nils-herrmann/clean_scirepeval huggingface dataset:
Effect of pedicle screw diameter on screw fixation efficacy in human osteoporotic thoracic vertebrae.
Venue: Journal of biomechanics

The selection of an ideal screw size plays a crucial role in the success of spinal instrumentation as larger diameter screws are thought to provide better fixation strength but increase the risk of pedicle failure during insertion. On the other hand, smaller diameter screws are with lesser risk of pedicle breakage but are thought to compromise the stability of the instrumentation. By investigating the relationship between screw diameter and the pullout strength of pedicle screws after fatigue loading, this study seeks to find quantitative biomechanical data for surgeons in determining the most ideal diameter size screws when performing surgical implementations on osteoporotic vertebrae. Twenty-seven osteoporotic (BMD ranged: 0.353-0.848 g/cm2) thoracic vertebrae (T3-T8) were harvested from 5 human cadavers. Two sizes of poly-axial screws (5.0 mm × 35 and 4.35 mm × 35) were implanted into each pedicles of the vertebrae by an experienced surgeon. Specimens were randomly distributed into control group, fatigue group of 5000 and 10,000 cycles with peak-to-peak loadings of 10-100 N at 1 Hz. Each specimen was then axial pullout tested at a constant rate of 5 mm/min. The ultimate pullout strength (N) & stiffness (N/mm) were obtained for analysis. The results showed that although the larger diameter screws achieved superior pullout strength immediately after the implantation, both sizes of screws exhibited comparable pullout strengths post fatigue loading. This indicates that the smaller diameter screws may be considered for surgical techniques performed on osteoporotic vertebrae for reduced risk of pedicle breakage without sacrificing fixation strength.
Balance study in asymptomatic subjects: Determination of significant variables and reference patterns to improve clinical application.
Venue: Journal of biomechanics

Postural control is essential when carrying out everyday activities and its possible disorders have a very significant impact on personal autonomy. To provide the means to accurately measure postural control in the clinical environment, this study checks and discusses the suitability of procedures for a new balance assessment system with a stabilometric platform (MoveHuman-Dyna © UZ-IDERGO), which meets the criteria of clinical stabilometric standardisation established by the International Society for Posture and Gait Research (ISPGR) at the Bologna meeting (2009). The study was applied to a sample of 30 healthy volunteers (12 women, 18 men) aged between 18 and 30 years. A total of six balance tests were performed: four variations of the Romberg test, one test for a study of the limits of stability (LoS) and one test for rhythmic weight shift (RWS). Analysis of the results confirms that the variables assessed yielded similar values to other studies, the consistency of values between tests was checked, and preliminary reference values were obtained for asymptomatic subjects. We propose the following variables as the most significant for balance diagnosis: CoP mean speed, RMS, Range of CoP displacement and area. As a result of the study, the system is considered of interest in the medical/legal and forensic settings to assess the balance control and degree of collaboration during the tests.
A novel patterned magnetic micropillar array substrate for analysis of cellular mechanical responses.
Venue: Journal of biomechanics

Traction forces generated at cellular focal adhesions (FAs) play an essential role in regulating various cellular functions. These forces (1-100 nN) can be measured by observing the local displacement of a flexible substrate upon which cells have been plated. Approaches employing this method include using microfabricated arrays of poly(dimethylsiloxane) (PDMS) micropillars that bend by cellular traction forces. A tool capable of applying a force to FAs independently, by actively moving the micropillars, should become a powerful tool to delineate the cellular mechanotransduction mechanisms. Here, we developed a patterned magnetic micropillar array PDMS substrate that can be used for the mechanical stimulation of cellular FAs and the measurement of associated traction forces. The diameter, length, and center-to-center spacing of the micropillars were 3, 9, and 9 µm, respectively. Iron particles were embedded into the micropillars, enabling the pillars to bend in response to an external magnetic field, which also controlled their location on the substrate. Applying a magnetic field of 0.3 T bent the pillars by ∼4 µm and allowed transfer of external forces to the actin cytoskeleton through FAs formed on the pillar top. Using this approach, we investigated the traction force changes in cultured aortic smooth muscle cells (SMCs) after local compressive stimuli to release cell pretension. The mechanical responses of SMCs were roughly classified into two types: almost a half of the cells showed a little decrease of traction force at each pillar following compressive stimulation, although cell area increased significantly; and the rest showed the opposite, with increased forces and a simultaneous decrease in area. The traction forces of SMCs fluctuated markedly during the local compression. The root mean square of traction forces significantly increased during the compression, and returned to the baseline level after its release. These results suggest that the fluctuation of forces may be caused by active reorganization of the actin cytoskeleton and/or its dynamic interaction with myosin molecules. Thus, our magnetic micropillar substrate would be useful in investigating the mechanotransduction mechanisms of cells.
Zonal variation of MRI-measurable parameters classifies cartilage degradation.
Venue: Journal of biomechanics

Osteoarthritis (OA) is a degenerative joint disease resulting in the deterioration of articular cartilage, a tissue with minimal ability to self-repair. Early diagnosis of OA with non-invasive imaging techniques such as magnetic resonance imaging (MRI) could provide an opportunity to intervene and slow or reverse this degeneration process. This study examines the classification of degradation states using MRI measurements. Enzymatic degradation was used to specifically target proteoglycans alone, collagen alone and both cartilage components sequentially. The resulting degradation was evaluated using MRI imaging techniques (T1, T2, diffusion tensor imaging, and gadolinium enhanced T1) and derived measures of water, glycosaminoglycan and collagen content. We compared the classification ability of full thickness averages of these parameters with zonal averages (superficial, medial, and deep). Finally, we determined minimum variables sets to identify the smallest number of variables that allowed for complete separation of all degradation groups and ranked them by impact on the separation. Zonal analysis was much more sensitive than full thickness averages and allowed perfect separation of all four groups. Superficial zone cartilage was more sensitive to enzymatic degradation than the medial or deep zone, or the full thickness average. Variable ranking consistently identified collagen content and organization as the most impactful variables in the classification algorithm. The aim of this study is to classify cartilage degradation using only non-invasive MRI parameters that could be applied to OA diagnosis. Our results highlight the importance of zonal variation in the diagnosis of cartilage degeneration. Our novel, non-invasive collagen content measurement was crucial for complete separation of degraded groups from control cartilage. These findings have significant implications for clinical cartilage MRI for disease diagnosis.
Effect of integration time on the morphometric, densitometric and mechanical properties of the mouse tibia.
Venue: Journal of biomechanics

Micro-Computed Tomography (microCT) images are used to measure morphometric and densitometric properties of bone, and to develop finite element (FE) models to estimate mechanical properties. However, there are concerns about the invasiveness of microCT imaging due to the X-rays ionising radiation induced by the repeated scans on the same animal. Therefore, the best compromise between radiation dose and image quality should be chosen for each preclinical application. In this study, we investigated the effect of integration time (time the bone is exposed to radiation at each rotation step during microCT imaging) on measurements performed on the mouse tibia. Four tibiae were scanned at 10.4 µm voxel size using four different procedures, characterized by decreasing integration time (from 200 ms to 50 ms) and therefore decreasing nominal radiation dose (from 513 mGy to 128 mGy). From each image, trabecular and cortical morphometric parameters, spatial distribution of bone mineral content (BMC) in the whole tibia and FE-based estimations of stiffness and strength were obtained. A high-resolution scan (4.3 µm voxel size) was used to quantify measurement errors. Integration time had the largest effect on trabecular morphometric parameters (7-28%). Lower effects were observed on cortical parameters (1-3%), BMC (1-10%) distribution, and FE-based estimations of mechanical properties (1-3%). In conclusion, the effect of integration time on image-based measurements has been quantified. This data should be considered when defining the in vivo microCT scanning protocols in order to find the best compromise between nominal radiation exposure and accuracy in the estimation of bone parameters.
The effect of microcracking in the peritubular dentin on the fracture of dentin.
Venue: Journal of biomechanics

Dentin is a biocomposite possessing elegant hierarchical structure, which allows it to resist fracture effectively. Despite the considerable efforts to unravel the peculiar fracture behavior of dentin, the effect of microstructural features on the fracture process is largely unknown. In this study, we explore the interaction between the primary crack with crack tip located in intertubular dentin (ITD) and microcracking of peritubular dentin (PTD) ahead of the primary crack. A micromechanical model accounting for the unique composite structure of dentin is developed, and computational simulations are performed. It is found that the microcracking of PTD located in the crack plane in front of the primary crack tip can promote the propagation of the primary crack, increasing the propensity of coalescence of primary crack and microcracks nucleating in PTD. We show that the two-layer microstructure of dentin enables reduction in driving force of primary crack, potentially enhancing fracture toughness. The high stiffness of PTD plays a critical role in reducing the driving force of primary crack and activating microcracking of PTD. It is further identified that the microcracking of PTD arranged parallel to the crack plane with an offset could contribute to the shielding of primary crack.
Examining tissue composition, whole-bone morphology and mechanical behavior of GorabPrx1 mice tibiae: A mouse model of premature aging.
Venue: Journal of biomechanics

Gerodermia osteodysplastica (GO) is a segmental progeroid disorder caused by loss-of-function mutations in the GORAB gene, associated with early onset osteoporosis and bone fragility. A conditional mouse model of GO (GorabPrx1) was generated in which the Gorab gene was deleted in long bones. We examined the biomechanical/functional relevance of the GorabPrx1 mutants as a premature aging model by characterizing bone composition, tissue-level strains, and whole-bone morphology and mechanical properties of the tibia. MicroCT imaging showed that GorabPrx1 tibiae had an increased anterior convex curvature and decreased cortical cross-sectional area, cortical thickness and moments of inertia, compared to littermate control (LC) tibiae. Fourier transform infrared (FTIR) imaging indicated a 34% decrease in mineral/matrix ratio and a 27% increase in acid phosphate content in the posterior metaphyseal cortex of the GorabPrx1 tibiae (p < .05), suggesting delayed mineralization. In vivo strain gauge measurement and finite element analysis showed ∼two times higher tissue-level strains within the GorabPrx1 tibiae relative to LC tibiae when subjected to axial compressive loads of the same magnitude. Three-point bending tests suggested that GorabPrx1 tibiae were weaker and more brittle, as indicated by decreasing whole-bone strength (46%), stiffness (55%), work-to-fracture (61%) and post-yield displacement (47%). Many of these morphological and biomechanical characteristics of the GorabPrx1 tibia recapitulated changes in other animal models of skeletal aging. Future studies are necessary to confirm how our observations might guide the way to a better understanding and treatment of GO.
Tissue viscoelasticity is related to tissue composition but may not fully predict the apparent-level viscoelasticity in human trabecular bone - An experimental and finite element study.
Venue: Journal of biomechanics

Trabecular bone is viscoelastic under dynamic loading. However, it is unclear how tissue viscoelasticity controls viscoelasticity at the apparent-level. In this study, viscoelasticity of cylindrical human trabecular bone samples (n=11, male, age 18-78 years) from 11 proximal femurs were characterized using dynamic and stress-relaxation testing at the apparent-level and with creep nanoindentation at the tissue-level. In addition, bone tissue elasticity was determined using scanning acoustic microscope (SAM). Tissue composition and collagen crosslinks were assessed using Raman micro-spectroscopy and high performance liquid chromatography (HPLC), respectively. Values of material parameters were obtained from finite element (FE) models by optimizing tissue-level creep and apparent-level stress-relaxation to experimental nanoindentation and unconfined compression testing values, respectively, utilizing the second order Prony series to depict viscoelasticity. FE simulations showed that tissue-level equilibrium elastic modulus (Eeq) increased with increasing crystallinity (r=0.730, p=.011) while at the apparent-level it increased with increasing hydroxylysyl pyridinoline content (r=0.718, p=.019). In addition, the normalized shear modulus g1 (r=-0.780, p=.005) decreased with increasing collagen ratio (amide III/CH2) at the tissue-level, but increased (r=0.696, p=.025) with increasing collagen ratio at the apparent-level. No significant relations were found between the measured or simulated viscoelastic parameters at the tissue- and apparent-levels nor were the parameters related to tissue elasticity determined with SAM. However, only Eeq, g2 and relaxation time τ1 from simulated viscoelastic values were statistically different between tissue- and apparent-levels (p<.01). These findings indicate that bone tissue viscoelasticity is affected by tissue composition but may not fully predict the macroscale viscoelasticity in human trabecular bone.
Estimation and validation of spatio-temporal parameters for sprint running using a radio-based tracking system.
Venue: Journal of biomechanics

Spatio-temporal parameters like step length, step frequency and ground contact time are directly related to sprinting performance. There is still a lack of knowledge, however, on how these parameters interact. Recently, various algorithms for the automatic detection of step parameters during sprint running have been presented which have been based on data from motion capture systems, video cameras, opto-electronic systems or Inertial measurement units. However, all of these methods suffer from at least one of the following shortcomings: they are (a) not applicable for more than one sprinter simultaneously, (b) only capable of capturing a small volume or (c) do not provide accurate spatial parameters. To circumvent these issues, the radio-based local position measurement system RedFIR could be used to obtain spatio-temporal information during sprinting based on lightweight transmitters attached to the athletes. To assess and optimize the accuracy of these parameters 19 100 m sprints of twelve young elite athletes (age: 16.5 ± 2.3 years) were recorded by a radio-based tracking system and a opto-electronic reference instrument. Optimal filter parameters for the step detection algorithm were obtained based on RMSE differences between estimates and reference values on an unseen test set. Attaching a transmitter above the ankle showed the best results. Bland-Altman analysis yielded 95% limits of agreement of [-14.65 cm, 15.05 cm] for step length [-0.016 s, 0.016 s] for step time and [-0.020 s, 0.028 s] for ground contact time, respectively. RMS errors smaller than 2% for step length and step time show the applicability of radio-based tracking systems to provide spatio-temporal parameters. This creates new opportunities for performance analysis that can be applied for any running discipline taking place within a stadium. Since analysis for multiple athletes is available in real-time this allows immediate feedback to coaches, athletes and media.
The rib cage reduces intervertebral disc pressures in cadaveric thoracic spines by sharing loading under applied dynamic moments.
Venue: Journal of biomechanics

The effects of the rib cage on thoracic spine loading are not well studied, but the rib cage may provide stability or share loads with the spine. Intervertebral disc pressure provides insight into spinal loading, but such measurements are lacking in the thoracic spine. Thus, our objective was to examine thoracic intradiscal pressures under applied pure moments, and to determine the effect of the rib cage on these pressures. Human cadaveric thoracic spine specimens were positioned upright in a testing machine, and Dynamic pure moments (0 to ±5 N·m) with a compressive follower load of 400 N were applied in axial rotation, flexion - extension, and lateral bending. Disc pressures were measured at T4-T5 and T8-T9 using needle-mounted pressure transducers, first with the rib cage intact, and again after the rib cage was removed. Changes in pressure vs. moment slopes with rib cage removal were examined. Pressure generally increased with applied moments, and pressure-moment slope increased with rib cage removal at T4-T5 for axial rotation, extension, and lateral bending, and at T8-T9 for axial rotation. The results suggest the intact rib cage carried about 62% and 56% of axial rotation moments about T4-T5 and T8-T9, respectively, as well as 42% of extension moment and 36-43% of lateral bending moment about T4-T5 only. The rib cage likely plays a larger role in supporting moments than compressive loads, and may also play a larger role in the upper thorax than the lower thorax.
Upper body accelerations during planned gait termination in young and older women.
Venue: Journal of biomechanics

Transitory tasks, such as gait termination, involve interactions between neural and biomechanical factors that challenge postural stability and head stabilization patterns in older adults. The aim of the study was to compare upper body patterns of acceleration during planned gait termination at different speeds between young and older women. Ten young and 10 older women were asked to carry out three gait termination trials at slow, comfortable and fast speed. A stereophotogrammetric system and a 15-body segments model were used to calculate antero-posterior whole-body Center of Mass (AP CoM) speed and to reconstruct the centroids of head, trunk and pelvis segments. RMS of three-dimensional linear accelerations were calculated for each segment and the transmission of acceleration between two segments was expressed as a percentage difference. Older women reported lower AP CoM speed and acceleration RMS of the three upper body segments than young women across the three speed conditions. A lower pelvis-to-trunk attenuation of accelerations in the transverse plane was observed in older compared to young women, and mainly in the medio-lateral direction. As possible explanations, older women may not need to reduce acceleration as young women because of their lower progression speed and the subsequent acceleration at upper body levels. On the other hand, older women may prioritize a decrease in the whole body progression speed at expense of the involvement of upper body segments. This limits the attenuation of the accelerations, particularly in the transverse plane, implying an increased dynamic unbalance in performing this transitory task.
Three-dimensional discrete element method for the prediction of protoplasmic seepage through membrane in a biological cell.
Venue: Journal of biomechanics

This paper presents a three-dimensional and compressible biological cell model based on discrete element method using multiple interacting agent that represent cellular structures within a simulated environment. The cytoplasm and nucleoplasm fluid behavior in the cell is time dependent. When taking this approach, it is important to calibrate protoplasmic flow behaviors through simulation techniques such as compressing the cell and examining the agents representing the cell cytoplasm seeping between the ones representing the confining cell membrane. This type of modelling may motivate future work on simulating simultaneous operations and interactions of multiple cellular agents in an attempt to re-create and predict the appearance of complex phenomena such as protoplasmic seepage that is caused by the force actuations of neighboring cells. Seepage occurs when a cytoplasm agent passes between three membrane particles connected in a triangular network. Based on the force-deformation response of spheres having variable size and stiffness, semi-analytic expressions are developed for the force required to cause seepage and solved numerically to find the maximum resistance offered by the membrane against cytoplasm seepage. The equations are based on force equilibrium and the constitutive relations for particle contact and membrane stiffness. In multi-particle representations of an individual cell undergoing deformation, different modes of cytoplasm seepage through confining cell membranes can occur. This can be avoided if simple criteria are satisfied. These findings can lead to certain fundamental laws for the improvement of novel cell-to-organ simulation techniques based on discrete element method.