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The generation of personalised and patient-specific musculoskeletal models is currently a cumbersome and time-consuming task that normally requires several processing hours and trained operators. We believe that this aspect discourages the use of computational models even when appropriate data are available and personalised biomechanical analysis would be beneficial. In this paper we present a computational tool that enables the fully automatic generation of skeletal models of the lower limb from three-dimensional bone geometries, normally obtained by segmentation of medical images. This tool was evaluated against four manually created lower limb models finding remarkable agreement in the computed joint parameters, well within human operator repeatability. The coordinate systems origins were identified with maximum differences between 0.5 mm (hip joint) and 5.9 mm (subtalar joint), while the joint axes presented discrepancies between 1° (knee joint) to 11° (subtalar joint). To prove the robustness of the methodology, the models were built from four datasets including both genders, anatomies ranging from juvenile to elderly and bone geometries reconstructed from high-quality computed tomography as well as lower-quality magnetic resonance imaging scans. The entire workflow, implemented in MATLAB scripting language, executed in seconds and required no operator intervention, creating lower extremity models ready to use for kinematic and kinetic analysis or as baselines for more advanced musculoskeletal modelling approaches, of which we provide some practical examples. We auspicate that this technical advancement, together with upcoming progress in medical image segmentation techniques, will promote the use of personalised models in larger-scale studies than those hitherto undertaken.

Place: England; International audience; Patient-specific finite element models (PSFEM) are becoming more and more used. Different methods for assigning their material properties were studied on PSFEMs of 9 tibias along with the minimal required length of the CT acquisition window. Material properties are generally attributed to the PSFEM using relationships linking the grayscale of CT scans to the elasticity moduli. Using cortical-specific and trabecular-specific relationships or a generic one, did not result in significant differences. However, the use of homogeneous elastic moduli in the cortical and trabecular regions led to considerable differences. The result highlight that the PSFEM must comprise at least 40% of the tibia to ensure consistent results in the proximal 20%.

At advanced knee osteoarthritis (OA) stages subchondral trabecular bone (STB) is altered. Lower limb alignment plays a role in OA progression and modify the macroscopic loading of the medial and lateral condyles of the tibial plateau. How the properties of the STB relate to alignment and OA stage is not well defined. OA stage (KL scores 2–4) and alignment (HKA from 17° Varus to 8° Valgus) of 30 patients were measured and their tibial plateau were collected after total knee arthroplasty. STB tissue elastic modulus, bone volume fraction (BV/TV) and trabecula thickness (Tb.Th) were evaluated with nanoindentation and µCT scans (8.1 µm voxel-size) of medial and lateral samples of each plateau. HKA and KL scores were statistically significantly associated with STB elastic modulus, BV/TV and Tb.Th. Medial to lateral BV/TV ratio correlated with HKA angle (R = −0.53, p = 0.016), revealing a higher ratio for varus than valgus subjects. STB properties showed lower values for KL stage 4 patients. Tissue elastic modulus ratios and BV.TV ratios were strongly correlated (R = 0.81, p

International audience

International audience; Increasing use of patient-specific surgical procedures in orthopaedics means that patient-specific anatomical coordinate systems (ACSs) need to be determined. For knee bones, automatic algorithms constructing ACSs exist and are assumed to be more reliable than manual methods, although both approaches are based on non-unique numerical reconstructions of true bone geometries. Furthermore, determining the best algorithms is difficult, as algorithms are evaluated on different datasets. Thus, in this study, we developed 3 algorithms, each with 3 variants, and compared them with 5 from the literature on a dataset comprising 24 lower-limb CT-scans. To evaluate algorithms’ sensitivity to the operator-dependent reconstruction procedure, the tibia, patella and femur of each CT-scan were each reconstructed once by three different operators.Our algorithms use principal inertia axis (PIA), cross-sectional area, surface normal orientations and curvature data to identify the bone region underneath articular surfaces (ASs). Then geometric primitives are fitted to ASs, and the ACSs are constructed from the geometric primitive points and/or axes. For each bone type, the algorithm displaying the least inter-operator variability is identified. The best femur algorithm fits a cylinder to posterior condyle ASs and a sphere to the femoral head, average axis deviations: 0.12°, position differences: 0.20 mm. The best patella algorithm identifies the AS PIAs, average axis deviations: 0.91°, position differences: 0.19 mm. The best tibia algorithm finds the ankle AS center and the 1st PIA of a layer around a plane fitted to condyle ASs, average axis deviations: 0.38°, position differences: 0.27 mm.

International audience; Obst SJ, Renault JB, Newsham-West R, Barrett RS. Three-dimensional deformation and transverse rotation of the human free Achilles tendon in vivo during isometric plantarflexion contraction.Freehand three-dimensional ultrasound (3DUS) was used to investigate longitudinal and biaxial transverse deformation and rotation of the free Achilles tendon in vivo during a voluntary submaximal isometric muscle contraction. Participants (n 8) were scanned at rest and during a 70% maximal voluntary isometric contraction (MVIC) of the plantarflexors. Ultra-sound images were manually digitized to render a 3D reconstruction of the free Achilles tendon for the computation of tendon length, volume, cross-sectional area (CSA), mediolateral diameter (MLD), anteroposterior diameter (APD), and transverse rotation. Tendon longitudinal and transverse (CSA, APD, and MLD) deformation and strain at 70% MVIC were calculated relative to the resting condition. There was a significant main effect of contraction on tendon length and mean CSA, MLD, and APD (P 0.05), but no effect on tendon volume (P 0.70). Group mean transverse strains for CSA, MLD, and APD averaged over the length of the tendon were 5.5%, 8.7% and 8.7%, respectively. Peak CSA, MLD, and APD transverse strains all occurred between 40% and 60% of tendon length. Transverse rotation of the free tendon was negligible at rest but increased under load, becoming externally rotated relative to the calcaneal insertion. The relationship between longitudinal and transverse strains of the free Achilles tendon during muscle-induced elongation may be indicative of interfascicle reorganization. The finding that transverse rotation and strain peaked in midportion of the free Achilles tendon may have important implications for tendon injury mechanisms and estimation of tendon stress in vivo. 3D ultrasound; diameter; cross-sectional area; rotation; tendon TWO-DIMENSIONAL ULTRASONOGRAPHY (2DUS) is an established tool for investigating human Achilles tendon morphology in vivo and can be used to quantify adaptations in response to ageing (55, 67), tendinopathy (11, 29, 31), neurological conditions (14, 30, 78), and exercise (57, 59). While 2DUS has advanced our understanding of Achilles tendon structure and function in vivo there are a number of inherent limitations for measuring tendon length, thickness, diameter, and cross-sectional area (CSA). Measurements are typically limited to single transverse or sagittal plane images acquired at predefined locations and, therefore, do not provide a three-dimensional (3D) representation of tendon morphology or account for error when structures or landmarks of interest move out of the image plane (19, 29). The image plane is also highly sensitive to probe position and orientation which can be difficult to control. Finally, the narrow field of view of a conventional ultrasound probe prevents simultaneous visualization of key anatomical structures of interest, such as the muscle-and osteotendinous junctions (29, 40). These limitations may be overcome using 3D ultrasound (3DUS), which combines conventional 2DUS imaging with 3D motion capture in order to generate 3D reconstructions of in vivo anatomical structures in a fixed coordinate system (71). 3DUS-based measures of lower limb muscle morphology have been validated in vivo against MRI (15, 44) and in vitro using cadaveric hand muscle (23). 3DUS has been shown to provide accurate measures of volume and length compared with objects or "phantoms" with known dimensions (15, 26, 58, 63), valid and repeatable measurements of intratendinous lesion volumes in equine flexor tendons (26), and repeatable measures of human Achilles tendon volume, length, and average cross-sectional area (CSA) in vivo at rest and during a submaximal isometric plantarflexion contraction [intraclass correlation coefficients (ICCs) 0.99] (58). Although 3DUS is limited to evaluating tendon morphology under static loading conditions, the ability to quantify the 3D morphology of the Achilles tendon at rest and during muscle contraction has a number of potential benefits. First, it would lead to improved characterization of tendon morphology by capturing the variation in transverse dimensions along the length of the tendon. Such information may be useful for identifying differences between individuals and monitoring tendon adaptation. Second, the ability to measure changes in minimum or average Achilles tendon CSA during tensile loading would enable estimation of "true" tendon stress and lead to more valid estimation of material properties including Young's modulus and Poisson's ratio in vivo (22, 73). Third, measuring the contribution of tendon diametral deformation to the overall change in CSA under load could have important implications for our understanding of tendon mechanobiology. The elliptical shape of the Achilles tendon may result in nonuniform transverse deformation during tensile loading that would vary along the length of tendon and provide evidence of regional tendon anisotropy in vivo. Regional variation in tendon deformation may create areas of increased stress and compression within the Achilles tendon affecting intratendi-nous fluid flow and increasing the risk of injury in these areas (4, 7, 62, 66). While there is evidence that isolated tendon fibers and fascicles reorganize and rotate under tensile load creating increased intratendinous compression (18, 33, 39), it is not known whether changes at the microstructural level translate to a measurable change in morphology at the organ level. Because tendon cells are sensitive to both tensile and compres-sive forces, evidence of regional deformation and potential stress concentration within the free Achilles tendon, will have direct impact on our understanding of tendon loading during Address for reprint requests and other correspondence: S. J. Obst

Between repression and freedom : the trembling of meaning, the “ multi-layered meaning” and his (an) architecture (especially in “ The third meaning”). We have first to examine the relation between Roland Barthes and the plural sense, whose striking feature is the often desperate quest of an elsewhere of meaning, a below or beyond the ordinary symbolic, to pull out the richness of his study on the “ quivering” of meaning from the impasses where his various utopias or dystopias of the sense lead him. The notion of connotation is questioned as particularly representative of the theoretical difficulties. Then, in a second time, we propose a reinterpretation of the article “ The third meaning” that seeks to untangle the various oppositions that complicate as much as they specify the distinction between the “ obvious” meaning and the “ obtuse”. The architecture of the meaning in Eisenstein’s movies is finely grasped then, especially through the idea of a multi-layered meaning, of a dialectic which includes a non-negating irony., Il s’agit d’abord d’interroger le rapport de Roland Barthes au sens pluriel, marqué par la quête souvent désespérée d’un ailleurs du sens, d’un en deçà ou d’un au-delà du symbolique ordinaire, pour dégager la richesse de son interrogation sur le «tremblé » de la signification des impasses où le mènent ses différentes utopies ou dystopies du sens. La notion de connotation est ainsi interrogée comme particulièrement représentative des difficultés théoriques. Puis, dans un second temps, une relecture est proposée de l’article «Le troisième sens » qui s’efforce de démêler les différentes oppositions qui compliquent autant qu’elles spécifient la distinction entre le sens obvie et le sens obtus. L’architecture du sens dans les films d’Eisenstein apparaît alors très finement cernée, notamment à travers l’idée d’un sens feuilleté, d’une dialectique qui accueille une ironie non négatrice., Tussen repressie en bevrijding : het trillen van betekenis, de «veelgelaagde betekenis » en haar (an) architectuur (in het bijzonder in «Le troisième sens » ). Eerst wordt de relatie tussen Roland Barthes en het meervoud onderzocht, met als als opvallend kenmerk de vaak hopeloze zoektocht naar een betekenis voorbije het alledaagse symbolische. Hierdoor wordt de rijkdom duidelijk van Barthes’ onderzoek naar de ‘ trilling’ van betekenis. Het begrip ‘ connotatie’ blijkt representatief te zijn voor de theoretische moeilijkheden van dit onderzoek. Vervolgens stellen we een nieuwe interpretatie voor Barthes’ artikel «Le troisième sens » , waarin we het onderscheid tussen «le sens obvie » en «le sens obtus » proberen te ontwarren. Dit alles laat toe om de «architectuur van betekenis » in de films van Eisenstein te vatten, in het bijzonder door de idee van een «veelgelaagde » betekenis, een dialectiek die een nietontkennende ironie omvat., Renault Jean-Baptiste. Entre répression et libération : le frisson de sens, le « sens feuilleté » et son (an)architecture. In: Revue belge de philologie et d'histoire, tome 94, fasc. 3, 2016. Langues et littératures modernes – Moderne Taal- en Letterkunde. pp. 647-659.

International audience

International audience