; it shows very complex microscale step architecture, in line with the obersvations of disjoining pressure Π(l) within a film of thickness l, pushing the two surfaces apart, would be of the (simplified) form Π(l) ~ A exp(−κl), with 0 the relative permittivity of the bulk and free space, respectively, and The importance of thin liquid films for the crystallization pressure was already underlined theoretically1516171819202121Na+ ~ 1.3 10−9 m2/s in water) over the typical time scale in the experiment (~1000s) there will be little exchange between the entrapped film and the remaining solution besides the crystal; the typical size of the reservoir is ~1 cm, whereas the diffusion length is at most a fraction of a mm.This suggests a rather strong variation of the pressure with the salt concentration in the solution. Indeed, performing a large number of experiments, a strong correlation is found between the measured pressure and the salt concentration in the solution around the crystal . We use As an independent check that the salt concentration in the liquid film entrapped between the crystal and the wall is indeed high, and hence comparable to that at the onset of salt precipitation, we stop the experiment when the maximum force and maximum shear modulus are achieved but a thin liquid film is still visible under the microscope (t ~ 150 min); the concentration at the onset of precipitation was 1.4 in this experiment. The crystal is gently removed and after further drying the upper crystal face (i.e. confined face) is observed using scanning-electron microscopy (SEM). The microphotographs reveal the formation of large amount of tiny dendritic crystals ; these al of about 1.5 nm (l ~ 2 nm)21263940414243Assuming, then, that the concentration in the film equals the supersaturation at the onset of crystallization, we can compare with the simplified model for an electrostatic repulsion. We find that the measured pressure as a function of the supersaturation closely follows the expression for the disjoining pressure Π(l) ~ A exp(−κl), with a constant film thickness t 1.5 nm . This va−6 M) and anionic dye  onto glass and crystals surfaces in contact with a highly concentrated salt solution. Methylene blue adsorption is widely used for the determination of both surface areas and exchange capacities of clay mineralsThe scenario of a repulsive force requires that the crystal/solution and the solution/glass interfaces carry a charge of identical sign. Although it is known that glass surfaces are charged negatively when in contact with water and a low concentration of salt4647σ at the silica surface in contact with water and both NaCl and KCl solutions  compared to Na+ (0.96 Å), which results in smaller hydrated radii. Due to a smaller radius, the K+ ions bind more easily to the negatively charged silica surface at high concentrationsMore quantitatively, these measurments allows to estimate the surface charge density ions see . In pureThus, the dependence of the force on salt concentration, surface charge and wettability of the glass makes a strong point that the observed forces are due to the disjoining pressure of the thin liquid film between two charged surfaces. It is interesting to compare this disjoining pressure with the thermodynamic crystallization pressure17In conclusion, we have performed a direct measurement of the pressure exerted by the spontaneous precipitation of a salt microcrystal during evaporation in a confinement similar to that found in porous materials The results obtained for the growth of KCl and NaCl crystals between hydrophilic and hydrophobic glass walls suggests that the pressure originates from a repulsive interaction between charged surfaces separated by the liquid film. The magnitude of the measured pressure can be very high. The subtle dependence of the generated stress on the wetting and the surface charge properties that we report can also explain the experimentally observed variability for different salts crystallizing in different materials1623242519515228535455How to cite this article: Desarnaud, J. et al. The Pressure induced by salt crystallization in confinement. Sci. Rep.6, 30856; doi: 10.1038/srep30856 (2016).


Protective mutualisms, where a symbiont reduces the negative effects of another species on a shared host, represent a common type of species interaction in natural communities, yet it is still unclear what ecological conditions might favor their emergence. Studies suggest that the initial evolution of protective mutualists might involve closely related pathogenic variants with similar life histories, but different competitive abilities and impacts on host fitness. We derive a model to evaluate this hypothesis and show that, in general, a protective variant cannot spread from rarity or exclude a more pathogenic strain. While the conditions allowing mutualist invasion are more likely with increased environmental productivity, they still depend on initial densities in the invaded patch exceeding a threshold, highlighting the likely importance of spatial structure and demographic stochasticity. Using a numerical simulation approach, we show that regional coexistence is in fact possible in an explicitly spatial system and that, under some circumstances, the mutualist population can exclude the enemy. More broadly, the establishment of protective mutualists may be favored when there are other life-history differences from more pathogenic symbionts, such as vertical transmission or additional direct benefits to hosts. Species interactions are fundamental drivers of ecological and evolutionary dynamics in natural ecosystems. Consequently, there is a vast literature on the role of predator–prey and competitive interactions in structuring communities  and “conditional protective mutualists” interacting with a host population  and the mutualist (M) have direct negative effects on the host (H) and that the mutualist's positive effect is due to the protection it provides by lowering the enemy attack rate and by having lower effects on mortality compared to the enemy, or through a combination of both. This may result in fewer hosts attacked and fewer enemies produced. Thus, the net effect of such a mutualist is a balance between its detrimental and protective effects . Our model is structurally similar to earlier models of directly competing species which exploit a dynamic resource base  and the transmission parameter (b) are assumed equal for both organisms, as might occur during early stages of evolutionary divergence. Mutualists can be either more (α > 1) or less (α < 1) virulent than the enemy with regard to impacts on host mortality  describes the effect of the mutualist on the enemy .We model a host–enemy–mutualist association as follows. We assume that the enemy  based on differences between equilibrium host population size in the presence of the mutualist alone (H*M) versus the enemy alone (H*E).When the enemy is present, the mutualist has both negative and positive effects on the host. We define a criterion for net mutualism , and the mutualist per capita death rate is high relative to that of the enemy.From equations H*M (3a) and for mutualists is We analyze the condition for invasion of a pathogenic mutant into a mutualist–host interaction. The two species equilibrium for hosts is rbαγ > qδM, as we do for the remainder of the study. Note that the situations in which the enemy cannot invade a resident mutualist correspond to sufficiently high values of the virulence parameter α such that the mutualist is actually more virulent than the enemy. Assuming that the system is at this equilibrium, the enemy mutant can invade from rarity  whenThis equilibrium yields positive values assuming that By replacing r  is sufficiently large, and host self-limitation is sufficiently low.This condition implies that the pathogen can invade the resident mutualist if H*E) is given in equation E*) isWe first derive the condition for initial invasion of the mutualist into a resident population of the host and its enemy at equilibrium. In the absence of the mutualist, the system has a single nontrivial equilibrium, which is always stable to small perturbations (Appendix S1). The host equilibrium . However, numerical experiments reveal that when m*), we substitute m for M in eqn  is found by substituting The criterion for mutualist invasion (U > 0), then the right hand side of α), or when mutualists have a strong protective effect (low u)  Fig.. Should w u) Fig. or (2) ww u) Fig.. Below wTo better understand the conditions under which a mutualist may invade a resident enemy population through immigration, we analyze a modified version of the model with two patches, one with the mutualist and the host (patch 1) and the other with the enemy and the host (patch 2). Such a scenario is not unrealistic; empirical studies have demonstrated geographical structure in symbiont populations, with  different strains of the same species shown to have either antagonistic or mutualistic effects on the same host depending on location and local environment  differs between patches so as to reflect variation in habitat quality, but that density-dependence (q) is intrinsic to the host population . We also assume constant directional emigration from patch 1 to patch 2, at rate ε1. The dynamics in patch 2 are given by equation .In the previous sections, we show that invasion of a conditional protective symbiont from rarity is not possible within a single population, but can occur in a two-patch system given a critical number of invading individuals, which is determined by the between-patch productivity gradient. We thus posit that in a broader context, assuming spatial variability in primary productivity , regional coexistence between conditional protective mutualists and enemies is possible. To examine this prediction, we simulate the system on a square toric lattice of 10 × 10 patches, with a uniform dispersal kernel from one focal patch to all of its eight neighbors. Computer code (C++11) to reproduce the simulation can be found at r  and variance v . Based on results from the previous sections, we expect that the potential for regional coexistence between conditional protective mutualists and enemies will be greater in more heterogeneous landscapes. To measure regional coexistence, we record the proportion of mutualists in the total symbiont population (averaged over the last 1000 time-steps for a given set of input conditions). Values close to 0 or 1 indicate that enemies or mutualists dominate, respectively, whereas intermediate values signify coexistence.We simulate the system by varying the dispersal rate of conditional protective mutualists and enemies, the pathogenic effect of protective mutualists, and primary productivity across patches. The primary productivity of each patch is drawn at random at the beginning of each simulation from a Gaussian distribution with mean α) and highly heterogeneous environments. Mutualists are able to exclude the enemy for intermediate dispersal values, especially when the enemy disperses more than the mutualist. However, for most of the parameter combinations explored, spatial structure allows regional coexistence of both symbiont types. In full agreement with the predictions made above for the two-patch model, the only situation in which the enemy can drive the mutualist to regional extinction is in the absence of environmental heterogeneity. Finally, mutualists are only able to persist regionally for intermediate values of dispersal. When values of mutualism dispersal are too low, this prevents the establishment of source-sink dynamics as determined above for the two-patch system. Conversely, when dispersal is too high, mutualists are unable to sustain a local population and are eventually outcompeted by enemies.As shown in Fig.r) in determining both the threshold for mutualist invasion and the production of migrating mutualists from alternative hosts or host populations in other patches. Host populations with higher r or lower intraspecific competition (q) are more likely to support the establishment and eventual maintenance of the mutualist in both the two-patch and spatially explicit systems. The small range of conditions resulting in the establishment of protective mutualists is in sharp contrast to the frequent observation, ecological importance, and broad taxonomic range of protective mutualisms in nature  also has a larger impact on host mortality  mutualisms is not always straightforward to demonstrate empirically. Most symbiotic associations cannot be categorized as purely antagonist or mutualistic  affect the strength and direction of these associations.None declared.


The analysis of shape is a key part of anatomical research and in the large majority of cases landmarks provide a standard starting point. However, while the technology of image capture has developed rapidly and in particular three‐dimensional imaging is widely available, the definitions of anatomical landmarks remain rooted in their two‐dimensional origins. In the important case of the human face, standard definitions often require careful orientation of the subject. This paper considers the definitions of facial landmarks from an interdisciplinary perspective, including biological and clinical motivations, issues associated with imaging and subsequent analysis, and the mathematical definition of surface shape using differential geometry. This last perspective provides a route to definitions of landmarks based on surface curvature, often making use of ridge and valley curves, which is genuinely three‐dimensional and is independent of orientation. Specific definitions based on curvature are proposed. These are evaluated, along with traditional definitions, in a study that uses a hierarchical (random effects) model to estimate the error variation that is present at several different levels within the image capture process. The estimates of variation at these different levels are of interest in their own right but, in addition, evidence is provided that variation is reduced at the observer level when the new landmark definitions are used. Biological shape is a topic of considerable scientific interest that has a very long history and that has many applications across the range of biological species. In terms of measurement, anatomical landmarks have been the basis of quantitative assessment and modelling of shape since the pioneering work of Thompson . The ideFor the important application area of the human face, detailed definitions of landmarks were provided by Farkas  and thisWeber & Bookstein  address The aim of the present paper is to propose new definitions of facial landmarks that are not dependent on the orientation of the head. These are based on three‐dimensional surface characteristics and the key information used to characterise landmarks is curvature. This refers in general to the local shape of the facial surface but, following Weber & Bookstein , anatomiThe approach is interdisciplinary, providing insights from biology, clinical use, computer vision, differential geometry and statistical analysis. Good landmark definitions require the relevant information to be readily identifiable, with good intra‐ and inter‐person reproducibility. These also need to apply to different imaging modalities such as stereophotogrammetry and laser scanning.In There are many reasons why the study of human facial shape is of interest. Two particular examples, involving issues of biological development and the need to assess the outcome of facial surgery, are described below in order to highlight the wide range of motivations for interest in facial shape and to identify issues that can inform the selection, definition and identification of anatomical landmarks.In the early embryological stages of human development, the anterior brain and the face are very closely connected. As a result, disorders of early brain development can be associated with facial dysmorphology. The origins of schizophrenia provide a particular example. A specific study is described by Hennessy et al. , who useIn a very different setting, facial surgery aims to alter an existing facial shape, usually to address the effects of trauma or of congenital issues. For example, cleft‐lip and/or palate is one of the commonest forms of facial disfigurement in children, and there have been a variety of initiatives to assess the effectiveness of surgical repair. This includes the study described by Hood et al.  where thThese examples underline the central role of anatomical landmarks in quantifying shape in general and important derived measures such as asymmetry in particular. The accuracy and reproducibility of landmarks is therefore of high importance as variation here will be transmitted to subsequent analysis. This strengthens the need to reconsider the definitions of landmarks, to overcome the difficulties associated with two‐dimensional perspectives and to take advantage of the direct three‐dimensional surface information available.The relatively recent advent of three‐dimensional surface imaging methods provides rich and complete representations of surface shape. However, the accuracy of subsequent landmarking will clearly be highly influenced by the accuracy of the underlying surface. Some approaches to three‐dimensional imaging are outlined here, with particular focus on the accuracy that can be achieved.Stereo‐camera systems capture the image of an object from two or more viewpoints in a synchronised manner. The main advantages of this type of system are the short capture time and the wide range of environments in which they can operate. The three‐dimensional reconstruction is performed offline at a high computational cost but with the availability of high‐quality cameras this approach can reach very high accuracy, up to 0.1 mm. Structured light approaches project two‐dimensional patterns of light onto the object of interest and this can achieve high accuracy, up to 0.3 mm, but these systems are sensitive to lighting conditions. Boehnen & Flynn  and Al‐KLaser methods project a beam of light (spot or stripe) onto the object of interest and extract three‐dimensional information by triangulation from the image captured by a camera. Convenient, hand‐held versions of this technology are now available. This approach is characterised by low computational cost, longer capture time and size limitation, but the accuracy achieved is very high, up to 0.05 mm  direction to the surface and the orthogonal axes x and y lie on the ‘tangent plane’. The axes x and y correspond to the directions of maximum and minimum curvature (rate of bending) of the surface. The values of these maximum and minimum curvatures, known as principal curvatures are κ1, κ2, where by convention κ1≥κ2. Note that the axes x, y and z are defined locally around the current surface point of interest and these axes will change as the point of interest is moved.The classical geometry of surfaces is well understood. Koenderink  gives a tan−1 denotes the inverse tan function. The purpose of this index is to characterise local surface shape in a systematic and interpretable manner. Values of S close to −1 indicate a ‘spherical cup’ shape where the curvatures κ1 and κ2 are positive and very close to one another. As S increases, the corresponding surfaces bend smoothly through ‘trough’ and ‘rut’ shapes, towards a ‘saddle’ that is most pronounced at S=0. As S increases through the positive half of the scale, this process is reversed until a ‘spherical cap’ is produced. This is the converse of the original ‘spherical cup’, now with negative rather than positive values of the principal curvatures κ1 and κ2. Koenderink & van Doorn , y(s), z(s), where s is arc length as described at (1), using the method of p‐splines . As the repeat landmarks from the lowest level of the hierarchy refer to the same images, gpa was applied to the averages of the pairs lying at the lowest level of Fig. As usual in the analysis of shape information, the collection of landmark configurations needs to be registered by Generalised Procrustes Analysis  The observer variation is interesting as this quantifies the extent to which different observers place the landmarks in different locations. In the case of nasion there is a high level of variation for both definitions, which is not surprising because of the intrinsic difficulty in locating this landmark on a relatively flat region. Interestingly, the curvature definition group shows substantial improvement in variation for gnathion and alare and modest improvement for several other landmarks. Table Figure y co‐ordinate, where location of gnathion is most problematic.A second small study was carried out for confirmation. Twenty observers were trained, 10 each on the curvature and orientation methods, with the larger number of observers allowing stronger focus on this key effect. The observers were asked to locate the difficult landmark gnathion on five subjects, each with two repeat images, but the landmarks alare crest L/R and crista philtrum L/R were also located in order to allow Procrustes registration. The curvature method showed a reduction of 13% in observer variability in the For a single landmark identification on one individual, the relevant measure of reproducibility combines the variability at all the levels shown in Table The principal aim of this paper has been to propose an approach to defining facial landmarks that avoids the need for careful orientation and that properly exploits the three‐dimensional nature of the images that are now routinely available. Methods of quantifying and classifying three‐dimensional surface shape have provided the key and, in particular, anatomical curves have proved to give a very useful basis for the identification of landmarks. This has the appeal of exploiting the familiar large‐scale structure of the face rather than basing definitions only on the immediate neighbourhoods of point locations. The majority of standard landmarks can be defined as points of maximal geodesic curvature or as the crossing points of two or more anatomical curves. A validation study, while can be regarded only as indicative because of the small number of observers involved, has nonetheless provided some supporting evidence for improvement in reproducibility through use of the curve‐based definitions.The availability of quantifiable measures of surface shape leads naturally to the question of the extent to which good definitions of landmarks might lead to helpful methods of automatic, rather than manual, identification. There is a considerable body of work on this topic; see, for example, Çeliktutan et al. . Some meIn contrast to the above, other methods use the information in sets of previously identified landmarks, and their relative configurations, to give guidance on the positions of the landmarks that might reasonably be expected in a new facial image. This approach seeks to build a statistical or ‘machine learning’ model that could be considered as an analogue of the ways in which the human brain exploits previous experience in making judgements about the plausibility of appropriate positions on a new face. Popular examples of this strategy include statistical shape models (Perakis et al. In terms of performance of automatic landmarking methods, the best results reported to date indicate average errors between 1.5 and 3.5 mm for the most distinctive facial landmarks. Sukno et al.  is an exHowever, the role of anatomical curves in the landmark definitions discussed within this paper also raises the prospect of using these to characterise faces in a much richer way than individual point locations. For example, the highlighted difficulty in defining and identifying gnathion may be circumvented by analysis of the entire underlying mid‐line curve that expresses the shape of the whole region. With suitable methods of statistical analysis this can provide a rich description of the local anatomy without the need to identify a single point as a definitive landmark.


Cells receive and send signals across the plasma membrane using the integrin family of receptors. What is it about their structure that can mediate their function? It goes without saying that the cellular plasma membrane effectively creates a barrier between the inside (intracellular area) and outside (extracellular area) of the cell it defines. In order for the cell to sense and respond to its environment (including other cells and the supporting structures that comprise the extracellular matrix [ECM]) and for the environment to influence cell function (including cell growth and movement), bidirectional signaling across the plasma membrane has to be mediated by receptors and other structures. About two decades ago, it became widely appreciated that many of the cell surface receptors that mediate cell–cell and cell–ECM interactions were structurally and functionally related, and the term “integrins” was coined to reflect the capacity of members of this family to integrate the extracellular and intracellular environment . IntegriThe integrin family comprises 20 or more members that are found in many animal species, ranging from sponges to mammals . They coMutational studies provided the initial hints that disruption of the non-covalent clasp between α and β cytoplasmic tails is clearly the event within the structure of the integrin that initiates inside-out signaling. Point mutations in the α and β cytoplasmic tails that are near the membrane or deletion of either region result in constitutive activation of the receptor . Mutatinvβ3 (the nomenclature identifies the particular α and β subunits) was determined  interacts with itself—called homotypic oligomerization of the transmembrane domains  Li et a. Ligand Despite the molecular level of our understanding of integrin activation, a number of key questions remain unresolved. Although we know that the membrane-proximal clasp on the integrin cytoplasmic face controls the integrin activation, the distal side of either the α or β cytoplasmic tails may also play a role in integrin activation, since other mutations indicate that the C-terminal membrane distal region is important in regulating integrin activation via a mechanism that is yet unknown. Thus, the picture for the cytoplasmic face-controlled inside-out activation may be substantially more complicated than specified in Upon the inside-out activation, integrins bind to specific extracellular matrix proteins. However, for the integrins to grip tightly to the extracellular matrix to mediate cell adhesion and migration, the integrin cytoplasmic domains must be anchored to the cytoskeleton . This is


It is now common for parents to measure tympanic temperatures in children. The objective of this study was to assess the diagnostic accuracy of these measurements.Parents and then nurses measured the temperature of 60 children with a tympanic thermometer designed for home use (home thermometer). The reference standard was a temperature measured by a nurse with a model of tympanic thermometer commonly used in hospitals . A difference of ≥ 0.5 °C was considered clinically significant. A fever was defined as a temperature ≥ 38.5 °C.The mean absolute difference between the readings done by the parent and the nurse with the home thermometer was 0.44 ± 0.61 °C, and 33% of the readings differed by ≥ 0.5 °C. The mean absolute difference between the readings done by the parent with the home thermometer and the nurse with the hospital thermometer was 0.51 ± 0.63 °C, and 72 % of the readings differed by ≥ 0.5 °C. Using the home thermometer, parents detected fever with a sensitivity of 76% (95% CI 50–93%), a specificity of 95% (95% CI 84–99%), a positive predictive value of 87% (95% CI 60–98%), and a negative predictive value of 91% (95% CI 79–98 %). In comparing the readings the nurse obtained from the two different tympanic thermometers, the mean absolute difference was 0.24 ± 0.22 °C. Nurses detected fever with a sensitivity of 94% (95 % CI 71–100 %), a specificity of 88% (95% CI 75–96 %), a positive predictive value of 76% (95% CI 53–92%), and a negative predictive value of 97% (95%CI 87–100 %) using the home thermometer. The intraclass correlation coefficient for the three sets of readings was 0.80, and the consistency of readings was not affected by the body temperature.The readings done by parents with a tympanic thermometer designed for home use differed a clinically significant amount from the reference standard  the majority of the time, and parents failed to detect fever about one-quarter of the time. Tympanic readings reported by parents should be interpreted with great caution. Parents and health care workers use temperatures measured by parents at home to determine if a child requires medical assessment. Health care workers sometimes make decisions about the need for investigations and hospital admission based on the temperature that parents report. This is especially true in the newborn or in the immunocompromised patient, where any temperature above the normal range can be indicative of bacterial infection.Health care workers have used commercial tympanic thermometers in hospitals for over 15 years. These thermometers are quick and easy to use and minimize the risk of nosocomial infection. Tympanic thermometers are now available for home use at a cost of about $50 US. There are no published studies comparing measurements obtained with tympanic thermometers designed for home use to measurements obtained with other types of thermometers, or comparing readings obtained by parents with these instruments to those obtained by health care workers. The primary objective of this study was to determine the diagnostic accuracy of readings obtained by parents with a tympanic thermometer designed for home use.The Health Research Ethics Board of the University of Alberta approved this study and parents and older children signed a consent form.Traditionally, rectal temperatures have been used as the reference standard in pediatrics. However, readings done by a nurse using a model of tympanic thermometer commonly used in hospitals were chosen as the reference standard for this study as they are easier to obtain than are rectal temperatures and tend to be closer to PA temperatures when the patient is febrile  or when Parents of patients from the General Pediatric Clinic, the Emergency Department, or on the inpatient units of the Stollery Children's Hospital were eligible for the study. Parents of febrile or afebrile children aged 6 months to 16 years were approached on the days when the study nurse was available, but preference was given to patients who were being assessed because of fever. Parents were not approached if it would be inconvenient for them to participate in the study, or if they did not communicate in English, but there were no other exclusion criteria.After informed consent was obtained from the parent , the parent was given the instruction sheet from the Braun Thermoscan  tympanic thermometer (home thermometer) to read. They were then asked to measure their child's temperature when they felt they understood the instructions. They then recorded the temperatures they measured on a sheet of paper. Without looking at this sheet of paper, one of three trained research nurses then measured the child's temperature using the same thermometer. The nurse then also measured the child's temperature with CORECHECK  tympanic thermometer . All readings were done in the same ear with a new probe cover.The mean absolute difference between the parents' reading and the reading by the nurse using the same thermometer was calculated. Readings were then analyzed separately for the febrile children. A temperature of ≥ 38.5 °C on the reading taken by the nurse using the hospital thermometer was defined as a fever. The percentage of times that the readings differed by 0.5 °C or more was calculated as this was considered a clinically significant difference.Even if the parent and the nurse obtained similar readings from the home thermometer, it would still be possible that these readings are inaccurate, as there are no published studies demonstrating the accuracy of this thermometer. Therefore, the readings obtained by the nurse and the parent from the home thermometer were compared to those obtained by the nurse using the hospital thermometer (the reference standard for the study). If the readings obtained by the parent differed considerably from those obtained by the nurse, but the nurse then obtained very consistent readings with the two different thermometers, one could conclude that the parents were inaccurate because of human error. On the other hand, if the nurse obtained inconsistent readings with the two different thermometers, this would suggest that either instrument or human error could be the problem.The measures of central tendency were determined, and the intraclass correlation coefficient determined for the three sets of readings. The three sets of measurements were also compared using the Bland-Altman method  where thIt was not possible to calculate a sample size, as the expected standard deviation between the three sets of readings could not be predicted. We estimated that a sample size of 60 children would be adequate.Sixty parents were approached and all agreed to participate in the study. Their children were 35 males and 25 females aged 5 months to 15 years (median 3 years). Although the majority of patients were being assessed because of fever, only 17 children were febrile at the time of the study. All 3 measurements were obtained within 5 minutes for 55 of the 60 cases.Table The mean absolute difference between the temperatures measured by the nurse using the home thermometer versus the hospital thermometer was 0.24 ± 0.22 °C. The higher reading was from the hospital thermometer in 25 of the 60 cases. There was agreement between the readings taken by the nurse from the two thermometers with regard to the presence of fever, except in one case where one reading was 38.4 °C and the other was 38.6 °C . The absolute differences were similar for febrile and afebrile children. Using the reference standard of a tympanic temperature measured by a nurse with a model of thermometer commonly used in hospitals, the parents did not detect a fever in four of 13 cases . This suggests that the readings obtained by a parent with a tympanic thermometer are sometimes not reliable. In fact, previous studies showed that parents' subjective assessment of whether their child had a fever had a sensitivity of 81.8%  and 88.9In comparing the readings taken by a nurse with a home tympanic thermometer to a hospital tympanic thermometer, the mean absolute difference was 0.24 °C, with 13 % of the readings differing by a clinically significant amount. It is not clear if this degree of discrepancy is to be expected when a skilled operator takes two tympanic readings, or if it was a true difference between the two types of tympanic thermometer. The nurse would have identified all but one of the 17 children with fever as being febrile with either thermometer, and that child had a temperature of 38.4 °C on one thermometer and 38.6 °C on the other thermometer. Therefore, it appears that with a skilled operator, the tympanic thermometer designed for home use is reasonably reliable, and is likely to detect fever even if the actual reading is not always accurate.The chief limitation of this study is that readings obtained by a nurse from the hospital tympanic thermometer must be reliable for the results of this study to be accurate. Some studies have concluded that tympanic thermometers do not give an accurate measurement of body temperature ,9,10. HoIt is possible that parents would have performed better had they leisurely read the instructions in their own home rather than doing so in a hospital-based setting, or had they had time to practice. However, it is also possible that they performed better than they would have in the home, as they knew evaluation of their performance was occurring. It is also possible that parents who would choose to buy a tympanic thermometer will differ from our study population. It is not clear what advice to give to parents about purchasing a thermometer. The ability of parents from the inner city to correctly use and read a mercury glass thermometer was poor in previous studies ,13. An eWith the recent outbreak of Severe Acute Respiratory Syndrome, rapid measurement of body temperature  has become an important tool to indicate if people can board airplanes and if staff can work. It is therefore important to determine the accuracy of non-health care workers at measuring body temperature. This study showed that the temperatures measured by parents with a tympanic thermometer often differ by a clinically significant amount from those measured by a nurse with a tympanic thermometer. There is not a consistent gradient or direction of the gradient between the two temperatures, which makes it difficult to interpret the temperatures reported by parents. There was a smaller gradient between the readings taken by a nurse with a tympanic thermometer designed for home use compared with those taken with a model of tympanic thermometer commonly used in hospitals, but there were still potentially clinically significant discrepancies 14% of the time. This makes it difficult to conclude if the poor performance of the parents relates entirely to human error, or if there is also an element of instrument error. The fact that in comparison with our reference standard  the readings taken with the home thermometer by the nurse correlated much better than those taken by the parent suggests that the parents did not use ideal technique. In any case, one should interpret temperatures taken by parents with a tympanic thermometer with great caution. Although parents will detect the majority of fevers with these instruments, the absolute numbers obtained may not be accurate. Again, we find that in pediatrics, the clinical picture is a more useful piece of information than are "the numbers"!°C – degrees CelsiusPA: pulmonary arteryThe author(s) declare that they have no competing interests.JLR wrote the protocol and the manuscript. HJ helped with patient recruitment and reviewed the manuscript. DWS did the statistical analysis and reviewed the manuscript.The pre-publication history for this paper can be accessed here:


Perineodynia , anal and urinary incontinence are the main symptoms of the pudendal canal syndrome (PCS) or entrapment of the pudendal nerve. The first aim of this study was to evaluate the effect of bilateral pudendal nerve decompression (PND) on the symptoms of the PCS, on three clinical signs  and on two neurophysiological tests: electromyography (EMG) and pudendal nerve terminal motor latencies (PNTML). The second aim was to study the clinical value of the aforementioned clinical signs in the diagnosis of PCS.In this retrospective analysis, the studied sample comprised 74 female patients who underwent a bilateral PND between 1995 and 2002. To accomplish the first aim, the patients sample was compared before and at least one year after surgery by means of descriptive statistics and hypothesis testing. The second aim was achieved by means of a statistical comparison between the patient's group before the operation and a control group of 82 women without any of the following signs: prolapse, anal incontinence, perineodynia, dyschesia and history of pelvi-perineal surgery.When bilateral PND was the only procedure done to treat the symptoms, the cure rates of perineodynia, anal incontinence and urinary incontinence were 8/14, 4/5 and 3/5, respectively. The frequency of the three clinical signs was significantly reduced. There was a significant reduction of anal and perineal PNTML and a significant increase of anal richness on EMG. The Odd Ratio of the three clinical signs in the diagnosis of PCS was 16,97 .This study suggests that bilateral PND can treat perineodynia, anal and urinary incontinence. The three clinical signs of PCS seem to be efficient to suspect this diagnosis. There is a need for further studies to confirm these preliminary results. The objective of perineology is to treat each defect of the perineum with the right procedure -3. PudenBefore going into details of this procedure, it is necessary to remember the anatomy of the pudendal nerve. This anatomy is still controversial.While summarizing the data of the literature and the results of our dissections, the likeliest anatomy of the pudendal nerve presents itself as follows. The pudendal nerve is a mixed nerve carrying motor and sensory fibers. Its fibers are derived from the sacral roots S2, S3 and S4 . Once thThe pudendal canal syndrome (PCS) and its surgical treatment have been described by Shafik in 1991 . This syThe cause of the PCS is not always clear but it is often possible to find a compression  or a stretching  of the pudendal nerve in the Alcock's canal -19 in thThe clinical signs and investigation results proposed by Shafik  to confiThe trans-gluteal approach proposed by Robert to treat pudendal neuralgia aimed to open also the "clamp" between the sacro-spinal and the sacro-tuberous ligament by cutting one or two of them .Since Shafik's study in 1991, some questions about the effect of PND on the PCS remained open. No peer reviewed publications confirming the efficacy of this surgery on anal incontinence or on urinary incontinence could be found. Even the existence of a genuine PCS has never been validated.The aim of this study was to answer the following questions:Is there any effect of the bilateral PND according to Shafik on:- three main symptoms of PCS ?           - perineodynia             - anal incontinence           - urinary incontinence- three clinical signs of PCS ?           - abnormal sensibility           - painful Alcock's canal           - painful "skin rolling test" - two neurophysiological tests ?           - electromyography (EMG) of the anal sphincter and of the bulbocavernosus muscles.           - pudendal nerve terminal motor latencies (PNTML) of the anal and perineal branches.What is the clinical value of the aforementioned three clinical signs in the diagnosis of PCS ?A retrospective analysis to study the effects of a bilateral PND. The studied sample comprised 74 female patients who underwent a bilateral PND between 1995 and 2002 done by the same surgeon. The average age was 56.1 years (range: 28 – 77). All these patients underwent a complete history and clinical examination following the three perineal axis  according to the concept of perineology .The frequency of the 3 main symptoms of the PCS  in the 74 patients before surgery is presented in Figure Associated surgical procedures were performed at the same time as the PND to treat all the defects revealed by the clinical examination, and are presented in Table The following variables were used:For perineodynia, four situations were encountered: no pain, proctalgia, unilateral pain, bilateral pain. The effect of surgery was estimated by the patient using one of the following proposals: cured, improved, unchanged or worsened.For anal incontinence, a four levels ordinal scale was used: no incontinence, gas incontinence, liquid incontinence, solid incontinence. "Cured" was defined as "no incontinence". The patient was considered "improved" if there was a change of at least one level in the scale going from "solid" to "gas" incontinence. The patient was defined as "worsened" if there was a change of at least one level in the opposite direction.For urinary incontinence, a four levels ordinal scale was used: no incontinence, mild incontinence, moderate incontinence and severe incontinence. The two types of urinary incontinence, stress and urge incontinence, were evaluated separately even if both were present in the same patient (mixed incontinence). "Cured" was defined as "no incontinence". The patient was considered "improved" if there was a change of at least one level in the scale going from "severe" to "mild" incontinence. If the change observed was in the opposite direction the patient was considered "worsened".Sensibility was tested with a needle comparing the left and the right sides of the vulva and of the skin 2 cm lateral to the anus. The interpretations of the results were done using a four levels ordinal scale: 0 = total anaesthesia, 1 = reduced sensibility, 2 = normal sensibility, 3 = hypersensibility. 0, 1 and 3 were considered as "abnormal sensibility".The pain induced by the palpation of the pudendal canal by rectal examination was evaluated using a seven levels ordinal scale : 0 = no pain, 1 = mild pain, 2 = mild pain with Tinel sign (irradiation of the pain), 3 = moderate pain, 4 = moderate pain with Tinel sign, 5 = severe pain, 6 = severe pain with Tinel sign. The Alcock's canal was considered "painful" if the pain was 4 or more.Beginning from 5 cm behind the level of anus the skin was pinched and then rolled to the front until the skin fold was at the level of the clitoris. The skin rolling test was considered "painful" if it induced a severe pain at least at one level Figure .Concentric needle EMG was done at rest and during voluntary contraction on both sides of the external anal sphincter and on each bulbocavernosus muscle. The richness of the EMG was grossly evaluated using a six levels scale: 1 = simple, 2 = poor, 3 = intermediate poor, 4 = intermediate, 5 = intermediate rich and 6 = rich.Anal and perineal PNTML were measured before and after the operation using the St Marks electrode to stimulate the pudendal nerve by the rectal route just under the ischial spine. For anal PNTML the electrical potentials induced in the striated anal sphincter were collected using the ring of this electrode. For the perineal PNTML the method described by Kiff  and SnooAt least one of the 3 following symptoms resistant to conservative treatments :a. Anal incontinenceb. Perineodyniac. Urinary incontinenceAssociated with at least two of the five following criteria:a. increased anal or perineal PNTMLb. pathological EMG of the anal sphincter or bulbocavernosus muscles .c. painful Alcock's canal on rectal examination (at least on one side)d. abnormal perineal sensibility (at least at one level)e. painful "skin rolling test" (at least on one side).Surgical procedure as described by Shafik in 1991 . The opeThe different steps of the procedure were:- Vertical incision of the skin between the anus and the ischial tuberosity.- Opening of the ischio-rectal fossa with scissors.- The inferior rectal nerve is hooked under the finger and followed to the entrance of the Alcock's canal Figures  and 4.- Opening of this canal .- Control of the haemostasis.- Self draining closing of the skin with nylon.The efficacy on the symptoms, on the clinical signs and on the neurophysiological tests was evaluated during a follow up consultation one year or more after the surgical procedure because the nerve healing can be very slow .Firstly, the efficiency of the PND on the symptoms and clinical signs was studied by means of descriptive statistics. Tests of hypothesis were done to compare the mean values of the neurophysiological tests before versus after PND.Secondly, the diagnostic value of the clinical signs was evaluated in a "case control" setting. A subject belongs to the "controls group" when PCS is considered to be absent, namely if the patient does not present any of the following symptoms, signs or risk factors for PCS: perineodynia, anal incontinence, prolapse, previous surgery in the area, dyschesia. The clinical signs are not used to decide if a subject belongs to the controls or cases group. The statistical comparison was done between the patient's group before ("cases group") and after the operation, and the "controls group" of 82 women .Statistical analysis of differences was performed using chi-square testing for categorical variables and t-tests for continuous variables.The effect of PND on the symptoms of PCS is presented in Table In order to treat completely the patient, PND was frequently associated with other procedures which might have an effect on the symptom studied. Therefore, the results for each symptom were presented in two columns: the first corresponds to the entire sample  and the second to the small group of patients in which the symptom was treated by PND only ("without").On the 26 patients with pain before the operation, 18 were reviewed 12 months or more after the operation. The pain had disappeared in 11 and was reduced or had another origin  in 3. The cure rate with a mean follow-up of 22,2 months was 61,1 % .As none of the surgical associated procedures used in this study were known to improve or cure perineodynia, the only procedure removed was levatorplasty. Theoretically this operation can reduce the stretching on the pudendal nerves by reducing the sagging of the levator plate. The results were similar in the group without levatorplasty.On the 46 patients with anal incontinence before the operation, 36 were reviewed 12 months or more after the operation. 23 of them were cured, 7 improved, 2 were worse and 4 reported no change. The cure rate with a mean follow-up of 26.4 months was 63.9 % .The results according to the severity of incontinence are presented in Table To study the real impact of PND on anal incontinence, we removed the following cases in which PND was associated with anal sphincteroplasty, levatorplasty or cure of rectocele by fascia and perineal body restoration:- 2 patients had anal sphincteroplasty together with the PND: one was cured and the other improved.- Levatorplasty according to Shafik  was used- 30 cases had a cure of rectocele by fascia and perineal body restoration  and 1 improved (liquid incontinence).Anal ultrasound was done before the operation in 13 of the 36 patients reviewed. Only 4 were normal, 3 showed a rupture of the internal and external sphincters, and 6 presented a disruption of the external sphincter alone.In the 7 patients who had a rupture of the anal sphincter  without anal sphincteroplasty and a follow up of more than 12 months (mean 18.5 months), 4 were cured and 3 were a failure.5 patients who were still incontinent after 1 year follow up (2 incontinences for flatus and 3 for liquid) became continent 2 years after the operation.Five patients presenting urinary incontinence (4 urge and 1 stress incontinence) had PND without any other procedure around the urethra. The mean follow up was 18,5 months for the 4 patients with urge incontinence. In this small group, 3 patients were cured and one was a failure. The patient with stress urinary incontinence was improved (the number of pads used per day was reduced from 9 to 4) one year after surgery.The effect of PND on the three clinical signs is described in Table Because levatorplasty can theoretically reduce the stretching of the pudendal nerve, the evaluation of the effect on the clinical signs has been done for the entire sample  and for the same group without the patients who had a levatorplasty ("without: levat").The cure rate of the 3 clinical signs was between 60 and 70 % depending of the sign and of the type of sample studied.38 patients underwent a complete EMG evaluation before and after surgery. A relevant comparison was possible in 35 patients. 3 patients were excluded because one of the two EMG explorations was insufficient for technical reasons. The average follow up was 16,9 months .Left and right values for one parameter correspond to two different nerves. Therefore, these values were considered independent .The effect of PND on EMG and PNTML is presented in Table The "Anal Richness" on EMG after surgery was significantly higher than before. The mean "Bulbocavernosus Richness" after surgery was slightly higher than before but this difference was not significant. Both anal and perineal PNTML after PND were significantly reduced compared to values before.The box-plots of the 4 studied parameters are presented in Figures We present here the results concerning the evaluation of the three clinical tests: abnormal sensibility, painful Alcock's canal and painful "skin rollling test" as diagnostic tests for PCS.The statistical analysis is based on the following contingency tables presented in Tables The proportions of observations in the "Cases Before Surgery" and "Controls" columns of the contingency table vary significantly from row to row , whereas no significant difference is observed between the proportions of observations between "Cases After Surgery" and "Controls" .Estimated sensibility, specificity, predictive values (positive and negative) and odd ratio  corresponding to each of the three clinical tests and combinations of all of them are presented in Tables The most sensible test is the "Painful Alcock's canal" and the most specific is the "Skin rolling test".Using the three signs altogether, the most sensible combination is "At least 1 positive versus All negative" and the most specific combination is the "All positive versus All negative".During one operation a heavy bleeding coming from the pudendal artery just near the pudendal nerve was very difficult to treat (selective ligature). This patient had a blood transfusion but no long term side effect. Since the operation, one patient has presented sometimes a short lasting clitoridal pain. This patient had also an increase in her anal incontinence (gas incontinence became a liquid incontinence). Three patients had wound healing problems which resolved with simple disinfection.In the literature there is no data available about the prevalence of the PCS. Therefore, it seems to be a rare event. In this study, we evaluated the prevalence of the PCS in an outpatient perineology clinic. By using three different methods during the last 24 months  the estimated prevalence should be around 20%.Before discussing the results of surgery, the first important issue is about the interest of a bilateral decompression. The benefit – risk ratio must be studied. The results of Shafik were obtained after bilateral decompression ,29,30. FThe treatment of pain starts with a holistic approach of the woman  with exclusion of other causes of pain: piriformis syndrome, coccygodynia, interstitial cystitis, endometriosis... The other neurological causes must be excluded by a complete electrophysiological study of the perineum  and imaging of the spinal cord . If the Even with the transgluteal approach where the "clamp" between the sacro-spinal and the sacro-tuberous ligament is opened by sectioning the sacro-spinal ligament, the cure rate remains around 50%. In the 4 cases of proctalgia fugax the results were better (3 cured and 1 improved). Shafik [For Robert early diagnosis appears to be the determining factor in improving results . He usedFor anal incontinence, our results were in the same range as Shafik . In a prMore interesting was the cure rate in the group of patients with a clear rupture of one or the two anal sphincters. The traumatic rupture of the anal sphincter  usually induces an immediate anal incontinence. In the patients who remained continent the power of the broken muscles remain sufficient to avoid flatus or faeces leakage. In the long term the continence is probably maintained with the help of the fibrous tissue located between the two edges of the ruptured muscle which acts like a bridge and therefore enables the sphincter to be efficient during many years. The aging process of the muscle and the pudendal neuropathy reduce the power of the muscle  with time and explain the appearance of an anal incontinence. Therefore it is logical to restore continence by improving the conduction in the pudendal nerve. This fact can also explain why the results of sphincteroplasty decrease with time especially in the non diagnosed or treated pudendal neuropathies .The fact that 5 patients were cured from their anal incontinence only 2 years after surgery emphasized the importance of a long follow up period to obtain relevant cure rates. Surprisingly, the cure rate seems to be not dependant of the degree of anal incontinence but the number of solid incontinences  was too small to validate this impression.The results of the pudendal nerve decompression seem to be equivalent to these of neuromodulation  and the For urinary incontinence the number of cases is too small to give a relevant cure rate but there were enough cases to suggest that this surgery can treat some patients with stress or urge incontinence.In a previous study, 3 of the 7 patients presenting a stress urinary incontinence were cured by bilateral pudendal nerve decompression alone ,37.In Shafik's study 6 patients were cured from their stress urinary incontinence, 5 improved and one was a failure . For thiThis study is the first one dealing with a possible effect of the pudendal nerve decompression on urge incontinence. It is probably due to a better control of the urethral sphincter which can reduce urethral instability  and imprOne weakness of this study is the rough evaluation of the symptoms. We did not use any scoring system, pad test, quality of life questionnaires or "visual analog pain scale". Furthermore the number of anal and urethro-vesical manometries done before and after PND was too small to give relevant results.The objective evaluation of PND was done using two neurophysiological tests and the clinical examination. Like Shafik ,30 we foShafik described many clinical signs of the PCS ,29,30. ICompared to patients with negative clinical signs, those having positive clinical signs have a 4,42 ; 5,52 and 6,56 higher likelihood of PCS for "Abnormal sensibility", "Painful Alcock's canal" and "Painful skin rolling test", respectively Table . When paThe most specific sign was the "Painful skin rolling test" and the most sensitive was the "Painful Alcock's canal". The association of the three positive tests had a very high specificity in the diagnosis of a PCS (89 %). This high specificity was confirmed by the low frequency of this association after the operation (return to the same level as the control group).Therefore, in some cases the clinical examination should be sufficient to prove the existence of a PCS. For example, a patient presenting anal incontinence, an intact sphincter proven by ultrasound and the three clinical signs positive has almost certainly a PCS. Of course, from a scientific point of view it is still interesting to perform a complete electrophysiological study and a precise neurological examination to exclude a central problem  or a polyneuropathy.However, making the diagnosis of PCS is not usually an easy task. Many times, there is a high degree of suspicion but, as in many illness, all the symptoms or signs are not present. In this study, we decided to operate when at least two of the five clinical and neurophysiological signs described in the methods section were associated with one or more of the 3 classical symptoms . At the beginning of this study, it was usually "increased PNTML" and "painful Alcock's canal". With the introduction of the "skin rolling test" and of the "sensibility test", clinical examination became more important in the decision. The more symptoms  and signs were present, the more confident we were in the diagnosis of PCS. Further studies are necessary to validate this and to define more precisely the minimal criteria needed for the PCS diagnosis.The pudendal nerve decompression by the perineal route is a blind procedure. The search for the inferior rectal nerve and the opening of the Alcock's canal are done under finger control. In our experience it is not easier with retractors. Therefore it is necessary to have a clear anatomical vision of this area before performing the operation.Maybe the use of a laparoscope would help  but the Despite the blind character of the procedure we only had one heavy bleeding probably coming from the pudendal artery. One patient still presents with a mild intermittent clitoridal pain and a worsening of anal incontinence. Because the nerve of the clitoris leaves the pudendal nerve just before the entrance into the Alcock's canal this problem is probably the result of a too large dissection in the upper part of this canal. The two cases of anal incontinence worsening (gas incontinence becoming liquid incontinence), including the aforementioned patient, are difficult to explain. Maybe the neuropathy increased with the stretching involved in the procedure, the scarring process or a too large dissection. It could also be the result of the changes in the posterior level anatomy induced by concomitant procedures (easier expulsion of gas or faeces). For the 2 patients the EMG data and the clinical examination after the operation did not improve therefore showing that the neuropathy was not healing.Because the roughly estimate prevalence of PCS is around 20%, this "defect" seems to be a very frequent problem in Perineology. Therefore it should be logical to search for it in each clinical examination of a patient presenting with prolapse, perineodynia, urinary or anal incontinence.Pudendal neuropathy is probably a frequent "defect" in perineology. Pudendal nerve decompression seems to be the defect specific procedure indicated in such a problem. In fact it can treat perineodynia, anal and probably urinary incontinence. Anal incontinence can be cured by pudendal nerve decompression alone even in the presence of a clear disruption of the anal sphincter on anal ultrasound. Anal richness on EMG increases and PNTML decrease significantly after surgery proving an objective effect on the nerve. The frequency of abnormal puncture sensibility, painful Alcock's canal and painful "skin rolling test" are significantly reduced by the operation. This study suggests that the three clinical tests could be used in practice to confirm or suspect the diagnosis of pudendal neuropathy in case of pain, urinary and/or anal incontinence. However, further studies are necessary to confirm these preliminary results.PCS = pudendal canal syndromePND = pudendal nerve decompressionEMG = electromyographyPNTML = pudendal nerve terminal motor latencyThe authors declare that they have no competing interests.JB conceived the study, carried out surgery and clinical follow up and drafted the manuscript.DC participated in the design of the study and performed the statistical analysis.MB carried out the neurophysiological examinations.All authors read and approved the final manuscript.The pre-publication history for this paper can be accessed here:


A finite difference scheme for integrating the Takagi–Taupin equations inside a slab-shaped crystal is demonstrated and tested. Calculating dynamical diffraction patterns for X-ray diffraction imaging techniques requires numerical integration of the Takagi–Taupin equations. This is usually performed with a simple, second-order finite difference scheme on a sheared computational grid in which two of the axes are aligned with the wavevectors of the incident and scattered beams. This dictates, especially at low scattering angles, an oblique grid of uneven step sizes. Here a finite difference scheme is presented that carries out this integration in slab-shaped samples on an arbitrary orthogonal grid by implicitly utilizing Fourier interpolation. The scheme achieves the expected second-order convergence and a similar error to the traditional approach for similarly dense grids. One often tries to avoid these dynamical effects [even if occasionally they are the subject of interest , Li et al.  materials.Ideally, one should be able to straightforwardly integrate the TTEs on an orthogonal grid that requires no intermediate interpolation step. In the kinematical case  grid in real space. In full period frequency, this corresponds to the pointsAs we are using discrete Fourier transforms we also specify a grid in  close to the path of the direct beam. Plots of the displacement field as well as the amplitudes of the converged solution are shown in Fig. 2y direction with the dimensions 50 × 115 µm at a point 1 µm from the dislocation core. The incident beam is a narrow Gaussian of width σ = 0.2 µm, with parameters chosen corresponding to the (111) reflection of a diamond crystal with a molybdenum source, given as: i is the imaginary unit. We set k = 8.85 Å−1 and x = 0.2 µm.The fields are simulated under low absorption and highly dynamical conditions, and we simulated only a single slice in the In order to accommodate the comparison with existing methods, we utilized a grid with step sizes a), the traditional half-step method does not show the expected second-order convergence with the edge dislocation sample (b). The first-order exponential Euler method suffers from an exponential instability and only gives a qualitatively correct result when impractically small step sizes are utilized.Fig. 3a) shows the convergence of the screw-dislocation test case at a rocking angle of c), 4d) show that the transmitted beam is approximately undisturbed by the crystal and that the beam is only significantly scattered in small areas close to the surface and the dislocation. Fig. 4b) shows the profile of the scattered beam at the exit surface as a function of rocking angle. We see that at low angles, the scattering is clearly dynamical and the profile shows Pendellösung fringes. At higher angles, the bulk of the crystal scatters less strongly and the scattering pattern is dominated by the defects. Because the divergence of the incident radiation is larger than the characteristic ‘Darwin width’ of dynamical diffraction, the crystal approximately acts as an analyser, and maps out the angular spectrum of the incident beam, which is further illustrated in Fig. 4e).To demonstrate that our method is not limited only to the exact Bragg condition, we also test the convergence of our method at the tails of the rocking curve. Fig. 46.We have described and demonstrated a finite difference scheme capable of integrating the TTEs on an orthogonal grid with few restrictions on the choice of grid. We achieve this by implicitly utilizing Fourier interpolation at the level of the individual finite difference step. The method results in approximately the same error as the traditional half-step finite difference scheme.The method utilizes FFTs (fast Fourier transforms) at each step and has to perform in total four 2D Fourier transforms of the entire sample volume (the Heun method makes two evaluations of the The ability to freely choose the computational grid makes implementation of this approach easier, especially when it needs to be combined with other numerical modelling methods, for example if the input for either the crystal microstructure or the incident field is given by a numerical simulation, or if the scattered fields should be propagated through image-forming optics.Click here for additional data file.10.1107/S2053273322004934/iv5022sup1.exePython3 implementation of the described algorithm. DOI: