nils-herrmann/clean_scirepeval huggingface dataset:
On the modeling of human intervertebral disc annulus fibrosus: Elastic, permanent deformation and failure responses.
Venue: Journal of biomechanics

As a primary load-resisting component, annulus fibrosus (AF) maintains structural integrity of the entire intervertebral disc. Experiments have demonstrated that permanent deformation and damage take place in the tissue under mechanical loads. Development of an accurate model to capture the complex behaviour of AF tissue is hence crucial in disc model studies. We, therefore, aimed to develop a non-homogenous model to capture elastic, inelastic and failure responses of the AF tissue and the entire disc model under axial load. Our model estimations satisfactorily agreed with results of existing uniaxial (along fiber, circumferential and axial directions) and biaxial tissue-level tests. The model accurately predicted the failure of the tissue in various directions in uniaxial extension. Collagen fiber content, type and orientation substantially altered AF tissue responses in uni- and bi-axial tests. Although collagen fiber content and type mostly affected failure stress, fiber orientation significantly influenced the tissue failure strain. The entire L2-L3 disc model accurately replicated load-displacement as well as loading-unloading responses of the disc under compression-tension forces. Preconditioning of the disc-body unit substantially stiffened response. Poisson's ratio of both AF and nucleus considerably affected compression-displacement responses of the disc (173% increase in compression at 1.49 mm displacement when it was changed from 0.499 to 0.49999). Any AF constitutive model should be calibrated under various tissue-level loads and directions as well as the entire disc model responses since using a single tissue-level loading (e.g. uniaxial) for calibration can lead to unrealistic responses in other tests (e.g., biaxial). Special attentions should be given to the choice of Poisson's ratio and the realistic consideration of preconditioning load.
An inverse model of the mechanical response of passive skeletal muscle: Implications for microstructure.
Venue: Journal of biomechanics

The constitutive response of passive skeletal muscle is important for many human body modelling applications, but modelling the tension-compression asymmetry and the anisotropy observed in ex-vivo samples is challenging. Existing microstructural models do not capture the full three-dimensional response while models suitable for application in finite element environments mostly have a limited microstructural basis and cannot capture the observed Poisson's ratios. The aim of this paper is to derive an inverse model based on the microstructure of a skeletal muscle that can predict its passive mechanical response. The model parameters and predictions were derived and assessed by comparison with published experimental stress-strain response and Poisson's ratio data. Results show a close match for both predicted stress-strain response for fibre and cross-fibre direction deformations and similar Poisson's ratio values. Some microstructural observations which strengthen our understanding of the role of the collagen network and intramuscular pressure are also provided.
A novel test reliably captures hip and knee kinematics and kinetics during unanticipated/anticipated diagonal hops in individuals with anterior cruciate ligament reconstruction.
Venue: Journal of biomechanics

Unanticipated land-and-cut maneuvers might emulate lower limb mechanics associated with anterior cruciate ligament (ACL) injury. Reliability studies on landing mechanics of such maneuvers are however lacking. This study investigated feasibility and within-session reliability of landing mechanics of a novel one-leg double-hop test, mimicking a land-and-cut maneuver, in individuals with ACL reconstruction (ACLR). Our test comprised a forward hop followed by a diagonal hop in either of two directions (medial/lateral) under anticipated and unanticipated conditions. Twenty individuals with a unilateral ACLR (aged 24.2 ± 4.2 years, 0.7-10.8 years post-surgery) performed three successful hops/direction per leg. We determined reliability (intraclass correlation coefficient [ICC]) and agreement (standard error of measurement [SEM]) of 3-dimensional hip and knee angles and moments during the deceleration phase of the land-and-cut maneuver (vulnerable for non-contact ACL injuries). Mean success rate for unanticipated hops was 71-77% and for anticipated hops 91-95%. Both limbs demonstrated moderate-excellent reliability (ICC 95% confidence intervals: 0.50-0.99) for almost all hip and knee peak angles and moments in all planes and conditions, with a few exceptions: poor-good reliability for hip and knee frontal and/or transverse plane variables, especially for lateral diagonal hops. The SEMs were ≤5° and ≤0.23 N·m/kg·m for most peak angles and moments, respectively. Our test seems feasible and showed satisfactory reliability for most hip and knee angles and moments; however, low knee abduction and internal rotation angles and moments, and moderate reliability of these moments deserve consideration. The test appears to challenge dynamic knee control and may prove valuable in evaluation during knee rehabilitation.
Effects of a passive back exoskeleton on the mechanical loading of the low-back during symmetric lifting.
Venue: Journal of biomechanics

Low-back pain is the number one cause of disability in the world, with mechanical loading as one of the major risk factors. Exoskeletons have been introduced in the workplace to reduce low back loading. During static forward bending, exoskeletons have been shown to reduce back muscle activity by 10% to 40%. However, effects during dynamic lifting are not well documented. Relative support of the exoskeleton might be smaller in lifting compared to static bending due to higher peak loads. In addition, exoskeletons might also result in changes in lifting behavior, which in turn could affect low back loading. The present study investigated the effect of a passive exoskeleton on peak compression forces, moments, muscle activity and kinematics during symmetric lifting. Two types (LOW and HIGH) of the device, which generate peak support moments at large and moderate flexion angles, respectively, were tested during lifts from knee and ankle height from a near and far horizontal position, with a load of 10 kg. Both types of the trunk exoskeleton tested here reduced the peak L5S1 compression force by around 5-10% for lifts from the FAR position from both KNEE and ANKLE height. Subjects did adjust their lifting style when wearing the device with a 17% reduced peak trunk angular velocity and 5 degrees increased lumbar flexion, especially during ANKLE height lifts. In conclusion, the exoskeleton had a minor and varying effect on the peak L5S1 compression force with only significant differences in the FAR lifts.
The effects of -80 °C short-term storage on the mechanical response of tricuspid valve leaflets.
Venue: Journal of biomechanics

Mechanical testing of soft tissues would ideally rely on using fresh specimens. In the event that fresh tissues are not readily available, alternative measures, such as storing fresh specimens at -80 °C, could be considered. Previous studies have shown that changes in the mechanical properties of the tissues due to freezing could be tissue-dependent. Prior to our study, however, such information was not available for the tricuspid valve leaflets. As such, for the first time, we examined whether fresh porcine specimens tested in a biaxial tensile machine would offer comparable results after being frozen at -80 °C. The stress-strain response of the tricuspid valve leaflets displayed no major deviation of the post-frozen leaflets as compared to fresh leaflets. We further compared the radial and circumferential strains as an indicator of deformation at similar stress states in fresh and thawed tissues, and we did not find any significant differences. Ice formation within the extra cellular matrix may modify the collagen fiber configuration, resulting in a slight change in the mechanical response. Nevertheless, our results indicated such a small deviation was negligible, thus enabling the possibility of using frozen porcine tricuspid valve specimens for future research.
Knee joint stiffness following immobilization and remobilization: A study in the rat model.
Venue: Journal of biomechanics

Deficits in extension can limit the function and performance of the knee joint. The range of motion (ROM) deficit in knee extension is often measured and reported at a single torque value applied in the flexion-extension axis. This static measurement of ROM omits key details about the biomechanical properties of the knee, such as its mechanical stiffness. Our objectives were (1) to quantify knee extension stiffness after various periods of immobilization and remobilization, and (2) to evaluate how stiffness correlated with the length of the posterior knee capsule. Two hundred fifty-six male Sprague Dawley rats had one knee immobilized at a 45° angle in flexion using a Delrin® plate for 6 different durations ranging from 1 to 32 weeks. Remobilization was initiated by removing the plate and lasted for 0-48 weeks. The contralateral knee and unoperated age-matched rats were used as controls. An automated arthrometer extended the knee at four pre-determined torques and these data were used to calculate mechanical stiffness. The stiffness of knees immobilized for 8 or more weeks was significantly greater than controls and persisted despite remobilization (p < 0.05). Remobilization after 16 and 32 weeks of immobilization resulted in a progressive increase in mechanical stiffness (p < 0.05). The length of the posterior capsule significantly correlated with knee stiffness in extension (p < 0.05). Deficit in knee extension was characterized by increased stiffness, which was irreversible upon unassisted remobilization.
Comparison of three kinematic gait event detection methods during overground and treadmill walking for individuals post stroke.
Venue: Journal of biomechanics

Detecting gait events using ground reaction forces (i.e. kinetic detection) is the gold standard, but it is not always possible. Kinematic methods exist; however, accuracy of these methods in stroke survivors during treadmill and overground walking is unknown. Thus, this study compared the accuracy of three kinematic methods during overground and treadmill walking in stroke survivors. Heel strike and toe off were calculated bilaterally using three kinematic methods (horizontal sacral-heel distance, horizontal ankle-heel distance, and horizontal velocity) and a kinetic method for ten stroke survivors. We calculated true and absolute error for each kinematic method relative to the kinetic method to evaluate accuracy. Repeated-measures ANOVAs compared the absolute error between the different methods for each condition. There was a significant effect of method for all conditions except heel strike during treadmill walking. Post hoc tests showed ankle-heel distance detected heel strike with significantly less error than the other methods during overground walking (p < 0.05). Ankle-heel distance identified 93.0% and 77.8% of gait events within 50 ms of the kinetic event for overground and treadmill walking, respectively. Sacral-heel distance detected toe-off with significantly less error than the other methods during overground and treadmill walking (p < 0.05) and identified 87.2% and 90.3% of gait events within 50 ms of the kinetic event for overground and treadmill walking, respectively. Results suggest that ankle-heel distance and sacral-heel distance accurately detect heel strike and toe-off, respectively, in stroke survivors.
3D printed clamps improve spine specimen fixation in biomechanical testing.
Venue: Journal of biomechanics

This study presents an anatomically customizable fixation technique for biomechanical spine experiments using a 3D printed clamping system. The aim of this study is to evaluate the feasibility and compare the fixation rigidity of the novel technique to PMMA potting with and without screw augmentation. For this purpose, 16 thoracic and lumbar functional spine units of bovine, porcine, ovine and human cadavers (4 each) were consecutively fixed with all three techniques and loaded in six degrees of freedom. The combined relative movement between the cranial and caudal vertebral body and their corresponding fixtures were recorded using a 3D motion capture system. The 3D printed clamps did provide multiple advantages, showed no failures and the fixation rigidity was superior to potting in all loading directions and superior to screw-augmented potting in two of six loading directions (p < 0.05). In conclusion, the here proposed novel fixation method showed equal to superior properties in comparison to both other methods used in this study. When considering all characteristics of 3D printing, 3D printed fixtures can be an effective alternative to potting.
In silico approaches to respiratory nasal flows: A review.
Venue: Journal of biomechanics

The engineering discipline of in silico fluid dynamics delivers quantitative information on airflow behaviour in the nasal regions with unprecedented detail, often beyond the reach of traditional experiments. The ability to provide visualisation and analysis of flow properties such as velocity and pressure fields, as well as wall shear stress, dynamically during the respiratory cycle may give significant insight to clinicians. Yet, there remains ongoing challenges to advance the state-of-the-art further, including for example the lack of comprehensive CFD modelling on varied cohorts of patients. The present article embodies a review of previous and current in silico approaches to simulating nasal airflows. The review discusses specific modelling techniques required to accommodate physiologically- and clinically-relevant findings. It also provides a critical summary of the reported results in the literature followed by an outlook on the challenges and topics anticipated to drive research into the future.
The association between periacetabular osteotomy reorientation and hip joint reaction forces in two subgroups of acetabular dysplasia.
Venue: Journal of biomechanics

Acetabular dysplasia is primarily characterized by an altered acetabular geometry that results in deficient coverage of the femoral head, and is a known cause of hip osteoarthritis. Periacetabular osteotomy (PAO) is a surgical reorientation of the acetabulum to normalize coverage, yet its effect on joint loading is unknown. Our objective was to establish how PAO, simulated with a musculoskeletal model and probabilistic analysis, alters hip joint reaction forces (JRF) in two representative patients of two different acetabular dysplasia subgroups: anterolateral and posterolateral coverage deficiencies. PAO reorientation was simulated within the musculoskeletal model by adding three surgical degrees of freedom to the acetabulum relative to the pelvis (acetabular adduction, acetabular extension, medial translation of the hip joint center). Monte Carlo simulations were performed to generate 2000 unique PAO reorientations for each patient; from which 99% confidence bounds and sensitivity factors were calculated to assess the influence of input variability (PAO reorientation) on output (hip JRF) during gait. Our results indicate that reorientation of the acetabulum alters the lines of action of the hip musculature. Specifically, as the hip joint center was medialized, the moment arm of the hip abductor muscles was increased, which in turn increased the mechanical force-generating capacity of these muscles and decreased joint loading. Independent of subgroup, hip JRF was most sensitive to hip joint center medialization. Results from this study improve understanding of how PAO reorientation affects muscle function differently dependent upon acetabular dysplasia subgrouping and can be used to inform more targeted surgical interventions.
Sensitivity of the knee joint response, muscle forces and stability to variations in gait kinematics-kinetics.
Venue: Journal of biomechanics

Sensitivity analysis of the knee joint response to variations in gait kinematics-kinetics as reported in the literature is crucial for improved understanding and more effective prevention-treatment strategies. Using our validated finite element-musculoskeletal (FE-MS) model of lower extremity, we investigate the sensitivity of knee anterior cruciate ligament (ACL), muscle, and contact forces plus stability to the reported scatter in asymptomatic gait data. Three highly loaded stance instants (25, 50 and 75%) with five levels (mean, ±0.5SD and ±SD) for each of six knee joint angles-moments are used employing Taguchi approach (25 experiments) and regression equations. ACL force drops significantly at larger flexion angles (all periods) and smaller internal moment (at 75% only) but increases with the flexion moment. Tibiofemoral (TF) medial-lateral contact force partitioning is found, contrary to the common claim, most sensitive to changes in the adduction angle and not in the adduction moment. Total TF contact force increases significantly at greater moments (but not angles), especially in the sagittal plane. Forces in lateral hamstrings are significantly influenced by changes in adduction angles-moments. Larger flexion moments (at 25 and 50%) significantly increase forces in quadriceps and on patellofemoral (PF) contact. Sagittal moment, adduction moment (at 75%) and flexion angle (at 25%) contribute most to the joint stability. A strong inverse correlation exists between the joint stability and the total TF compression force. These findings can be exploited to adapt and modify intact, injured and reconstructed knee joint responses during gait.
An ex vivo technique for quantifying mouse lung injury using ultrasound surface wave elastography.
Venue: Journal of biomechanics

Idiopathic pulmonary fibrosis is a progressively fatal disease with limited treatments. The bleomycin mouse model is often used to simulate the disease process in laboratory studies. The aim of this study was to develop an ex vivo technique for assessing mice lung injury using lung ultrasound surface wave elastography (LUSWE) in the bleomycin mouse model. The surface wave speeds were measured at three frequencies of 100, 200, and 300 Hz for mice lungs from control, mild, and severe groups. The results showed significant differences in the lung surface wave speeds, pulse oximetry, and compliance between control mice and mice with severe pulmonary fibrosis. LUSWE is an evolving technique for evaluating lung stiffness and may be useful for assessing pulmonary fibrosis in the bleomycin mouse model.
Validating diverse human body models against side impact tests with post-mortem human subjects.
Venue: Journal of biomechanics

This study aimed at evaluating the ability of morphed finite element (FE) human body models (HBMs) to reproduce the impact responses of post-mortem human subjects (PMHS) with various stature and shape. Ten side impact tests previously performed using seven PMHS under 3 m/s and 8 m/s impact velocities were selected for model evaluation. With weight, stature, sex, and age of PMHS, seven FE HBMs were developed by morphing the midsize male THUMS model into the target geometries predicted by the statistical skeleton and external body shape models. The model-predicted force histories, accelerations along the spine, and deflections in the chest and abdomen were compared to the test data. For comparison, simulations in all testing conditions were also conducted with the original midsize male THUMS, and the results from the THUMS simulations were scaled to the weight and stature from each PMHS. The CORrelation and Analysis (CORA) was used to evaluate the model accuracy, with CORA scores close to one indicating excellent agreement. Ten simulations using the morphed models exhibited 0.80 ± 0.01, 0.80 ± 0.01, 0.78 ± 0.02, and 0.78 ± 0.02 CORA scores for the impact forces to the thorax, abdomen, iliac-wings, and greater-trochanter, respectively; the corresponding CORA scores with the original THUMS were markedly lower at 0.60 ± 0.06, 0.69 ± 0.05, 0.71 ± 0.05, and 0.69 ± 0.04; while those for the scaled THUMS were 0.65 ± 0.05, 0.71 ± 0.05, 0.73 ± 0.05, and 0.72 ± 0.02, also lower than the morphed models. Across all simulations, the morphed HBMs demonstrated significantly higher accuracy than the THUMS with or without scaling. These results suggested the necessity of accounting for size and shape effects on predicting human responses in side impacts.
A patient-specific cerebral blood flow model.
Venue: Journal of biomechanics

In clinical practice, many complex choices in treatment of complex cerebrovascular diseases have to be made. A patient-specific mathematical blood flow could aid these decisions. For certain cases, less accuracy is required and more simplistic models might be feasible. The current study is aiming to validate a patient-specific simplistic blood flow model in 20 healthy subjects. All subjects underwent MRI and Noninvasive Optimal Vessel Analysis (NOVA) to obtain patient-specific vascular morphology and flow measurements of all major cerebral arteries for validation. The mathematical model used was based on the Hagen-Poiseuille equations. Proximal boundary conditions were patient-specific blood pressure cuff measurements. For distal boundary conditions, a structured tree and a simple autoregulatory model were applied. Autoregulatory parameters were optimized based on the data of 10 additional healthy subjects. A median percentual flow difference of -3% (interquartile range -36% to 17%) was found. Regression analysis to an identity line resulted in R2 values of 0.71 for absolute flow values. Bland-Altman plots showed a bias (levels of agreement) of 5% (-70 to 80%) for absolute flow. Based on these results the model proved to be accurate within a range that might be feasible for use in clinic. Major limitations to the model arise from the simplifications made compared to the actual physiological situation and limitations in the validation method. As the model is validated in healthy subjects only, further validation in actual patients is needed.
Age-associated changes in the mechanical properties of human cadaveric pelvic floor muscles.
Venue: Journal of biomechanics

Proper function of the female pelvic floor requires intact pelvic floor muscles (PFMs). The prevalence of pelvic floor disorders (PFDs) increases substantially with age, in part due to clinically identified deterioration of PFM function with age. However, the etiology of this decline remains largely unknown. We previously demonstrated that PFMs undergo age-related fibrotic changes. This study sought to determine whether aging also impacts PFMs' passive mechanical properties that are largely determined by the intramuscular extracellular matrix. Biopsies from younger (≤52y) and older (>52y) female cadaveric donors were procured from PFMs, specifically coccygeus (C) and two portions of the levator ani - iliococcygeus (IC) and pubovisceralis (PV), and the appendicular muscles - obturator internus (OI) and vastus lateralis (VL). Muscle bundles were subjected to a passive loading protocol, and stress-sarcomere length (Ls) relationships calculated. Muscle stiffness was compared between groups using 2-way ANOVA and Sidak pairwise comparisons, α < 0.05. The mean age was 43.4 ± 11.6y and 74.9 ± 11.9y in younger (N = 5) and older (N = 10) donors, respectively. In all PFMs, the quadratic coefficient of parabolic regression of the stress-Ls curve, a measure of stiffness, was lower in the younger versus older group: C: 33.7 ± 13.9 vs 87.2 ± 10.7, P = 0.02; IC: 38.3 ± 12.7 vs 84.5 ± 13.9, P = 0.04; PV: 24.7 ± 8.8 vs 74.6 ± 9.6, P = 0.04. In contrast, non-PFM stiffness was not affected by aging: OI: 14.5 ± 4.7 vs 32.9 ± 6.2, P = 0.8 and VL: 13.6 ± 5.7 vs 30.1 ± 5.3, P = 0.9. Age-associated increase in PFM stiffness is predicted to negatively impact PFM function by diminishing muscle load-bearing, excursional, contractile, and regenerative capacity, thus predisposing older women to PFDs.