Determinants of gait as applied to children with cerebral palsy

Simulation study on assist-as-needed control of a rehabilitation robotic walker

BACKGROUND

Along with China entering an aging society, the percentage of people that over 60 will reach 34.9% in 2050, resulted in a significant increase in stroke patients.

OBJECTIVE

This paper proposes a rehabilitation robotic walker for walking assistance during the daily life, and a control method for the motor relearning during the gait training. The walker consists of an omni-directional mobile platform (OMP) which ensures the walker can move on the ground, a body weight support system (BWS) which is capable of providing the desired unloading force, and a pelvic assist mechanism (PAM) to provide the user with four degrees of freedom and avoid the rigid impact. The study goal is to gain a better understanding of the assist-as-needed control strategy during the gait training.

METHODS

For the man-machine interaction control, the assist-as-needed control strategy is adopted to guide the users' motions and improve the interaction experience. To build the force field in the three-dimensional space, the dynamics of the system is derived to increase the accuracy of force control.

RESULTS

The simulation results show that the force field around the motion trajectory was generated in the three-dimensional space. In order to understand the force field, we designed the simulation on sagittal plane and the controller can generate the appropriate force field. The preliminary experiment results were consistent with the simulation results.

CONCLUSION

Based on the mathematical simulation and the preliminary test, the results demonstrate that the proposed system can provide the guide force around the target trajectory, the accuracy of force control still remains to be improved.

Providing a Primary Care Medical Home for Children and Youth With Cerebral Palsy

Cerebral palsy (CP) is the most common motor disorder of childhood, with prevalence estimates ranging from 1.5 to 4 in 1000 live births. This clinical report seeks to provide primary care physicians with guidance to detect children with CP; collaborate with specialists in treating the patient; manage associated medical, developmental, and behavioral problems; and provide general medical care to their patients with CP.

Lower limb inter-joint coordination patterns are associated with walking experience in toddlers according to limb and stance periods

Walking experience is crucial for inter-joint coordination during gait acquisition. Toddlers show asymmetrical lower limb function during early locomotion for transferring body weight (regulatory limb) and steering the direction of walking (impulse limb). This study aimed to investigate the association between coordination patterns and walking experience, and between coordination variability and walking experience according to healthy toddlers' lower limb function and stance periods. Typically developing toddlers (n = 22; 17.27 ± 3.13 months) were distributed into two groups: up to (LWE) and greater than (GWE) three months of walking experience. The lower limbs were classified as regulatory or impulse limb and analyzed during the onset (SO), mid (MS), and late (LS) stance intervals. Hip-ankle, knee-ankle, and hip-knee coupling angle (CA) and its variability (CAV) were assessed. A relationship was found between inter-joint coordination pattern and groups, which was distinct according to stance period and lower limb function: (a) hip-ankle CA: at SO for both limbs, MS for the regulatory limb, and LS for the impulse limb; (b) knee-ankle CA: at SO for both limbs and MS for the regulatory limb; (c) hip-knee CA: at SO for both limbs, at MS for the regulatory limb, and LS for the impulse limb. These findings were linked to differences observed in distal joints between groups, mainly at the ankle during stance onset. The CAV was negatively associated with walking experience only in the regulatory limb in the following variables: hip-ankle at MS, knee-ankle at SO, and hip-knee at LS. Findings showed different functional roles of the lower limbs in dealing with the demands of balance and propulsion during early walking.

Machine Learning Strategies for Low-Cost Insole-Based Prediction of Center of Gravity during Gait in Healthy Males

Whole-body center of gravity (CG) movements in relation to the center of pressure (COP) offer insights into the balance control strategies of the human body. Existing CG measurement methods using expensive measurement equipment fixed in a laboratory environment are not intended for continuous monitoring. The development of wireless sensing technology makes it possible to expand the measurement in daily life. The insole system is a wearable device that can evaluate human balance ability by measuring pressure distribution on the ground. In this study, a novel protocol (data preparation and model training) for estimating the 3-axis CG trajectory from vertical plantar pressures was proposed and its performance was evaluated. Input and target data were obtained through gait experiments conducted on 15 adult and 15 elderly males using a self-made insole prototype and optical motion capture system. One gait cycle was divided into four semantic phases. Features specified for each phase were extracted and the CG trajectory was predicted using a bi-directional long short-term memory (Bi-LSTM) network. The performance of the proposed CG prediction model was evaluated by a comparative study with four prediction models having no gait phase segmentation. The CG trajectory calculated with the optoelectronic system was used as a golden standard. The relative root mean square error of the proposed model on the 3-axis of anterior/posterior, medial/lateral, and proximal/distal showed the best prediction performance, with 2.12%, 12.97%, and 12.47%. Biomechanical analysis of two healthy male groups was conducted. A statistically significant difference between CG trajectories of the two groups was shown in the proposed model. Large CG sway of the medial/lateral axis trajectory and CG fall of the proximal/distal axis trajectory is shown in the old group. The protocol proposed in this study is a basic step to have gait analysis in daily life. It is expected to be utilized as a key element for clinical applications.

Machine learning approach to predict center of pressure trajectories in a complete gait cycle: a feedforward neural network vs. LSTM network

Center of pressure (COP) trajectories of human can maintain regulation of forward progression and stability of lateral sway during walking. The insole pressure system can only detect COP trajectories of each foot during single stance. In this study, we developed artificial neural network models that could present COP trajectories in an integrated coordinate system during a complete gait cycle using pressure information of the insole system. A feed forward artificial neural network (FFANN) and a long short-term memory (LSTM) model were developed. For FFANN, among 198 pressure sensors from Pedar-X insoles, proper input variables were selected using sequential forward selection to reduce input dimension. The LSTM model used all 198 signals as inputs because of its self-learning characteristic. As results of cross-validation, the FFANN model showed correlation coefficients of 0.98-0.99 and 0.93-0.95 in anterior/posterior and medial/lateral directions, respectively. For the LSTM model, correlation coefficients were similar to those of FFANN. However, the relative root mean square error (12.5%) of the FFANN model was higher than that (9.8%) of the LSTM model in medial/lateral direction (p = 0.03). This study can be used for quantitative evaluation of clinical diagnosis and rehabilitation status for patient with various diseases through further training using varied databases. Graphical abstract Architectures of neural networks developed in this study (a feed forward artificial neural network; b LSTM network).

On the Adaptation of Pelvic Motion by Applying 3-dimensional Guidance Forces Using TPAD

Pelvic movement is important to human locomotion as the center of mass is located near the center of pelvis. Lateral pelvic motion plays a crucial role to shift the center of mass on the stance leg, while swinging the other leg and keeping the body balanced. In addition, vertical pelvic movement helps to reduce metabolic energy expenditure by exchanging potential and kinetic energy during the gait cycle. However, patient groups with cerebral palsy or stroke have excessive pelvic motion that leads to high energy expenditure. In addition, they have higher chances of falls as the center ofmass could deviate outside the base of support. In this paper, a novel control method is suggested using tethered pelvic assist device (TPAD) to teach subjects to walk with a specified target pelvic trajectory while walking on a treadmill. In this method, a force field is applied to the pelvis to guide it to move on a target trajectory and correctional forces are applied, if the pelvis motion has excessive deviations from the target trajectory. Three different experimentswith healthy subjects were conducted to teach them to walk on a new target pelvic trajectory with the presented control method. For all three experiments, the baseline trajectory of the pelvis was experimentally determined for each participating subject. To design a target pelvic trajectory which is different from the baseline, Experiment I scaled up the lateral component of the baseline pelvic trajectory, while Experiment II scaled down the lateral component of the baseline trajectory. For both Experiments I and II, the controller generated a 2-D force field in the transverse plane to provide the guidance force. In this paper, seven subjects were recruited for each experiment who walked on the treadmill with suggested control methods and visual feedback of their pelvic trajectory. The results show that the subjects were able to learn the target pelvic trajectory in each experiment and also retained the training effects after the completion of the experiment. In Experiment III, both lateral and vertical components of the pelvic trajectory were scaled down from the baseline trajectory. The force field was extended to three dimensions in order to correct the vertical pelvic movement as well. Three subgroups (force feedback alone, visual feedback alone, and both force and visual feedback) were recruited to understand the effects of force feedback and visual feedback alone to distinguish the results from Experiments I and II. The results showthat a trainingmethod that combines visual and force feedback is superior to the training methods with visual or force feedback alone. We believe that the present control strategy holds potential in training and correcting abnormal pelvic movements in different patient populations.

Feasibility of using a large amplitude movement therapy to improve ambulatory function in children with cerebral palsy

Cerebral palsy (CP) is the most common cause of motor disability among children. Limited evidence exists regarding the efficacy of traditional rehabilitation strategies on improving ambulatory function in this population. The purpose of the study was to investigate the feasibility and short-term effects of a novel large amplitude movement therapy on ambulatory functions in children with CP. Temporal-spatial gait characteristics were examined before and after a single intervention session, replicated over five children. Five children with CP (7.0 ± 1.0 years); Gross Motor Function Classification System Levels I-II, participated. Baseline gait parameters were obtained as the participant walked across an instrumented walkway at self-selected and fast speeds. Children then participated in a 20-30 min intervention focused on making body and limb movements as large as possible with gait assessment repeated immediately. All children tolerated testing and therapy with no adverse effects. Outcomes after one intervention included: significantly greater stride velocity; reduced double support time; and greater stride length after training for three of the five participants. Results for this pilot study suggested that the large amplitude movement therapy was feasible for children with CP. There is a need for a larger scale study to determine if the protocol can be effective at an appropriate clinical dose.

Effect of balance training on postural balance control and risk of fall in children with diplegic cerebral palsy

PURPOSE

The purpose of this study was to evaluate the effects of balance training on postural control and fall risk in children with diplegic cerebral palsy.

METHODS

Thirty spastic diplegic cerebral palsied children (10-12 years) were included in this study. Children were randomly assigned into two equal-sized groups: control and study groups. Participants in both groups received a traditional physical therapy exercise program. The study group additionally received balance training on the Biodex balance system. Treatment was provided 30 min/d, 3 d/week for 3 successive months. To evaluate the limit of stability and fall risk, participated children received baseline and post-treatment assessments using the Biodex balance system. Overall directional control, total time to complete the test, overall stability index of the fall risk test and total score of the pediatric balance scale were measured.

RESULTS

Children in both groups showed significant improvements in the mean values of all measured variables post-treatment (p < 0.05). The results also showed significantly better improvement in the measured parameters for the study group, as compared to the control group (p < 0.05).

CONCLUSION

Balance training on Biodex system is a useful tool that can be used in improving postural balance control in children with diplegic cerebral palsy.

Frontal Plane Motion of the Pelvis and Hip during Gait Stance Discriminates Children with Diplegia Levels I and II of the GMFCS

Objective. To determine if gait waveform could discriminate children with diplegic cerebral palsy of the GMFCS levels I and II. Patients. Twenty-two children with diplegia, 11 classified as level I and 11 as level II of the GMFCS, aged 7 to 12 years. Methods. Gait kinematics included angular displacement of the pelvis and lower limb joints during the stance phase. Principal components (PCs) analyses followed by discriminant analysis were conducted. Results. PC1s of the pelvis and hip in the frontal plane differ significantly between groups and captured 80.5% and 86.1% of the variance, respectively. PC1s captured the magnitude of the pelvic obliquity and hip adduction angle during the stance phase. Children GMFCS level II walked with reduced pelvic obliquity and hip adduction angles, and these variables could discriminate the groups with a cross-validation of 95.5%. Conclusion. Reduced pelvic obliquity and hip adduction were observed between children GMFCS level II compared to level I. These results could help the classification process of mild-to-moderate children with diplegia. In addition, it highlights the importance of rehabilitation programs designed to improve pelvic and hip mobility in the frontal plane of diplegic cerebral palsy children level II of the GMFCS.

BALANCE CONTROL DURING LEVEL WALKING IN CHILDREN WITH SPASTIC DIPLEGIC CEREBRAL PALSY

Children with cerebral palsy (CP) have been reported to have various levels of deficits in balance control, which can be described using the relationship between the body's centre of mass (COM) and the centre of pressure (COP). This study aimed to investigate the balance control of children with spastic diplegic CP during level walking. The COM-COP inclination angles and angular velocities, as well as temporal-spatial variables from 12 children with spastic diplegic CP (seven girls and five boys, aged 12.4 ± 4.4 years) and 12 normal controls (eight girls and four boys, aged 11.2 ± 4.4 years) were obtained using a motion analysis system and two forceplates. With compromised balance control as a result of neuromusculoskeletal pathologies, the CP group walked with reduced walking speed and stride length (p < 0.05), but increased stride time and step width (p < 0.05), indicating reduced gait efficiency. They also showed significantly reduced anterioposterior COM-COP inclination angles and angular velocities (p < 0.05), but increased mediolateral COM-COP inclination angles and angular velocities (p < 0.05) when compared to the normal controls. The latter phenomenon may be related to an increased risk of falling in these patients. Therefore, it appears that programs and/or devices for preventing falls are needed for children with spastic diplegic CP.

The gait of children with and without cerebral palsy: work, energy, and angular momentum

This paper describes a method to characterize gait pathologies like cerebral palsy using work, energy, and angular momentum. For a group of 24 children, 16 with spastic diplegic cerebral palsy and 8 typically developed, kinematic data were collected at the subjects self selected comfortable walking speed. From the kinematics, the work-internal, external, and whole body; energy-rotational and relative linear; and the angular momentum were calculated. Our findings suggest that internal work represents 53% and 40% respectively of the whole body work in gait for typically developed children and children with cerebral palsy. Analysis of the angular momentum of the whole body, and other subgroupings of body segments, revealed a relationship between increased angular momentum and increased internal work. This relationship allows one to use angular momentum to assist in determining the kinetics and kinematics of gait which contribute to increased internal work. Thus offering insight to interventions which can be applied to increase the efficiency of bipedal locomotion, by reducing internal work which has no direct contribution to center of mass motion, in both normal and pathologic populations.

The dynamic balance of the children with cerebral palsy and typical developing during gait. Part I: Spatial relationship between COM and COP trajectories

Analysis of the COM or COP movement has been a simplified method to illustrate the balance disorders in static stance and gait, but has its limitation when examined alone. Dynamic stability of 32 children with cerebral palsy (CP) was examined and compared with 10 typically developing (TD) children by measuring the displacement of center of mass (COM) and center of pressure (COP) and their spatial relationship. The children with CP were further divided into two groups based on topographical involvement, hemiplegia (Hemi) and diplegia (Di). The participants walked with their preferred speed at least 5 successful trials on a walkway with two force plates mounted in the middle. An eight-camera motion analysis was used to capture 26 reflective markers secured at the bony landmarks of the participant. The data obtained from motion analysis and force plates was used to calculate COM and COP. The results showed either of two CP groups demonstrated significantly greater peak-to-peak COM and COP displacement in medio-lateral (ML) and lower peak-to-peak COM and COP displacement in anterio-posterior (AP) direction than TD group. The root mean square (RMS) of COM-COP divergence of Hemi and Di groups were higher than that of TD group in AP and ML direction, but only the difference in ML direction was significant. Present study demonstrates that COM-COP divergence can characterize the dynamic balance of the CP children in walking, and thus assist in comparing and differentiating balance patterns.