Taking Both Sides: Seeking Symbiosis Between Intelligent Prostheses and Human Motor Control during Locomotion.

Robotic lower-limb prostheses aim to replicate the power-generating capability of biological joints during locomotion to empower individuals with lower-limb loss. However, recent clinical trials have not demonstrated clear advantages of these devices over traditional passive devices. We believe this is partly because the current designs of robotic prothesis controllers and clinical methods for fitting and training individuals to use them do not ensure good coordination between the prosthesis and user. Accordingly, we advocate for new holistic approaches in which human motor control and intelligent prosthesis control function as one system (defined as human-prosthesis symbiosis). We hope engineers and clinicians will work closely to achieve this symbiosis, thereby improving the functionality and acceptance of robotic prostheses and users' quality of life.

Human-prosthesis coordination: A preliminary study exploring coordination with a powered ankle-foot prosthesis.

BACKGROUND: Powered ankle-foot prostheses were developed to replicate the mechanics of the biological ankle by providing positive work during the push-off phase of gait. However, the benefits of powered prostheses on improving overall human gait efficiency (usually quantified by metabolic cost) have not been consistently shown. Here, we have focused on the mechanical work produced at the prosthetic ankle and its interaction with the amputee's movement. METHODS: Five unilateral transtibial amputees walked on a treadmill using 1) a powered ankle-foot prosthesis and 2) their daily passive device. We determined the net ankle work and ankle work loops on the prosthesis-side to quantify the efficiency of the human-prosthesis physical interaction. We further studied peak propulsion timing and the posture of the amputee's lower limb and prosthesis as indicators of the human-prosthesis coordination. Comparisons were made between the passive and powered prosthesis conditions for each participant. FINDINGS: The powered prosthesis did not consistently increase net ankle work compared to each participant's passive device. For participants that lacked efficiency in interacting with the powered prosthesis, we observed 1) early prosthesis-side peak propulsion timing (≥ 4% earlier) and 2) a more vertical residual shank at the time of peak propulsion (> 2° more vertical) indicating that the human's limb movement and the prosthesis control during push-off were not well coordinated. INTERPRETATION: Results from this preliminary study highlight the need for future work to systematically quantify the coordination between the human and powered prosthesis and understand how such coordination at the joint level influences overall gait efficiency.

Online Reinforcement Learning Control for the Personalization of a Robotic Knee Prosthesis.

Robotic prostheses deliver greater function than passive prostheses, but we face the challenge of tuning a large number of control parameters in order to personalize the device for individual amputee users. This problem is not easily solved by traditional control designs or the latest robotic technology. Reinforcement learning (RL) is naturally appealing. The recent, unprecedented success of AlphaZero demonstrated RL as a feasible, large-scale problem solver. However, the prosthesis-tuning problem is associated with several unaddressed issues such as that it does not have a known and stable model, the continuous states and controls of the problem may result in a curse of dimensionality, and the human-prosthesis system is constantly subject to measurement noise, environmental change and human-body-caused variations. In this paper, we demonstrated the feasibility of direct heuristic dynamic programming, an approximate dynamic programming (ADP) approach, to automatically tune the 12 robotic knee prosthesis parameters to meet individual human users' needs. We tested the ADP-tuner on two subjects (one able-bodied subject and one amputee subject) walking at a fixed speed on a treadmill. The ADP-tuner learned to reach target gait kinematics in an average of 300 gait cycles or 10 min of walking. We observed improved ADP tuning performance when we transferred a previously learned ADP controller to a new learning session with the same subject. To the best of our knowledge, our approach to personalize robotic prostheses is the first implementation of online ADP learning control to a clinical problem involving human subjects.

Effects of extended stance time on a powered knee prosthesis and gait symmetry on the lateral control of balance during walking in individuals with unilateral amputation.

BACKGROUND: Individuals with lower limb amputation commonly exhibit large gait asymmetries that are associated with secondary health issues. It has been shown that they are capable of attaining improved temporal and propulsive symmetry when walking with a powered knee prosthesis and visual feedback, but they perceive this pattern of gait to be more difficult. Rather than improving the efficiency of gait, improved gait symmetry may be increasing individuals' effort associated with maintaining lateral balance. METHODS: In this study, we used a simple visual feedback paradigm to increase the prosthesis-side stance time of six individuals with unilateral TFA or KD as they walked on a powered knee prosthesis at their self-selected speed. As they walked more symmetrically, we evaluated changes in medial-lateral center-of-mass excursion, lateral margin of stability, stride width, and hip abductor activity. RESULTS: As the subjects increased their prosthesis-side stance time, their center-of-mass excursion and hip abductor activity significantly increased, while their lateral margin of stability significantly decreased on the prosthesis-side only. Stride width remained relatively unchanged with testing condition. CONCLUSIONS: Extended stance time on a powered knee prosthesis (yielding more symmetric gait) challenged the lateral balance of individuals with lower limb amputation. Lateral stability may be a reason they prefer an asymmetric gait, even with more advanced technology. Hip muscular changes post-amputation may contribute to the decline in stability on the prosthesis side. Interventions and advancements in prosthesis control aimed at improving their control of lateral balance may ameliorate the difficulty in walking with improved gait symmetry.

Effects of extended powered knee prosthesis stance time via visual feedback on gait symmetry of individuals with unilateral amputation: a preliminary study.

BACKGROUND: Establishing gait symmetry is a major aim of amputee rehabilitation and may be more attainable with powered prostheses. Though, based on previous work, we postulate that users transfer a previously-learned motor pattern across devices, limiting the functionality of more advanced prostheses. The objective of this study was to preliminarily investigate the effect of increased stance time via visual feedback on amputees' gait symmetry using powered and passive knee prostheses. METHODS: Five individuals with transfemoral amputation or knee disarticulation walked at their self-selected speed on a treadmill. Visual feedback was used to promote an increase in the amputated-limb stance time. Individuals were fit with a commercially-available powered prosthesis by a certified prosthetist and practiced walking during a prior visit. The same protocol was completed with a passive knee and powered knee prosthesis on separate days. We used repeated-measures, two-way ANOVA (alpha = 0.05) to test for significant effects of the feedback and device factors. Our main outcome measures were stance time asymmetry, peak anterior-posterior ground reaction forces, and peak anterior propulsion asymmetry. RESULTS: Increasing the amputated-limb stance time via visual feedback significantly improved the stance time symmetry (p = 0.012) and peak propulsion symmetry (p = 0.036) of individuals walking with both prostheses. With the powered knee prosthesis, the highest feedback target elicited 36% improvement in stance time symmetry, 22% increase in prosthesis-side peak propulsion, and 47% improvement in peak propulsion symmetry compared to a no feedback condition. The changes with feedback were not different with the passive prosthesis, and the main effects of device/ prosthesis type were not statistically different. However, subject by device interactions were significant, indicating individuals did not respond consistently with each device (e.g. prosthesis-side propulsion remained comparable to or was greater with the powered versus passive prosthesis for different subjects). Overall, prosthesis-side peak propulsion averaged across conditions was 31% greater with the powered prosthesis and peak propulsion asymmetry improved by 48% with the powered prosthesis. CONCLUSIONS: Increasing prosthesis-side stance time via visual feedback favorably improved individuals' temporal and propulsive symmetry. The powered prosthesis commonly enabled greater propulsion, but individuals adapted to each device with varying behavior, requiring further investigation.

Interactions Between Transfemoral Amputees and a Powered Knee Prosthesis During Load Carriage.

Machines and humans become mechanically coupled when lower limb amputees walk with powered prostheses, but these two control systems differ in adaptability. We know little about how they interact when faced with real-world physical demands (e.g. carrying loads). Here, we investigated how each system (i.e. amputee and powered prosthesis) responds to changes in the prosthesis mechanics and gravitational load. Five transfemoral amputees walked with and without load (i.e. weighted backpack) and a powered knee prosthesis with two pre-programmed controller settings (i.e. for load and no load). We recorded subjects' kinematics, kinetics, and perceived exertion. Compared to the no load setting, the load setting reduced subjects' perceived exertion and intact-limb stance time when they carried load. When subjects did not carry load, their perceived exertion and gait performance did not significantly change with controller settings. Our results suggest transfemoral amputees could benefit from load-adaptive powered knee controllers, and controller adjustments affect amputees more when they walk with (versus without) load. Further understanding of the interaction between powered prostheses, amputee users, and various environments may allow researchers to expand the utility of prostheses beyond simple environments (e.g. firm level ground without load) that represent only a subset of real-world environments.

Does the impedance of above-knee powered prostheses need to be adjusted for load-carrying conditions?

Powered knee prostheses provide substantial advantages for amputees compared to traditional passive devices during basic walking tasks (i.e. level-ground, stairs, ramps), but the impedance control parameters are fixed. For environments that differ from the well-controlled setting of the clinic, amputees must compensate their gait patterns because fixed control parameters ideal for walking on level ground in the clinic do not meet real-life task demands. Load carriage is one instance where fixed control parameters may lead to undesired gait patterns and potentially result in injury. To evaluate the importance of impedance control parameters for different walking tasks, we tested one above-knee amputee walking using an experimental powered prosthesis under four walking conditions. The amputee walked with and without added mass with both load-specific and non-specific impedance control parameters. The load-specific parameters significantly reduced the amputee's intact-leg compensations, asymmetry, and perceived exertion compared to the non-specific control parameters. Powered lower limb prostheses that modulate impedance control parameters for load-carrying tasks may improve the gait performance, safety, and comfort of amputees.

Dental injuries among children and adolescents aged 1-15 years attending to public hospital in Temuco, Chile.

A cross-sectional study was carried out in children and adolescents of both sexes, aged 1-15 years that sought dental emergency attention to the Regional Hospital between 2004 and 2007 in Temuco, Chile. The purpose of this study was to identify the aetiology, types of traumatic dental injuries in primary and permanent dentitions, sex and age distributions, accident location; and time elapsed before emergency treatment in children and adolescents. The sample consisted of 359 patients with 145 primary teeth and 525 permanent teeth affected by dental trauma. The results showed a 2:1 male:female ratio distribution (242/117) with a mean age of 8.4 years. The 7- to 12-year-old group had the highest frequency of dental injuries (66.6%). Unspecific accidental falls were the main cause of injury to primary and permanent dentition (51.8%), followed by striking teeth against objects (15.6%) and bike accidents (13.9%). In primary dentition the most common diagnosis were subluxation (38.6%) and avulsion (16.6%), whereas in permanent dentition was uncomplicated crown fracture (32.9%). A high proportion of the patients received their first emergency attention 24 h after the accident (32.6%). This study revealed a high frequency (37.9%) in 1-15 aged population that sought emergency attention by dental trauma in the period of time study. A large proportion of children with dental trauma received delayed first emergency care, even 24 h after the accident. Considering the high frequency of traumatic dental injuries in 1-15 aged population and the high percentage of delayed emergency attention is necessary to develop effective educational campaigns in regard to causes, prevention and emergency management of traumatic dental injuries, especially in deprived areas. In conclusion, traumatic dental injury may be considered as a serious dental public health problem especially in children of deprived areas.

Active Video Games and Energy Expenditure in Overweight Children.

The prevalence of overweight in children has increased significantly in recent years. Frequent television viewing and the playing of video games have often been linked to the high prevalence of overweight. The purpose of this study was to determine if overweight children, given access to active video games, will play them at an intensity that will significantly increase energy expenditure. Twenty-three children, classified as "at risk for overweight" or "overweight," participated in this study. After a 10-minute baseline period in which the children watched a cartoon, the participants played the Jackie Chan Fitness Studio® (Xavix, Hong Kong) games for 30 minutes while rotating through the games as desired and resting whenever needed. Energy expenditure significantly increased from a mean at baseline of 1.15 ± 0.32 kcal/min to 4.08±1.18 kcal/min during the 30-minutes that the participants were given access to the games (p <.001). The total energy expenditure during the 30-minute time frame was 122.30 ± 35.40 kcal. The energy expenditure varied between individuals, with a low value of 75.00 kcal to a high of 205.86 kcal. Although a modest level of energy expenditure, this level of exertion could contribute to an overall weight control program in children.