Wireless Instrumented Ankle Foot Orthosis (AFO) for Gait Cycle Monitoring

In the past decade, advanced technologies in robotics have been explored to enhance the rehabilitation of post-stroke patients. Previous works have shown that gait assistance for post-stroke patients can be provided through the use of robotics technology in ancillary equipment, such as Ankle Foot Orthosis (AFO). An AFO is usually used to assist patients with spasticity or foot drop problems. There are several types of AFOs, depending on the flexibility of the joint, such as rigid, flexible rigid, and articulated AFOs. A rigid AFO has a fixed joint, and a flexible rigid AFO has a more flexible joint, while the articulated AFO has a freely rotating ankle joint, where the mechanical properties of the AFO are more controllable compared to the other two types of AFOs. This paper reviews the control of the mechanical properties of existing AFOs for gait assistance in post-stroke patients. Several aspects that affect the control of the mechanical properties of an AFO, such as the controller input, number of gait phases, controller output reference, and controller performance evaluation are discussed and compared. Thus, this paper will be of interest to AFO researchers or developers who would like to design their own AFOs with the most suitable mechanical properties based on their application. The controller input and the number of gait phases are discussed first. Then, the discussion moves forward to the methods of estimating the controller output reference, which is the main focus of this study. Based on the estimation method, the gait control strategies can be classified into subject-oriented estimations and phase-oriented estimations. Finally, suggestions for future studies are addressed, one of which is the application of the adaptive controller output reference to maximize the benefits of the AFO to users.

BackgroundImpairments of trunk movements in gait of stroke are often reported. Ankle foot orthosis (AFO) is commonly used to improve gait of stroke; however, the effect of different types of AFOs on the pelvic and thoracic movements during gait in stroke has not been clarified.MethodsThirty-four patients with stroke were randomly allocated to undergo 2 weeks of gait training by physiotherapists while wearing a rigid AFO (RAFO) with a fixed ankle or an AFO with an oil damper (AFO-OD) that provides plantarflexion resistance and free dorsiflexion. A motion capture system was used for measurements of shod gait without AFO at baseline and with and without AFO after gait training. Two-way repeated ANOVA, Wilcoxon signed-rank test, and Mann–Whitney U test were performed for the data after the gait training to know the effect of different kinds of AFOs.ResultsTwenty-nine patients completed the study (AFO-OD group: 14, RAFO group: 15). Interactions were found in pelvic rotation angle, change of shank-to-vertical angle (SVA) in the stance, and paretic to non-paretic step length, which increased in AFO-OD group with AFOs (p < 0.05), while the SVA decreased in RAFO group with AFOs (p < 0.05). The main effects were found in pelvic rotation at the contralateral foot off, and thoracic tilt at foot off when an AFO was worn. The change of SVA in stance was positively correlated with the pelvic rotation in the AFO-OD group (r = 0.558). At initial contact, pelvic rotation was positively correlated with thoracic rotation in both groups.ConclusionsThe findings in 29 patients with stroke showed that pelvic and thoracic movements especially the rotation were affected by the type of AFOs. Pelvic rotation and lower limb kinematics exhibited significant improvements with AFO-OD, reflecting more desirable gait performance. On the other hand, the increase in thoracic in-phase rotation might expose the effect of insufficient trunk control and dissociation movement.Trial registration UMIN000038694, Registered 21 November 2019, https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_his_list.cgi?recptno=R000044048.

Purpose Ankle foot orthosis (AFO) stiffness is a key characteristic that determines how much support or restraint an AFO can provide. Thus, the goal of the current study is twofold: (1) to quantify AFO prescriptions for a group of patients; (2) to evaluate what impact these AFO have on the push-off phase. Method Six patients were included in the study. Three patients were prescribed an AFO for ankle support and three patients were prescribed an AFO for ankle and knee support. Two types of AFO – a traditional polypropylene AFO (AFOPP) and a novel carbon-selective laser sintered polyamide AFO (AFOPA), were produced for each patient. AFO ankle stiffness was measured in a dedicated test rig. Gait analysis was performed under shod and orthotic conditions. Results Patient mass normalized AFOPP stiffness for ankle support ranged from 0.042 to 0.069 N·m·deg−1·kg−1, while for ankle and knee support it ranged from 0.081 to 0.127 N·m·deg−1·kg−1. On the group level, the ankle range of motion and mean ankle velocity in the push-off phase significantly decreased in both orthotic conditions, while peak ankle push-off power decreased non-significantly. Accordingly, on the group level, no significant improvements in walking speed were observed. However, after patient differentiation into good and bad responders it was found that in good responders peak ankle push-off power tended to be preserved and walking speed tended to increase. Conclusions Quantification of AFO stiffness may help to understand why certain orthotic interventions are successful (unsuccessful) and ultimately lead to better AFO prescriptions. Implications for rehabilitation AFO ankle stiffness is key characteristic that determines how much support or restraint an AFO can provide. In a typical clinical setting, AFO ankle stiffness is not quantified. AFO has to meet individual patient’s biomechanical needs. More objective AFO prescription and more controlled AFO production methods are needed to increase AFO success rate.

The ankle foot orthosis (AFO) has been used for control of ankle motion in stroke patients for a long time. However, studies on the materials used in construction of AFOs have been limited. In this study, the authors attempted to investigate the effect of a hybrid AFO made with polypropylene and fabric in comparison with a conventional plastic AFO in terms of convenience and effect in patients with chronic hemiparetic stroke. Seventeen patients with chronic hemiparetic stroke who have used plastic AFOs were recruited for this study. Two types of AFOs were used: plastic AFO made with polypropylene and hybrid AFO made with polypropylene covered with canvas fabric, which were individually molded and fitted. Convenience was evaluated using a self-developed questionnaire on patients' satisfaction and weights of AFO, and effect was evaluated using gait analysis. On the satisfaction questionnaire, satisfaction was greater for the hybrid AFO, and it was lighter in weight than the plastic AFO (P < 0.05). In gait analysis, faster walking speed, larger mean and peak ankle dorsiflexion angles, and ankle dorsiflexion angles at heel strike and toe off were observed for the hybrid and plastic AFOs compared with barefoot (P < 0.05). No significant difference was observed between the two orthoses, except for ankle dorsiflexion angle at heel strike, in which the plastic AFO showed higher ankle dorsiflexion angle than did the hybrid AFO. According to the results of this study, the hybrid AFO showed a similar effect in function, except for ankle dorsiflexion angle at heel strike, and was superior with regard to convenience compared with the conventional plastic AFO in chronic hemiparetic stroke patients. Therefore, it seems that, in general, the hybrid AFO can be recommended for hemiparetic stroke patients who require an AFO.

Compared to the last few decades, there is an increase in prevalence of neuromuscular diseases like stroke, multiple sclerosis, and cerebral palsy. These diseases cause lower limb disability like drop foot. The main reason for drop foot is weakness in dorsiflexor muscles. Drop foot results in ‘toe drag during swing phase’ and ‘foot slap during heel contact’. Ankle foot orthosis (AFO) is a mechanical device, which is used to treat drop foot. Based on usage of sensors, actuators, and control systems, there are three types of AFOs: Semi active, Active, and Passive AFOs. Semi active and Active AFOs contain sensors, actuators, control systems, and onboard power source. Passive AFOs do not contain electrical boards but contain mechanical elements to control relative motion between foot part and shank part of the AFOs. Based on relative motion between foot and shank parts of AFOs, AFOs are also classified into two types: Non-articulated (or Fixed) and Articulated AFOs. Non-articulated AFOs are single piece devices having no relative motion between foot part and shank part of the device. Articulated AFOs are two-piece devices, having relative motion between foot part and shank part of the device, and the relative motion is controlled by passive and active actuators. In this paper, different working principles, advantages, and disadvantages of the existing AFOs are presented.

Foot drop is a condition where individuals are unable to lift the foot through the ankle. It results in slap foot after heel contact and toe drag during the swing phase. Ankle Foot Orthosis (AFO) is a mechanical device that supports both the ankle and foot of the individual and guides the movements of the foot to prevent slap foot and toe drag. There are two types of AFOs:Passive AFO and Active AFO. In this 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 of two different materials (Polypropylene and High-Density Polyethylene (HDPE)) with two different thicknesses (3mm and 4mm). Based on the results obtained from the static analysis, the design of AFO was optimized for shape and thickness.Further dynamic analysis was carried out on the optimized AFO to know its behaviour in walking condition. The results obtained from the static and dynamic analyses showed that the polypropylene AFO was better compared to that of HDPE AFO by generating less stress, deformation, and factor of safety. The proposed AFO can be fabricated and tested for real-time walking conditions.

The custom ankle foot orthosis (AFO) is an externally medical-assisted device used to support and improve the function of lower limb during walking and to modify the structural or functional characteristics of the neuromuscular system. There are two kinds of orthoses: custom and off-the-shelf. Custom orthoses give fit the patient’s body and better performance than off-the-shelf orthoses. The stringent design requirements such as light weight, small size, high efficiency, good mechanical properties and these challenges are subject to produce this device. There are two types of design AFO solid and hollow with three types of materials were used in this work, polypropylene (PP), composite materials of carbon fiber (CF) and a polylactic acid (PLA). The composite materials depend on the number of Perlon layers (12 layers, 10 layers and 6 layers) with two layers of carbon fiber and (6 layers) without carbon fiber. The mechanical properties of the AFOs’ materials were tested by tensile test and flexural bending test. The data of interface pressure were collected from one patient with drop foot (wearing three types of AFO) as the subject. Further, FEM by (ANSYS) was used to compute the safety factor of test for all types of AFOs’ models and the equivalent stress (von Misses). The interface pressure between the patient’s leg and the brace was tested by using a piezoelectric sensor. The results obtained from ANSYS gave the profile of safety factor of test, for (PLA-AFO) > (CF-AFO) > (PP-AFO).KeywordsOptimization designFinite element method (FEM)Ankle foot orthoses (AFO)Drop foot

Ankle Foot Orthoses: Standardisation of terminology

The modification of a new design in orthosis usually has its clinical indication. In this study, a low-temperature thermoplastic ankle foot orthosis (AFO) was designed in anterior leaf type, called anterior AFO, to meet the need of indoor barefoot walking in Taiwan. It could be easily molded and remolded to fit the foot, as well as to adjust the position of the foot and ankle. Sixty-eight patients with acute hemiplegia were fitted with this anterior AFO during ambulation training: 46 had good fitting (67.6%), 15 had fair fitting (22.1%) and 7 had poor fitting (10.3%). Two patients were observed to have ankle clonus, and four patients experienced breakage or tear of the AFO within 4 wk. The gait characteristics were measured in six chronic hemiplegia patients to compare the effect of anterior AFO with posterior AFO (Teufel style). Their gait pattern did improve by AFO fitting, especially from the foot pressure distribution, but no significant difference between the two types of AFO was found.

PurposeThe purpose of this study is improvement of human gait by customized design of ankle foot orthosis (AFO). An has been the most frequently used orthosis in children with cerebral palsy. AFOs are designed to boost existing features or to avoid depression or traumatize muscle contractures. The advantages of AFO’s utilized for advancement in human walk attributes for the improvement in foot deformities patients or youngsters with spastic loss of motion. In this research on the customized design of AFO's to improve gait, there are limitations during walking of foot drop patients. In children with foot drops, specific AFOs were explicitly altered to improve parity and strength which are beneficial to walking positions.Design/methodology/approachThis study proposes the customized design of AFOs using computerized and additive manufacturing for producing advances to alter the design and increase comfort for foot drop patients. Structuring the proposed design fabricated by using additive manufacturing and restricted material, the investigation was finalized at the Design Analysis Software (ANSYS). The system that performs best under investigation can additionally be printed using additive manufacturing.FindingsThe results show that the customized design of AFOs meets the patient’s requirements and could also be an alternative solution to the existing AFO design. The biomechanical consequences and mechanical properties of additive manufactured AFOs have been comparable to historically synthetic AFOs. While developing the novel AFO designs, the use of 3D printing has many benefits, including stiffness and weight optimization, to improve biomechanical function and comfort. To defeat the issues of foot drop patients, a customized AFO is used to improve the human gait cycle with new material and having better mechanical properties.Originality/valueThis research work focuses on the biomechanical impacts and mechanical properties of customized 3D-printed AFOs and compares them to traditionally made AFOs. Customized AFO design using 3D printing has numerous potential advantages, including new material with lightweight advancement, to improve biomechanical function and comfort. Normally, new applications mean an incremental collection of learning approximately the behavior of such gadgets and blending the new design, composite speculation and delivered substance production. The test results aim to overcome the new AFO structure issues and display the limited components and stress examination. The outcome of the research is the improved gait cycle of foot drop patients.

BackgroundPeople with plantar flexor weakness generate less ankle push-off work during walking, resulting in inefficient proximal joint compensations. To increase push-off work, spring-like ankle foot orthoses (AFOs) can be provided. However, whether and in which patients AFOs increase push-off work and reduce compensatory hip and knee work is unknown. MethodsIn 18 people with bilateral plantar flexor weakness, we performed a 3D gait analysis at comfortable walking speed with shoes-only and with AFOs of which the stiffness was optimized. To account for walking speed differences between conditions, we compared relative joint work of the hip, knee and ankle joint. The relationships between relative work generated with shoes-only and changes in joint work with AFO were tested with Pearson correlations. ResultsNo differences in relative ankle, knee and hip work over the gait cycle were found between shoes-only and AFO (p>0.499). Percentage of total ankle work generated during pre-swing increased with the AFO (AFO: 85.3±9.1% vs Shoes: 72.4±27.1%, p=0.026). At the hip, the AFO reduced relative work in pre-swing (AFO: 31.9±7.4% vs Shoes: 34.1±10.4%, p=0.038) and increased in loading response (AFO: 18.0±11.0% vs Shoes: 11.9±9.8%, p=0.022). Ankle work with shoes-only was inversely correlated with an increase in ankle work with AFO (r=-0.839, p<0.001) and this increase correlated with reduction in hip work with AFO (r=-0.650, p=0.004). DiscussionAlthough stiffness-optimized AFOs did not alter the work distribution across the ankle, knee and hip joint compared to shoes-only walking, relative more ankle work was generated during push-off, causing a shift in hip work from pre-swing to loading response. Furthermore, larger ankle push-off deficits when walking with shoes-only were related with an increase in ankle work with AFO and reduction in compensatory hip work, indicating that more severely affected individuals benefit more from the energy storing-and-releasing capacity of AFOs.

A non-articulated plantarflexion resist ankle foot orthosis (AFO), commonly known as a posterior leaf spring AFO, is indicated for patients with motor impairment to the dorsiflexors. The AFO is often custom molded to a patient's lower limb anatomy and fabricated from polypropylene. There are no established guidelines for fabricating this type of AFO with predetermined stiffness of the ankle region for normal walking speeds. Therefore an AFO may not meet the biomechanical needs of the patient. Quantify the biomechanical ankle stiffness requirement for an individual with complete dorsiflexor impairment and develop a method for fabricating an AFO with ankle stiffness to meet that requirement. Experimental, bench research. The literature on sagittal biomechanics of non-pathological adults was reviewed to derive the stiffness of the ankle during loading response. Computer models of 144 AFOs were created with geometric variations to account for differences in human anthropometrics. Computer-based finite element analysis was employed to determine the stiffness and safety factor of the models. Stiffness of the AFOs ranged from 0.04 to 1.8 Nm/deg. This ample range is expected to account for the stiffness required for most adults with complete dorsiflexor impairment. At 5° deflection the factor of safety (ratio of strength to stress) ranged from 2.8 to 9.1. A computer program was generated that computes AFO stiffness from user-input variables of AFO geometry. The stiffness is compared to a theoretically appropriate stiffness based on the patient mass. The geometric variables can be modified until there is a close match, resulting in AFO design specification that is appropriate for the patient. Through validation on human subjects, this method may benefit patient outcomes in clinical practice by avoiding the current uncertainty surrounding AFO performance and reducing the labor and time involved in rectifying a custom AFO post-fabrication. This method provides an avenue for improving patient outcomes by avoiding the current uncertainty surrounding non-articulated plantarflexion resist ankle foot orthosis performance. The ability to quantify the biomechanical ankle stiffness requirement for an individual with complete dorsiflexor impairment provides insight into how other AFO types should be designed as well.

The effect of two different types of functional ankle-foot orthosis on the gait of patients with spastic hemiplegia was studied. A gap was cut into the conventional stiff orthosis to allow a limited dorsiflexion of 10-15 degrees, while plantarflexion was blocked (spring type). This gap was bridged by an aluminum bar to stiffen the orthosis for the experiment. Fourteen patients of different ages (6.5-20.1 years) walked barefoot and with the orthosis, once springy and once stiff. Kinetics and kinematics were analyzed. Gait was significantly improved into normal pattern by using any type of ankle-foot orthosis. While walking barefoot with a toe-heel-toe gait, the physiological heel-toe gait was restored with any type of orthosis. The spring type of orthosis was significantly superior to the stiff orthosis. This was most clearly expressed in the general parameters of gait-like cadence, velocity, and step length. Kinetic data gave a significant improvement by using any ankle-foot orthosis. Whereas break force was similar with both types, push-off was further improved with the spring type. Kinematics revealed little statistical difference between the two types, although gait was more dynamic and physiological with the spring type of orthosis. Any functional ankle-foot orthosis ameliorates the gait pattern in patients with spastic hemiplegia, but a spring type of orthosis renders the gait more dynamic and best corrects the pathology of gait.

The effect of two different types of functional ankle-foot orthosis on the gait of patients with spastic hemiplegia was studied. A gap was cut into the conventional stiff orthosis to allow a limited dorsiflexion of 10-15°, while plantarflexion was blocked (spring type). This gap was bridged by an aluminum bar to stiffen the orthosis for the experiment. Fourteen patients of different ages (6.5-20.1 years) walked barefoot and with the orthosis, once springy and once stiff. Kinetics and kinematics were analyzed. Gait was significantly improved into normal pattern by using any type of ankle-foot orthosis. While walking barefoot with a toe-heel-toe gait, the physiological heel-toe gait was restored with any type of orthosis. The spring type of orthosis was significantly superior to the stiff orthosis. This was most clearly expressed in the general parameters of gait-like cadence, velocity, and step length. Kinetic data gave a significant improvement by using any ankle-foot orthosis. Whereas break force was similar with both types, push-off was further improved with the spring type. Kinematics revealed little statistical difference between the two types, although gait was more dynamic and physiological with the spring type of orthosis. Any functional ankle-foot orthosis ameliorates the gait pattern in patients with spastic hemiplegia, but a spring type of orthosis renders the gait more dynamic and best corrects the pathology of gait.

Three-dimensional laser scanning has been used for patient measurement for cranial helmets and spinal braces. Ankle-foot orthoses are commonly prescribed for children with orthopaedic conditions. This trial sought to compare ankle-foot orthoses produced by laser scanning or traditional plaster casting. Assessment of the effectiveness and efficiency of using laser scanning to produce ankle-foot orthoses. Randomised controlled trial with blinding of orthotists and patients to the construction technique used. A randomised double-blind trial comparing fabrication of ankle-foot orthoses from casts or laser scans. The time spent in the rectification and moulding of scanned ankle-foot orthoses was around 50% less than for cast ankle-foot orthoses. A non-significant increase of 9 days was seen in the time to delivery to the patient for laser scanning with computer-aided design and computer-aided manufacturing. There was a higher incidence of problems with the scan-based ankle-foot orthoses at delivery of the device, but no difference in how long the ankle-foot orthoses lasted. Costs associated with laser scanning were not significantly different from traditional methods of ankle-foot orthosis manufacture. Compared with conventional casting techniques, laser scan-based ankle-foot orthosis manufacture did not significantly improve either the quality of the final product or the time to delivery. Ankle-foot orthoses (AFOs) are a common requirement for chronic neurological conditions during childhood. Improved efficiency of provision of AFOs would benefit children and families by reducing the delay in provision of devices and would benefit the health service by making best use of valuable orthotist time.