An upper extremity kinematic model for evaluation of hemiparetic stroke

Improved multi-unit decoding at the brain-machine interface using population temporal linear filtering

Current efforts to decode control signals from multi-unit (MU) recordings rely on the use of spike sorting to differentiate neurons and the use of firing rates estimated over tens of milliseconds to reconstruct sensorimotor signals. The computational bottleneck associated with the need to identify and sort individual neuron responses poses challenges for the development of portable, real-time, neural decoding systems that can be incorporated into assistive and prosthetic devices for the disabled. Here, we investigate the ability of spike-based linear filtering to reduce computational overhead and improve the accuracy of decoding neuronal signals for populations of spiking neurons. Using a population temporal (PT) decoding framework, the speed and accuracy of spike-based MU decoding were compared with firing rate-based approaches using simulated populations of motor neurons tuned for the velocity of intended movement. For the two linear filtering approaches, the accuracy of decoded movements was examined as a function of the number of recorded neurons, amount of noise, with and without spike sorting, and for training and test motions whose statistics were either similar or dissimilar. Our results suggest that the use of a PT decoding framework can offset the loss in accuracy associated with decoding unsorted MU neural signals. Coupled with up to a 20-fold reduction in the number of decoding weights and the ability to implement the filtering in hardware, this approach could reduce the computational requirements and thus increase the portability of next generation brain-machine interfaces.

Upper extremity inverse dynamics model for crutch-assisted gait assessment

Current inverse dynamics models of the upper extremity (UE) are limited for the measurement of Lofstrand crutch-assisted gait. The objective of this study is to develop, validate, and demonstrate a three-dimensional (3-D) UE motion assessment system to quantify crutch-assisted gait in children. We propose a novel 3-D dynamic model of the UEs and crutches for quantification of joint motions, forces, and moments during Lofstrand crutch-assisted gait. The model is composed of the upper body (i.e., thorax, upper arms, forearms, and hands) and Lofstrand crutches to determine joint dynamics of the thorax, shoulders, elbows, wrists, and crutches. The model was evaluated and applied to a pediatric subject with myelomeningocele (MM) to demonstrate its effectiveness in the characterization of crutch gait during multiple walking patterns. The model quantified UE dynamics during reciprocal and swing-through crutch-assisted gait patterns. Joint motions and forces were greater during swing-through gait than reciprocal gait. The model is suitable for further application to pediatric crutch-user populations. This study has potential for improving the understanding of the biomechanics of crutch-assisted gait and may impact clinical intervention strategies and therapeutic planning of ambulation.

Stroke-related differences in axial body segment coordination during preplanned and reactive changes in walking direction

This study quantitatively describes differences between participants with hemiparetic stroke and age-matched healthy participants in axial body segment and gait kinematics during a direction change task. Participants were required to change walking direction by 45 degrees, either to their left or right, at the midpoint of a 6-m path. Participants were visually cued either at the start of the walk (pre-planned) or one stride before they reached the turn point (reactive). The sequence and inter-segmental timing of axial orientation onset was preserved in participants with stroke. Analysis of a subgroup of stroke survivors indicated that participants with lesions affecting the basal ganglia (BG) took significantly longer time than control participants to initiate the reorientation synergy when making turns to their non-paretic side. We hypothesize that these differences are a product of asymmetrical activity of dopaminergic pathways in the brain resulting from compromised BG function.

Upper extremity biomechanical model of crutch-assisted gait in children

A 3D biomechanical model with a novel instrumented Lofstrand crutch system is presented. The novel Lofstrand crutch system consists of two six-axis load cells incorporated in the crutch to study the reaction forces occurring at the crutch handle and the cuff. The goal of this study is to quantify the effect of the cuff forces with the help of this improved crutch system. The kinematic model developed is verified based on previous studies. The kinetic model, consisting of the forces, is derived using the kinematic data, anthropometric data and the reaction forces generated from the load cells. The kinetic data is also in accordance with previous studies. Thus, the novel crutch system has been verified for evaluating the force loading on shoulder, elbow and wrist. This model would be further implemented on children suffering from Osteogenesis Imperfecta (OI), which would help in evaluating injury prevention criteria for long-term crutch users.

Muscle fatigue does not lead to increased instability of upper extremity repetitive movements

Muscle fatigue alters neuromuscular responses. This may lead to increased sensitivity to perturbations and possibly to subsequent injury risk. We studied the effects of muscle fatigue on movement stability during a repetitive upper extremity task. Twenty healthy young subjects performed a repetitive work task, similar to sawing, synchronized with a metronome before and after performing each of two fatiguing tasks. The first fatigue task (LIFT) primarily fatigued the shoulder flexor muscles, while the second fatigue task (SAW) fatigued all of the muscles of the arm. Subjects performed each task in random order on two different days at least seven days apart. Instantaneous mean EMG frequencies (IMNF) decreased over both fatiguing tasks indicating that subjects did experience significant muscle fatigue. The slopes of the IMNF over time and the decreases in maximum force measurements demonstrated that the LIFT fatigue task successfully fatigued the shoulder flexors to a greater extent than any other muscle. On average, subjects exhibited more locally stable shoulder movements after the LIFT fatigue task (p=0.035). They also exhibited more orbitally stable shoulder (p=0.021) and elbow (p=0.013) movements after the SAW fatigue task. Subjects also had decreased cocontraction at the wrist post-fatigue for both tasks (p=0.001) and at the shoulder (p<0.001) for the LIFT fatigue task. Therefore, increased dynamic stability of these repeated movements cannot be explained by increased muscle cocontraction. Possible alternative mechanisms are discussed.

A new kinematic model of the upper extremity based on functional joint parameter determination for shoulder and elbow

A new upper extremity model is introduced for clinical application. It combines the advantages of functional methods to determine the joint parameters for the shoulder joint centre and the elbow axis location with the ease of a minimal skin mounted marker set. Soft tissue artefacts at the shoulder and upper arm are reduced via a coordinate transfer between dynamic calibration and the actual motion analyzed. A unique technical frame linked to markers on the forearm is defined for the humerus. The protocol has been applied to 50 subjects over a wide age range (5-85 years) and with varying physical status, proving clinical feasibility. Variability in joint centre localization in repeated measures was typically below 1 cm. Based on these estimated joint centre locations for shoulder and elbow, three shoulder joint angles together with elbow flexion and forearm pro-/supination were determined in a large set of static arm postures in 5 subjects. These were compared to synchronous universal goniometer measurements to analyse intra-tester, inter-tester, and inter-subject repeatability. Differences between the computed angles and the angles obtained directly with the goniometer remained below +/-5 degrees for joint angles up to 120 degrees and +/-10 degrees above 120 degrees.

Review of quantitative measurements of upper limb movements in hemiplegic cerebral palsy

This review provides an overview of results found in literature on objective measurements of upper limb movements in children with hemiplegic cerebral palsy (HCP). Seventeen articles were selected following a systematic search. Analysed tasks varied from simple reaching and gross motor functions to complex, fine motor tasks. Spatiotemporal characteristics have been extensively studied and longer movement durations, slower movement speed and reduced trajectory straightness at the affected upper limb, compared to the non-affected side or healthy children, were most frequently reported. Joint kinematics has been far less studied. The limited data confirm the clinical impression of children with HCP using less elbow extension and supination to reach for an object, which is compensated by increased trunk flexion. Increased trunk involvement was also reported during gross motor functions. Although three-dimensional (3D) movement analysis seems promising to provide additional insights in the pathological upper limb movements observed in HCP, future standardisation of the entire protocol is crucial. No consensus exists on the procedures for data collection, processing, analysing and reporting of results, or what upper limb tasks should be assessed. The International Society of Biomechanics recently proposed recommendations on the definition of upper limb joint coordinate systems and rotation sequences. These guidelines were not yet applied in these studies. Although the diverse methodological approaches used in the studies complicate the comparison of published results, some general conclusions could be drawn. A further standardisation of the protocol for 3D upper limb movement analysis will provide the foundation for comparable and repeatable results and eventually facilitate the selection and planning of treatment interventions.

Upper extremity dynamics during Lofstrand crutch-assisted gait in children with myelomeningocele

The use of quantitative models for evaluating upper extremity (UE) dynamics in children with myelomeningocele (MM) is limited. A biomechanical model for assessment of UE dynamics during Lofstrand crutch-assisted gait in children with MM is presented. This pediatric model may be a valuable tool for clinicians to characterize crutch-assisted gait, which may advance treatment monitoring, crutch prescription, and rehabilitation planning for children with MM. Nine subjects with L3 or L4 level myelodysplasia (mean+/-S.D. age: 11.1+/-3.8 years) were analyzed during forearm crutch-assisted gait: (1) reciprocal gait and (2) swing-through gait. Three-dimensional (3D) dynamics of the UE were acquired and the Pediatric Outcomes Data Collection Instrument (PODCI) was administered. The goal of this study was to determine if meaningful differences occur between gait patterns in UE kinematics and kinetics, and if correlations exist between dynamics and functional outcomes. Temporal-distance parameters showed significant differences between reciprocal and swing-through gait in stride length, and stance duration. All joint ranges of motion were greater during swing-through gait. Thorax, elbow and crutch ranges of motion were found to be significantly different between gait patterns. Kinetic results demonstrated significant differences between reciprocal and swing-through gait, bilaterally, at all joints for the force variables of mean superior/inferior force, range of force, and maximum inferior force. Functional outcomes were strongly correlated with joint dynamics. Accurate quantitative assessment is essential for preventing injury in long-term crutch users. This study has potential for improving clinical intervention strategies and therapeutic planning of ambulation for children with MM.

Kinematics of turning 180 degrees during the timed up and go in stroke survivors with and without falls history

BACKGROUND

Community-dwelling, chronic stroke survivors are at risk of falling during turning and are more likely to sustain a hip fracture when they fall.

OBJECTIVE

This study quantifies kinematic differences between stroke survivors (mean +/- SD: 38.3 +/- 31.3 months post-stroke, 59.9 +/- 10.1 years of age), with (n = 9) and without a falls history (n = 9), and age-matched healthy counterparts (n = 18) in turning coordination during the 180 degrees turn around in the Timed "Up & Go" (TUG) test.

METHODS

Full-body kinematics were recorded while participants performed the 180 degrees turn around in the TUG. Dependent measures were time to turn, number of steps to turn, and measures of axial segment coordination. Result. Although participants who had a stroke and falls history took significantly longer to turn (mean +/- SD: 4.4 +/- 1.7 seconds) than age-matched controls (2.5 +/- 0.6 seconds), no kinematic differences were found in performance or in the axial segment coordination during turning that could contribute to falls history or falls risk.

CONCLUSIONS

These results indicate incidences of falls during turning following stroke may not be due to impaired movement patterns but due to the many other factors that are associated with falls, such as deficits in cognitive processes--attention or central integration--and/or sensory deficits.

A model of the upper extremity using FES for stroke rehabilitation

A model of the upper extremity is developed in which the forearm is constrained to lie in a horizontal plane and electrical stimulation is applied to the triceps muscle. Identification procedures are described to estimate the unknown parameters using tests that can be performed in a short period of time. Examples of identified parameters obtained experimentally are presented for both stroke patients and unimpaired subjects. A discussion concerning the identification's repeatability, together with results confirming the accuracy of the overall representation, is given. The model has been used during clinical trials in which electrical stimulation is applied to the triceps muscle of a number of stroke patients for the purpose of improving both their performance at reaching tasks and their level of voluntary control over their impaired arm. Its purpose in this context is threefold: Firstly, changes occurring in the levels of stiffness and spasticity in each subject's arm can be monitored by comparing frictional components of models identified at different times during treatment. Secondly, the model is used to calculate the moments applied during tracking tasks that are due to a patient's voluntary effort, and it therefore constitutes a useful tool with which to analyze their performance. Thirdly, the model is used to derive the advanced controllers that govern the level of stimulation applied to subjects over the course of the treatment. Details are provided to show how the model is applied in each case, and sample results are shown.

Finite element analysis of forearm crutches during gait in children with myelomeningocele

A finite element analysis of a commercial forearm crutch for children during gait is presented. The geometric features of the crutch structure were acquired and modeled. The finite element model was created using shell elements based on the frame surfaces. Linear elastic material properties for aluminum alloy were utilized. Upper extremity kinetic data from reciprocal and swing-through gait patterns were applied to the model as boundary conditions and loads. Stress distributions during two gait patterns were determined. Stress distributions during swing-through gait were found to be statistically greater than those during reciprocal gait (p = 0.01). This work provides novel quantitative data to improve crutch design and stimulate further analyses of upper extremity joint loads during forearm crutch-assisted gait in children with myelomeningocele (spina bifida).

Foot and ankle kinematics in patients with posterior tibial tendon dysfunction

The purpose of this study is to provide a quantitative characterization of gait in patients with posterior tibial tendon dysfunction (PTTD), including temporal-spatial and kinematic parameters, and to compare these results to those of a Normal population. Our hypothesis was that segmental foot kinematics were significantly different in multiple segments across multiple planes. A 15 camera motion analysis system and weight-bearing radiographs were employed to evaluate 3D foot and ankle motion in a population of 34 patients with PTTD (30 females, 4 males) and 25 normal subjects (12 females, 13 males). The four-segment Milwaukee Foot Model (MFM) with radiographic indexing was used to analyze foot and ankle motion and provided kinematic data in the sagittal, coronal and transverse planes as well as temporal-spatial information. The temporal-spatial parameters revealed statistically significant deviations in all four metrics for the PTTD population. Stride length, cadence and walking speed were all significantly diminished, while stance duration was significantly prolonged (p<0.0125). Significant kinematic differences were noted between the groups (p<0.002), including: (1) diminished dorsiflexion and increased eversion of the hindfoot; (2) decreased plantarflexion of the forefoot, as well as abduction shift and loss of the varus thrust in the forefoot; and (3) decreased range of motion (ROM) with diminished dorsiflexion of the hallux. The study provides an impetus for improved orthotic and bracing designs to aid in the care of distal foot segments during the treatment of PTTD. It also provides the basis for future evaluation of surgical efficacy. The course of this investigation may ultimately lead to improved treatment planning methods, including orthotic and operative interventions.

Upper limb impairments associated with spasticity in neurological disorders

Background

While upper-extremity movement in individuals with neurological disorders such as stroke and spinal cord injury (SCI) has been studied for many years, the effects of spasticity on arm movement have been poorly quantified. The present study is designed to characterize the nature of impaired arm movements associated with spasticity in these two clinical populations. By comparing impaired voluntary movements between these two groups, we will gain a greater understanding of the effects of the type of spasticity on these movements and, potentially a better understanding of the underlying impairment mechanisms.

Methods

We characterized the kinematics and kinetics of rapid arm movement in SCI and neurologically intact subjects and in both the paretic and non-paretic limbs in stroke subjects. The kinematics of rapid elbow extension over the entire range of motion were quantified by measuring movement trajectory and its derivatives; i.e. movement velocity and acceleration. The kinetics were quantified by measuring maximum isometric voluntary contractions of elbow flexors and extensors. The movement smoothness was estimated using two different computational techniques.

Results

Most kinematic and kinetic and movement smoothness parameters changed significantly in paretic as compared to normal arms in stroke subjects (p < 0.003). Surprisingly, there were no significant differences in these parameters between SCI and stroke subjects, except for the movement smoothness (p ≤ 0.02). Extension was significantly less smooth in the paretic compared to the non-paretic arm in the stroke group (p < 0.003), whereas it was within the normal range in the SCI group. There was also no significant difference in these parameters between the non-paretic arm in stroke subjects and the normal arm in healthy subjects.

Conclusion

The findings suggest that although the cause and location of injury are different in spastic stroke and SCI subjects, the impairments in arm voluntary movement were similar in the two spastic groups. Our results also suggest that the non-paretic arm in stroke subjects was not distinguishable from the normal, and might therefore be used as an appropriate control for studying movement of the paretic arm.

A dynamic model of the upper extremities for quantitative assessment of Lofstrand crutch-assisted gait

Appropriate models for quantitative evaluation of upper extremity dynamics in children with myelomeningocele are limited. Therefore, a three-dimensional (3D) biomechanical model of the upper extremities was developed for quantification during Lofstrand crutch-assisted gait in children with myelomeningocele. The model accurately tracks the joint angles of the trunk, shoulders, elbows, wrists, and crutches. Lofstrand crutches are instrumented with six-axis load cells to obtain force and moment components. The model is applied while performing crutch-assisted ambulatory patterns (alternate gait and swing-through gait). Analysis indicates that the model is suitable for quantifying upper extremity motion during crutch-assisted gait. This model has been designed for dynamic assessment of ambulatory patterns (upper and lower extremities) that present with pediatric myelomeningocele. It is hoped that the study findings will prove useful through advances in treatment monitoring, crutch prescription and therapeutic planning.

Use of multiple wearable inertial sensors in upper limb motion tracking

This paper presents a new human motion tracking system using two wearable inertial sensors that are placed near the wrist and elbow joints of the upper limb. Each inertial sensor consists of a tri-axial accelerometer, a tri-axial gyroscope and a tri-axial magnetometer. The turning rates of the gyroscope were utilised for localising the wrist and elbow joints on the assumption that the two upper limb segment lengths are known a priori. To determine the translation and rotation of the shoulder joint, an equality-constrained optimisation technique is adopted to find an optimal solution, incorporating measurements from the tri-axial accelerometer and gyroscope. Experimental results demonstrate that this new system, compared to an optical motion tracker, has RMS position errors that are normally less than 0.01 m, and RMS angle errors that are 2.5-4.8 degrees .

Upper extremity dynamics during Lofstrand crutch-assisted gait in children with myelomeningocele

BACKGROUND/OBJECTIVE

We present a 3-dimensional biomechanical model of the upper extremities to characterize joint dynamics during 2 patterns of Lofstrand crutch-assisted gait in children with myelomeningocele. The upper extremity model incorporates recommendations by the International Society of Biomechanics.

METHODS

A Vicon motion analysis system (14 cameras) captured the marker patterns. Instrumented crutches measured reaction forces. Five subjects with L3 or L4 level myelodysplasia (aged 9.8 +/- 1.6 years) were analyzed during reciprocal and swing-through Lofstrand crutch-assisted gait.

RESULTS

The mean walking speed, cadence, and stride length were greatest during swing-through gait. Although the gait patterns had different morphologies, the thorax and elbows remained in flexion, the wrists remained in extension, and the shoulders demonstrated both flexion and extension throughout the gait cycles. Swing-through gait showed larger ranges of motion for all joints than reciprocal gait. Peak crutch forces were highest during swing-through gait. The model was effective in detecting significant differences in upper extremity joint dynamics between reciprocal and swing-through crutch-assisted gait in children with myelomeningocele.

CONCLUSIONS

Results support continued testing. Future work should include clinical and functional assessment in a correlated study of dynamics and function. Knowledge from the study may be useful in treatment planning and intervention.