nils-herrmann/clean_scirepeval huggingface dataset:
Contact conditions for total hip head-neck modular taper junctions with microgrooved stem tapers.
Venue: Journal of biomechanics

Implant failure due to fretting-corrosion of head-neck modular junctions is a rising problem in total hip arthroplasty. Fretting-corrosion initiates when micromotion leads to metal release; however, factors leading to micromotion, such as microgrooves on the stem taper, are not fully understood. The purpose of this study is to describe a finite element analysis technique to determine head-neck contact mechanics and investigate the effect of stem taper microgroove height during head-neck assembly. Two-dimensional axisymmetric finite element models were created. Models were created for a ceramic femoral head and a CoCrMo femoral head against Ti6Al4V stem tapers and compared to available data from prior experiments. Stem taper microgroove height was investigated with a generic 12/14 model. Head-neck assembly was performed to four maximum loads (500 N, 2000 N, 4000 N, 8000 N). For the stem taper coupled with the ceramic head, the number of microgrooves in contact and plastically deformed differed by 2.5 microgrooves (4%) and 6.5 microgrooves (11%), respectively, between the finite element models and experiment. For the stem taper coupled with the CoCrMo head, all microgrooves were in contact after all assembly loads in the finite element model due to an almost identical conical angle between the taper surfaces. In the experiments, all grooves were only in contact for the 8000 N assembly load. Contact area, plastic (permanent) deformation, and contact pressure increased with increasing assembly loads and deeper microgrooves. The described modeling technique can be used to investigate the relationship between implant design factors, allowing for optimal microgroove design within material couples.
Validation and application of dynamic biplane radiography to study in vivo ankle joint kinematics during high-demand activities.
Venue: Journal of biomechanics

Ankle ligament injuries are the most common musculoskeletal injury in physically active populations. Failure to restore native kinematics post-injury often leads to long-term consequences including chronic instability and arthritis. Using traditional motion capture, it is difficult to distinguish independent motions of the tibiotalar and subtalar joints to assess the effects of injury, surgical repair, and rehabilitation on ankle joint complex (AJC) kinematics. Therefore, the aims of this study were to determine the accuracy of dynamic biplane radiography for determining in vivo AJC kinematics and arthrokinematics, and to identify sport-related movements that require the largest AJC range of motion (ROM) during support. Two subjects had three to five 1.0 mm diameter tantalum beads implanted into the tibia, fibula, talus, and calcaneus during lateral ankle ligament repair. Six months after surgery, the subjects executed seven movements while biplane radiographs were collected. Bone motion was tracked using radiostereophotogrammetric analysis (RSA) as a "gold standard", and compared to a volumetric CT model-based tracking algorithm that matched digitally reconstructed radiographs to the original biplane radiographs. Over all movements, the average tibiotalar, subtalar and tibiofibular RMS errors were 0.5 mm ± 0.2 mm, 0.8 mm ± 0.5 mm and 0.8 mm ± 0.3 mm in translation and 1.4° ± 0.4°, 1.5° ± 0.5° and 1.7° ± 0.6° in rotation, respectively. Tibiotalar joint space was determined with an average precision of 0.5 mm. ROM results indicate that jumping and a forward-to-backward push-off movement are the best of the seven sport-related movements evaluated for eliciting full ROM kinematics.
Reliability and robustness of optimization properties for stabilization of the upright stance as determined using posturography.
Venue: Journal of biomechanics

Diagnostic value of static posturography depends on its methodological features, measurement properties, and on computational methods that extract meaningful information from the postural sway i.e. the center-of-pressure (CoP) displacements. In this study, we assessed the reliability and robustness of the postural system based on the optimization properties of the CoP signal: descending, local and global stability, and convergence. For the analysis, we used CoP data from 146 participants (104 [71%] female, age 46 ± 23 years, body mass index 23.6 ± 3.4 kg/m2) recorded while standing quietly on a foam surface without visual input. Reliability was estimated using the intraclass correlation coefficient from a single (ICC2,1) and averaged (ICC2,3) measurements. Robustness was assessed through main and interaction effects for the signal duration (60, 30 s), sampling frequency (100, 50 Hz), and lowpass filtering cutoff frequency (10, 5 Hz). The observed reliability depended on the use of average or single measurements as it was excellent for the stability property (ICC2,k ≥ 0.772); excellent-to-acceptable (ICC2,3 ≥ 0.540) or excellent-to-unacceptable (ICC2,1 ≥ 0.281) for the descending property; and excellent-to-unacceptable (ICC2,3 > 0.295; ICC2,1 > 0.122) for the convergence property. Robustness analysis showed large main effects of signal duration (ω2 ≤ 0.834, p < 0.001), sampling frequency (ω2 ≤ 0.526, p < 0.001), and the lowpass filter cutoff frequency (ω2 ≤ 0.523, p < 0.001) on the optimization properties; but all two-way and three-way effects varied from medium to trivial. Reliability is thus excellent to acceptable for deriving the descending, stability, and convergence properties from the average of three measurements. Those optimization properties are robust to the interaction but not the main effects of methodological sources of variation of posturography.
Smart orthopaedic implants: A targeted approach for continuous postoperative evaluation in the spine.
Venue: Journal of biomechanics

Real-time health monitoring systems are emerging in diverse medical fields, tracking biological and physiological signals for direct feedback to the user. Orthopaedics is yet to adapt to innovative trends in health monitoring. Despite an evident entry point during orthopaedic surgeries, clinicians remain unable to objectively examine the structural integrity and biomechanics in the operated region through implantable sensors. As such, postoperative advice can be non-specific and poorly guided. This perspective discusses the clinical need for load-sensing implants that address biomechanical postoperative monitoring, taking the example of spinal interbody cages. Research has attempted to establish sensing approaches in different orthopaedic settings; however, they fail to meet mechanical sensing requirements or lack in vivo translatability, especially in the spine. Polymeric flexible sensors and Microelectromechanical Systems (MEMS) have favourable attributes aligned to the required features for in vivo load-sensing, although these approaches are yet to be tested extensively in orthopaedics. While inductive powering is promising, wireless energy transfer and telemetry are areas of ongoing research. This perspective proposes a thorough understanding of the relevant biomechanics to identify the pertinent sensing parameters, concurrent treatment of sensing and powering aspects, and utilisation of energy harvesting for sensing and data transmission. While sensing advancements have contributed to the rise of real-time health monitoring in other fields of medicine, orthopaedics has so far been overlooked. It is the application of these innovations that will lead to the development of a new generation of 'smart' implants for continuous postoperative evaluation.
How healthy older adults regulate lateral foot placement while walking in laterally destabilizing environments.
Venue: Journal of biomechanics

Gait variability is generally associated with falls, but specific connections remain disputed. To reduce falls, we must first understand how older adults maintain lateral balance while walking, particularly when their stability is challenged. We recently developed computational models of lateral stepping, based on Goal Equivalent Manifolds, that separate effects of step-to-step regulation from variability. These show walking humans seek to strongly maintain step width, but also lateral position on their path. Here, 17 healthy older (ages 60+) and 17 healthy young (ages 18-31) adults walked in a virtual environment with no perturbations and with laterally destabilizing perturbations of either the visual field or treadmill platform. For step-to-step time series of step widths and lateral positions, we computed variability, statistical persistence and how much participants directly corrected deviations at each step. All participants exhibited significantly increased variability, decreased persistence and tighter direct control when perturbed. Simulations from our stepping regulation models indicate people responded to the increased variability imposed by these perturbations by either maintaining or tightening control of both step width and lateral position. Thus, while people strive to maintain lateral balance, they also actively strive to stay on their path. Healthy older participants exhibited slightly increased variability, but no differences from young in stepping regulation and no evidence of greater reliance on visual feedback, even when subjected to substantially destabilizing perturbations. Thus, age alone need not degrade lateral stepping control. This may help explain why directly connecting gait variability to fall risk has proven difficult.
Effect of continuous, mechanically passive, anti-gravity assistance on kinematics and muscle activity during dynamic shoulder elevation.
Venue: Journal of biomechanics

Passive shoulder exoskeletons, which provide continuous anti-gravitational force at the shoulder, could assist with dynamic shoulder elevation movements involved in activities of daily living and rehabilitation exercises. However, prior biomechanical studies of these exoskeletons primarily focused on static overhead tasks. In this study, we evaluated how continuous passive anti-gravity assistance affects able-bodied neuromuscular activity and shoulder kinematics during dynamic and static phases of shoulder elevation movements. Subjects, seated upright, elevated the shoulder from a rest posture (arm relaxed at the side) to a target shoulder elevation angle of 90°. Subjects performed the movement in the frontal (abduction) and scapular (scaption) planes with and without passive anti-gravity assistance. Muscles that contribute to positive shoulder elevation, based on their reported moment arms, had significantly lower muscle activations with assistance during both dynamic and static elevation. Muscles that contribute to negative shoulder elevation, which can decelerate the shoulder during dynamic shoulder elevation, were not significantly different between assistance conditions. This may be partly explained by the trend of subjects to reduce their maximum angular decelerations near the target to offset the positive shoulder elevation moment due to the anti-gravity assistance. Our results suggest that passive anti-gravity assistance could reduce the muscle activations needed to perform dynamic movements. Consequently, the anti-gravity assistance of passive shoulder exoskeletons may enhance motor function and reduce muscle and joint loads for both able-bodied and disabled users.
Fluid-structure interaction modeling of lactating breast.
Venue: Journal of biomechanics

There are two theories for the dynamics of milk expression by the infant. One hypothesis is that milk expression is due to the negative pressure applied by the infant sucking; the alternative hypothesis is that the tongue movement and squeezing of nipple/areola due to mouthing is responsible for the extraction of milk from the nipple. In this study, 3-D two-way Fluid-Structure Interaction (FSI) simulations are conducted to investigate the factors that play the primary role in expressing milk from the nipple. The models include the solid deformation and periodic motion of the tongue and jaw movement. To obtain the boundary conditions, ultrasound images of the oral cavity and motion of the tongue movement during breastfeeding are extracted in parallel to the intra-oral vacuum pressure. The numerical results are cross-validated with clinical data. The results show that, while vacuum pressure plays an important role in the amount of milk removal, the tongue/jaw movement is essential for facilitating this procedure by decreasing the shear stress within the main duct in the nipple. The developed model can contribute to a better understanding of breastfeeding complications due to infant or breast abnormalities and for the design of medical devices such as breast pumps and artificial teats.
Hemodynamic effects of pulsatile unloading of left ventricular assist devices (LVAD) on intraventricular flow and ventricular stress.
Venue: Journal of biomechanics

The role of pulsatile unloading in hemodynamic changes in intraventricular flow and ventricular wall stress remains unknown. In this study, a finite element model of the left ventricle (LV) is proposed to calculate the mechanical response. The constitutive model of the LV is composed of a quasi-incompressible transversely isotropic model and an active contraction of the myocardium model. Pulsatile unloading is provided by the left ventricular assist device (LVAD), which is implanted between the aortic root and aortic arch. Support models (constant speed and co-pulse) were utilized to study the effect of pulsatile unloading on intraventricular flow and ventricular stress. The result indicates that the formation time of the vortex increases under pulsatile unloading. The area rate of high time-averaged wall shear stress (TAWSS) increased after pulsatile unloading. The area of the high oscillatory shear index (OSI) region (OSI > 0.375) was calculated for heart failure, constant speed, and co-pulse (9.9 cm2, 9.6 cm2, and 9.2 cm2, respectively). The maximum value of the stress that reflects the level of stretch declined after pulsatile unloading (66.4 kPa, 30.9 kPa, and 21.3 kPa, respectively). Besides, pulsatile unloading impacts the maximum value of thickness at the ventricular wall (-0.75 mm, -1 mm, and -1.25 mm, respectively). The change ratios of the thickness are 10%, 14%, and 17%, respectively. In conclusion, pulsatile unloading contributes to the distribution of intraventricular flow and the formation time of the vortex. Co-pulse support significantly reduces the maximum value of the ventricular wall stress and the area of high stress on the ventricular wall.
Integrated iterative musculoskeletal modeling predicts bone morphology following brachial plexus birth injury (BPBI).
Venue: Journal of biomechanics

Brachial plexus birth injury (BPBI) is the most common nerve injury among children. The glenohumeral joint of affected children can undergo severe osseous deformation and altered muscle properties, depending on location of the injury relative to the dorsal root ganglion (preganglionic or postganglionic). Preganglionic injury results in lower muscle mass and shorter optimal muscle length compared to postganglionic injury. We investigated whether these changes to muscle properties over time following BPBI provide a mechanically-driven explanation for observed differences in bone deformity between preganglionic and postganglionic BPBI. We developed a computational framework integrating musculoskeletal modeling to represent muscle changes over time and finite element modeling to simulate bone growth in response to mechanical and biological stimuli. The simulations predicted that the net glenohumeral joint loads in the postganglionic injury case were nearly 10.5% greater than in preganglionic. Predicted bone deformations were more severe in the postganglionic case, with the glenoid more declined (pre: -43.8°, post: -51.0°), flatter with higher radius of curvature (pre: 3.0 mm, post: 3.7 mm), and anteverted (pre: 2.53°, post: 4.93°) than in the preganglionic case. These simulated glenoid deformations were consistent with previous experimental studies. Thus, we concluded that the differences in muscle mass and length between the preganglionic and postganglionic injuries are critical mechanical drivers of the altered glenohumeral joint shape.
Sensitivity of musculoskeletal model-based lumbar spinal loading estimates to type of kinematic input and passive stiffness properties.
Venue: Journal of biomechanics

The study investigated the potential for obtaining more accurate spine joint reaction force (JRF) estimates from musculoskeletal models by incorporating dynamic stereo X-ray imaging (DSX)-based in vivo lumbar vertebral rotational and translational kinematics compared to generic, rhythm (RHY)-based kinematics, while also observing the influence of accompanying inputs: intervertebral segment stiffness and neutral state. A full-body OpenSim® musculoskeletal model, constructed by combining existing lower- and upper-body models, was driven based on one volunteer's (female; age 25; 60.8 kg; 176 cm) anthropometrics and kinematics from a series of upright standing and straight-legged dynamic lifting tasks. The lumbar spine portion was modified in a step-wise manner to observe effects of: (1) RHY vs. DSX lumbar kinematics; (2) No disc (bushing) stiffness (NBS); generic, linear bushing stiffness (LBS); subject-specific nonlinear bushing stiffness (NLBS); (3) Upright standing (UP) vs. Supine (SUP) neutral state; (4) Weight lifted: 4.5 kg vs. 13.6 kg. L4L5 JRF from 24 model variations based on combinations of aforementioned parameters were compared. Rhythm-based kinematics without translational components tends to over-predict JRF (31% and 39% for compression and shear, respectively) compared to DSX-based kinematics. Additionally, differences due to accompanying passive stiffness and neutral state choice combinations were even larger (>50%), indicating heightened demand on the quality of these accompanying inputs. The study not only highlights model sensitivity to choices made regarding the three primary inputs-kinematics, passive stiffness and neutral state- separately, but also how interactions between these choices can result in significant variability in joint loading estimates.
The sensitivity of joint kinematics and kinetics to marker placement during a change of direction task.
Venue: Journal of biomechanics

The conventional gait model (CGM) refers to several closely related biomechanical models used in the objective analysis of human motion. Their use has become popular in the analysis of change of direction tasks to inform best practice in the prevention and rehabilitation of anterior cruciate ligament injury. As externally-placed markers define segment axes origins and orientations, kinematic and kinetic outputs from the CGM are sensitive to marker placement. The aim of this investigation was to quantify the sensitivity of lower extremity kinematics and knee moments to systematic differences in marker placement across the stance phase of a change of direction task. Systematic anterior/posterior displacements were applied to the lateral thigh, femoral epicondyle and tibia markers in software. One-dimensional statistical parametric mapping was used to determine the effect of marker placement across the entire stance phase of a 90° change of direction task. Marker placement error within previously reported inter-tester variability ranges caused significant differences in knee abduction moment, hip rotation angle, knee rotation angle, ankle abduction and rotation angle across various periods of stance. Discrete measures of these variables have been associated with increased frontal plane knee loading during change of direction, considered a key mechanism of anterior cruciate ligament injury. Systematic differences in marker placement may lead to incorrect group statistical inferences in such discrete measures.
The metabolic power required to support body weight and accelerate body mass changes during walking on uphill and downhill slopes.
Venue: Journal of biomechanics

The metabolic cost of walking is due to muscle force generated to support body weight (BW), external work performed to redirect and accelerate the center of mass (CoM), and internal work performed to swing the limbs and maintain balance. We hypothesized that BW support would incur a greater and lower percentage of Net Metabolic Power (NMP) for uphill and downhill slopes, respectively, compared to level-ground walking. Additionally, we hypothesized that mass redirection would incur a greater and lower percentage of NMP for uphill and downhill slopes, respectively compared to level-ground walking. 10 subjects walked at 1.25 m/s on 0°, ±3°, and ±6° slopes with reduced/added weight and added mass while we measured metabolic rates. We calculated NMP per Newton of reduced BW at each slope and found that BW support required 58% and 64% of the NMP to walk at +3° and +6°, respectively, both greater than the 15% required for level-ground walking (p < 0.025). We calculated NMP per kg of added mass at each slope and found that mass redirection required 19% and 23% of the NMP to walk at +3° and +6°, respectively, both lower than the 35% required for level-ground walking (p < 0.025). We found no significant differences in the percentage of NMP for BW support or mass redirection during downhill compared to level ground walking (p > 0.05). Our findings elucidate that the percentage of NMP attributed to BW support and mass redirection is different for sloped compared to level-ground walking. These results inform biomimetic assistive device designs aimed at reducing metabolic cost.
Changes in ambulatory knee adduction moment with lateral wedge insoles differ with respect to the natural foot progression angle.
Venue: Journal of biomechanics

Lateral wedge insoles (LWI) have been proposed to reduce the knee adduction moment (KAM) during walking; a biomechanical modification notably sought in case of medial knee osteoarthritis. However, the inter-individual inconsistency in KAM changes with LWI limits their therapeutic use. Although the foot progression angle (FPA) has been frequently discussed in KAM modifications literature, there is a lack of data regarding a possible relationship between this gait measure and changes in KAM with LWI. This study aimed to test if KAM changes with LWI differ with respect to the natural FPA and to compare KAM-related variables between individuals walking with smaller and larger natural FPA. Twenty-two healthy participants (14 males, 24 ± 3 years, 22.7 ± 2.7 kg/m2) underwent gait analysis with and without LWI. They were divided into two groups based on their natural FPA, and changes in KAM 1st peak, KAM impulse, and KAM-related variables were compared between groups. KAM 1st peak and impulse decreased with LWI in the smaller natural FPA group (p ≤ 0.006), while only KAM impulse decreased in the larger natural FPA group (p < 0.001). The difference in KAM 1st peak changes was explained by a less reduced lever arm in participants walking with larger natural FPA. In conclusion, this study brought new insight into the variability in KAM response to LWI. If the findings are confirmed in patients with medial knee osteoarthritis, the FPA could become a simple measure to help identify the patients more likely to reduce their KAM with LWI.