Minimization of metabolic cost of transport predicts changes in gait mechanics over a range of ankle-foot orthosis stiffnesses in individuals with bilateral plantar flexor weakness.

Neuromuscular disorders often lead to ankle plantar flexor muscle weakness, which impairs ankle push-off power and forward propulsion during gait. To improve walking speed and reduce metabolic cost of transport (mCoT), patients with plantar flexor weakness are provided dorsal-leaf spring ankle-foot orthoses (AFOs). It is widely believed that mCoT during gait depends on the AFO stiffness and an optimal AFO stiffness that minimizes mCoT exists. The biomechanics behind why and how an optimal stiffness exists and benefits individuals with plantar flexor weakness are not well understood. We hypothesized that the AFO would reduce the required support moment and, hence, metabolic cost contributions of the ankle plantar flexor and knee extensor muscles during stance, and reduce hip flexor metabolic cost to initiate swing. To test these hypotheses, we generated neuromusculoskeletal simulations to represent gait of an individual with bilateral plantar flexor weakness wearing an AFO with varying stiffness. Predictions were based on the objective of minimizing mCoT, loading rates at impact and head accelerations at each stiffness level, and the motor patterns were determined via dynamic optimization. The predictive gait simulation results were compared to experimental data from subjects with bilateral plantar flexor weakness walking with varying AFO stiffness. Our simulations demonstrated that reductions in mCoT with increasing stiffness were attributed to reductions in quadriceps metabolic cost during midstance. Increases in mCoT above optimum stiffness were attributed to the increasing metabolic cost of both hip flexor and hamstrings muscles. The insights gained from our predictive gait simulations could inform clinicians on the prescription of personalized AFOs. With further model individualization, simulations based on mCoT minimization may sufficiently predict adaptations to an AFO in individuals with plantar flexor weakness.

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.

Examination of the prediction of the planar piecewise continuous lumped muscle parameter model for walking gait with ankle-foot orthosis.

GOAL: This work examines the use of a previously described piecewise continuous lumped muscle parameter (PPCLMP) model for predicting selected gait parameters for walking without and with ankle-foot orthoses (AFOs) of varying stiffnesses. METHODS: Two AFOs with low (3.4 Nm/deg) and high (6.9 Nm/deg) stiffnesses were tested on the left leg of six healthy subjects to examine the model prediction on the influence of different AFO stiffnesses on gait. RESULTS: The model prediction errors ranged from 0 % to 70 % for step lengths with root mean square error (RMSE) of 0.15 m and ranged from 0 % to 67 % for swing time with RMSE of 0.07 s. The prediction precision of step length was more consistent among subjects than of swing time. DISCUSSIONS AND CONCLUSIONS: The model predicts the observed shortened step lengths and swing times, but there were significant differences between predicted and observed swing times and step lengths. The causes of these differences might be differences in the lumped muscle parameters taken from the literature and those of the subjects tested. Also, the model assumption that muscle stiffness is proportional to joint angle may not be corrected.

Effects of community ambulation training with 3D-printed ankle-foot orthosis on gait and functional improvements: a case series of three stroke survivors.

Introduction: Many of the patients using ankle-foot orthoses (AFOs) experience poor fit, pain, discomfort, dislike of the aesthetics of the device, and excessive range of motion restrictions, which diminish the use of AFOs. Although 3D-printed ankle-foot orthoses (3D-AFOs) affect patient satisfaction and overall gait functions such as ankle moment, joint range of motion (ROM), and temporal-spatial parameters, the material properties and manufacturing process of 3D-AFOs are still diverse; the clinical effects of community ambulation using 3D-AFOs and satisfaction in patients with stroke are poorly understood. Case description: Case 1: A 30-year-old man, with a history of right basal ganglia hemorrhage, presented with marked foot drop and genu recurvatum. Case 2: A 58-year-old man, with a history of multifocal scattered infarction, presented with an asymmetrical gait pattern due to abnormal pelvic movement. Case 3: A 47-year-old man, with a history of right putamen hemorrhage, presented with recent poor balance and a prominent asymmetrical gait pattern due to increased ankle spasticity and tremor. All patients could walk independently with AFOs. Interventions and outcomes: Gait was assessed under three walking (even, uneven, and stair ascent/descent) and four AFO (no shoes, only shoes, shoes with AFOs, and shoes with 3D-AFOs) conditions. After 4 weeks of community ambulation training with 3D-AFO or AFO, the patients were followed up. Spatiotemporal parameters; joint kinematics; muscle efficiency; clinical evaluations including impairments, limitations, and participation; and patient satisfaction with wearing 3D-AFO were evaluated. Results and conclusion: 3D-AFOs were suitable for community ambulation of patients with chronic stroke and effective on step length, stride width, symmetry, ankle range of motion, and muscle efficiency during even surface walking and stair ascent in patients with chronic stroke. The 4-week community ambulation training with 3D-AFOs did not promote patient participation; however, it increased ankle muscle strength, balance, gait symmetry, and gait endurance and reduced depression among patients with a history of stroke. The participants were satisfied with 3D-AFO's thinness, lightweight, comfortable feeling with wearing shoes, and gait adjustability.

The effects of anterior and posterior ankle-foot orthoses on sit-to-stand transfer performance in stroke patients.

BACKGROUND: Nonarticulated and low-temperature thermoplastic ankle-foot orthoses (AFOs) have a semirigid design and are effective in improving the postural control mechanism (PCM) in individuals with poststroke hemiparesis. AFOs with an anterior leaf (AAFOs) are more often prescribed than are AFOs with a posterior leaf (PAFOs); however, the effects of AAFOs on the PCM during sit-to-stand transfer (STST) have not been explored. RESEARCH QUESTIONS: Do AAFOs and PAFOs change the PCM differently during STST? METHODS: A cross-sectional quasi-experimental design was adopted in this study. Fourteen individuals with poststroke hemiparesis (10 men and 4 women, aged between 38 and 71 years, stroke onset between 1 and 17 months) performed STST with shoes only, an AAFO with shoes, or a PAFO with shoes. Vertical ground reaction force (VGRF) and center-of-pressure (CoP) coordinates were collected using a pressure mat to calculate PCM parameters. A single-factor repeated measures analysis of variance was performed to answer the research question. RESULTS: (1) The weight-bearing percentage of the paretic leg was significantly lower when the participants wore a PAFO (p = 0.018) than when they wore an AAFO (p = 0.019) during the first 5 and 5-10 s after rising. (2) A small rate of change of the VGRF increment (dF/dT) was detected when participants wore AFOs, particularly AAFO. (3) The maximum mediolateral displacement of the CoP when standing up was significantly different among the three conditions (p = 0.012). SIGNIFICANCE: For patients with poststroke hemiparesis, AAFO and PAFOs change the PCM during STST performance. Only AAFO improved the PCM possibly because of the rigidity and clearance of the heel region, which provide somatic sensory feedback. Therefore, rehabilitation professionals should educate hemiplegic patients who use AAFOs or PAFOs to perform dynamic daily tasks slowly for their safety.

A novel apparatus to assess the mechanical properties of Ankle-Foot Orthoses: Stiffness analysis of the Codivilla spring.

Ankle-Foot Orthoses (AFOs) are the most common devices prescribed to support the ankle and restore a quasi-normal gait pattern in drop-foot patients. AFO stiffness is possibly the main mechanical property affecting foot and ankle biomechanics. A variety of methods to evaluate this property have been reported, however no standard procedure has been validated and widely used. This study is reporting the repeatability of a novel apparatus to measure AFO stiffness in ideal frictionless conditions. The apparatus is based on a servo-hydraulic testing machine and allows to apply a displacement-controlled rotation of the AFO shell, simulating the physiological ankle dorsi/plantarflexion movement. The repeatability of the apparatus in measuring AFO stiffness in dorsiflexion and plantarflexion was assessed intra- and inter-session in a sample of standard polypropylene AFOs of different sizes (Codivilla spring). The repeatability of the apparatus in measuring the AFO stiffness was high. The Intra- and Inter-session Coefficient of Variation ranged between 0.02 ÷ 1.3 % and 1.3 ÷ 5 %, respectively. The Intra Class Correlation Coefficient ranged between 0.999 ÷ 1 intra- and 0.993 ÷ 0.997 inter-session. AFOs stiffness was observed to increase with the AFO size. The setup is easy to replicate and can be implemented with any torsion-controlled servo-hydraulic testing machine and has resulted simple to use and flexible enough to adapt to AFOs with different sizes. The frictionless contacts characterizing the apparatus make it possible to measure the ideal AFO stiffness by excluding the effect of the fixation methods to the leg and help to improve the repeatability of measurements.

Anterior or Posterior Ankle Foot Orthoses for Ankle Spasticity: Which One Is Better?

Background and Objectives: Ankle foot orthoses (AFOs) are commonly used by stroke patients to walk safely and efficiently. Both posterior AFOs (PAFOs) and anterior AFOs (AAFOs) are available. The objective of this study was to compare the efficacy of AAFOs and PAFOs in the treatment of ankle spasticity. Materials and Methods: A crossover design with randomization for the interventions and blinded assessors was used. Twenty patients with chronic stroke, a Modified Ashworth Scale (MAS) score of the ankle joint of 2, and a Tardieu angle ≥20 degrees were recruited. The patients were assigned to wear either an AAFO or PAFO at random and subsequently crossover to the other AFO. Results: Twenty stroke patients with ankle spasticity were recruited. The mean age was 46.60 (38−60) years. The mean time since stroke onset was 9.35 (6−15) months. It was discovered that the AAFO improved walking speed as well as the stretch reflex dynamic electromyography (dEMG) and walking dEMG amplitudes of the medial gastrocnemius muscles more significantly than the PAFO (p < 0.05). Conclusions: The AAFO had greater efficacy in reducing both static and dynamic ankle spasticity, and allowed for faster walking than the PAFO. The stretch reflex and walking dEMG amplitudes could be used for quantitative spasticity assessment.

Development of an Anterior Foot Drop Ankle Foot Orthosis with Adjustable Stiffness / 医用生物力学

Objective For patients with foot drop gait, to design a kind of anterior ankle foot orthosis (AFO) with adjustable stiffness, so as to restore natural gait of the ankle by limiting the patients’ unusual plantar flexion to the optimum extent. Methods The minimum orthodontic moment of 10 foot drop male patients was measured by self-made experimental equipment, which could be used to select optimum material modulus of the AFO. The relationship between elastic modulus and different filling structures and filling ratio parameters was studied by tensile test. A typical patient with foot drop was selected, and the anterior AFO fitting the shape of patient’s foot was quickly made by three-dimensional (3D) printing with foot geometric data and specific filling material, filling structure and filling rate. The kinematics and surface electromyography (sEMG) of plantar flexors were tested under barefoot and wearing two kinds of AFOs, so as to verify the effect of the AFO on plantar flexion. The effectiveness of the limitation and the degree of preservation of ankle valgus and plantar flexion were discussed. Results The minimum corrective torque required for 10 male patients with foot drop was 2.16 N·m. Compared with the rigid AFO, the range of motion (ROM) of plantar flexion and valgus increased by 67.8% and 88.6% respectively with the flexible AFO. The activation of the muscles responsible for plantar flexion (soleus, medial head of gastrocnemius and lateral head of gastrocnemius) also decreased by 38.3%, 46.6% and 55.8%. Conclusions This AFO with adjustable stiffness can be used for orthosis customization of patients with foot drop, providing more effective and long-term orthosis function and potential.

Effect of Ankle Torque on the Ankle-Foot Orthosis Joint Design Sustainability.

The ankle joint of a powered ankle-foot orthosis (PAFO) is a prominent component, as it must withstand the dynamic loading conditions during its service time, while delivering all the functional requirements such as reducing the metabolic effort during walking, minimizing the stress on the user's joint, and improving the gait stability of the impaired subjects. More often, the life of an AFO is limited by the performance of its joint; hence, a careful design consideration and material selection are required to increase the AFO's service life. In the present work, a compact AFO joint was designed based on a worm gear mechanism with steel and brass counterparts due to the fact of its large torque transfer capability in a single stage, enabling a compact joint. Further, it provided an added advantage of self-locking due to the large friction that prevents backdrive, which is beneficial for drop-foot recovery. The design was verified using nonlinear finite element analysis for maximum torque situations at the ankle joint during normal walking. The results indicate stress levels within its design performance; however, it is recommended to select high-grade structural steel for the ankle shaft as the highest stresses in AFO were located on it.

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.

A validated computational framework to evaluate the stiffness of 3D printed ankle foot orthoses.

The purpose of this study was to create and validate a standardized framework for the evaluation of the ankle stiffness of two designs of 3D printed ankle foot orthoses (AFOs). The creation of four finite element (FE) models allowed patient-specific quantification of the stiffness and stress distribution over their specific range of motion during the second rocker of the gait. Validation was performed by comparing the model outputs with the results obtained from a dedicated experimental setup, which showed an overall good agreement with a maximum relative error of 10.38% in plantarflexion and 10.66% in dorsiflexion. The combination of advanced computer modelling algorithms and 3D printing techniques clearly shows potential to further improve the manufacturing process of AFOs.

A novel experimental setup for evaluating the stiffness of ankle foot orthoses.

OBJECTIVE: The purpose of this study was the construction of a new semi-automated experimental setup for the evaluation of the stiffness of ankle foot orthoses (AFOs) around an axis aligned to the anatomical ankle joint during the second rocker of the gait. The setup, developed in close collaboration with the orthopedic device company V!GO NV (Wetteren, Belgium), allows measurement of plantarflexion and dorsiflexion in the sagittal plane for a maximal range of motion of 50° (- 25° plantarflexion up to 25° dorsiflexion) in a non-destructive way. RESULTS: The mechanical properties of four 3D printed AFOs are investigated, based on the ranges of motion derived from the gait assessment of the patients when they walked with their AFO. The reliability of the stiffness measures was studied by the evaluation of the test-retest repeatability and the intra-tester and inter-tester variability. These studies revealed that the ankle stiffness can be measured with high reliability (ICC = 0.94-1.00). The obtained outcomes indicate that the experimental setup could be applied to measure the ankle stiffness of any topology of AFOs and, in the future, help finding the correlation with the information coming from the gait assessment of the patients.

Application of the Superelastic NiTi Spring in Ankle Foot Orthosis (AFO) to Create Normal Ankle Joint Behavior.

Hinge-based Ankle Foot Orthosis (HAFO) is one of the most common non-surgical solutions for the foot drop. In conventional HAFOs, the ankle joint is almost locked, and plantar flexion is restricted due to the high stiffness of the hinge mechanism. This often leads to a rigid walking gate cycle, poor muscle activity, and muscle atrophy. Since the ankle torque-angle loop has a non-linear profile, the use of a superelastic NiTi spring within the hinge, due to its nonlinear behavior, could recreate a close-to-normal stiffness of the normal ankle joint, which, in turn, could create a more natural walk. The focus of this study is to evaluate the performance of a superelastic NiTi spring versus a conventional Stainless Steel spring in a hinge mechanism of a custom-fit HAFO. To this aim, a custom-fit HAFO was fabricated via the fast casting technique. Then, motion analysis was performed for two healthy subjects (Case I and Case II): (i) subjects with bare foot; (ii) subjects wearing a conventional HAFO with no spring; (iii) subjects wearing a conventional Stainless Steel-based HAFO; and (iv) subjects wearing a NiTi spring-based HAFO. The data related to the ankle angle and the amount of moment applied to the ankle during walking were recorded using Cortex software and used for the evaluations. Finally, Finite Element Analysis (FEA) was performed to evaluate the safety of the designed HAFO. The NiTi spring offers a higher range of motion (7.9 versus 4.14 degree) and an increased level of moment (0.55 versus 0.36 N·m/kg). Furthermore, a NiTi spring offers an ankle torque-angle loop closer to that of the healthy subjects.

Benefits from using an ankle-foot orthosis in children with myelomeningocele / Benefícios do uso da órtese tornozelo-pé nas crianças com mielomeningocele

Myelomeningocele (MMC) or spina bifida is a defect of the neural tube in which the spinal cord, its envelopes (meninges), and vertebral arches develop abnormally in the beginning of gestation, and owing to this failure of closure there appear a series of congenital defects and associated comorbidies, impairing in several aspects the functioning of the life of children with MMC. The congenital clubfoot has been found the most common orthopaedic anomaly in patients with MMC. The ankle-foot orthosis (AFO) is an orthopaedic device commonly used by these children to minimize the sequelae caused by this anomaly. OBJECTIVE: Identify the functional benefits brought about by the use of the AFO to children with MMC, as reported by their guardians. METHOD: Descriptive, transversal study. Convenience sample consisting of 25 guardians of children with MMC who were using/had used an AFO. RESULTS: Eighty percent of the guardians have reported at least one benefit brought about by the use of the AFO, among them: improvement in foot position (68%), foot growth (40%), improvement in foot balance (32%), and balance sitting position (15%). CONCLUSION: The use of the AFO by children with MMC can provide several benefits reported by their guardians.

A mielomeningocele (MMC) ou espinha bífida é um defeito do tubo neura no qual a medula espinal, seus envoltórios (meninges) e os arcos vertebrais desenvolvem-se anormalmente no início da gestação e, como consequências, temos uma série de defeitos congênitos e comorbidades associadas prejudicando a funcionalidade em diversos aspectos da vida das crianças com MMC. O pé torto congênito foi apontado como a anomalia ortopédica mais comum nos pacientes com MMC e a órtese tornozelo-pé (OTP) é um aparelho ortopédico que pode ser usado nessas crianças para amenizar as sequelas geradas por essa anomalia. OBJETIVO: Identificar os benefícios funcionais trazidos pelo uso da OTP em crianças com MMC relata-dos pelos seus responsáveis. MÉTODO: Estudo descritivo, transversal. Amostra de conveniência composta por responsáveis de 25 crianças com MMC que usavam/usaram a OTP que responderam a uma entrevista estruturada que contemplava as variáveis estudadas. RESULTADOS: Oitenta por cento dos responsáveis relataram pelo menos um benefício causado pelo uso da OTP, dentre eles: melhorou a postura do pé (68%), o pé cresceu (40%), melhorou o equilíbrio em pé (32%), melhorou o equilíbrio sentado (15%). CONCLUSÃO: O uso da OTP em crianças com MMC pode proporcionar benefícios identificados pelos responsáveis.

Direct measurement of plantarflexion resistive moments and angular positions of an articulated ankle-foot orthosis while walking in individuals post stroke: A preliminary study.

The plantarflexion resistive moments of an articulated ankle-foot orthosis play an important role in improving gait in individuals post stroke. However, the evidence regarding their magnitude required from the articulated ankle-foot orthosis to improve walking is still limited. Therefore, the primary aim of this study was to directly measure the plantarflexion resistive moments and the joint angular positions while walking using a prototype instrumented articulated ankle-foot orthosis in five individuals post stroke. The secondary aim was to investigate their moment-angle relationship by changing its preset plantarflexion stiffness. Each subject was fitted with the instrumented articulated ankle-foot orthosis and walked on a treadmill under four different preset plantarflexion stiffness conditions (0.35 N·m/°, 0.51 N·m/°, 0.87 N·m/°, and 1.27 N·m/°). For each subject, the plantarflexion resistive moments and the joint angular positions of five continuous gait cycles were extracted and averaged for each condition. Data were plotted and presented as case series. Both plantarflexion resistive moments and joint angular positions of the ankle-foot orthosis changed according to the preset plantarflexion stiffness in all subjects. Using the instrumented articulated ankle-foot orthosis could potentially advance the understanding of the biomechanics of an ankle-foot orthosis, as well as contribute to more evidence-based orthotic care of patients.

A new method for measuring AFO deformation, tibial and footwear movement in three dimensional gait analysis.

Solid ankle-foot orthoses (AFOs) are designed to immobilise the ankle but numerous studies have measured a considerable ankle range of motion (ROM) in AFO users. Measurement of ankle kinematics may be affected by soft-tissue artefact (STA) of the knee marker, deformation of the AFO or tibial movement within the AFO. A new model based on the Conventional Gait Model (CGM) was developed to calculate these effects. Although movement of the AFO within the shoe should not affect the measured ankle joint angle the model also allows an estimation of this movement. Seven children (13 limbs) with spastic diplegic cerebral palsy were assessed to present the benefits of the new model compared to the CGM. STA of the knee marker was estimated to result in a 1.5° overestimation of total ankle ROM (from 8.2° to 9.7°). STA error was strongly related to angle of knee flexion (r=0.82) with an average maximum error of 3.8°. AFO deformation contributed approximately two thirds of the ankle ROM (6.0±4.3°) with the remaining third from tibial movement relative to the AFO (2.8±0.9°). Movement of the AFO within the footwear was very small (1.8±0.8°). A strong positive relationship (r=0.9) was found between body mass (kg) and AFO deformation which was statistically significant (p<0.001). This is the first model to attempt to quantify different contributions to ankle dorsiflexion measured during gait analysis of people wearing AFOs.

Effect of Ankle-foot Orthosis on Activities of Daily Living and Walking Ability of Patients with Low Lumbar Spinal Cord Injury / 中国康复理论与实践

@#Objective To observe the effect of ankle-foot orthosis(AFO)on the activities of daily living(ADL)and walking ability of patients with low lumbar spinal cord injury.Methods29 cases with low lumbar spinal cord injury were trained by systematic rehabilitation.According to patients' condition,static AFO or dynamic AFO were assembled for them.All patients were evaluated with Modified Barthel Index(MBI)and Functional Independence Measure(FIM)before and after training,and the walking distances were also measured.ResultsAfter AFO dressed,the ADL scores of patients increased,especially walking ability increased significantly(P<0.05).Of 29 patients,26 cases had outdoor walking ability,3 cases had domestic walking ability.ConclusionSelecting different kinds of AFO according to condition of individual can help patients with low lumbar spinal cord injury to reconstruct their walking ability and improve ability of self-management.