Decoding kinetic parameters of grasping movements from single unit activity in monkey motor cortex

Development of neuronal prosthetics, where neuronal activity is used to control artificial limbs, has so far relied on decoding kinematic parameters of movements, such as movement position or velocity. In addition to kinematic control, proper control of forces exerted by the prosthetic device is necessary for successful interaction with the environment. In our study, we analysed the possibility of classifying and decoding different grasp related forces during active grasping. Two macaque monkeys were trained to reach, grasp and pull an object in response to visual cues. Cues instructed the monkeys to grasp the object with one out of two grip types (precision or side grip) and pull the object with one of two different forces (0.5N or 2N). Monkeys obtained a food reward after successfully performing the instructed grip and pull. During the task execution, we recorded electrophysiological signals from the multielectrode arrays implanted intracortically in the hand and arm area of the monkey’s motor cortex. Six different parameters of the grip: four pressure forces on each side of the object, pull force on the object and the object displacement, were recorded simultaneously with the neuronal activity. Recorded neuronal activity was used to classify different grip types or loading forces, and to decode the continuous traces of different forces during the grip. Our results show that kinetic grip parameters can be decoded with high accuracy, thereby improving the feasibility of constructing fully functional anthropomorphic neuronal prosthesis that relies on kinetic (force) control.

Listed In: Biomechanical Engineering, Neuroscience

Flexion Angle Dependent Differences in Joint Kinematics and ACL Force In Response to Applied Loads Are Conserved Throughout Skeletal Growth in the Porcine Stifle Joint

The anterior cruciate ligament (ACL) stabilizes the lower limb against translational and rotational loads while the knee is is multiple postures. Surgical reconstruction, the most common treatment for ACL tears, is intended to replicate the biomechanical function of the native ACL in the postures and activities related to daily living and high-impact activities. In order to improve outcomes from ACL reconstructions in patients in pediatric and adolescent age groups, we need to improve our understanding of the knee posture dependent biomechanical function of the ACL. As such, the objective of this study was to quantify flexion angle dependent changes in the response of the ACL and the total knee to applied loads in the anterior-posterior and varus-valgus directions using a skeletally immature porcine model. To do this, we collected stifle (knee) joints from female Yorkshire-cross pigs at ages ranging from 1.5 to 18 months (n=30 total). The joints were tested using a 6 degree-of-freedom universal force sensing robotic system under applied anterior-posterior loads and varus-valgus moments at 40° and 60° of flexion. Studied parameters included anterior-posterior tibial translation (APTT), varus-valgus rotation (VVR), and anterior force carried by the ACL and its anteromedial and posterolateral bundles. We found increased knee laxity (APTT and VVR) was associated with both younger age and increased knee flexion. Greater anterior force carried in the ACL, and specifically in the anteromedial bundle, was associated with increased flexion, regardless of age. These findings have implications in intraoperative graft assessment and biomechanical models.
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research, Sports Science

Gait as a Potential Marker of Cognitive Decrements in Type 2 Diabetes (T2DM): Early Results from the ENBIND Study

Background and Aim: Type 2 Diabetes (T2DM) in midlife represents a potent risk factor for the development of dementia in later life. Early indicators to highlight particular individuals with T2DM who are at risk of cognitive decline are lacking. Subtle abnormalities in gait (and particularly dual-task gait with a cognitive task) have emerged as a potential predictor of cognitive decline in older adults, but have not been investigated in patients with T2DM. The ENBIND Study (Exploring Novel Biomarkers of Brain health IN Diabetes) aims to assess patients with T2DM in midlife without cognitive impairment and follow participants over the course of several years to establish early predictors of cognitive decline in this poorly characterised yet high-risk group. Methods: Patients with midlife T2DM (40-65 yrs) were recruited at the time of their diabetic clinic appointment. Patients were excluded if they had a diagnosis of peripheral neuropathy, peripheral vascular disease, musculoskeletal disease, previous stroke, any form of diagnosed cognitive impairment or diabetic retinopathy/nephropathy. Patients underwent medical/diabetes assessment and examination by a physician. Cognition was screened using the Montreal Cognitive Assessment (MoCA) and assessed using a computerised cognitive battery designed for prodromal Alzheimer's Disease (CANTAB®). Gait was then assessed using both a raw clinical measure (stopwatch) and Shimmer® Inertial Measurement Units (IMUs) across four tasks: (i) 30 metre walk at a normal pace (turn at 15m), (ii) 30 metre fast walk (turn at 15m) (iii) dual cognitive-gait task (reciting alternate letters of the alphabet) and (iv) a long walk at a self-selected pace. Between group differences were assessed using t-tests and appropriate non-parametric equivalents Results: 20 participants with T2DM (52.05 yrs ± 2.13) and 10 matched healthy volunteers (mean age 52.2 yrs ± 2.74) were recruited. T2DM was associated with a significantly lower score on the MoCA (29.2 vs 27.6; p=0.0452). Participants with T2DM had slower but non-significant self-selected (0.87 ms-1 vs 0.8ms-1) and fast gait speed (0.66 ms-1 vs 0.59 ms-1). On the dual-cognitive task, participants with T2DM made more errors (1.1 vs 0.6), and had higher dual-task cost (9.17% vs 2.7%, p=0.014). Dual-task cost (the percentage decrement in walking speed due to introduction of the cognitive task) was significantly correlated with total MoCA score (R2 = 0.17, p =0.031). Discussion: Otherwise healthy participants with midlife T2DM display significantly poorer scores on MoCA. Performance on the dual-cognitive gait task was significantly correlated with MoCA score. Our study adds evidence to the presence of cognitive decrements in midlife T2DM, in-keeping with its role as a potent risk factor for the later development of dementia. We provide early data to support the utility of simple clinical gait analysis, particularly where a dual-cognitive paradigm is employed. Expansion of the sample size of patients in this study as well as longitudinal follow up should afford more detailed insight into using gait as a potential marker for cognition in this high risk cohort
Listed In: Biomechanical Engineering, Biomechanics, Gait, Neuroscience

Fluid load support in the migrating contact area: How much migration is necessary?

It is well-accepted that cartilage maintains interstitial fluid load support under long-term joint loading because contact migration leaves insufficient time for fluid exudation. However, it’s also evident that the benefits of migration dissipate as range of motion first approaches the contact length, a situation typical of moving diarthrodial joints, and then zero—typical of static joints. This study aims to elucidate the transition from full fluid load support to zero fluid load support under restricted ranges of motion. Testing was performed on osteochondral plugs using varied probe sizes, loads and track-lengths at Pe >> 1; fluid load support, contact area, and contact stress were quantified in-situ. Fluid load support depended primarily on the migration length per unit contact length (S*) and maintained maximal magnitude (F*=100%) at S* > 10. At S* < 10, it varied as a sigmoidal function of S*, falling to F* = 50% by S* = 0.1 on average. This transition migration length was independent of probe radius and varied slightly, yet significantly with contact area, load, and contact stress over the ranges tested. When migration length approached the contact length, the fluid load support of cartilage fell below that predicted by the established mechanics of migrating contacts. Based on our results, we propose a simple analytical correction that should be used when S*<10. These results demonstrate that fluid retention and load support are impaired by reduced activity and reduced ranges of motion, especially given the relatively short tracks of most joints at full range of motion.
Listed In: Biomechanical Engineering, Biomechanics, Biotribology

Could lowering the tackle height law to below the chest in rugby union reduce long-term brain degeneration?

The tackle height law in rugby union has been an area of concern for many years. It is currently set at the line of the ball carrier’s shoulder. The goal of this study is to use Model-Based Image-Matching (MBIM) and human volunteer tackles in a marker-based 3D motion analysis laboratory to examine the severity of a legal tackle to the shoulder/chest of the ball carrier (with no head contact) and the effect of tackles above and below the chest on ball carrier inertial head kinematics, respectively. From the real-world tackles, the estimated ball carrier peak resultant change in head angular velocity was 30.4 rad/s (23.1 rad/s, 14.0 rad/s and 21.8 rad/s in the coronal, sagittal and transverse direction, respectively). In the staged tackles, the median peak resultant head linear and angular acceleration and change in head angular velocity values for tackles above the chest were greater than for below the chest. The results support the proposition of lowering the current tackle height law. Due to the real-world tackle (MBIM), the ball carrier head kinematics indicated a greater than 75% chance of sustaining a concussion, based on the literature. This was the case even though no contact was made with the ball carrier’s head. Therefore, repeatedly engaging in this type of legal tackle may be detrimental for long-term brain health. However, by lowering the tackle height law to below the chest, ball carrier inertial head kinematics can be reduced significantly, thus reducing the repetitive loading placed on the brain.
Listed In: Biomechanical Engineering, Biomechanics, Sports Science

Increased Role of the Secondary Passive Stabilizers Following Complete but Not Partial Loss of Anterior Cruciate Ligament Function During Post-Natal Growth

Robotic testing was performed with a 6-degree of freedom load cell in order to analyze functional contributions of the soft tissues in the knee under physiologically relevant loading conditions. Age groups ranging from 1.5 months to 18 months, porcine equivalent to early youth through late adolescent human ages, were studied. Complete ACL transection resulted in increased APTT and VVR across all ages (p<0.05), while injury to the AM bundle did not affect APTT or VVR. Additionally, increasing age resulted in decreased APTT normalized to the tibial plateau (p<0.05) and an average 19° decrease in VVR across states from 0 to 18 months of age (p<0.05). The ACL was the primary restraint against anterior drawer in the intact knee state [75-111%]. Following AM bundle dissection, the PL bundle carried the vast majority of the anterior load regardless of age [66-112%]. Following complete ACL transection, the MCL and medial meniscus carried most of the force across ages under anterior drawer. The LCL contributed increasing resistance to varus torque across states with age, as did the MCL under valgus torque.
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research, Sports Science

Multigenerational growth approach to incorporate residual stress in an intervertebral disc finite element model with validation in multi-axial loading

Residual stresses are known to exist in human intervertebral discs but have not been incorporated in finite element models. A multigeneration model was applied to the annulus fibrosus of the intervertebral disc to simulate residual stresses arising from growth and remodeling. The intervertebral disc shape and compressive creep were used to verify that the multigeneration approach generates realistic values of residual stress. The model was then validated by comparing its 6 degree-of-freedom mechanical response to experimental data. Human intervertebral discs were tested in a custom-built hexapod in all 6 degrees-of-freedom (lateral shear, anterior-posterior shear, torsion, bending, flexion, and compression). Incorporating residual stresses resulted in a finite element model which can predict 4 degrees-of-freedom while excluding residual stresses produces a finite element model that can only predict 2 degrees-of-freedom.
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research

In Vivo MRI Quantification of Human Disc Compression and Flexion/Extension

Disc function is mechanical, and measures of disc mechanical function are important to address spine function, degenerative disc disease, and low back pain. In vivo measures of disc mechanical function are needed, however the current standard in disc imaging is to acquire a single static image and classify the disc’s appearance using qualitative integer scales for degree of degeneration. Current grading standards are acknowledged as insufficient to identify symptomatic discs for treatment. In addition, static T2 weighted MRI cannot provide mechanical function information – mechanics must be measured as the change following a load or deformation perturbation. Because the disc experiences significant compression and height loss throughout the day, and because flexion-extension postures are often associated with low back pain, these physiological mechanical perturbations have potential to be used to quantify disc mechanics in vivo. The objective of this study was to use MRI-based methods to quantify in vivo disc function by measuring changes in disc geometry and T2 relaxation time with diurnal changes and with controllable posture. Quantification of in vivo disc mechanics by using diurnal loading or prescribed posture changes has potential to improve our ability to identify, evaluate, and treat degenerative disc disease. Symptomatic discs may have aberrant mechanics; if so, in vivo measurements of mechanical function may, with continued development, facilitate diagnosis of pathological discs.
Listed In: Biomechanical Engineering

Measuring Soft Tissue Contributions to Elbow Joint Motion and Virtual Ligament Modelling An In-Vitro Study

Knowledge of ligamentous contributions to joint stability is essential to restore normal joint range of motion and functionality through reconstruction procedures. Although, there has been numerous studies on the pathomechanics of the elbow joint, there have been very few rigorous and systematic attempts to characterize the roles of soft tissues during clinically relevant motions. Five fresh frozen cadaveric elbows from three male subjects were used for this study. In-vitro simulations were performed using a VIVO six degree-of-freedom (6-DOF) joint motion simulator (AMTI, Watertown, MA) capable of virtually simulating the effects of soft tissue constraints (virtual ligaments). This study introduces a unique, hybrid experimental-computational technique for measuring and simulating the biomechanical contributions of ligaments to elbow joint kinematics and stability. In vitro testing of cadaveric joints is enhanced by the incorporation of fully parametric virtual ligaments, which are used in place of the native joint stabilizers to characterize the contribution of elbow ligaments during simple flexion-extension motions using the principle of superposition. our results demonstrate the importance of AMCL and RCL structures as primary stabilizers under valgus and varus loading respectively. Virtual ligaments demonstrate the ability to restore the VV stability of the joint in the absence of any soft tissues attached to the osseous structures. This demonstrates the effectiveness of “virtual” ligaments for in vitro testing of elbow joint biomechanics, with applications in pre-clinical assessment of elbow implants.
Listed In: Biomechanical Engineering, Biomechanics, Mechanical Engineering, Orthopedic Research

More Push from your Push-Off: Joint-Level Modifications to Modulate Propulsive Forces in Old Age

Even prior to walking slower, older adults walk with a diminished push-off – decreased propulsive forces (FP) accompanied by reduced ankle moment and power generation. The purpose of this study was to identify age-related differences in the joint-level modifications used to modulate FP generation during walking. We posit that there are two possibilities for older adults to enhance FP generation. First, older adults may increase ankle power generation and thereby alleviate compensatory demands at the hip. Alternatively, older adults may opt to exacerbate their distal to proximal redistribution by relying even more on the hip musculature. 10 healthy young adults and 16 healthy older adults participated in this study. Subjects walked at their preferred speed while watching a video monitor displaying their instantaneous FP while instructed to modify their FP to match target values representing normal and ±10% and ±20% of normal. For all trials, we estimated lower extremity joint kinematics and kinetics. During normal walking, older adults exerted smaller FP and ankle power than young adults. Enhancing FP via biofeedback alleviated mechanical power demands at the hip, without changes in ankle power. Further, older adults walked with increased FP without increasing their total positive joint work. Thus, given the same total requisite power generation, older adults got ‘more bang for their ankle power buck’ using biofeedback.
Listed In: Biomechanical Engineering, Biomechanics, Gait