Passive Ankle-foot Orthoses Research Articles

A Portable Passive Ankle-Foot Orthosis for Walking Propulsion and Drop-Foot Prevention

Abstract Individuals with a drop-foot generally have issues of foot-slap and toe-drag, and ankle-foot orthoses (AFOs) have been developed for them to address the drop-foot gait. However, the currently available active AFOs usually have heavier mass, larger volume, and additional power sources, and almost all of the passive AFOs can achieve dorsiflexion assistance at the cost of making plantarflexion more difficult, which increases the wearer's metabolic cost of walking. This paper illustrates the development and validation of a passive AFO for walking propulsion and drop-foot prevention of individuals with a drop-foot gait. The AFO is primarily composed of a propulsion module, a drop-foot prevention module, and a support module. The propulsion module can detect the wearer's gait stages, and it can control the energy storage and release of an energy storage spring-A by switching the state of a clutch-A mechanism. The drop-foot prevention module is designed to correct the abnormal gait of individuals with a drop-foot gait during the swing phase. Experiments are conducted to evaluate the performance of the developed AFO. The experimental results demonstrate that during a gait cycle, reductions of 7.74%, 6.72%, and 16.36% of the average muscle activities of the gastrocnemius, soleus, and tibialis anterior are observed, respectively. The significance of this study is the development of a portable passive AFO that has the potential to provide plantarflexion assistance and dorsiflexion assistance for the wearers during the late stance phase and swing phase, respectively.

Study of Gait and Posture Kinematic Indices for the Evaluation of Ankle-Foot Orthoses *

Motor disabilities resulting from pathologies such as brain injuries, strokes, spinal cord injuries and other neurological diseases usually lead to deficits in locomotion. One such problem is Drop Foot (DF), which can severely impair walking function. To cope with this pathology, ankle-foot orthoses (AFOs) can be used, which allow the patient to improve ankle dorsiflexion during the swing phase of the foot. The aim of this research work is to evaluate the impact of the use of a passive AFO orthosis on gait by studying the kinematic indices of gait in patients with DF. The study was conducted on a population of 19 patients at the IRCCS Istituti Clinici Maugeri in Bari. Ninteen subjects (12 males, 7 females), with unilateral DF syndrome, were involved in this research. The experimental data collection procedures consisted of gait analysis sessions performed with the Mobility Lab system by APDM (APDM Inc, Portland, OR, USA, http://apdm.com). In this test subjects wore 3 IMUs (low back and dorsal surface of the feet) and are instructed to stand quietly for 30 s and then asked to walk over a 7 meters walkway, turn around a pivot and walk back to the starting point. Each subject performed two sessions in two different gait conditions: (i) unconstrained gait (without any AFO); (ii) gait with an AFO attached to the participant’s affected limb. The median value of each parameter among the three selected trials was extracted and considered for the analysis. We focused on the following set of spatio-temporal parameters, which have clinical relevance in patients with DF: Elevation at Midswing ( cm ) (EMS), Gait Cycle Time ( s ) (GCT), Stride Length ( m ) (SL). These metrics were statistically analysed with two-way ANOVA test to explore the effects produced by the variables ‘Condition’ (With/Without AFO), ‘Limb’ (Affected/Contralateral) and the interaction between these two factors. Statistical analyses were performed using R version 4.0.3 (R Foundation, Vienna, Austria). Table 1 presents the results of the statistical test, reporting p-values when a significant difference was obtained (p−value < 0.05). Otherwise the absence of statistical significance is reported (ns). The level of statistical significance is specified by a different number of stars (∗): the higher number of stars, the lower α value threshold for the p − value. Fig. 1 shows the boxplots representing the distribution of the analysed data. This paper presented a clinical study regarding the impact of using a solid plastic AFO on spatio-temporal gait metrics of 19 patients with DF syndrome. Our analysis pointed out that EMS is generally higher in affected limb than in contralateral limb, as the patient compensates for difficulties in lifting the front part of the foot by increasing foot elevation during swing. However the use of the AFO has no significant effects on either foot. On the contrary, the GCT is reduced when the AFO is worn by the patient demonstrating higher confidence in step execution. The use of the AFO also tends to improve the stride length of both feet, however this difference is not statistically significant. In future studies, it would be better to evaluate changes in gait metrics on a longer walking trial, to carry out the assessment on a larger number of steps.

DESIGN AND ANALYSIS OF THERMOPLASTIC POLYPROPYLENE ANKLE FOOT ORTHOSIS

Ankle-Foot-Orthoses (AFOs) are assistive devices used for neurological and physical disorders affecting the movement of the lower limbs. The needs of an increasingly young and active orthotic patient population have led to advancements in ankle foot orthosis (AFO) design and materials to enable higher function. Proper selection of material for manufacturing of AFO leads to greater increase in popularity to patients during walking providing better and compatible ankle foot orthotic device for patient specific. The purpose of this study is to develop design guide to find out the structural characteristics of polypropylene of AFO. In this research work, design and static analysis of a passive AFO to fit a human foot is presented. The static analysis was carried out for AFO made up of Polypropylene material with thicknesses 4 mm. Based on the results obtained from the static analysis. The results obtained from the static analysis showed that the polypropylene AFO was performing better results, generating less stress, deformation, and good factor of safety.

Evaluation of various design concepts in passive ankle-foot orthoses using finite element analysis

Ankle-foot orthoses (AFOs) are typically prescribed to improve the gait function of ambulatory children with neurological conditions such as cerebral palsy or spina bifida. Due to the excessive and repetitive loading conditions, plastic material deformation can be observed in AFOs, especially over the lateral and medial parts of the ankle, which limits the effect of AFOs in the stabilization of the ankle joint. Trimline design and severity influence the rotational stiffness of an AFO considerably. In this study, we proposed novel trimming approaches for AFOs such that the trimlines were performed on the dorsal side rather than lateral and medial sides to reduce the magnitude of peak stresses and provide a homogenous stress distribution over AFOs. We analyzed eight dorsal trimline designs having different basic geometries by using the finite element method. To objectively evaluate the stress levels, the same boundary and loading conditions were considered for all design alternatives. We found that low peak stress values were observed in the AFO models with trimline geometries of the circle, ellipse, and slot variations. The vertical elliptic trimline on the dorsal side of the AFO was the most effective to decrease the magnitude of the peak stresses. The findings of our study are expected to contribute a complementary solution to orthotists in the fabrication of AFOs with high durability.

Investigating the effect of innovative storing-restoring hybrid passive ankle-foot orthosis on braking and propulsion impulse of walking in drop-foot patients: a prospective cohort study

Background: Drop foot is a disorder that is characterized by reduction in speed and the patients’ inability to propel the paretic side, which disrupts the walking patterns. Ankle-foot orthoses (AFO) are widely prescribed in these patients in order to facilitate their leg propulsion and foot clearance during the swing phase. The purpose of this study was to use the correlation between effect of innovative AFO on braking and propulsion impulse and speed, in order to interpret the innovative AFO’s influence on the paretic and nonparetic side in drop-foot patients. Methods: Ten participants with drop foot walked at their self-selected speed, in order to collect the kinetic and kinematic data. The anteroposterior ground reaction force (GRF) components were extracted from the decomposition method with an innovative storing-restoring hybrid passive AFO and compared with baseline shoes only for both paretic and nonparetic sides. Results: There is a strong correlation between the innovative AFO speed and the anteroposterior component of GRF. After that, correlation was found between anteroposterior GRF and the storing-restoring hybrid passive AFO in comparison with baseline shoes only in both the paretic and nonparetic sides. Conclusions: This study demonstrated a strong correlation during walking between speed and the propulsion and braking impulses of the anteroposterior component of GRF on both sides. Level of Evidence: Level II.

Effect of Novel Spring Damper and Posterior Leaf Spring Ankle Foot Orthosis on the Vertical Component of Ground Reaction Forces During Walking in Patients With Drop Foot

Background: Ankle Foot Orthoses (AFOs) are often prescribed in patients with drop foot. The purpose of this study was to investigate the effect of the novel designed storing-restoring hybrid passive AFO versus Posterior Leaf Spring (PLS) AFO on the peak and timing of vertical component of ground reaction force (vGRF) in patients with drop foot. Objectives: the effect of novel designed storing-restoring hybrid passive AFO versus posterior leaf spring AFO on the peak and timing of Vertical Ground Reaction Force (vGRF) in drop foot patients. Methods: Ten adults with drop foot (7 males and 3 females) were included in this study. Then, these patients walked at a self-selected speed with two AFOs. For each trial, the vGRF components were obtained using a Kistler force plate. Results: the Independent t-test results showed a significant increase in the impact force in spring damper AFO than PLS (p&lt;0.001). Significant differences were also found in the first and third peaks of vertical force and time of occurrence as well as the first minimum force and time of occurrence in spring damper than PLS AFO (p&lt;0.001). Conclusion: the novel AFO affects not only the impact force and peak of vGRF but also the timing of these forces. These changes indicate an improvement in the overall performance of the novel AFO.

Analysis of EMG Signals during Stance and Swing Phases for Controlling Magnetorheological Brake applications

Abstract The development of ankle foot orthoses (AFO) for lower limb rehabilitation have received significant attention over the past decades. Recently, passive AFO equipped with magnetorheological brake had been developed based on ankle angle and electromyography (EMG) signals. Nonetheless, the EMG signals were categorized in stance and swing phases through visual observation as the signals are stochastic. Therefore, this study aims to classify the pattern of EMG signals during stance and swing phases. Seven-time domains features will be extracted and fed into artificial neural network (ANN) as a classifier. Two different training algorithms of ANN namely Levenberg-Marquardt (LM) and Scaled Conjugate Gradient (SCG) will be applied. As number of inputs will affect the classification performance of ANN, different number of input features will be employed. In this study, three participants were recruited and walk on the treadmills for 60 seconds by constant the speed. The ANN model was designed with 2, 10, 12, and 14 inputs features with LM and SCG training algorithms. Then, the ANN was trained ten times and the performances of each inputs features were measured using classification rate of training, testing, validation and overall. This study found that all the inputs with LM training algorithm gained more than 2% average classification rate than SCG training algorithm. On the other hand, classification accuracy of 10, 12 and 14 inputs were 5% higher than 2 inputs. It can be concluded that LM training algorithm of ANN was performed better than SCG algorithm with at least 10 inputs.

The comparison of the effect of innovative designed storing-restoring hybrid passive AFO versus posterior leaf spring AFO on ankle joint kinematic in drop foot patients: A case series using a single subject design.

Background: Drop foot syndrome is a disorder characterized by foot slapping after the initial contact and foot-dragging during the swing phase. Passive and hybrid passive ankle foot orthoses (AFOs) are often prescribed in these patients; however, the effects of these AFO designs on kinematic parameters during gait are unclear. The aim of this study was to compare the effect of innovative designed storing-restoring hybrid passive AFOs versus posterior leaf spring AFO on ankle joint kinematics in drop foot patients. Methods: The present study was a case series where a single case and 3 cases with drop foot syndrome were recruited. This study was designed in 2 phases: the baseline phase with their PLS AFOs and an intervention phase in which innovative designed AFO were assessed. Each phase included 5 measurement sessions which were performed in 5 consecutive weeks. The celeration line method was used to detect the significant differences between the phases. Results: The results of this study showed a significant increase in the kinematic angles parameters at the initial contact, the loading response, the mid stance, terminal stance, pre swing, initial swing, mid swing, and terminal swing with the innovative designed AFO than with PLS AFO (p<0.05). Conclusion: The results of the present study suggested that use of the innovative designed AFO may have a positive effect on ankle joint kinematics parameters in people with drop foot.

Numerical study of patient-specific ankle-foot orthoses for drop foot patients using shape memory alloy

Drop foot is a nerve-muscle disorder that affects the muscles that lift the foot. The two main side effects of drop foot are slapping/kicking the foot after heel strike (foot) and dragging the foot during the swing (toe drag). Treatment methods such as ankle-foot orthoses (AFO) have some biomechanical benefits, but are not applicable to all walking conditions and cannot mitigate significant gait complications. This study introduces the design of a passive AFO system, which combines an ordinary AFO and a shape memory alloy (SMA) element. OpenSim was used to simulate patients with muscle weakness and to calculate the torque needed to imitate normal ankle joint stiffness. The calculated torque was then reproduced for different levels of muscle weakness by the superelasticity of SMAs. The study showed that the normal joint stiffness profile for each patient with a certain level of muscle weakness can be restored by designing a patient-specific orthosis.

State of the Prescription Process for Dynamic Ankle-Foot Orthoses

Purpose of Review Dynamic ankle-foot orthoses (AFOs) are assistive devices that can be prescribed to individuals with mobility limitations to support and align joints. Dynamic AFOs are a category of passive AFOs that can control ankle motion to address both ankle joint range of motion limitations and ankle muscle weakness. This control of motion is achieved through the dynamic AFO’s functional characteristics, namely bending stiffness, which need to be customized to each individual’s needs. However, current conventions for customizing dynamic AFOs for each individual are variable and often not clearly documented. The purpose of this review was to synthesize the current state of customizing functional characteristics of dynamic AFOs to provide a foundation for ultimately optimizing the prescription of AFOs.

Simulated impacts of ankle foot orthoses on muscle demand and recruitment in typically-developing children and children with cerebral palsy and crouch gait.

Passive ankle foot orthoses (AFOs) are often prescribed for children with cerebral palsy (CP) to assist locomotion, but predicting how specific device designs will impact energetic demand during gait remains challenging. Powered AFOs have been shown to reduce energy costs of walking in unimpaired adults more than passive AFOs, but have not been tested in children with CP. The goal of this study was to investigate the potential impact of powered and passive AFOs on muscle demand and recruitment in children with CP and crouch gait. We simulated gait for nine children with crouch gait and three typically-developing children with powered and passive AFOs. For each AFO design, we computed reductions in muscle demand compared to unassisted gait. Powered AFOs reduced muscle demand 15–44% compared to unassisted walking, 1–14% more than passive AFOs. A slower walking speed was associated with smaller reductions in absolute muscle demand for all AFOs (r2 = 0.60–0.70). However, reductions in muscle demand were only moderately correlated with crouch severity (r2 = 0.40–0.43). The ankle plantarflexor muscles were most heavily impacted by the AFOs, with gastrocnemius recruitment decreasing 13–73% and correlating with increasing knee flexor moments (r2 = 0.29–0.91). These findings support the potential use of powered AFOs for children with crouch gait, and highlight how subject-specific kinematics and kinetics may influence muscle demand and recruitment to inform AFO design.