Ambulatory measurement of 3D knee joint angle

Three-dimensional measurement of joint motion is a promising tool for clinical evaluation and therapeutic treatment comparisons. Although many devices exist for joints kinematics assessment, there is a need for a system that could be used in routine practice. Such a system should be accurate, ambulatory, and easy to use. The combination of gyroscopes and accelerometers (i.e., inertial measurement unit) has proven to be suitable for unrestrained measurement of orientation during a short period of time (i.e., few minutes). However, due to their inability to detect horizontal reference, inertial-based systems generally fail to measure differential orientation, a prerequisite for computing the three-dimentional knee joint angle recommended by the Internal Society of Biomechanics (ISB). A simple method based on a leg movement is proposed here to align two inertial measurement units fixed on the thigh and shank segments. Based on the combination of the former alignment and a fusion algorithm, the three-dimensional knee joint angle is measured and compared with a magnetic motion capture system during walking. The proposed system is suitable to measure the absolute knee flexion/extension and abduction/adduction angles with mean (SD) offset errors of -1 degree (1 degree ) and 0 degrees (0.6 degrees ) and mean (SD) root mean square (RMS) errors of 1.5 degrees (0.4 degrees ) and 1.7 degrees (0.5 degrees ). The system is also suitable for the relative measurement of knee internal/external rotation (mean (SD) offset error of 3.4 degrees (2.7 degrees )) with a mean (SD) RMS error of 1.6 degrees (0.5 degrees ). The method described in this paper can be easily adapted in order to measure other joint angular displacements such as elbow or ankle.     

Dynamic stability of superior vs. inferior body segments in individuals with transtibial amputation walking in destabilizing environments

Interestingly, young and highly active people with lower limb amputation appear to maintain a similar trunk and upper body stability during walking as able-bodied individuals. Understanding the mechanisms underlying how this stability is achieved after lower-leg amputation is important to improve training regimens for improving walking function in these patients. This study quantified how superior (i.e., head, trunk, and pelvis) and inferior (i.e., thigh, shank, and feet) segments of the body respond to continuous visual or mechanical perturbations during walking. Nine persons with transtibial amputation (TTA) and 12 able-bodied controls (AB) walked on a 2 m×3 m treadmill in a Computer Assisted Rehabilitation Environment (CAREN). Subjects were perturbed by continuous pseudo-random mediolateral movements of either the treadmill platform or the visual scene. TTA maintained a similar local and orbital stability in their superior body segments as AB throughout both perturbation types. However, for their inferior body segments, TTA subjects exhibited greater dynamic instability during perturbed walking. In TTA subjects, these increases in instability were even more pronounced in their prosthetic limb compared to their intact leg. These findings demonstrate that persons with unilateral lower leg amputation maintain upper body stability in spite of increased dynamic instability in their impaired lower leg. Thus, transtibial amputation does significantly impair sensorimotor function, leading to substantially altered dynamic movements of their lower limb segments. However, otherwise relatively healthy patients with unilateral transtibial amputation appear to retain sufficient remaining sensorimotor function in their proximal and contralateral limbs to adequately compensate for their impairment.     

Should a standing or seated reference posture be used when normalizing seated spine kinematics?

Currently in the literature there is no consensus on which procedure for normalizing seated spine kinematics is most effective. The objective of this study was to examine the changes in the range of motion (ROM) of seated posture trials when expressed as a percent of maximum standing and seated ROM. A secondary purpose was to determine whether the typical maximum planar calibration movements (flexion, lateral-bend, and axial twist) elicited the respective maximum ROM values for each spine region versus postures with specific movement instruction. Thirteen male participants completed seven different movement trials. These consisted of the maximum planar movement trials, with the remaining four postures being combinations of specific lumbar and thoracic movements. Global and relative angles for the upper-thoracic, mid-thoracic, lower-thoracic, and lumbar regions were calculated and normalized to both a seated and standing reference posture. When normalizing both global and relative angles the standing reference appears optimal for flexion, twisting and lateral bend angles in all spine regions, with the exception of relative flexion angle in the mid-thoracic region. The maximum planar movement trials captured the greatest ROM for each global angle, relative lower-thoracic angle and relative lumbar flexion angle, but did not for all other relative angles in the upper-thoracic, mid-thoracic, and lumbar regions. If future researchers can only collect one reference posture these results recommend that a standing reference posture be collected for normalizing seated spine kinematics, although a seated reference posture should be collected if examining relative flexion angles at the mid-thoracic region.     

Assessment of anatomical frame variation effect on joint angles: A linear perturbation approach

Although the interpretability and reliability of joint kinematics depends strongly on the accuracy and precision of determining the anatomical frame (AF) orientation, the exact dependency of joint angle error on AF misalignment is still not clear. To fully understand the behavior, this study uses linear perturbations to quantify joint angle error due to known modifications of the AFs, where the joint angles are calculated according to the Cardanic convention. The result is a functional representation of joint angle error with dependence on nominal joint angles and on the orientations of the alternative AFs relative to the nominal AFs. The results are validated using numerical analysis on knee joint angle data during walking. The derived relationship elucidates results from previous work studying this effect and allows AF differences to be inferred by joint angle curves when multiple sets of joint angle curves are collected simultaneously.     

Joint forces in the human pelvis-leg skeleton during walking

For the calculation of the forces in the hip, knee and ankle joints during walking the knowledge of the three-dimensional movements of the human body and of the forces between foot and ground is a prerequisite. It is shown how this information may be obtained and what accuracy is obtainable. For the calculation of the statically indeterminate system of the lower limbs, consisting of muscles, bones and joints an optimization method is applied. The optimization criterion is the minimization of the muscle forces. Measurements were taken with seventeen male and five female persons. The maximum joint forces are plotted against gait speed, body weight and body size. In addition some statistical distributions are presented.     

Mathematical model that predicts lower leg motion in response to electrical stimulation

Electrical stimulation of skeletal muscles of patients with upper motor neuron lesions can be used to restore functional movements such as standing or walking. Mathematical muscle models can assist in designing stimulation patterns that will enable patients to perform particular tasks more efficiently. In this study we extend our previous model to allow us to predict changes in knee joint angle in response to electrical stimulation of the human quadriceps femoris muscle. The model was tested both with and without inertial loads placed around the ankle joints of healthy subjects. Results showed that the model predicted the knee extensions with a RMS angle error that was generally 相似文献   

Kinematic characteristics of the voluntary cyclic trunk movements in patients at the early stage of Parkinson's disease

Patients with the initial stage of Parkinson disease (PD) and matched controls performed repetitive bendings and turnings in standing position. Tasks included trunk movements in each of the anatomical planes: sagittal, frontal and axial. Electromagnetic system Flock of Birds was used for movement registration. Sensors were fixed at different segments of subject's body. Joint angles in the ankle, hip and torso as well as coordinates of the center of pressure served as output parameters. The amplitudes of joint angles were found to be lower in PD patients. Performance of the axial rotation revealed most pronounced differences. Thus, the amplitudes of joint angles of trunk movements in different anatomical planes reliably discriminate between PD patients and healthy subjects.     

On the estimation of joint kinematics during gait.

In gait analysis, the concepts of Euler and helical (screw) angles are used to define the three-dimensional relative joint angular motion of lower extremities. Reliable estimation of joint angular motion depends on the accurate definition and construction of embedded axes within each body segment. In this paper, using sensitivity analysis, we quantify the effects of uncertainties in the definition and construction of embedded axes on the estimation of joint angular motion during gait. Using representative hip and knee motion data from normal subjects and cerebral palsy patients, the flexion-extension axis is analytically perturbed +/- 15 degrees in 5 degrees steps from a reference position, and the joint angles are recomputed for both Euler and helical angle definitions. For the Euler model, hip and knee flexion angles are relatively unaffected while the ab/adduction and rotation angles are significantly affected throughout the gait cycle. An error of 15 degrees in the definition of flexion-extension axis gives rise to maximum errors of 8 and 12 degrees for the ab/adduction angle, and 10-15 degrees for the rotation angles at the hip and knee, respectively. Furthermore, the magnitude of errors in ab/adduction and rotation angles are a function of the flexion angle. The errors for the ab/adduction angles increase with increasing flexion angle and for the rotation angle, decrease with increasing flexion angle. In cerebral palsy patients with flexed knee pattern of gait, this will result in distorted estimation of ab/adduction and rotation. For the helical model, similar results are obtained for the helical angle and associated direction cosines.(ABSTRACT TRUNCATED AT 250 WORDS)     

Analysis of 3D multi-segment lumbar spine motion during gait and prone hip extension

Modeling the lumbar spine as a single rigid segment does not consider the relative contribution of regional or segmental motion that may occur during a task. The current study used a multi-segment model to measure three-dimensional (3D) upper and lower lumbar spine motion during walking and prone hip extension (PHE). The degree of segmental redundancy during these movements was assessed by calculating the cross-correlation of the segmental angle time series (R₀) and the correlation of the segmental ranges of motion (R_ROM). All correlation coefficients (R₀, R_ROM) were interpreted as follows: very strong (0.80–1.00), strong (0.60–0.79), moderate (0.40–0.59), weak (0.20–0.39), and very weak (0.00–0.19). Strong/very strong positive R₀ were demonstrated between the two segments in all three planes during PHE and in the transverse plane during walking. Weak/moderate R₀ were demonstrated in the sagittal and frontal planes during walking. Strong/very strong positive R_ROM were demonstrated in the transverse plane during PHE, and moderate positive R_ROM was demonstrated in the sagittal plane during walking. Non-significant R_ROM were demonstrated for all other planes and movements. These results suggest the motion patterns of the upper and lower lumbar regions during walking and PHE are sufficiently distinct to warrant the use a multi-segment model for these movements. It also appears that the degree of redundancy between the upper and lower lumbar regions may be task-dependent.     

Order error in the calculation of continuous relative phase

The aims of this study were to demonstrate “order error” in the calculation of continuous relative phase (CRP) and to suggest two alternative methods—(i) constructing phase-plane portraits by plotting position over velocity; and (ii), the Hilbert transform—to rectify it. Order error is the change of CRP order between two degrees of freedom (e.g., body segments) when using the conventional method of constructing phase-plane portraits (i.e., velocity over position). Both sinusoidal and non-sinusoidal simulated signals as well as signals from human movement kinematics were used to investigate order error and the performance of the two alternative methods. Both methods have been shown to lead to correct results for simulated sinusoidal and non-sinusoidal signals. For human movement data, however, the Hilbert transform is superior for calculating CRP.     

The kinematic consequences of invariant dynamics in children 6-18 years of age

The effect of limb dynamics on trajectory formation is unclear. The natural frequency of a limb is the major factor in its dynamics. It has previously been shown with an indirect measurement method that the natural frequency of body segments is invariant during human growth from the age of 6 to 18. The aim of our study was to determine, using a direct measurement method, whether human growth affects: (1) lower limb dynamics (i.e. the natural frequency of the lower leg) and (2) the maximum velocities of the knee during selected motor tasks. In 20 non-disabled children, 6-18 years of age, measurements were taken of the natural frequency of the lower leg (including the foot), and the maximum velocities of knee flexion and extension during voluntary movement (MVV) and at initial and terminal swing phases of self-paced walking (WAL). The velocities were also estimated using a dynamic model and the results were compared to the measured velocities with a paired t-test. Correlations among the frequencies, velocities, and body height (an indicator of growth) were calculated. The natural frequency of the lower leg (mean+/-standard deviation, omega(0)=6.58+/-0.54s(-1)), maximum velocities of knee extension and flexion during voluntary movement (MVV(e)=10.1+/-1.8rads(-1) and MVV(f)=7.8+/-1.3rads(-1), respectively), and maximum velocities of knee flexion and extension during the swing phase of walking (WAL(f)=5.4+/-0.6rads(-1) and WAL(e)=6.3+/-0.87rads(-1), respectively) were each found to be independent of body height. The MVV measured velocities were 22% larger and WAL(f) measured velocities were 25% smaller than the velocities predicted from the dynamic model (p<0.05). The study found that a segment's dynamic properties, as well as selected kinematics, may be considered invariant with human growth.     

In vitro measurement of the restraining role of the anterior cruciate ligament during walking and stair ascent

The study aimed to test the hypothesis that the restraining role of the anterior cruciate ligament (ACL) of the knee is significant during the activities of normal walking and stair ascent. The role of the ACL was determined from the effect of ACL excision on tibiofemoral displacement patterns measured in vitro for fresh-frozen knee specimens subjected to simulated knee kinetics of walking (n = 12) and stair ascent (n = 7). The knee kinetics were simulated using a newly developed dynamic simulator able to replicate the sagittal-plane knee kinetics with reasonable accuracy while ensuring unconstrained tibiofemoral kinematics. The displacements were measured using a calibrated six degree-of-freedom electromechanical goniometer. For the simulation of the walking cycle, two types of knee flexion/extension moment patterns were used: the more common "biphasic" pattern, and an extensor muscle force intensive pattern. For both of these patterns, the restraining role of the ACL to tibial anterior translation was found to be significant throughout the stance phase and in the terminal swing phase, when the knee angle was in the range of 4 degrees to 30 degrees. The effect of ACL excision was an increase in tibial anterior translation by 4 mm to 5 mm. For the stair ascent cycle, however, the restraining role of the ACL was significant only during the terminal stance phase, and not during the initial and middle segments of the phase. Although, in these segments, the knee moments were comparable to that in walking, the knee angle was in the range of 60 degrees to 70 degrees. These results have been shown to be consistent with available data on knee mechanics and ACL function measured under static loading conditions.     

Similar sensorimotor transformations control balance during standing and walking

Standing and walking balance control in humans relies on the transformation of sensory information to motor commands that drive muscles. Here, we evaluated whether sensorimotor transformations underlying walking balance control can be described by task-level center of mass kinematics feedback similar to standing balance control. We found that delayed linear feedback of center of mass position and velocity, but not delayed linear feedback from ankle angles and angular velocities, can explain reactive ankle muscle activity and joint moments in response to perturbations of walking across protocols (discrete and continuous platform translations and discrete pelvis pushes). Feedback gains were modulated during the gait cycle and decreased with walking speed. Our results thus suggest that similar task-level variables, i.e. center of mass position and velocity, are controlled across standing and walking but that feedback gains are modulated during gait to accommodate changes in body configuration during the gait cycle and in stability with walking speed. These findings have important implications for modelling the neuromechanics of human balance control and for biomimetic control of wearable robotic devices. The feedback mechanisms we identified can be used to extend the current neuromechanical models that lack balance control mechanisms for the ankle joint. When using these models in the control of wearable robotic devices, we believe that this will facilitate shared control of balance between the user and the robotic device.     

Error reduction in the finite helical axis for knee kinematics

Traditionally the FHA is calculated stepwise between data points (sFHA), requiring down sampling to achieve a sufficiently large step size to minimize error. This paper proposes an alternate FHA calculation approach (rFHA), using a unique reference position to reduce error associated with small rotation angles. This study demonstrated error reduction using the rFHA approach relative to the sFHA approach. Furthermore, the rFHA in the femur is defined at each time point providing a continuous representation of joint motion. These characteristics enable the rFHA to quantify small differences in knee joint motion, providing an excellent measure to quantify knee joint stability.     

Optimization of the mechanical performance of a two-duct semicircular duct system--part 3: the positioning of the ducts in the head

In the majority of vertebrates, the horizontal duct of the vestibular system lies approximately in the yawing plane of the head. The positioning of the vertical ducts, however, is not in the pitch- and roll planes but the vertical ducts generally lie under an angle of about 30-45 degrees relative to the medial plane. Using the equations for a hydrodynamically interconnected two-duct system, optimal positions of the vertical and horizontal ducts in different vertebrate groups can be derived. It was stated that the mean response of the vertical ducts should be optimized. This leads to a symmetrical positioning of the vertical ducts with respect to the medial plane. In all observed vertebrate groups, a solution of mu =(pi-alpha)/2 is found (mu is the angle of the vertical ducts relative to the medial plane, alpha is the angle between the vertical duct planes). For alpha=90 degrees, this provides an equal sensitivity for pitch- and roll- movements. For alpha>90 degrees, a larger sensitivity for pitch movements is obtained, at the expense of a lower sensitivity for roll movements. It is argued that the angle alpha between the vertical ducts may vary from 90 to 120 degrees. In most vertebrates, the centre of mass is stabilized by e.g. fins, tri- or quadrupedal stability, a crawling body or upside-down resting positions (e.g. bats). Birds are generally biped, so in walking they are also rather sensitive to roll. These features are related to labyrinth positioning in the head.     

Optimal muscular coordination strategies for jumping

This paper presents a detailed analysis of an optimal control solution to a maximum height squat jump, based upon how muscles accelerate and contribute power to the body segments during the ground contact phase of jumping. Quantitative comparisons of model and experimental results expose a proximal-to-distal sequence of muscle activation (i.e. from hip to knee to ankle). We found that the contribution of muscles dominates both the angular acceleration and the instantaneous power of the segments. However, the contributions of gravity and segmental motion are insignificant, except the latter become important during the final 10% of the jump. Vasti and gluteus maximus muscles are the major energy producers of the lower extremity. These muscles are the prime movers of the lower extremity because they dominate the angular acceleration of the hip toward extension and the instantaneous power of the trunk. In contrast, the ankle plantarflexors (soleus, gastrocnemius, and the other plantarflexors) dominate the total energy of the thigh, though these muscles also contribute appreciably to trunk power during the final 20% of the jump. Therefore, the contribution of these muscles to overall jumping performance cannot be neglected. We found that the biarticular gastrocnemius increases jump height (i.e. the net vertical displacement of the center of mass of the body from standing) by as much as 25%. However, this increase is not due to any unique biarticular action (e.g. proximal-to-distal power transfer from the knee to the ankle), since jumping performance is similar when gastrocnemius is replaced with a uniarticular ankle plantarflexor.     

Full-body motion assessment: Concurrent validation of two body tracking depth sensors versus a gold standard system during gait

RGB-D cameras provide 3-D body joint data in a low-cost, portable and non-intrusive way, when compared with reference motion capture systems used in laboratory settings. In this contribution, we evaluate the validity of both Microsoft Kinect versions (v1 and v2) for motion analysis against a Qualisys system in a simultaneous protocol. Two different walking directions in relation to the Kinect (towards – WT, and away – WA) were explored. For each gait trial, measures related with all body parts were computed: velocity of all joints, distance between symmetrical joints, and angle at some joints. For each measure, we compared each Kinect version and Qualisys by obtaining the mean true error and mean absolute error, Pearson’s correlation coefficient, and optical-to-depth ratio. Although both Kinect v1 and v2 and/or WT and WA data present similar accuracy for some measures, better results were achieved, overall, when using WT data provided by the Kinect v2, especially for velocity measures. Moreover, the velocity and distance presented better results than angle measures. Our results show that both Kinect versions can be an alternative to more expensive systems such as Qualisys, for obtaining distance and velocity measures as well as some angles metrics (namely the knee angles). This conclusion is important towards the off-lab non-intrusive assessment of motor function in different areas, including sports and healthcare.     

Lower extremity control and dynamics during backward angular impulse generation in forward translating tasks

Observation of complex whole body movements suggests that the nervous system coordinates multiple operational subsystems using some type of hierarchical control. When comparing two forward translating tasks performed with and without backward angular impulse, we have learned that both trunk-leg coordination and reaction force-time characteristics are significantly different between tasks. This led us to hypothesize that differences in trunk-leg coordination and reaction force generation would induce between-task differences in the control of the lower extremity joints during impulse generation phase of the tasks. Eight highly skilled performers executed a series of forward jumps with and without backward rotation (reverse somersault and reverse timer, respectively). Sagittal plane kinematics, reaction forces, and electromyograms of lower extremity muscles were acquired during the take-off phase of both tasks. Lower extremity joint kinetics were calculated using inverse dynamics. The results demonstrated between-task differences in the relative angles between the lower extremity segments and the net joint forces/reaction force and the joint angular velocity profiles. Significantly less knee extensor net joint moments and net joint moment work and greater hip extensor net joint moments and net joint moment work were observed during the push interval of the reverse somersault as compared to the reverse timer. Between-task differences in lower extremity joint kinetics were regulated by selectively activating the bi-articular muscles crossing the knee and hip. These results indicate that between-task differences in the control of the center of mass relative to the reaction force alters control and dynamics of the multijoint lower extremity subsystem.     

Muscle contributions to support during gait in an individual with post-stroke hemiparesis

Walking requires coordination of muscles to support the body during single stance. Impaired ability to coordinate muscles following stroke frequently compromises walking performance and results in extremely low walking speeds. Slow gait in post-stroke hemiparesis is further complicated by asymmetries in lower limb muscle excitations. The objectives of the current study were: (1) to compare the muscle coordination patterns of an individual with flexed stance limb posture secondary to post-stroke hemiparesis with that of healthy adults walking very slowly, and (2) to identify how paretic and non-paretic muscles provide support of the body center of mass in this individual. Simulations were generated based on the kinematics and kinetics of a stroke survivor walking at his self-selected speed (0.3 m/s) and of three speed-matched, healthy older individuals. For each simulation, muscle forces were perturbed to determine the muscles contributing most to body weight support (i.e., height of the center of mass during midstance). Differences in muscle excitations and midstance body configuration caused paretic and non-paretic ankle plantarflexors to contribute less to midstance support than in healthy slow gait. Excitation of paretic ankle dorsiflexors and knee flexors during stance opposed support and necessitated compensation by knee and hip extensors. During gait for an individual with post-stroke hemiparesis, adequate body weight support is provided via reorganized muscle coordination patterns of the paretic and non-paretic lower limbs relative to healthy slow gait.     

Passive resistance of the human knee: The effect of immobilization

The effects of immobilization on both the circumferential dimensions of the lower limb, and the passive resistance of the knee to sinusoidal motion in the flexion-extension plane, were studied in patients immobilized after tibial fractures or ligamentous injuries of the knee. Immobilization resulted in a decrease of circumferential dimensions of the lower limb, indicating atrophy of thigh and calf musculature. The equilibrium angle of the knee, i.e. the angle at which the net passive moment equals zero, approached the angle of the knee during immobilization. At knee angles of 60° (the maximal angle imposed on the immobilized knee) and 45°, the resistance was increased, and at angles of 30° and 15°, the resistance was decreased. The passive resistances at ± 22.5, 15 and 7.5° relative to the equilibrium angle were all increased. A simple model, taking into account changes in the length of muscles at the anterior and posterior side of the knee, explains changes in passive resistance. The duration of immobilization for patients with ligamentous injuries of the knee was less than 50% of that for patients with tibial fractures, whose ankle joint was not immobilized, both resulted in a smaller muscular atrophy for patients with ligamentous injuries. Differences in passive resistance between unaffected and immobilized legs were the same in both groups of patients. Changes in passive resistance in the immobilized leg for those with ligamentous injury are probably not the effect of immobilization alone but the combined effect of immobilization and ligamentous lesions.