Institut de Biomécanique Humaine Georges Charpak

Level III, therapeutic study.

Lower limbs can play a major compensating role for sagittal malalignment; however, little is known about the different types of compensation. This study aimed to identify different patterns of lower limb compensation and to determine which parameters may affect the recruitment of knee flexion versus hip extension. This study included adult spinal deformity (ASD) patients with full-body X-rays in erect position from a multicentric prospective database. All parameters were measured at baseline: demographics, clinical scores and radiographic parameters: pelvic parameters, pelvic incidence-lumbar lordosis (PI-LL) mismatch, T1 pelvic angle (TPA), sacro-femoral angle (SFA), knee flexion angle (KA), ankle dorsi-flexion angle (AA), pelvic shift (PSh), hip and knee osteoarthritis (OA) grade.A K-means cluster analysis was conducted to identify patterns of lower limb compensation based on SFA and KA. The optimal number of clusters was determined using the silhouette score. The different parameters were then compared across clusters. 871 ASD patients were included, of whom 66.9% were females. Mean age was 62.3±14.6 years, mean BMI was 27.7±5.5 kg.m-2. Four patterns of lower limb compensations were identified: "No compensators", "Recliners" (mainly hip extension), "Squatters" (mainly knee flexion) and "Mixed compensators" (both)."Mixed" and "Squatters" had significantly larger BMI. The proportion of females was the least in the "Squatters" cluster (47.0%) while it was the highest in the "Recliners" group (79.3%) (p<0.001). The proportion of patients with severe hip OA was the lowest in the "Recliners" (38.5%) while it was the highest in the "Squatters" group (71.9%). Knee OA rate was the highest in the"Squatters" group (72.7%). "Mixed compensators" had the greatest PI-LL mismatch (30.4±20.0°) and "No compensators" the lowest (5.3±21.3°). Pelvic incidence values were the highest in "Recliners" and "Mixed compensators" (59.2±13.1° and 57.0±14.1° respectively). TPA values were the highest in the "Mixed compensators" and the lowest in the "No compensators" (33.3±11.7° versus 16.1±11.5°). The "Squatters" presented the significantly poorest values for disability, frailty, and SRS score. Cluster analysis determined four types of lower limb compensation:"Recliners" using only hip extension, "Squatters" using only knee flexion,"Mixed compensators" and "No compensators". Lower limb compensatory mechanisms recruitment is multifactorial and varies with age, sex, BMI, frailty, knee and hip OA, pelvic incidence, and spinal alignment.

Modeling of fasciae remains limited, despite their recognized role in chronic pain. Developing a comprehensive mechanical model of fasciae could significantly enhance our understanding of their pain-related mechanisms and improve their prevention. This paper presents a computational approach capable of simulating the mechanical behavior of fibrous tissues based on their mesostructure. The thoracolumbar fascia was selected as a case study due to the availability of its experimentally derived mechanical properties in the literature. A discrete element model was developed, representing collagen fibers as bilinear springs and the proteoglycan matrix as elastic beams. The model was subjected to uniaxial tensile tests across various parameter sets defining fiber threshold distributions. Four test configurations were implemented to evaluate key aspects of the model: the influence of fiber properties, validation against experimental data, anisotropic response, and the role of inter-fiber contact. The simulations revealed a broad range of hyperelastic behaviors resulting from subtle variations in fiber properties, suggesting potential adaptability across different fascia types. The numerical outcomes closely matched experimental results, despite the absence of a precise microstructural description of the tested samples. The model demonstrated anisotropic behavior aligned with the preferential fiber orientations, as expected in fibrous tissues. Additionally, contact interactions produced internal force reactions and localized stress within the sample. Overall, the proposed model successfully reproduced experimental tensile behavior while offering valuable insights into local mechanical responses and anisotropy, contributing to a better understanding of fascia mechanics and their potential role in chronic pain. Significance statement Growing evidence links chronic low back pain to altered mechanical properties of the thoracolumbar fascia. As fascia mechanics emerges from its fibrous mesostructure, elucidating this relationship is crucial. Yet, no existing numerical models directly derive macroscopic mechanical behavior from mesoscale structural organization. We developed a discrete element model that predicts the thoracolumbar fascia's mechanical response from its mesostructural architecture. Validated against previous experimental tensile data, the model accurately reproduced the fascia's elastic behavior. By quantitatively bridging mesostructure and mechanical response within the elastic range, this work provides a numerical framework to explore how fascial architecture governs the tissue mechanical properties which contribute to pain mechanisms.

Abstract Introduction Improving emergency protocols during space missions is a topic of current interest with the upcoming long-lasting missions and the advent of space tourism (1–3). In the unique environment of spaceflight, cardiac arrest is a particularly challenging emergency as both the rescuer and the patient are floating due to microgravity, thus requiring the development of specific positions to provide efficient chest compression during cardiopulmonary resuscitation (CPR). As recommended by international guidelines (4), the Hand-Stand method is the current gold standard CPR method since it achieves the best compression depth and rate (5) but necessitates specific training to be accurately performed. Here, we postulated that automatic chest compression devices (ACCDs) routinely used on Earth by physicians facing cardiac arrests, particularly in hostile environments or during refractory (i.e. sustained) cardiac arrests(6-8), could improve CPR in microgravity. We aimed to compare ACCDs versus manual CPR in weightlessness simulated through parabolic flights. Methods This prospective, open, controlled study compared CPR performed by 3 ACCDs (one standard mechanical piston device, one compression band device, and one small-sized piston device) to manual CPR during a CNES (Centre National d’Etudes Spatiales, the French space agency) parabolic flights campaign onboard a modified A310 aircraft turned into a flying laboratory. This setup could re-create accurate microgravity, during the free falling phases of parabolic flight. Chest compression depths and rates were monitored by a high fidelity CPR training manikin. Results (presented as median [IQR]) The standard piston device had a median compression depth of 53.0 [53.0 - 54.0] mm, significantly higher than the other two devices, and than Manual CPR (Handstand method), measured at 29.0 [26.0 - 32.0] mm, 29.0 [27.5 - 30.7] mm and 34.5 [29.6 - 43.3] mm, respectively (p value &amp;lt;0.001). Compression rates were 101 [101 - 101], 100 [100 - 100] and 80 [80 - 80] compressions per minute (cpm) for the standard piston device, compression band device, and small sized piston device, respectively. Manual CPR provided a significantly higher compression rate with 115 [109 - 123] cpm (p value &amp;lt;0.001). Conclusion Manual CPR remains undereffective under Zero Gravity and ACCDs, especially the standard piston device (i.e., the only experimental group reproducing CPR matching with international guidelines), should be considered in emergency procedures to manage cardiac arrest in microgravity. Other keystones of cardiac arrest management should also be translated to the spaceflight environment, such as early defibrillation or emergency drug administration if required (epinephrine), as these are already described in the NASA emergency protocols for the International Space Station.Visual abstract

The thoracolumbar fascia (TLF) and the erector spinae aponeurosis (ESA) play an important role in the biomechanics of the spine and could be a source of low back pain. Although the TLF and ESA are key structures in several musculoskeletal dysfunctions and in tissue engineering, there is still a lack of evidence in the literature to prove that they have different mechanical properties and roles when considered as a single tissue. Furthermore, no methods are currently available to study these structures in vivo. The objective of this study was to analyze the ex-vivo tensile properties TLF and ESA, and to test the potential of ultrasound shearwave elastography (SWE) to characterize these tissues. Hundred samples from N=10 fresh-frozen human donors were studied. Shear wave speed (SWS) was measured in all samples with SWE, and their tensile properties were measured with mechanical testing. Results show that TLF is anisotropic, and more compliant than ESA. SWS was not significantly correlated to tensile moduli. These findings could potentially aid surgeons in their daily practices, assist engineers with in silico simulations, and support physiotherapists in musculoskeletal rehabilitation by enabling them to customize medical interventions for each specific patient and clinical condition. However, further research is necessary to further investigate the behavior in terms of time-dependent response and link between the tissue anisotropy and microstructural organization.