The relationship between the electromyogram-amplitude and isometric extension torques of neck muscles at different positions of the cervical spine

A group of 12 healthy men volunteered for the experiment. Electromyograms (EMG) were obtained from semispinalis capitis, splenius capitis, levator scapulae, and trapezius muscles. The flexion angle of the cervical spine was precisely adjusted to 0°, 10°, 20°, and 30° relative to the horizontal, with a constant angle of the atlanto-occipital joint. The subjects made eight short (about 2 s) vertical extension forces (6%, 12%,18%, 24%, 30%, 36%, 42%, and 48% of maximal voluntary peak contraction force). For each position, the centre of pressure under the head was determine as the basis for the calculation of the external lever arm. The presence of motor endplate regions was ascertained by multiple surface electrodes. The slopes of individual linear regression lines for the root mean square (rms)-values were dependent on the existence of endplates in the area of the electrodes — endplates caused smaller rms values per Newton metres of external torque. Significant intersubject differences between regression equations could not be eliminated by the normalization of EMG-parameters and/or torques. The elimination of gravity, the continuous monitoring of positions, and the consideration of localization of motor endplate regions were essential prerequisites for the acquisition of reliable relationships between EMG of different neck muscles and external torques. Two important conclusions were derived for the prediction of torques from EMG measurements: firstly, individual regression equations which take into account the position of the head and neck should be used; secondly, normalization procedures do not justify the application of average regressions to a group of subjects.     

Estimation of musculotendon kinematics in large musculoskeletal models using multidimensional B-splines

We present a robust and computationally inexpensive method to estimate the lengths and three-dimensional moment arms for a large number of musculotendon actuators of the human lower limb. Using a musculoskeletal model of the lower extremity, a set of values was established for the length of each musculotendon actuator for different lower limb generalized coordinates (joint angles). A multidimensional spline function was then used to fit these data. Muscle moment arms were obtained by differentiating the musculotendon length spline function with respect to the generalized coordinate of interest. This new method was then compared to a previously used polynomial regression method. Compared to the polynomial regression method, the multidimensional spline method produced lower errors for estimating musculotendon lengths and moment arms throughout the whole generalized coordinate workspace. The fitting accuracy was also less affected by the number of dependent degrees of freedom and by the amount of experimental data available. The spline method only required information on musculotendon lengths to estimate both musculotendon lengths and moment arms, thus relaxing data input requirements, whereas the polynomial regression requires different equations to be used for both musculotendon lengths and moment arms. Finally, we used the spline method in conjunction with an electromyography driven musculoskeletal model to estimate muscle forces under different contractile conditions, which showed that the method is suitable for the integration into large scale neuromusculoskeletal models.     

Mid-sagittal dimensions of cervical vertebral bodies.

A series of lateral radiographs of the cervical spinal column was evaluated in order to determine vertebral body dimensions. The sample included males (N=30) and females (N=31) 18 to 24 years old, comprising three stature percentile ranges (1-20; 40-60; 80-99) of the U.S. adult population. A two-dimensional analysis of vertebral body height (average distance between superior-inferior surgaces), depth (average distance between anteriorposterior surfaces), and area (average height X average depth) revealed minimal effects due to stature. In all subjects, average depth exceeded average height for vertebral bodies C3 through C7. Upon combining stature groups, both sexes revealed maximum average values for these dimensions at the seventh cervical vertebral body. Minimum average height occurred at C5 whereas minimum average depth was found at C3. Significant correlation (alpha greater than 0.05) was found for males between ponderal index and height and depth of the C7 vertebra. Male head weight correlated significantly with C3, C4, C5 and C6 vertebral body height and with C3, C5 and C6 vertebral body depth. For females, C7 height and C6 depth correlated significantly with ponderal index and head weight respectively. Probable biomechanical relationships of specific cervical vertebral bodies are noted     

The development of locomotor kinematics in neonatal rats: an agent-based modeling analysis in group and individual contexts

An agent-based model of infant rat (pup) locomotion and aggregation was developed by modifying a previous model of pup aggregation [Schank, J.C., Alberts, J.R., 2000a. The developmental emergence of coupled activity as cooperative aggregation in rat pups. Proc. R. Soc. London B 267, 2307-2315]. The main difference between the earlier and current models is the incorporation of whole-body kinematics of directional locomotion. Data on locomotion and aggregation are presented for individuals and groups of 7- and 10-day-old pups and the data were used to evolve models (with a genetic algorithm) that fit these data. Aggregation between 7- and 10-day-old pups was considerably different and could be explained by agent-based models, in particular, models with directional-kinematic matrices specifying the probabilities of moving to adjacent cells. The directional kinematics of whole-body movement differed between the two age classes and differed between group and individual contexts for 10-day-old pups. This may indicate a developmental transition (by day 10) to more central control of behavior and the ability to change patterns of movement based on social context. The behavior analyzed with agent-based models may provide a precise way to measure motor and nervous system development in rats and other rodents.     

The effect of lateral eccentricity on failure loads,kinematics, and canal occlusions of the cervical spine in axial loading

Current neck injury criteria do not include limits for lateral bending combined with axial compression and this has been observed as a clinically relevant mechanism, particularly for rollover motor vehicle crashes. The primary objectives of this study were to evaluate the effects of lateral eccentricity (the perpendicular distance from the axial force to the centre of the spine) on peak loads, kinematics, and spinal canal occlusions of subaxial cervical spine specimens tested in dynamic axial compression (0.5 m/s). Twelve 3-vertebra human cadaver cervical spine specimens were tested in two groups: low and high eccentricity with initial eccentricities of 1 and 150% of the lateral diameter of the vertebral body. Six-axis loads inferior to the specimen, kinematics of the superior-most vertebra, and spinal canal occlusions were measured. High speed video was collected and acoustic emission (AE) sensors were used to define the time of injury. The effects of eccentricity on peak loads, kinematics, and canal occlusions were evaluated using unpaired Student t-tests. The high eccentricity group had lower peak axial forces (1544±629 vs. 4296±1693 N), inferior displacements (0.2±1.0 vs. 6.6±2.0 mm), and canal occlusions (27±5 vs. 53±15%) and higher peak ipsilateral bending moments (53±17 vs. 3±18 Nm), ipsilateral bending rotations (22±3 vs. 1±2°), and ipsilateral displacements (4.5±1.4 vs. −1.0±1.3 mm, p<0.05 for all comparisons). These results provide new insights to develop prevention, recognition, and treatment strategies for compressive cervical spine injuries with lateral eccentricities.     

Finite element analyses of human vertebral bodies embedded in polymethylmethalcrylate or loaded via the hyperelastic intervertebral disc models provide equivalent predictions of experimental strength

Quantitative computer tomography (QCT)-based finite element (FE) models of vertebral body provide better prediction of vertebral strength than dual energy X-ray absorptiometry. However, most models were validated against compression of vertebral bodies with endplates embedded in polymethylmethalcrylate (PMMA). Yet, loading being as important as bone density, the absence of intervertebral disc (IVD) affects the strength. Accordingly, the aim was to assess the strength predictions of the classic FE models (vertebral body embedded) against the in vitro and in silico strengths of vertebral bodies loaded via IVDs. High resolution peripheral QCT (HR-pQCT) were performed on 13 segments (T11/T12/L1). T11 and L1 were augmented with PMMA and the samples were tested under a 4° wedge compression until failure of T12. Specimen-specific model was generated for each T12 from the HR-pQCT data. Two FE sets were created: FE-PMMA refers to the classical vertebral body embedded model under axial compression; FE-IVD to their loading via hyperelastic IVD model under the wedge compression as conducted experimentally. Results showed that FE-PMMA models overestimated the experimental strength and their strength prediction was satisfactory considering the different experimental set-up. On the other hand, the FE-IVD models did not prove significantly better (Exp/FE-PMMA: R²=0.68; Exp/FE-IVD: R²=0.71, p=0.84). In conclusion, FE-PMMA correlates well with in vitro strength of human vertebral bodies loaded via real IVDs and FE-IVD with hyperelastic IVDs do not significantly improve this correlation. Therefore, it seems not worth adding the IVDs to vertebral body models until fully validated patient-specific IVD models become available.     

Ergonomic Risk Assessment of Developing Musculoskeletal Disorders in Workers with the Microsoft Kinect: TRACK TMS

Background

Routine ergonomic assessment of postures and gestures in the workplace are mostly conducted by visual observations, either direct or based on video recordings. Nowadays, low-cost three-dimensional cameras like Microsoft Kinect offers the possibility of recording the full kinematics of workers in a non-intrusive way, providing a more precise, and reliable assessment of their motor strategies.

Uncertainty analysis of material properties and morphology parameters in numerical models regarding the motion of lumbar vertebral segments

Abstract

The kinematics of a spinal motion segment is determined by the material properties of the soft-tissue and the morphology. The material properties can vary within subjects and between vertebral levels, leading to a wide possible range of motion of a spinal segment independently on its morphology. The goal of this numerical study was to identify the most influential material parameters concerning the kinematics of a spinal motion segment and their plausible ranges. Then, a method was tested to deduce the material properties automatically, based on a given ROM and morphology. A fully parametric finite element model of the morphology and material properties of a lumbar spinal motion segment was developed. The impact of uncertainty of twelve spinal material parameters, as well as the size of the gap between the articular surfaces of the facet joints was examined. The simulation results were compared to our own in vitro data. The flexibility of a lumbar segment was especially influenced by the properties of the anterior annulus region, the facet gap size and the interspinous ligament. The high degree of uncertainty in the material properties and facet gap size published in the literature can lead to a wide scatter in the motion of a spinal segment, with a range of 6°-17° in the intact condition in flexion/extension, from 5°-22° in lateral bending and from 3°-14° in axial rotation. Statistical analysis of the variability might help to estimate the sensitivity and total uncertainty propagated through biomechanical simulations, affecting the reliability of the predictions.     

Relationship between reaction time of eye movement and activity of the neck extensors

This study investigated the relationship between the reaction time of eye movement (RTEM) and activity of the superficial neck extensor muscles when the shoulder girdle elevator muscles contracted isometrically. The results were compared with those of a previous study in which the subjects's head was fixed and loaded with the neck flexed. When the shoulder girdle elevator muscles contracted isometrically, RTEM decreased significantly in comparison to RTEM at rest. This demonstrated that the reaction time significantly decreased not only as a result of the neck in flexion, which activated the deep and superficial neck extensor muscles, but also from contraction of the shoulder girdle elevator muscles which mainly activated the superficial extensor muscles. The relationship between RTEM and relative muscle load of the shoulder girdle elevator muscles showed that RTEM decreased up to 30% loading, and with loading above 40% the RTEM was longer than with 30%. The relative muscle load for the shortest RTEM demonstrated a subject-to-subject variance ranging from 24.7% to 49.6%. The difference between RTEM at rest and at their shortest reaction time was approximately 20 ms, which was consistent with the data for the neck in flexion. However, the relative muscle load for the shortest RTEM differed between the current and previous studies. The parameters obtained in this study were higher than for those in the previous study.     

Behaviour and kinematics of continuous ram filtration in bowhead whales (Balaena mysticetus)

Balaenid whales perform long breath-hold foraging dives despite a high drag from their ram filtration of zooplankton. To maximize the volume of prey acquired in a dive with limited oxygen supplies, balaenids must either filter feed only occasionally when prey density is particularly high, or they must swim at slow speeds while filtering to reduce drag and oxygen consumption. Using digital tags with three-axis accelerometers, we studied bowhead whales feeding off West Greenland and present here, to our knowledge, the first detailed data on the kinematics and swimming behaviour of a balaenid whale filter feeding at depth. Bowhead whales employ a continuous fluking gait throughout the bottom phase of foraging dives, moving at very slow speeds (less than 1 m s⁻¹), allowing them to filter feed continuously at depth. Despite the slow speeds, the large mouth aperture provides a water filtration rate of approximately 3 m³ s⁻¹, amounting to some 2000 tonnes of water and prey filtered per dive. We conclude that a food niche of dense, slow-moving zooplankton prey has led balaenids to evolve locomotor and filtering systems adapted to work against a high drag at swimming speeds of less than 0.07 body length s⁻¹ using a continuous fluking gait very different from that of nekton-feeding, aquatic predators.     

Probabilistic description of infant head kinematics in abusive head trauma

Abusive head trauma (AHT) is a potentially fatal result of child abuse, but the mechanisms by which injury occur are often unclear. To investigate the contention that shaking alone can elicit the injuries observed, effective computational models are necessary. The aim of this study was to develop a probabilistic model describing infant head kinematics in AHT. A deterministic model incorporating an infant’s mechanical properties, subjected to different shaking motions, was developed in OpenSim. A Monte Carlo analysis was used to simulate the range of infant kinematics produced as a result of varying both the mechanical properties and the type of shaking motions. By excluding physically unrealistic shaking motions, worst-case shaking scenarios were simulated and compared to existing injury criteria for a newborn, a 4.5 month-old, and a 12 month-old infant. In none of the three cases were head kinematics observed to exceed previously-estimated subdural haemorrhage injury thresholds. The results of this study provide no biomechanical evidence to demonstrate how shaking by a human alone can cause the injuries observed in AHT, suggesting either that additional factors, such as impact, are required, or that the current estimates of injury thresholds are incorrect.     

In vivo three-dimensional intervertebral kinematics of the subaxial cervical spine during seated axial rotation and lateral bending via a fluoroscopy-to-CT registration approach

Accurate measurement of the coupled intervertebral motions is helpful for understanding the etiology and diagnosis of relevant diseases, and for assessing the subsequent treatment. No study has reported the in vivo, dynamic and three-dimensional (3D) intervertebral motion of the cervical spine during active axial rotation (AR) and lateral bending (LB) in the sitting position. The current study fills the gap by measuring the coupled intervertebral motions of the subaxial cervical spine in ten asymptomatic young adults in an upright sitting position during active head LB and AR using a volumetric model-based 2D-to-3D registration method via biplane fluoroscopy. Subject-specific models of the individual vertebrae were derived from each subject’s CT data and were registered to the fluoroscopic images for determining the 3D poses of the subaxial vertebrae that were used to obtain the intervertebral kinematics. The averaged ranges of motion to one side (ROM) during AR at C3/C4, C4/C5, C5/C6, and C6/C7 were 4.2°, 4.6°, 3.0° and 1.3°, respectively. The corresponding values were 6.4°, 5.2°, 6.1° and 6.1° during LB. Intervertebral LB (ILB) played an important role in both AR and LB tasks of the cervical spine, experiencing greater ROM than intervertebral AR (IAR) (ratio of coupled motion (IAR/ILB): 0.23–0.75 in LB, 0.34–0.95 in AR). Compared to the AR task, the ranges of ILB during the LB task were significantly greater at C5/6 (p=0.008) and C6/7 (p=0.001) but the range of IAR was significantly smaller at C4/5 (p=0.02), leading to significantly smaller ratios of coupled motions at C4/5 (p=0.0013), C5/6 (p<0.001) and C6/7 (p=0.0037). The observed coupling characteristics of the intervertebral kinematics were different from those in previous studies under discrete static conditions in a supine position without weight-bearing, suggesting that the testing conditions likely affect the kinematics of the subaxial cervical spine. While C1 and C2 were not included owing to technical limitations, the current results nonetheless provide baseline data of the intervertebral motion of the subaxial cervical spine in asymptomatic young subjects under physiological conditions, which may be helpful for further investigations into spine biomechanics.     

Comparison of hierarchical and six degrees-of-freedom marker sets in analyzing gait kinematics

The objective of this study was to determine how marker spacing, noise, and joint translations affect joint angle calculations using both a hierarchical and a six degrees-of-freedom (6DoF) marker set. A simple two-segment model demonstrates that a hierarchical marker set produces biased joint rotation estimates when sagittal joint translations occur whereas a 6DoF marker set mitigates these bias errors with precision improving with increased marker spacing. These effects were evident in gait simulations where the 6DoF marker set was shown to be more accurate at tracking axial rotation angles at the hip, knee, and ankle.     

Level of subject-specific detail in musculoskeletal models affects hip moment arm length calculation during gait in pediatric subjects with increased femoral anteversion

Biomechanical parameters of gait such as muscle's moment arm length (MAL) and muscle-tendon length are known to be sensitive to anatomical variability. Nevertheless, most studies rely on rescaled generic models (RGMo) constructed from averaged data of cadaveric measurements in a healthy adult population. As an alternative, deformable generic models (DGMo) have been proposed. These models integrate a higher level of subject-specific detail by applying characteristic deformations to the musculoskeletal geometry. In contrast, musculoskeletal models based on magnetic resonance (MR) images (MRMo) reflect the involved subject's characteristics in every level of the model. This study investigated the effect of the varying levels of subject-specific detail in these three model types on the calculated hip MAL during gait in a pediatric population of seven cerebral palsy subjects presenting aberrant femoral geometry. Our results show large percentage differences in calculated MAL between RGMo and MRMo. Furthermore, the use of DGMo did not uniformly reduce inter-model differences in calculated MAL. The magnitude of these percentage differences stresses the need to take these effects into account when selecting the level of subject-specific detail one wants to integrate in musculoskeletal. Furthermore, the variability of these differences between subjects and between muscles makes it very difficult to a priori estimate their importance for a biomechanical analysis of a certain muscle in a given subject.     

Changes in Parkinsonian gait kinematics with self-generated and externally-generated cues: a comparison of responders and non-responders

Abstract

Purpose: Rhythmic auditory stimulation such as listening to music can alleviate gait bradykinesia in people with Parkinson disease (PD) by increasing spatiotemporal gait features. However, evidence about what specific kinematic alterations lead to these improvements is limited, and differences in responsiveness to cueing likely affect individual motor strategies. Self-generated cueing techniques, such as singing or mental singing, provide similar benefits but no evidence exists about how these techniques affect lower limb joint movement. In this study, we assessed immediate effects of external and self-generated cueing on lower limb movement trajectories during gait.

Methods: Using 3D motion capture, we assessed sagittal plane joint angles at the hip, knee, and ankle across 35 participants with PD, divided into responders (n?=?23) and non-responders (n?=?12) based on a clinically meaningful change in gait speed. Joint motion was assessed as overall range of motion as well as at two key time points during the gait cycle: initial contact and toe-off.

Results: Responders used both cue types to increase gait speed and induce increases in overall joint ROM at the hip while only self-generated cues also increased ROM at the ankle. Increased joint excursions for responders were also evident at initial contact and toe-off.

Conclusions: Our results indicate that self-generated rhythmic cues can induce similar increases in joint excursions as externally-generated cues and that some people may respond more positively than others. These results provide important insight into how self-generated cueing techniques may be tailored to meet the varied individual needs of people with PD.     

Kalman smoothing improves the estimation of joint kinematics and kinetics in marker-based human gait analysis

We developed a Kalman smoothing algorithm to improve estimates of joint kinematics from measured marker trajectories during motion analysis. Kalman smoothing estimates are based on complete marker trajectories. This is an improvement over other techniques, such as the global optimisation method (GOM), Kalman filtering, and local marker estimation (LME), where the estimate at each time instant is only based on part of the marker trajectories. We applied GOM, Kalman filtering, LME, and Kalman smoothing to marker trajectories from both simulated and experimental gait motion, to estimate the joint kinematics of a ten segment biomechanical model, with 21 degrees of freedom. Three simulated marker trajectories were studied: without errors, with instrumental errors, and with soft tissue artefacts (STA). Two modelling errors were studied: increased thigh length and hip centre dislocation. We calculated estimation errors from the known joint kinematics in the simulation study. Compared with other techniques, Kalman smoothing reduced the estimation errors for the joint positions, by more than 50% for the simulated marker trajectories without errors and with instrumental errors. Compared with GOM, Kalman smoothing reduced the estimation errors for the joint moments by more than 35%. Compared with Kalman filtering and LME, Kalman smoothing reduced the estimation errors for the joint accelerations by at least 50%. Our simulation results show that the use of Kalman smoothing substantially improves the estimates of joint kinematics and kinetics compared with previously proposed techniques (GOM, Kalman filtering, and LME) for both simulated, with and without modelling errors, and experimentally measured gait motion.