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See detail3D shape of asteroid (6)~Hebe from VLT/SPHERE imaging: Implications for the origin of ordinary H chondrites
Marsset, M.; Carry, B.; Dumas, C. et al

E-print/Working paper (2017)

Context. The high-angular-resolution capability of the new-generation ground-based adaptive-optics camera SPHERE at ESO VLT allows us to assess, for the very first time, the cratering record of medium ... [more ▼]

Context. The high-angular-resolution capability of the new-generation ground-based adaptive-optics camera SPHERE at ESO VLT allows us to assess, for the very first time, the cratering record of medium-sized (D~100-200 km) asteroids from the ground, opening the prospect of a new era of investigation of the asteroid belt's collisional history. Aims. We investigate here the collisional history of asteroid (6) Hebe and challenge the idea that Hebe may be the parent body of ordinary H chondrites, the most common type of meteorites found on Earth (~34% of the falls). Methods. We observed Hebe with SPHERE as part of the science verification of the instrument. Combined with earlier adaptive-optics images and optical light curves, we model the spin and three-dimensional (3D) shape of Hebe and check the consistency of the derived model against available stellar occultations and thermal measurements. Results. Our 3D shape model fits the images with sub-pixel residuals and the light curves to 0.02 mag. The rotation period (7.274 47 h), spin (343 deg,+47 deg), and volume-equivalent diameter (193 +/- 6km) are consistent with previous determinations and thermophysical modeling. Hebe's inferred density is 3.48 +/- 0.64 g.cm-3 , in agreement with an intact interior based on its H-chondrite composition. Using the 3D shape model to derive the volume of the largest depression (likely impact crater), it appears that the latter is significantly smaller than the total volume of close-by S-type H-chondrite-like asteroid families. Conclusions. Our results imply that (6) Hebe is not the most likely source of H chondrites. Over the coming years, our team will collect similar high-precision shape measurements with VLT/SPHERE for ~40 asteroids covering the main compositional classes, thus providing an unprecedented dataset to investigate the origin and collisional evolution of the asteroid belt. [less ▲]

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See detailGaia Data Release 1. Open cluster astrometry: performance, limitations, and future prospects
Gaia Collaboration, ; van Leeuwen, F.; Vallenari, A. et al

in Astronomy and Astrophysics (2017), 601

Context. The first Gaia Data Release contains the Tycho-Gaia Astrometric Solution (TGAS). This is a subset of about 2 million stars for which, besides the position and photometry, the proper motion and ... [more ▼]

Context. The first Gaia Data Release contains the Tycho-Gaia Astrometric Solution (TGAS). This is a subset of about 2 million stars for which, besides the position and photometry, the proper motion and parallax are calculated using Hipparcos and Tycho-2 positions in 1991.25 as prior information. <BR /> Aims: We investigate the scientific potential and limitations of the TGAS component by means of the astrometric data for open clusters. <BR /> Methods: Mean cluster parallax and proper motion values are derived taking into account the error correlations within the astrometric solutions for individual stars, an estimate of the internal velocity dispersion in the cluster, and, where relevant, the effects of the depth of the cluster along the line of sight. Internal consistency of the TGAS data is assessed. <BR /> Results: Values given for standard uncertainties are still inaccurate and may lead to unrealistic unit-weight standard deviations of least squares solutions for cluster parameters. Reconstructed mean cluster parallax and proper motion values are generally in very good agreement with earlier Hipparcos-based determination, although the Gaia mean parallax for the Pleiades is a significant exception. We have no current explanation for that discrepancy. Most clusters are observed to extend to nearly 15 pc from the cluster centre, and it will be up to future Gaia releases to establish whether those potential cluster-member stars are still dynamically bound to the clusters. <BR /> Conclusions: The Gaia DR1 provides the means to examine open clusters far beyond their more easily visible cores, and can provide membership assessments based on proper motions and parallaxes. A combined HR diagram shows the same features as observed before using the Hipparcos data, with clearly increased luminosities for older A and F dwarfs. Tables D.1 to D.19 are also available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/601/A19">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/601/A19</A> [less ▲]

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See detailHow unique is Plaskett's star? A search for organized magnetic fields in short period, interacting or post-interaction massive binary systems★
Nazé, Yaël ULg; Neiner, Coralie; Grunhut, Jason et al

in Monthly Notices of the Royal Astronomical Society (2017), 467

Amongst O-type stars with detected magnetic fields, the fast rotator in the close binary called Plaskett's star shows a variety of unusual properties. Since strong binary interactions are believed to have ... [more ▼]

Amongst O-type stars with detected magnetic fields, the fast rotator in the close binary called Plaskett's star shows a variety of unusual properties. Since strong binary interactions are believed to have occurred in this system, one may wonder about their potential role in generating magnetic fields. Stokes V spectra collected with the low-resolution FORS2 and high-resolution ESPaDOnS and Narval spectropolarimeters were therefore used to search for magnetic fields in 15 interacting or post-interaction massive binaries. No magnetic field was detected in any of them, with 0 G always being within 2σ of the derived values. For 17 out of 25 stars in the systems observed at high resolution, the 90 per cent upper limit on the individual dipolar fields is below the dipolar field strength of Plaskett's secondary; a similar result is found for five out of six systems observed at low resolution. If our sample is considered to form a group of stars sharing similar magnetic properties, a global statistical analysis results in a stringent upper limit of ∼200 G on the dipolar field strength. Moreover, the magnetic incidence rate in the full sample of interacting or post-interaction systems (our targets + Plaskett's star) is compatible with that measured from large surveys, showing that they are not significantly different from the general O-star population. These results suggest that binary interactions play no systematic role in the magnetism of such massive systems. [less ▲]

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See detailFirst constraints on the magnetic field strength in extra-Galactic stars: FORS2 observations of Of?p stars in the Magellanic Clouds
Bagnulo, S.; Nazé, Yaël ULg; Howarth, I. D. et al

in Astronomy and Astrophysics (2017), 601(A136), 10

Massive O-type stars play a dominant role in our Universe, but many of their properties remain poorly constrained. In the last decade magnetic fields have been detected in all Galactic members of the ... [more ▼]

Massive O-type stars play a dominant role in our Universe, but many of their properties remain poorly constrained. In the last decade magnetic fields have been detected in all Galactic members of the distinctive Of?p class, opening the door to a better knowledge of all O-type stars. With the aim of extending the study of magnetic massive stars to nearby galaxies, to better understand the role of metallicity in the formation of their magnetic fields and magnetospheres, and to broaden our knowledge of the role of magnetic fields in massive star evolution, we carried out spectropolarimetry of five extra-Galactic Of?p stars, and of a couple of dozen neighbouring stars. We were able to measure magnetic fields with typical error bars from 0.2 to 1.0 kG, depending on the apparent magnitude and on weather conditions. No magnetic field was firmly detected in any of our measurements, but we were able to estimate upper limits on the field values of our target stars. One of our targets, 2dFS 936, exhibited an unexpected strengthening of emission lines. We confirm the unusual behaviour of BI 57, which exhibits a 787 d period with two photometric peaks and one spectroscopic maximum. The observed strengthening of the emission lines of 2dFS 936, and the lack of detection of a strong magnetic field in a star with such strong emission lines is at odd with expectations. Together with the unusual periodic behaviour of BI 57, it represents a challenge for the current models of Of?p stars. The limited precision that we obtained in our field measurements (in most cases as a consequence of poor weather) has led to field-strength upper limits that are substantially larger than those typically measured in Galactic magnetic O stars. Further higher precision observations and monitoring are clearly required. [less ▲]

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See detailThe 67P/Churyumov-Gerasimenko observation campaign in support of the Rosetta mission
Snodgrass, C.; A'Hearn, M. F.; Aceituno, F. et al

in Philosophical Transactions of the Royal Society of London Series A (2017), 375

We present a summary of the campaign of remote observations that supported the European Space Agency's Rosetta mission. Telescopes across the globe (and in space) followed comet 67P/Churyumov-Gerasimenko ... [more ▼]

We present a summary of the campaign of remote observations that supported the European Space Agency's Rosetta mission. Telescopes across the globe (and in space) followed comet 67P/Churyumov-Gerasimenko from before Rosetta's arrival until nearly the end of the mission in September 2016. These provided essential data for mission planning, large-scale context information for the coma and tails beyond the spacecraft and a way to directly compare 67P with other comets. The observations revealed 67P to be a relatively `well-behaved' comet, typical of Jupiter family comets and with activity patterns that repeat from orbit to orbit. Comparison between this large collection of telescopic observations and the in situ results from Rosetta will allow us to better understand comet coma chemistry and structure. This work is just beginning as the mission ends-in this paper, we present a summary of the ground-based observations and early results, and point to many questions that will be addressed in future studies. This article is part of the themed issue 'Cometary science after Rosetta'. [less ▲]

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See detailThe Spitzer search for the transits of HARPS low-mass planets. II. Null results for 19 planets
Gillon, Michaël ULg; Demory, B.-O.; Lovis, C. et al

in Astronomy and Astrophysics (2017), 601

Short-period super-Earths and Neptunes are now known to be very frequent around solar-type stars. Improving our understanding of these mysterious planets requires the detection of a significant sample of ... [more ▼]

Short-period super-Earths and Neptunes are now known to be very frequent around solar-type stars. Improving our understanding of these mysterious planets requires the detection of a significant sample of objects suitable for detailed characterization. Searching for the transits of the low-mass planets detected by Doppler surveys is a straightforward way to achieve this goal. Indeed, Doppler surveys target the most nearby main-sequence stars, they regularly detect close-in low-mass planets with significant transit probability, and their radial velocity data constrain strongly the ephemeris of possible transits. In this context, we initiated in 2010 an ambitious Spitzer multi-Cycle transit search project that targeted 25 low-mass planets detected by radial velocity, focusing mainly on the shortest-period planets detected by the HARPS spectrograph. We report here null results for 19 targets of the project. For 16 planets out of 19, a transiting configuration is strongly disfavored or firmly rejected by our data for most planetary compositions. We derive a posterior probability of 83% that none of the probed 19 planets transits (for a prior probability of 22%), which still leaves a significant probability of 17% that at least one of them does transit. Globally, our Spitzer project revealed or confirmed transits for three of its 25 targeted planets, and discarded or disfavored the transiting nature of 20 of them. Our light curves demonstrate for Warm Spitzer excellent photometric precisions: for 14 targets out of 19, we were able to reach standard deviations that were better than 50 ppm per 30 min intervals. Combined with its Earth-trailing orbit, which makes it capable of pointing any star in the sky and to monitor it continuously for days, this work confirms Spitzer as an optimal instrument to detect sub-mmag-deep transits on the bright nearby stars targeted by Doppler surveys. The photometric and radial velocity time series used in this work are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/601/A117">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/601/A117</A> [less ▲]

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See detailPeculiar architectures for the WASP-53 and WASP-81 planet-hosting systems★
Triaud, Amaury H. M. J.; Neveu-VanMalle, Marion; Lendl, Monika et al

in Monthly Notices of the Royal Astronomical Society (2017), 467

We report the detection of two new systems containing transiting planets. Both were identified by WASP as worthy transiting planet candidates. Radial velocity observations quickly verified that the ... [more ▼]

We report the detection of two new systems containing transiting planets. Both were identified by WASP as worthy transiting planet candidates. Radial velocity observations quickly verified that the photometric signals were indeed produced by two transiting hot Jupiters. Our observations also show the presence of additional Doppler signals. In addition to short-period hot Jupiters, we find that the WASP-53 and WASP-81 systems also host brown dwarfs, on fairly eccentric orbits with semimajor axes of a few astronomical units. WASP-53c is over 16 M[SUB]Jup[/SUB]sin i[SUB]c[/SUB] and WASP-81c is 57 M[SUB]Jup[/SUB]sin i[SUB]c[/SUB]. The presence of these tight, massive companions restricts theories of how the inner planets were assembled. We propose two alternative interpretations: the formation of the hot Jupiters within the snow line or the late dynamical arrival of the brown dwarfs after disc dispersal. We also attempted to measure the Rossiter-McLaughlin effect for both hot Jupiters. In the case of WASP-81b, we fail to detect a signal. For WASP-53b, we find that the planet is aligned with respect to the stellar spin axis. In addition we explore the prospect of transit-timing variations, and of using Gaia's astrometry to measure the true masses of both brown dwarfs and also their relative inclination with respect to the inner transiting hot Jupiters. [less ▲]

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See detailAnesthesia Case of the Month
Tutunaru, Alexandru-Cosmin ULg; Sandersen, Charlotte ULg

in Journal of the American Veterinary Medical Association [=JAVMA] (2017), 250(9), 984-987

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See detailAn Optical and Infrared Photometric Study of the Young Open Cluster IC 1805 in the Giant H ii Region W4 †
Sung, Hwankyung; Bessell, Michael S.; Chun, Moo-Young et al

in Astrophysical Journal Supplement Series (2017), 230

We present deep wide-field optical CCD photometry and mid-infrared Spitzer/IRAC and MIPS 24 μm data for about 100,000 stars in the young open cluster IC 1805. The members of IC 1805 were selected from ... [more ▼]

We present deep wide-field optical CCD photometry and mid-infrared Spitzer/IRAC and MIPS 24 μm data for about 100,000 stars in the young open cluster IC 1805. The members of IC 1805 were selected from their location in the various color–color and color–magnitude diagrams, and the presence of Hα emission, mid-infrared excess emission, and X-ray emission. The reddening law toward IC 1805 is nearly normal (R [SUB] V [/SUB] = 3.05 ± 0.06). However, the distance modulus of the cluster is estimated to be 11.9 ± 0.2 mag (d=2.4+/- 0.2 kpc) from the reddening-free color–magnitude diagrams, which is larger than the distance to the nearby massive star-forming region W3(OH) measured from the radio VLBA astrometry. We also determined the age of IC 1805 ({τ }[SUB]{MSTO[/SUB]}=3.5 Myr). In addition, we critically compared the age and mass scale from two pre-main-sequence evolution models. The initial mass function with a Salpeter-type slope of Γ = ‑1.3 ± 0.2 was obtained and the total mass of IC 1805 was estimated to be about 2700 ± 200 {M}[SUB]ȯ [/SUB]. Finally, we found our distance determination to be statistically consistent with the Tycho-Gaia Astrometric Solution Data Release 1, within the errors. The proper motion of the B-type stars shows an elongated distribution along the Galactic plane, which could be explained by some of the B-type stars being formed in small clouds dispersed by previous episodes of star formation or supernova explosions. The optical imaging data in this article were gathered with two facilities: the AZT-22 1.5 m telescope at Maidanak Astronomical Observatory in Uzbekistan and the Canada–France–Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. [less ▲]

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See detailMulti-phase volcanic resurfacing at Loki Patera on Io
de Kleer, K.; Skrutskie, M.; Leisenring, J. et al

in Nature (La) (2017), 545

The Jovian moon Io hosts the most powerful persistently active volcano in the Solar System, Loki Patera. The interior of this volcanic, caldera-like feature is composed of a warm, dark floor covering 21 ... [more ▼]

The Jovian moon Io hosts the most powerful persistently active volcano in the Solar System, Loki Patera. The interior of this volcanic, caldera-like feature is composed of a warm, dark floor covering 21,500 square kilometres surrounding a much cooler central ‘island’. The temperature gradient seen across areas of the patera indicates a systematic resurfacing process, which has been seen to occur typically every one to three years since the 1980s. Analysis of past data has indicated that the resurfacing progressed around the patera in an anti-clockwise direction at a rate of one to two kilometres per day, and that it is caused either by episodic eruptions that emplace voluminous lava flows or by a cyclically overturning lava lake contained within the patera. However, spacecraft and telescope observations have been unable to map the emission from the entire patera floor at sufficient spatial resolution to establish the physical processes at play. Here we report temperature and lava cooling age maps of the entire patera floor at a spatial sampling of about two kilometres, derived from ground-based interferometric imaging of thermal emission from Loki Patera obtained on 8 March 2015 UT as the limb of Europa occulted Io. Our results indicate that Loki Patera is resurfaced by a multi-phase process in which two waves propagate and converge around the central island. The different velocities and start times of the waves indicate a non-uniformity in the lava gas content and/or crust bulk density across the patera. [less ▲]

See detailGC×GC-(HR)TOFMS : Why we Love it !
Focant, Jean-François ULg

Scientific conference (2017, May)

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See detailGérer le changement: une dynamique multidimensionnelle et participative
Lisein, Olivier ULg

Scientific conference (2017, May)

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See detailWork environment and work-to-family conflict: Mediating role of work investment.
Babic, Audrey ULg; Stinglhamber, Florence; Barbier, Marie ULg et al

Conference (2017, May)

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See detailEffect of changing size and composition of a crop model ensemble on impact and adaptation response surfaces
A., Rodríguez; R., Ferrise; M., Ruiz-Ramos et al

in Book of Abstracts - MACSUR2017 Scientific Conference (2017, May)

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See detailProbabilistic assessment of adaptation options from an ensemble of crop models: a case study in the Mediterranean"
R., Ferrise; M., Ruiz-Ramos; A., Rodríguez et al

in Book of Abstracts - MACSUR2017 Scientific Conference (2017, May)

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See detailTesting a general approach to assess the degree of disturbance in tropical forests
Sellan, Giacomo; Simini, Filippo; Maritan, Amos et al

in Journal of Vegetation Science (2017), 28(3), 459668

Questions: Is there any theoretical model enabling predictions of the optimal tree size distribution in tropical communities? Can we use such a theoretical framework for quantifying the degree of ... [more ▼]

Questions: Is there any theoretical model enabling predictions of the optimal tree size distribution in tropical communities? Can we use such a theoretical framework for quantifying the degree of disturbance? Location: Reserve of Yangambi, northeast region of the Democratic Republic of Congo. Methods: We applied an allometricmodel based on the assumption that a vir- tually undisturbed forest uses all available resources. In this condition, the forest structure (e.g. the tree size distribution) is theoretically predictable fromthe scal- ing of the tree crown with tree height at an individual level. The degree of dis- turbance can be assessed through comparing the slopes of the tree size distribution curves in the observed and predicted conditions. We tested this tool in forest stands subjected to different degrees of disturbance. We inventoried trees >1.3 m in height by measuring the DBH in three plots of 1 ha each, and measured tree height, crownradius and crownlength in a sub-sample of trees. Results: All tree species, independently of the site, shared the same exponents of allometric relationships: tree height vs tree diameter, crown radius vs tree height, crown length vs tree height and consequently crown volume vs tree height, suggesting that similar trajectories of biomass allocation have evolved irrespective of species. The observed tree size distributions appeared to be power laws (excluding the finite size effect) and, as predicted, the slope was steeper in the less disturbed forest (?2.34) compared to the most disturbed (?1.99). The difference in the slope compared to the theoretical fully functional forest (?2.65) represents the metric for assessing the degree of disturbance. Conclusions: We developed a simple tool for operationalizing the concept of ‘disturbance’ in tropical forests. This approach is species-independent, needs minimal theoretical assumptions, the measurement of only a few structural traits and requires a low investment in equipment, time and computer skills. Its simple implementation opens new perspectives for effectively addressing initiatives of forest protection and/or restoration. [less ▲]

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See detailIsokinetic profil of subjects with proximal patellar tendinopathy
Croisier, Jean-Louis ULg; Roberjot, Mathieu; DELVAUX, François ULg et al

in The Future of Football Medicine (2017, May)

Introduction: Proximal patellar tendinopathy is relatively common among sportsmen, even among football players who do repetitive shooting sessions. However, the strength profile of subjects with proximal ... [more ▼]

Introduction: Proximal patellar tendinopathy is relatively common among sportsmen, even among football players who do repetitive shooting sessions. However, the strength profile of subjects with proximal patellar tendinopathies is rarely described and the isokinetic profile remains unknown. Purpose: We aimed to determine the strength profile of subjects suffering from this frequently recurrent pathology. Methods: Forty-three players (29,1±8.5 y.o.; 78.1±11.9kg; 179.3±7.2cm) with chronic proximal patellar tendinopathy confirmed by ultrasounds were recruited. Quadriceps and hamstrings muscular performances of the healthy and pathological side were measured using an isokinetic dynamometer (Cybex Norm) at the concentric speed of 60°/s (C60) and 240°/s (C240) and at the eccentric speed of 30°/s (E30 - only for hamstrings). A visual analogic scale of pain (VAS) has also been used after each isokinetic test in order to associate the level of complaints and the intensity of contractions. Results: The results (Table 1) for the isokinetic tests comparing the healthy (HS) to the pathological side (PS) are significant for the different conditions of contraction and test speeds, as for the results of the VAS associated to those tests (p<0.01). Indeed, pathological limbs had a maximum peak torque for the quadriceps at C60 and at C240 lower than healthy limbs (2.17 ± 0.68 N.m/kg vs 2.47 ± 0.55 N.m/kg, p = 0.0003 and 1.46 ± 0.42 N.m/kg vs. 1.56 ± 0.31 N.m/kg, p = 0.02, respectively); this represents a bilateral difference of 14% for C60 and 7% in C240. In E30, pathological limbs were also weaker than the healthy limbs (2.46 ± 0.91 N.m/kg vs 2.79 ± 0.96 N.m/kg, p = 0.0008) which represents a difference of 13% between healthy and pathological limbs. For the hamstrings of the pathological limbs, we observed a maximum peak torque at C60 and C240 lower than for the hamstrings of the healthy limbs (1.26 ± 0.37 N.m/kg vs. 1.37 ± 0.36 N.m/kg, p = 0.006 and 0.80 ± 0.23 N.m/kg vs 0.85 ± 0.20 N.m/kg, p = 0.04). The bilateral differences of hamstring strength were 8.7% in C60 and 6% in C240. The PS were more painful than the HS (VAS C60: 3.47 ± 2.65 vs 0.20 ± 1.05; p>0.01; VAS C240: 2.83 ± 2.47 vs. 0.68 ± 0.10; p>0.01; VAS E30: 5,26 ± 2.78 vs 0.58 ± 1.93; p>0.01). The difference of pain can be seen especially in eccentric mode. This observation suggest that isokinetic tests, beyond the measure of strength, could represent a pain provocation test, even with a possible pronostic value for the efficacy of treatment. Conclusions: In our study, the isokinetic results of patients with proximal patellar tendinopathy showed a significant difference in strength profile between the HS and the PS as well as VAS associated with each tests. However, the diversity of outcomes recorded in our population suggests that an individualized rehabilitation treatment is probably more relevant than a common protocol for the healing of this tendon pathology. Isokinetic tests can also represent a tool for assessment of treatment planning. Finally, it would seem that isokinetic tests in the eccentric mode on the quadriceps can be a pain assessment tool for the pathological tendon. [less ▲]

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See detailHow to manage a case of ischial tuberosity avulsion fracture?
Tyberghein, Maëlle; Kaux, Jean-François ULg; GODON, Bernard ULg et al

in The Future of Football Medicine (2017, May)

Introduction Apophyseal avulsion fractures of the pelvis are common among teenage football player. Usually, they are the result of a sudden forceful concentric or eccentric contraction of the muscle ... [more ▼]

Introduction Apophyseal avulsion fractures of the pelvis are common among teenage football player. Usually, they are the result of a sudden forceful concentric or eccentric contraction of the muscle attached to the apophysis. Indeed, before ossification, the apophyseal growth cartilage is the weakest point in the musculotendinous unit, making the apophysis vulnerable to injure. Athletes most commonly affected are soccer players when they tackle or shot powerful at goal and gymnasts during floor exercises which imposed sudden and excessive lengthening. Management of these fractures remains unclear. There are no guidelines between conservative and surgical approach even if most publications recommend a surgery if the diastasis exceeds 2cm and a conservative approach on the other hand. Case report A sixteen-year-old high-level player presented at the consultation with right ischial pain. Three months earlier, while he was sprinting, he had felt acute pain opposite the ischial tuberosity which compelled him to stop the training. He had already consulted another physician, who prescribed an X-ray which revealed an avulsion fracture of the ischial tuberosity with a maximal diastasis of 1.9 cm (Fig 1.a.). According to most publications (1,3), surgery is advisable from 2 cm of diastasis. 1.9 cm was within the range between a surgical and a conservative approach, and the conservative one was applied. An isokinetic assessment was planned. It highlighted hamstring strength imbalances with bilateral difference of 31% in concentric strength and 28% in eccentric strength in comparison with the healthy side. The mixed ratio of the hamstrings in eccentric mode at 30°/s to quadriceps in concentric mode at 240°/s was decreased to 0.8, while the lower limit in our clinical practice corresponded to 0.9. The patient was not allowed to resume competition and a rehabilitation by specific and progressive strengthening in both modes of contraction was initiated; in particular the eccentric training was initially submaximal and progressively intensified. Six weeks later, isokinetic assessment was repeated and showed significant improvement of right hamstring strength, particularly for eccentric contraction. The greatest improvement was the mixed Hecc/Qconc ratio wich had increased from 0.8 to 1.44. In regard to radiology, we observed no change since the previous X-Ray (Fig 1.b.). Intensified training on the field was allowed in order to resume competition. Less than one year after the injury, the patient restarted competition successfully with performance levels which were almost the same as before the injury. Discussion Many publications have discussed the surgical versus the conservative approach to treating ischiatic avulsion. Most of the published literature advocate the relevance of surgery when the diastasis exceeds 2 cm because widely displaced fractures may lead to chronic symptomatology if the treatment remains conservative. Different criteria, such as pain relief, ability to perform in sport, gross strength, activity score, X-Rays, are used by authors to demonstrate the recovery after treatment. No study accurately measured the hamstring strength before and after treatment. However, strength imbalance, especially as regards the H/Q mixed ratio, significantly increases the risk of sustaining hamstring injury in soccer player (2). For our patient, the rehabilitation enabled him to re-establish hamstring strength in six weeks with substantial improvement of eccentric assessment. The mixed Hecc/Qconc ratio increased from 0.8 to 1.44. This improvement significantly decreased the risk of recurrence of hamstring injury. Regarding X-Ray imagery, there was no evidence of healing. We advocate that radiological assessment should not be the main recovery criterion and that specific strengthening should be started even when avulsion persists on the X-Ray. Furthermore, hamstring strength should be measured accurately and objectively, e.g. by isokinetism, to be one of the main return to play criterion in association with clinical data. [less ▲]

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