Experimental comparisons of passive and powered ankle-foot orthoses in individuals with limb reconstruction

A patient-centered 'test-drive' strategy for ankle-foot orthosis prescription: Protocol for a randomized participant-blinded trial

BACKGROUND

Ankle-foot orthoses (AFOs) are commonly used to overcome mobility limitations related to lower limb musculoskeletal injury. Despite a multitude of AFOs to choose from, there is scant evidence to guide AFO prescription and limited opportunities for AFO users to provide experiential input during the process. To address these limitations in the current prescription process, this study evaluates a novel, user-centered and personalized 'test-drive' strategy using a robotic exoskeleton ('AFO emulator') to emulate commercial AFO mechanical properties (i.e., stiffness). The study will determine if brief, in-lab trials (with emulated or actual AFOs) can predict longer term preference, satisfaction, and mobility outcomes after community trials (with the actual AFOs). Secondarily, it will compare the in-lab experience of walking between actual vs. emulated AFOs.

METHODS AND ANALYSIS

In this participant-blinded, randomized crossover study we will recruit up to fifty-eight individuals with lower limb musculoskeletal injuries who currently use an AFO. Participants will walk on a treadmill with three actual AFOs and corresponding emulated AFOs for the "in-lab" assessments. For the community trial assessment, participants will wear each of the actual AFOs for a two-week period during activities of daily living. Performance-based and user-reported measures of preference and mobility will be compared between short- and long-term trials (i.e., in-lab vs. two-week community trials), and between in-lab trials (emulated vs. actual AFOs).

TRIAL REGISTRATION

The study was prospectively registered at www.clininicaltrials.gov (Clinical Trials Study ID: NCT06113159). Date: November 1st 2023. https://classic.clinicaltrials.gov/ct2/show/NCT06113159.

Walking with unilateral ankle-foot unloading: a comparative biomechanical analysis of three assistive devices

BACKGROUND

Foot and ankle unloading is essential in various clinical contexts, including ulcers, tendon ruptures, and fractures. Choosing the right assistive device is crucial for functionality and recovery. Yet, research on the impact of devices beyond crutches, particularly ankle-foot orthoses (AFOs) designed to unload the ankle and foot, is limited. This study investigates the effects of three types of devices-forearm crutches, knee crutch, and AFO-on biomechanical, metabolic, and subjective parameters during walking with unilateral ankle-foot unloading.

METHODS

Twenty healthy participants walked at a self-selected speed in four conditions: unassisted able-bodied gait, and using three unloading devices, namely forearm crutches, iWalk knee crutch, and ZeroG AFO. Comprehensive measurements, including motion capture, force plates, and metabolic system, were used to assess various spatiotemporal, kinematic, kinetic, and metabolic parameters. Additionally, participants provided subjective feedback through questionnaires. The conditions were compared using a within-subject crossover study design with repeated measures ANOVA.

RESULTS

Significant differences were found between the three devices and able-bodied gait. Among the devices, ZeroG exhibited significantly faster walking speed and lower metabolic cost. For the weight-bearing leg, ZeroG exhibited the shortest stance phase, lowest braking forces, and hip and knee angles most similar to normal gait. However, ankle plantarflexion after push-off using ZeroG was most different from normal gait. IWalk and crutches caused significantly larger center-of-mass mediolateral and vertical fluctuations, respectively. Participants rated the ZeroG as the most stable, but more participants complained it caused excessive pressure and pain. Crutches were rated with the highest perceived exertion and lowest comfort, whereas no significant differences between ZeroG and iWalk were found for these parameters.

CONCLUSIONS

Significant differences among the devices were identified across all measurements, aligning with previous studies for crutches and iWalk. ZeroG demonstrated favorable performance in most aspects, highlighting the potential of AFOs in enhancing gait rehabilitation when unloading is necessary. However, poor comfort and atypical sound-side ankle kinematics were evident with ZeroG. These findings can assist clinicians in making educated decisions about prescribing ankle-foot unloading devices and guide the design of improved devices that overcome the limitations of existing solutions.

Effect of crutch and walking-boot use on whole-body angular momentum during gait

Crutches are the most prescribed ambulatory assistive device and are used for mobility and maintaining weight-bearing restrictions after injury or surgery. However, standard axillary crutches (SACs) can lead to overuse and other injuries and restrict upper limb movement. Hands-free crutches (HFC) do not restrict upper limb movement but their effect on balance control, with or without commonly prescribed walking boots, is poorly understood. The purpose of this study was to compare the effect of crutch type (SACs vs. HFC) and boot use on whole-body angular momentum (RAM), a measure of balance control. Participant's balance confidence, pain, comfort, and device preference were assessed. Seventeen participants were evaluated while walking without a crutch (NONE), with SACs, and with an HFC, and walked with and without a walking boot in each crutch condition. The gait pattern used with SACs resulted in significantly greater limb angular velocity (p < .05), and an 84% increase in RAM (p < .001) as compared to the HFC. There were no differences between the SAC and HFC for balance confidence, pain, or comfort, however most (71.1%) participants preferred the HFCs. These results suggest that individuals can better control angular momentum with the HFCs and thus may be less susceptible to loss of balance.

A systematic investigation of sensorimotor mechanisms with intelligent prostheses in patients with ankle amputation while walking

It is thought that creating sensorimotor feedback in people with ankle joint amputation can affect motor biomechanics during gait, but there is little evidence or previous research. This study e aim ed to investigate the sensorimotor mechanism of smart prostheses in with ankle amputations while walking. Search in Google Scholar, Scopus, PubMed and Medline databases between April 2017 and February 2023, in addition to a detailed review in specialized clinical and engineering databases, 29 articles were selected based on the inclusion and exclusion criteria. Trials that mainly include; Proprioception, walking process in movement disorders, ankle amputation were included. Qualitative assessments of selected trials using PEDro' scale was used. The review of studies showed that the use of pressure sensors, neural stimulation through encoded algorithms can provide continuous tactile and positional information of the artificial leg in the direction of neural stimulation throughout the entire walking cycle. These findings indicate that restoration of intraneuronal sensory feedback leads to functional and cognitive benefits. With these definitions, different companies and research centers are trying to improve the mechanics of walking, however, movement strategies are unknown despite little research in creating sense and movement in the use of smart prostheses.

Ankle and Foot Arthroplasty and Prosthesis: A Review on the Current and Upcoming State of Designs and Manufacturing

The foot and ankle serve vital roles in weight bearing, balance, and flexibility but are susceptible to many diverse ailments, making treatment difficult. More commonly, Total Ankle Arthroplasty (TAA) and Total Talus Replacement (TTR) are used for patients with ankle degeneration and avascular necrosis of the talus, respectively. Ankle prosthesis and orthosis are also indicated for use with lower limb extremity amputations or locomotor disability, leading to the development of powered exoskeletons. However, patient outcomes remain suboptimal, commonly due to the misfitting of implants to the patient-specific anatomy. Additive manufacturing (AM) is being used to create customized, patient-specific implants and porous implant cages that provide structural support while allowing for increased bony ingrowth and to develop customized, lightweight exoskeletons with multifunctional actuators. AM implants and devices have shown success in preserving stability and mobility of the joint and achieving fast recovery, as well as significant improvements in gait rehabilitation, gait assistance, and strength for patients. This review of the literature highlights various devices and technologies currently used for foot and ankle prosthesis and orthosis with deep insight into improvements from historical technologies, manufacturing methods, and future developments in the biomedical space.

Carbon fiber ankle-foot orthoses in impaired populations: A systematic review

BACKGROUND

Carbon fiber is increasingly being used in ankle-foot orthoses (AFOs). Orthotic devices and carbon fiber-containing devices have been shown to reduce pain and improve function in multiple patient populations. Although the number of publications and interest in carbon fiber AFOs is growing, a systematic evaluation of their effects is lacking.

OBJECTIVES

To characterize the effects of carbon fiber AFOs in impaired individuals.

STUDY DESIGN

Qualitative systematic review.

METHODS

Systematic searches in PubMed, Embase, CINAHL, and Cochrane Library were completed in July 2020. The results were deduplicated, screened, and assessed for quality by independent reviewers. Articles were excluded if they had nonhuman subjects, only healthy subjects, or included active control systems, motors, or other power sources.

RESULTS

Seventy-eight articles were included in the qualitative synthesis. Most articles were of low to moderate methodological quality. Five commonly used devices were identified: the Intrepid Dynamic Exoskeletal Orthosis, ToeOff, WalkOn, Neuro Swing, and Chignon. The devices have unique designs and are associated with specific populations. The Intrepid Dynamic Exoskeletal Orthosis was used in individuals with lower-limb trauma, the Neuro Swing and ToeOff in individuals with neurological disorders, the Chignon in individuals with hemiplegia and stroke, and the WalkOn in people with hemiplegia and cerebral palsy. Each device produced favorable outcomes in their respective populations of interest, such as increased walking speed, reduced pain, or improved balance.

CONCLUSIONS

The mechanical characteristics and designs of carbon fiber AFOs improve outcomes in the populations in which they are most studied. Future literature should diligently report patient population, device used, and fitting procedures.

A Scientometric Analysis and Visualization of Prosthetic Foot Research Work: 2000 to 2022

This study aims to highlight recent research work on topics around prosthetic feet through a scientometric analysis and historical review. The most cited publications from the Clarivate Analytics Web of Science Core Collection database were identified and analyzed from 1 January 2000 to 31 October 2022. Original articles, reviews with full manuscripts, conference proceedings, early access documents, and meeting abstracts were included. A scientometric visualization analysis of the bibliometric information related to the publications, including the countries, institutions, journals, references, and keywords, was conducted. A total of 1827 publications met the search criteria in this study. The related publications grouped by year show an overall trend of increase during the two decades from 2000 to 2022. The United States is ranked first in terms of overall influence in this field (n = 774). The Northwestern University has published the most papers on prosthetic feet (n = 84). Prosthetics and Orthotics International has published the largest number of studies on prosthetic feet (n = 151). During recent years, a number of studies with citation bursts and burst keywords (e.g., diabetes, gait, pain, and sensor) have provided clues on the hotspots of prosthetic feet and prosthetic foot trends. The findings of this study are based on a comprehensive analysis of the literature and highlight the research topics on prosthetic feet that have been primarily explored. The data provide guidance to clinicians and researchers to further studies in this field.

Recent advances in wearable actuated ankle-foot orthoses: Medical effects, design, and control

This paper presents a survey on recent advances of wearable actuated ankle-foot orthoses (AAFOs). First of all, their medical functions are investigated. From the short-term aspect, they lead to rectification of pathological gaits, reduction of metabolic cost, and improvement of gait performance. After AAFO-based walking training with sufficient time, free walking performance can be enhanced. Then, key design factors are studied. First, primary design parameters are investigated. Second, common actuators are analysed. Third, human-robot interaction (HRI), ergonomics, safety, and application places, are considered. In the following section, control technologies are reviewed from the aspects of rehabilitation stages, gait feature quantities, and controller characteristics. Finally, existing problems are discussed; development trends are prospected.

Effects of powered ankle-foot orthoses mass distribution on lower limb muscle forces-a simulation study

This simulation study aimed to explore the effects of mass and mass distribution of powered ankle-foot orthoses, on net joint moments and individual muscle forces throughout the lower limb. Using OpenSim inverse kinematics, dynamics, and static optimization tools, the gait cycles of ten subjects were analyzed. The biomechanical models of these subjects were appended with ideal powered ankle-foot orthoses of different masses and actuator positions, as to determine the effect that these design factors had on the subject's kinetics during normal walking. It was found that when the mass of the device was distributed more distally and posteriorly on the leg, both the net joint moments and overall lower limb muscle forces were more negatively impacted. However, individual muscle forces were found to have varying results which were attributed to the flow-on effect of the orthosis, the antagonistic pairing of muscles, and how the activity of individual muscles affect each other. It was found that mass and mass distribution of powered ankle-foot orthoses could be optimized as to more accurately mimic natural kinetics, reducing net joint moments and overall muscle forces of the lower limb, and must consider individual muscles as to reduce potentially detrimental muscle fatigue or muscular disuse. OpenSim modelling method to explore the effect of mass and mass distribution on muscle forces and joint moments, showing potential mass positioning and the effects of these positions, mass, and actuation on the muscle force integral.

Implementation of Robotic Ankle–Foot Orthosis With an Impedance-Based Assist-as-Needed Control Strategy

In this paper, a robotic ankle–foot orthosis (AFO) is developed for individuals with a paretic ankle, and an impedance-based assist-as-needed controller is designed for the robotic AFO to provide adaptive assistance. First, a description of the robotic AFO hardware design is presented. Next, the design of the finite state machine is introduced, followed by an introduction to the modeling of the robotic AFO. Additionally, the control of the robotic AFO is presented. An impedance-based high-level controller that is composed of an ankle impedance based torque generation controller and an impedance controller is designed for the high-level control. A compensated low-level controller that is composed of a braking controller and a proportional-derivative controller with a compensation part is designed for the low-level control. Finally, a pilot study with eight healthy participants is conducted, and the experimental results demonstrate that with the proposed control algorithm, the robotic AFO has the potential for ankle rehabilitation by providing adaptive assistance. In the assisted condition with a high level of assistance, reductions of 8% and 20.1% of the root mean square of the tibialis anterior and lateral soleus activities are observed, respectively.

Application of Wearable Sensors in Actuation and Control of Powered Ankle Exoskeletons: A Comprehensive Review

Powered ankle exoskeletons (PAEs) are robotic devices developed for gait assistance, rehabilitation, and augmentation. To fulfil their purposes, PAEs vastly rely heavily on their sensor systems. Human–machine interface sensors collect the biomechanical signals from the human user to inform the higher level of the control hierarchy about the user’s locomotion intention and requirement, whereas machine–machine interface sensors monitor the output of the actuation unit to ensure precise tracking of the high-level control commands via the low-level control scheme. The current article aims to provide a comprehensive review of how wearable sensor technology has contributed to the actuation and control of the PAEs developed over the past two decades. The control schemes and actuation principles employed in the reviewed PAEs, as well as their interaction with the integrated sensor systems, are investigated in this review. Further, the role of wearable sensors in overcoming the main challenges in developing fully autonomous portable PAEs is discussed. Finally, a brief discussion on how the recent technology advancements in wearable sensors, including environment—machine interface sensors, could promote the future generation of fully autonomous portable PAEs is provided.

Design of a segmented custom ankle foot orthosis with custom-made metal strut and 3D-printed footplate and calf shell

BACKGROUND

3D-printing is a potential manufacturing process for optimizing the design and manufacture of ankle foot orthosis (AFOs). The feasibility of an AFO with interchangeable strut that is suitable for 3D-printing is created and evaluated.

OBJECTIVE

A segmented AFO with 3D-printed custom footplate and calf shell connected by a custom-made strut is studied.

STUDY DESIGN

The duration of a healthy subject wearing the 3D-printed segmented AFO in daily activities is used to evaluate the feasibility and durability to integrate 3D-printed AFOs into orthotics practice.

TECHNIQUE

The 3D-scanning of a patient's leg is first conducted. The scanned 3D surface is modified by creating the clearance around bony prominences and trimlines for the footplate and calf shell. The footplate has a custom-shaped inside to match with the foot and a standard shape outside at the top to match and connect with the strut. For the calf shell, the inside shape is custom fit with the shank and the outside shape is standard to connect with the strut. Material extrusion is the 3D-printing process selected. Tree-like support structures are used to avoid the use of soluble support material and to eliminate the risk of residual chemical solvent in the orthosis.

RESULTS

The segmented AFO with material extrusion footplate and calf shell was tested in a healthy subject with an active lifestyle, offering comfort, and stability for over 4 months without breakage.

CONCLUSIONS

This segmented AFO is durable, requires short 3D-printing time, and enables the quick adjustment of bending stiffness via an interchangeable strut design.

Carbon Fiber-Based Twisted and Coiled Artificial Muscles (TCAMs) for Powered Ankle-Foot Orthoses

Ankle foot orthoses (AFOs) control the position and motion of the ankle, compensate for weakness, and correct deformities. AFOs can be classified as passive or powered. Powered AFOs overcome the limitations of passive AFOs by adapting their performance to meet a variety of requirements. However, the actuators currently used to power AFOs are typically heavy, bulky, expensive, or limited to laboratory settings. Thus, there is a strong need for lightweight, inexpensive, and flexible actuators for powering AFOs. In this technical brief, carbon fiber/silicone rubber (CF/SR) twisted and coiled artificial muscles (TCAMs) are proposed as novel actuators for powered AFOs. CF/SR TCAMs can lift to 12,600 times their weight with an input power of only 0.025 W cm-1 and are fabricated from inexpensive materials through a low-cost manufacturing process. Additionally, they can provide a specific work of 758 J kg-1 when an input voltage of 1.64 V cm-1 is applied. Mechanical characterization of CF/SR TCAMs in terms of length/tension, tension/velocity, and active-passive length/tension is presented, and results are compared with the performance of skeletal muscles. A gait analysis demonstrates that CF/SR TCAMs can provide the performance required to supplement lower limb musculature and replicate the gait cycle of a healthy subject. Therefore, the preliminary results provided in this brief are a stepping stone for a dynamic AFO powered by CF/SR TCAMs.

Evaluation of Physical Interaction during Walker-Assisted Gait with the AGoRA Walker: Strategies Based on Virtual Mechanical Stiffness

Smart walkers are commonly used as potential gait assistance devices, to provide physical and cognitive assistance within rehabilitation and clinical scenarios. To understand such rehabilitation processes, several biomechanical studies have been conducted to assess human gait with passive and active walkers. Several sessions were conducted with 11 healthy volunteers to assess three interaction strategies based on passive, low and high mechanical stiffness values on the AGoRA Smart Walker. The trials were carried out in a motion analysis laboratory. Kinematic data were also collected from the smart walker sensory interface. The interaction force between users and the device was recorded. The force required under passive and low stiffness modes was 56.66% and 67.48% smaller than the high stiffness mode, respectively. An increase of 17.03% for the hip range of motion, as well as the highest trunk’s inclination, were obtained under the resistive mode, suggesting a compensating motion to exert a higher impulse force on the device. Kinematic and physical interaction data suggested that the high stiffness mode significantly affected the users’ gait pattern. Results suggested that users compensated their kinematics, tilting their trunk and lower limbs to exert higher impulse forces on the device.

Custom Dynamic Orthoses and Physical Therapist Intervention for Bilateral Midfoot Amputation: A Case Report

OBJECTIVE

Partial foot amputation is often associated with decreased mobility and function. Recent advances in custom carbon-fiber dynamic ankle-foot orthoses (CDOs) have improved gait, pain, and function following musculoskeletal trauma and can benefit individuals with partial foot amputation. However, limited information is available related to CDO use outside the military. The purpose of this case report is to describe the course of care and outcomes of a civilian provided with CDOs after bilateral transmetatarsal amputation.

CASE DESCRIPTION

A 72-year-old man had a blood-borne bacterial infection (septicemia) of unknown origin at 68 years of age, developed limb-threatening necrosis of the hands and feet, and received bilateral transmetatarsal amputations with skin grafting. The patient initially used foam toe fillers and cushioned shoes but was functionally limited and experienced recurrent ulceration. He was fitted with bilateral CDOs 39 months after amputation and completed device-specific training with a physical therapist.

RESULTS

After 1 week with the CDOs, ankle range of motion during gait was reduced, but greater than 40% increases were observed in bilateral ankle plantarflexor moments and ankle plantarflexion push-off power compared with the toe fillers. With additional therapist-directed training focused on gait and activity performance, ankle plantarflexor moments and plantarflexion push-off power further increased when compared with results after 1 week of CDO use. The patient reported marked improvement in quality of life with the CDOs due to improved walking ability on level and uneven terrain, marked improvement in confidence, and reduced pain.

CONCLUSION

This case reflects the lessons learned and outcomes of a civilian using bilateral CDOs after bilateral transmetatarsal amputation and with poor skin quality. The results from this case study suggest that carbon-fiber CDOs and focused training by a physical therapist can result in improved gait biomechanics, mobility, and quality of life.