Reliability and Repeatability Analysis of Indices to Measure Gait Deterioration in MS Patients during Prolonged Walking.

Gait deterioration caused by prolonged walking represents one of the main consequences of multiple sclerosis (MS). This study aims at proposing quantitative indices to measure the gait deterioration effects. The experimental protocol consisted in a 6-min walking test and it involved nine patients with MS and twenty-six healthy subjects. Pathology severity was assessed through the Expanded Disability Status Scale. Seven inertial units were used to gather lower limb kinematics. Gait variability and asymmetry were assessed by coefficient of variation (CoV) and symmetry index (SI), respectively. The evolution of ROM (range of motion), CoV, and SI was computed analyzing data divided into six 60-s subgroups. Maximum difference among subgroups and the difference between the first minute and the remaining five were computed. The indices were analyzed for intra- and inter-day reliability and repeatability. Correlation with clinical scores was also evaluated. Good to excellent reliability was found for all indices. The computed standard deviations allowed us to affirm the good repeatability of the indices. The outcomes suggested walking-related fatigue leads to an always more variable kinematics in MS, in terms of changes in ROM, increase of variability and asymmetry. The hip asymmetry strongly correlated with the clinical disability.

Quantification of postural stability in minimally disabled multiple sclerosis patients by means of dynamic posturography: an observational study.

BACKGROUND: Multiple Sclerosis (MS) is a widespread progressive neurologic disease with consequent impairments in daily activities. Disorders of balance are frequent and equilibrium tests are potentially useful to quantify disability and to verify treatment effectiveness. The fair sensitivity of the widely used not-perturbed tests to detect balance disturbances in MS patients have prompted the development of mechatronic systems capable to impose known equilibrium perturbations, in order to challenge the balance control and, consequently, to better assess the level of impairment. We sought to clarify whether the proposed perturbed-test is capable to discriminate healthy subjects from patients with MS, even in mild or in the absence of clinically evident balance disturbances. METHODS: We assessed balance performances of 17 adults with MS and 13 age-matched healthy controls (HC) using both perturbed (PT) and not-perturbed (NPT) postural tests by means of a 3 Degree Of Freedom (DOF) rotational mechatronic platform. Participants stood barefoot on the platform in standing position and their center of pressure (CoP) was gathered by using a pressure matrix. Each trial lasted 30 s and was carried out with and without visual stimuli. Several postural indices were computed for each trial. Correlations between postural indices and clinical scales were analyzed. RESULTS: No significant differences were found between groups for all indices when subjects performed NPTs. Conversely, significant differences in postural indices between MS and HC emerged during PTs. Additionally, PTs revealed significant differences between patients without any cerebellar impairment (cerebellar EDSS subscore equal to 0) and HC. The discrimination capability of PTs was confirmed by the ROC analysis. No significant change of the selected metrics occurred in HC when NPTs were performed with eyes closed, while indices presented a significant worsening in MS subjects. CONCLUSIONS: Not-perturbed tests showed lower sensitivity than perturbed ones in the identification of equilibrium impairments in minimally disabled MS patients. However, not-perturbed tests allow to better evaluate the influence of visual flow disturbances on balance control in MS. In conclusion, our findings proved that the use of the novel tests based on a 3DOF mechatronic device represents an effective tool to investigate early balance disturbances in MS.

In Memoriam: Paolo Cappa.

Prof. Paolo Cappa passed away on 26 August 2016, at the age of 59, after a long and courageous fight against cancer. Paolo Cappa was a Professor in Mechanical and Thermal Measurements and Experimental Biomechanics in the Department of Mechanical and Aerospace Engineering of Sapienza University of Rome, where he had also served as the Head of the Department, and a Research Professor in the Department of Mechanical and Aerospace Engineering of New York University Tandon School of Engineering. During his intense, yet short, career, he made several significant scientific contributions within the discipline of Mechanical and Thermal Measurements, pioneering fundamental applications to Biomechanics. He co-founded the Motion Analysis and Robotics Laboratory (MARLab) within the Neurorehabilitation Division of IRCCS Pediatric Hospital "Bambino Gesu", in Rome, to fuel transitional research from the laboratory to clinical practice. Through collaboration with neurologists and physiatrists at MARLab, Prof. Cappa led the development of a powerful array of novel mechanical solutions to wearable robotics for pediatric patients, addressing dramatic needs for children's health and contributing to the training of an entire generation of Mechanical Engineering students.

A novel HMM distributed classifier for the detection of gait phases by means of a wearable inertial sensor network.

In this work, we decided to apply a hierarchical weighted decision, proposed and used in other research fields, for the recognition of gait phases. The developed and validated novel distributed classifier is based on hierarchical weighted decision from outputs of scalar Hidden Markov Models (HMM) applied to angular velocities of foot, shank, and thigh. The angular velocities of ten healthy subjects were acquired via three uni-axial gyroscopes embedded in inertial measurement units (IMUs) during one walking task, repeated three times, on a treadmill. After validating the novel distributed classifier and scalar and vectorial classifiers-already proposed in the literature, with a cross-validation, classifiers were compared for sensitivity, specificity, and computational load for all combinations of the three targeted anatomical segments. Moreover, the performance of the novel distributed classifier in the estimation of gait variability in terms of mean time and coefficient of variation was evaluated. The highest values of specificity and sensitivity (>0.98) for the three classifiers examined here were obtained when the angular velocity of the foot was processed. Distributed and vectorial classifiers reached acceptable values (>0.95) when the angular velocity of shank and thigh were analyzed. Distributed and scalar classifiers showed values of computational load about 100 times lower than the one obtained with the vectorial classifier. In addition, distributed classifiers showed an excellent reliability for the evaluation of mean time and a good/excellent reliability for the coefficient of variation. In conclusion, due to the better performance and the small value of computational load, the here proposed novel distributed classifier can be implemented in the real-time application of gait phases recognition, such as to evaluate gait variability in patients or to control active orthoses for the recovery of mobility of lower limb joints.

Bimanual Motor Strategies and Handedness Role in Human-Robot Haptic Interaction.

Bimanual object manipulation involves using both hands to interact with objects in the environment, and the process requires the central nervous system to process sensory feedback and translate it into motor commands. Although there have been significant advancements in haptics and robotics, the kinematic strategies involved in bimanual coupled tasks are still not fully understood. This study aimed to investigate the dynamic interaction between hands during the manipulation of a shared object using two impedance-controlled exoskeletons programmed to simulate bimanual coupled manipulation of virtual objects. Twenty-six participants (right-handed and left-handed) were asked to use both hands to grab and place simulated objects in specific locations. The virtual objects were rendered with four different dynamic properties, affecting the manipulation strategies used to complete the tasks. The results showed that force asymmetries were related to movement direction and handedness preference, with right-handers exhibiting asymmetries related to movement direction and left-handers showing better control of the force applied between their hands. This is possibly due to their constant exposure to objects designed for right-handed use. Additionally, the haptic properties of the virtual objects influenced task performance in terms of timing and failure for all participants. This study demonstrates the potential of advanced technologies to provide realistic simulations of multi-joint movements involving the entire upper extremities. The findings have implications for the development of training programs for bimanual object manipulation tasks and the design of virtual environments that can enhance the learning process.

Robotic Assessment of Wrist Proprioception During Kinaesthetic Perturbations: A Neuroergonomic Approach.

Position sense refers to an aspect of proprioception crucial for motor control and learning. The onset of neurological diseases can damage such sensory afference, with consequent motor disorders dramatically reducing the associated recovery process. In regular clinical practice, assessment of proprioceptive deficits is run by means of clinical scales which do not provide quantitative measurements. However, existing robotic solutions usually do not involve multi-joint movements but are mostly applied to a single proximal or distal joint. The present work provides a testing paradigm for assessing proprioception during coordinated multi-joint distal movements and in presence of kinaesthetic perturbations: we evaluated healthy subjects' ability to match proprioceptive targets along two of the three wrist's degrees of freedom, flexion/extension and abduction/adduction. By introducing rotations along the pronation/supination axis not involved in the matching task, we tested two experimental conditions, which differed in terms of the temporal imposition of the external perturbation: in the first one, the disturbance was provided after the presentation of the proprioceptive target, while in the second one, the rotation of the pronation/ supination axis was imposed during the proprioceptive target presentation. We investigated if (i) the amplitude of the perturbation along the pronation/supination would lead to proprioceptive miscalibration; (ii) the encoding of proprioceptive target, would be influenced by the presentation sequence between the target itself and the rotational disturbance. Eighteen participants were tested by means of a haptic neuroergonomic wrist device: our findings provided evidence that the order of disturbance presentation does not alter proprioceptive acuity. Yet, a further effect has been noticed: proprioception is highly anisotropic and dependent on perturbation amplitude. Unexpectedly, the configuration of the forearm highly influences sensory feedbacks, and significantly alters subjects' performance in matching the proprioceptive targets, defining portions of the wrist workspace where kinaesthetic and proprioceptive acuity are more sensitive. This finding may suggest solutions and applications in multiple fields: from general haptics where, knowing how wrist configuration influences proprioception, might suggest new neuroergonomic solutions in device design, to clinical evaluation after neurological damage, where accurately assessing proprioceptive deficits can dramatically complement regular therapy for a better prediction of the recovery path.

Stable or able? Effect of virtual reality stimulation on static balance of post-stroke patients and healthy subjects.

Over the last decades, virtual reality (VR) emerged as a potential tool for developing new rehabilitation treatments in neurological patients. However, despite the increasing number of studies, a clear comprehension about the impact of immersive VR-treatment on balance and posture is still scarce. In the present study, we aimed to investigate the effects of VR cues on balance performances of subjects affected by stroke, age-matched healthy subjects, and young healthy subjects. Fifteen patients with sub-acute stroke, fifteen healthy elderly subjects and fifteen healthy young adults took part in this study. All groups were immersed in a CAVE system on a stabilometric platform. The experiment consisted in fourteen trials: (i) ten VR trials, which differed in term of speed and movement direction; (ii) two-stabilometric static sessions, with opened and closed eyes (one at the start and one at the end of the experimental session). Results showed that VR trials increased the sway path length (representative of the body sway amplitudes), in young subjects. Elderly and patients showed less changes in postural sway during virtual reality stimulation than young group. These findings may suggest that a physiological postural performance is not simply evaluable assessing stability, but also assessing the ability of adapting body oscillations to the external stimuli.

Effect of changing visual condition and frequency of horizontal oscillations on postural balance of standing healthy subjects.

The goal of this study was to describe the movement pattern of the body-segment rotations of healthy subjects in the horizontal plane while they were standing on a supporting platform that imposed steady sinusoidal horizontal rotations under three visual conditions: (a) eyes closed with no instructions (EC-NI), (b) eyes open with instructions to gaze at a stationary black dot located at eye level on a wall surface about four meters in front of them (EO-WI), and (c) eyes closed with instructions to imagine looking at the same target (EC-WI). The selected input signal was a sinusoid with an amplitude of +/-45 deg at different frequencies equal to 0.25, 0.50 and 0.75 Hz, which were referred to as L, M and H. Bipedal balance measurements were taken in 10 adult subjects (mean age 30+/-9 years; three men and seven women). Subjects' kinematics were analyzed with an optoelectronic system. Under the three visual conditions, the movements of the pelvis, the trunk, and the head decreased and were inversely dependent on platform frequency; specifically, both the head and the trunk decreased their gain rotation of about 1.8-2.9 times from L to H, while the pelvis decreased its by about 1.3 times. However, the arm oscillations showed a gain and phase tendency opposite to that of the other body segments, with the gain rotation having increased of about 1.8-3.7 times from L to H. Comparing the three visual conditions, the finding suggests that the subjects were able to stabilize their head as a reference frame to maintain postural balance in a similar way under the EC-WI and EO-WI conditions. Instead, in the EC-NI trials, the subjects compensated less, in particular at the hip, the external perturbation producing higher absolute body rotations and lower relative body rotations. In fact, the head rotation was about four and three times the one showed in EC-WI and EO-WI, while for the trunk and the pelvis it was always equal to two and 1.5 times the correspondent rotation observed under the WI conditions. These results provide a quantitative assessment of compensatory balance reactions in healthy subjects to periodical horizontal perturbations.

WAKE-Up Exoskeleton to Assist Children With Cerebral Palsy: Design and Preliminary Evaluation in Level Walking.

This paper presents the modular design and control of a novel compliant lower limbmulti-joint exoskeleton for the rehabilitation of ankle kneemobility and locomotion of pediatric patients with neurological diseases, such as Cerebral Palsy (CP). The device consists of an untethered powered knee-ankle-foot orthosis (KAFO), addressed as WAKE-up (Wearable Ankle Knee Exoskeleton), characterized by a position control and capable of operating synchronously and synergistically with the human musculoskeletal system. The WAKE-up mechanical system, control architecture and feature extraction are described. Two test benches were used to mechanically characterize the device. The full system showed a maximum value of hysteresis equal to 8.8% and a maximum torque of 5.6 N m/rad. A pre-clinical use was performed, without body weight support, by four typically developing children and three children with CP. The aims were twofold: 1) to test the structure under weight-bearing conditions and 2) to ascertain its ability to provide appropriate assistance to the ankle and the knee during overground walking in a real environment. Results confirm the effectiveness of the WAKE-up design in providing torque assistance in accordance to the volitionalmovements especially in the recovery of correct foot landing at the start of the gait cycle.

Stepping over obstacles of different heights: kinematic and kinetic strategies of leading limb in hemiplegic children.

Twelve hemiplegic children (HC) and five normally developing children (NDC) were instructed to walk barefoot over a level surface and to cross obstacles of various heights (0%, 10%, 15% and 20% of their leg lengths). Kinematic and kinetic strategies of their leading limb were mainly examined. For the starting position of the trials HC was adjusted so that the affected limb was the leading one, while NDC step over the obstacle with their preferred selection of leading and trailing limb. The results demonstrated that the crossing speed was decreased and the crossing swing phase was increased in both groups. The toe vertical clearance augmented with the presence of the obstacle, but it remained constant with obstacle heights. The toe and heel horizontal distances of the leading limb remained constant with all obstacle heights. The toe horizontal distances of the trailing limb in HC increased with obstacle heights outlying a peculiar strategy. A comparison of joint angles and power variations revealed substantial differences in height changes between the two groups: HC exhibited a preferential modulation of pelvis and hip joints and a reduced modulation of knee and ankle joints. The knee flexor limitation in HC was accomplished by knee power variations near the toe-off. HC showed also an increased ankle involvement of the support limb, i.e. the almost normal limb. Collectively, the results provided insights into multijoint variations of locomotor act caused by visible obstacle in HC and indicate that a correct rehabilitation treatment should be focused on the use of dynamic constraints preferentially at the plegic knee.

A 3-DOF parallel robot with spherical motion for the rehabilitation and evaluation of balance performance.

In this paper a novel electrically actuated parallel robot with three degrees-of-freedom (3 DOF) for dynamic postural studies is presented. The design has been described, the solution to the inverse kinematics has been found, and a numerical solution for the direct kinematics has been proposed. The workspace of the implemented robot is characterized by an angular range of motion of about ±10° for roll and pitch when yaw is in the range ±15°. The robot was constructed and the orientation accuracy was tested by means of an optoelectronic system and by imposing a sinusoidal input, with a frequency of 1 Hz and amplitude of 10°, along the three axes, in sequence. The collected data indicated a phase delay of 1° and an amplitude error of 0.5%-1.5%; similar values were observed for cross-axis sensitivity errors. We also conducted a clinical application on a group of normal subjects, who were standing in equilibrium on the robot base with eyes open (EO) and eyes closed (EC), which was rotated with a tri-axial sinusoidal trajectory with a frequency of 0.5 Hz and amplitude 5° for roll and pitch and 10° for the yaw. The postural configuration of the subjects was recorded with an optoelectronic system. However, due to the mainly technical nature of this paper, only initial validation outcomes are reported here. The clinical application showed that only the tilt and displacement on the sagittal pane of head, trunk, and pelvis in the trials conducted with eyes closed were affected by drift and that the reduction of the yaw rotation and of the mediolateral translation was not a controlled parameter, as happened, instead, for the other anatomical directions.

Moment measurement accuracy of a parallel spherical robot for dynamic posturography.

This paper characterizes the moment measurement accuracy for a novel parallel spherical robot (SR) for dynamic posturography, controllable by position or impedance. The SR consists of three linear motors placed on a support base, a moving base, and three passive arms equipped with uniaxial load cells permitting impedance controlled perturbations. To evaluate the accuracy, a subject stood still on the SR, set in position control mode, while selected sinusoidal trajectories were applied. The moments computed by the load cells were compared to the value measured by a six-component force platform, placed on top of the rotating base. For the intended application of the SR, the errors were negligible with the worse case of only 4 Nm in a total of 15 trials (five conditions, three repetitions). The observed moment error was related mainly to the intrinsic accuracy of the sensors, equal to about 7 N. To demonstrate clinical applicability, the platform was set to impedance control mode and a protocol was tested with a 12-year-old girl with brain injury and a group of four healthy subjects. In total, 24 trials (eight conditions, three repetitions) were recorded for each subject. The results of this pilot study identified distinctive postural behaviors and therefore showed that the SR can be considered as an effective tool for dynamic posturography.

Reach-to-grasp interjoint coordination for moving object in children with hemiplegia.

OBJECTIVE: To evaluate interjoint coordination in children with hemiplegia as they reach to grasp objects, in both static and dynamic conditions. An ad hoc robotic device was used to study the dynamic condition. DESIGN: Observational study. PATIENTS: Six children with hemiplegia and 6 young adults. METHODS: Kinematics of the trunk and arm were studied using an optoelectronic system. In the dynamic condition the target object, a cup, was moved by the robotic device along clockwise and counterclockwise circular trajectories. RESULTS: Two main strategies were used to study the onset and offset of shoulder and elbow movements and their maximum velocities. The hand velocity profile was bell-shaped in the static condition and compatible with ramp movements for the more affected side in the dynamic condition. The time to object contact was higher for the more affected side in the dynamic condition. The temporal coordination index illustrated an immature and less flexible behaviour in children's reaching in all the examined conditions. CONCLUSION: Study of the hand velocity profiles, the time to object contact and the temporal coordination index highlighted, first, the dependence of upper limb interjoint coordination on task, context, residual resources and individual solution, and secondly, the sensory-motor deficit characteristics of the children's more affected side during dynamic reaching, raising the prospect of a promising training context in children with hemiplegia.

Numerical validation of linear accelerometer systems for the measurement of head kinematics.

The purpose of this study was to analytically exploit the capabilities of head-mounted systems instrumented with linear accelerometers (ACs) for field use in redundant configurations. We simulated different headsets equipped with uni-, bi- or triaxial sensors with a number of axes that lie in the range of 12-24; the ACs were located on a hemispherical surface by adopting a priori criterion while their orientation was randomized. In addition, for a comparative purpose the nine accelerometer scheme (one triaxial AC and three biaxial ACs addressed in the following as "3-2-2-2 configuration") was also analyzed in the present paper. We simulated and statistically assessed the performances of hemispherical headsets in the test case of a healthy subject walking freely at normal pace over level ground. The numerical results indicated that a well designed instrumented headset can retrieve the angular acceleration and (a0-g) component with rms errors of about 2% and 0.5%, respectively, and angular velocity with a drift error of about 20% in a 6 s trial. On the contrary, the pose of the headset cannot be evaluated because of the drift induced by the integration process. In general, we can state that headsets with uni-, bi- or triaxial ACs have comparable performances. The main implications of the above-mentioned observations are (a) neither expensive triaxial ACs nor assembling procedure based on the use of orthogonal mounting blocks are needed; (b) redundant arrays of low-cost uni- or biaxial ACs can effectively be used to reach adequate performances in biomechanical studies where head acceleration and velocity are investigated; (c) while estimates of angular acceleration with accelerometers are accurate, estimations of angular velocities, linear velocities and pose are not.

A continuous loading apparatus for measuring three-dimensional stiffness of ankle-foot orthoses.

This paper describes a novel device to evaluate the mechanical properties of ankle foot orthoses (AFOs). The apparatus permits the application to AFOs of continuous three-dimensional (3D) movements between specified and settable endpoints. Using an x-y robot with a rotary stage and a six-component load cell, characteristic displacement versus reaction force curves can be generated and consequently the ankle moments can be determined as a function of dorsi/plantar flexion, inv/eversion and int/external rotation. Representative curves for two polypropylene lateral leaf AFOs, different in shape but produced for the same leg by a skilled orthotist, are presented to illustrate the capabilities of the novel testing system. The metrological investigation showed that the apparatus creates a highly repeatable data set (uncertainty < or = 1% FSO).