Ankle Foot Orthosis Stiffness Research Articles

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.

Effects of trimline cut in ankle foot orthosis: An experimental and finite element analysis

An Ankle-foot orthosis (AFO) is a structure that spans from the lower leg to the foot and controls ankle joint movement. It prevents or assists the human body's lower leg and foot in replicating a normal human gait. The purpose of AFO is to achieve a stable gait by controlling the musculoskeletal system adequately. The mechanical features of AFO stiffness will play an essential role in helping gait, if this stiffness is not matching to the patient's conditions, gait will decrease and knee joint motion will be compromised. In general, trimline cut were introduced in the AFO medial and lateral side to control the stiffness of orthosis. However, this will result in stress concentration in the ankle region and lead to failure of AFO. In this study first evaluate the effects of trimline cut in AFOs using finite element analysis with three geometrical shapes like circle, elliptical and slot were introduced on the dorsal side. The stress concentration and stiffness of AFOs in the ankle region were computed. The stiffness of the basic model and trimline cut AFO model were compared and found elliptical trimline cut model is optimum one. The experimental analysis was performed using 3D Printed AFOs and calculated stiffness. It was observed that finite element analysis results, stress concentration of trimline cut models were reduced maximum of 2 % with basic model (without trimline cut)., whereas, in the experimental study of 3D-Printed AFO of trimline cut model, stiffness were reduced around 16 % compared with basic models. This study clearly indicates that, geometrical shapes trimline cut influencing on stiffness of AFOs. It will give the insight's for orthosis designers to make custom design of AFOs in particularly foot drop conditions to optimized the stiffness of orthosis.

Design and characterization of a variable-stiffness ankle-foot orthosis.

Ankle-foot orthoses (AFOs) are a type of assistive device that can improve the walking ability of individuals with neurological disorders. Adjusting stiffness is a common way to customize settings according to individuals' impairment. This study aims to design a variable-stiffness AFO by stiffness module and characterize the AFO stiffness range to provide subject-specific settings for the users. We modeled AFO using bending beams with varying fulcrum positions to adjust the stiffness. To characterize the stiffness range and profile, we used the superposition method to generate the theoretical model to analyze the AFO numerically. The intrinsic deformation of the bending beam in the AFO is considered a combination of 2 bending deformations to replicate actual bending conditions. The corresponding experiments in different fulcrum positions were performed to compare with and optimize the theoretical model. The curve fitting method was applied to tune the theoretical model by adding a fulcrum position-related coefficient. The AFO stiffness increased as the fulcrum moved to the proximal position. The maximum stiffness obtained was 1.77 Nm/° at a 6-cm fulcrum position, and the minimum stiffness was 0.82 Nm/° at a 0.5-cm fulcrum position with a 0.43-cm thick fiberglass beam. The corresponding theoretical model had maximum and minimum stiffness of 1.71 and 0.80 Nm/°, respectively. The theoretical model had a 4.08% difference compared with experimental values. The stiffness module can provide adjustable stiffness with the fulcrum position and different kinds of fiberglass bars, especially the thickness and material of the beam. The theoretical model with different fulcrum positions can be used to profile the real-time stiffness of the AFO in a dynamic motion and to determine the appropriate dimensions of the bending beam.

Interacting effects of AFO stiffness, neutral angle and footplate stiffness on gait in case of plantarflexor weakness: A predictive simulation study

To maximize effects of dorsal leaf ankle foot orthoses (AFOs) on gait in people with bilateral plantarflexor weakness, the AFO properties should be matched to the individual. However, how AFO properties interact regarding their effect on gait function is unknown. We studied the interaction of AFO bending stiffness with neutral angle and footplate stiffness on the effect of bending stiffness on walking energy cost, gait kinematics and kinetics in people with plantarflexor weakness by employing predictive simulations.Our simulation framework consisted of a planar 11 degrees of freedom model, containing 11 muscles activated by a reflex-based neuromuscular controller. The controller was optimized by a comprehensive cost function, predominantly minimizing walking energy cost. The AFO bending and footplate stiffness were modelled as torsional springs around the ankle and metatarsal joint. The neutral angle of the AFO was defined as the angle in the sagittal plane at which the moment of the ankle torsional spring was zero. Simulations without AFO and with AFO for 9 bending stiffnesses (0–14 Nm/degree), 3 neutral angles (0–3-6 degrees dorsiflexion) and 3 footplate stiffnesses (0–0.5–2.0 Nm/degree) were performed.When changing neutral angle towards dorsiflexion, a higher AFO bending stiffness minimized energy cost of walking and normalized joint kinematics and kinetics. Footplate stiffness mainly affected MTP joint kinematics and kinetics, while no systematic and only marginal effects on energy cost were found.In conclusion, the interaction of the AFO bending stiffness and neutral angle in bilateral plantarflexor weakness, suggests that these should both be considered together when matching AFO properties to the individual patient.

A quantitative analysis of optimum design for rigid ankle foot orthoses: The effect of thickness and reinforcement design on stiffness.

An ankle foot orthosis (AFO) which is prescribed to be rigid should only deform a small amount to achieve its clinical goals. Material thickness and the design of reinforcing features can significantly affect AFO rigidity, but their selection remains based on anecdotal evidence. To quantify the effect of these parameters on AFO stiffness and to set the basis for quantitative guidelines for the design optimisation of rigid AFOs. Experimental and computational study. A polypropylene AFO was produced according to UK standard practice and its stiffness was experimentally measured for 30Nm of dorsiflexion. Its geometry and mechanical characteristics were utilised to create a finite element (FE) model of a typical AFO prescribed to be rigid. Following validation, the model was used to quantify the effect of material thickness and reinforcement design (i.e., reinforcement placement, length) on stiffness. A final set of AFO samples was produced to experimentally confirm key findings. For a specific AFO geometry and loading magnitude, there is a thickness threshold below which the AFO cannot effectively resist flexion and buckles. FE modelling showed that stiffness is maximised when reinforcements are placed at the anterior-most position possible. This key finding was also experimentally confirmed. The stiffness of an AFO reinforced according to standard practice with lateral and medial ribbing was 4.4 ± 0.1 Nm/degree. Instructing the orthotic technician to move the ribbings anteriorly increased stiffness by 22%. Further stiffening is achieved by ensuring the reinforcements extend from the footplate to at least two-thirds of the AFO's total height.

Comparison of five different methodologies for evaluating ankle–foot orthosis stiffness

BackgroundThe mechanical properties of an ankle–foot orthosis (AFO) play an important role in the gait mechanics of the end user. However, testing methodologies for evaluating these mechanical properties are not standardized. The purpose of this study was to compare five different evaluation frameworks to assess AFO stiffness.MethodThe same 13 carbon composite AFOs were tested with five different methods. Four previously reported custom test fixtures (the BRUCE, KST, SMApp, and EMPIRE) rotated an AFO into dorsiflexion about a defined axis in the sagittal plane. The fifth method involved quasi-static deflection of AFOs into dorsiflexion by hanging weights (HW) from the footplate. AFO rotational stiffness was calculated as the linear fit of the AFO resistive torque and angular deflection. Differences between methods were assessed using descriptive statistics and a repeated measures Friedman with post-hoc Bonferroni–Holm adjusted Wilcoxon signed-rank tests.ResultsThere were significant differences in measured AFO stiffnesses between test methods. Specifically, the BRUCE and HW methods measured lower stiffness than both the EMPIRE and the KST. Stiffnesses measured by the SMApp were not significantly different than any test method. Stiffnesses were lowest in the HW method, where motion was not constrained to a single plane. The median difference in absolute AFO stiffness across methods was 1.03 Nm/deg with a range of [0.40 to 2.35] Nm/deg. The median relative percent difference, measured as the range of measured stiffness from the five methods over the average measured stiffness was 62% [range 13% to 156%]. When the HW method was excluded, the four previously reported test fixtures produced a median difference in absolute AFO stiffness of 0.52 [range 0.38 to 2.17] Nm/deg with a relative percent difference between the methods of 27% [range 13% to 89%].ConclusionsThis study demonstrates the importance of developing mechanical testing standards, similar to those that exist for lower limb prosthetics. Lacking standardization, differences in methodology can result in large differences in measured stiffness, particularly for different constraints on motion. Non-uniform measurement practices may limit the clinical utility of AFO stiffness as a metric in AFO prescription and future research.

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.

Computational modelling of ankle-foot orthosis to evaluate spatially asymmetric structural stiffness: Importance of geometric nonlinearity.

An ankle-foot orthosis (AFO) constructed as a single piece of isotropic elastic material is a commonly used assistive device that provides stability to the ankle joint of patients with spastic diplegic cerebral palsy. The AFO has asymmetric stiffness that restricts plantarflexion during the swing phase while it is flexible to allow dorsiflexion during the stance phase with a large deflection, including buckling originating from geometric nonlinearity. However, its mechanical implications have not been sufficiently investigated. This study aims to develop a computational model of an AFO considering geometric nonlinearity and examine AFO stiffness asymmetry during plantarflexion and dorsiflexion using physical experiments. Three-dimensional AFO mechanics with geometric nonlinearities were expressed using corotational triangle-element formulations that obeyed Kirchhoff-Love plate theory. Computational load tests for plantarflexion and dorsiflexion, using idealised AFOs with two different ankle-region designs (covering or not covering the apexes of the malleoli), showed that plantarflexion moment-ankle angle relationships were linear and dorsiflexion moment-ankle angle relationships were nonlinear; increases in dorsiflexion led to negative apparent stiffness of the AFO. Both ankle-region designs resisted both plantarflexion and dorsiflexion, and out-of-plane elastic energy was locally concentrated on the lateral side, resulting in large deflections during dorsiflexion. These findings give insight into appropriate AFO design from a mechanical viewpoint by characterising three-dimensional structural asymmetry and geometric nonlinearity.

Multiplanar Stiffness of Commercial Carbon Composite Ankle-Foot Orthoses.

The mechanical properties of an ankle-foot orthosis (AFO) can impact how a user's movement is either restricted or augmented by the device. However, standardized methods for assessing stiffness properties of AFOs are lacking, posing a challenge for comparing between devices and across vendors. Therefore, the purpose of this study was to quantify the rotational stiffness of thirteen commercial, nonarticulated, carbon composite ankle-foot orthoses. A custom, instrumented test fixture, for evaluating mechanical properties in rotating exoskeletons (EMPIRE), deflected an AFO through 20 deg of plantar/dorsiflexion motion about a specified, but adjustable, ankle axis. Sagittal, frontal, and transverse plane rotational stiffness were calculated, and reliability was assessed between cycles, sessions, and testers. The EMPIRE demonstrated good-to-excellent reliability between testers, sessions, and cycles (intraclass correlation coefficients all ≥0.95 for sagittal plane stiffness measures). Sagittal plane AFO stiffness ranged from 0.58 N·m/deg to 3.66 N·m/deg. AFOs with a lateral strut demonstrated frontal plane stiffnesses up to 0.71 N·m/deg of eversion while those with a medial strut demonstrated frontal plane stiffnesses up to 0.53 N·m/deg of inversion. Transverse plane stiffnesses were less than 0.30 N·m/deg of internal or external rotation. These results directly compare AFOs of different models and from different manufacturers using consistent methodology and are intended as a resource for clinicians in identifying a device with stiffness properties for individual patients.

Comparison of Sagittal Plane Stiffness of Nonarticulated Pediatric Ankle-Foot Orthoses Designed to be Rigid.

When studying the effect of ankle-foot orthoses (AFOs) on gait, it is important to know their sagittal plane stiffness. However, there are no established thresholds for stiffness of non-articulated AFOs designed to be rigid. If wanting to implement published algorithms for ankle-foot orthosis-footwear combinations (AFO-FCs), the AFOs must be equally as stiff as those of the developer of the published AFO-FC algorithms. Hence, the aim of this work was to compare the sagittal plane stiffness of AFOs designed to be rigid, made for a clinical trial in the USA, and following algorithms for AFO-FC designs, to those made and used clinically in the UK by the developer of the AFO-FC algorithms. Stiffness of 9 pediatric polypropylene AFOs was tested (UK: 6; USA: 3). A computer-controlled motorized device was used in which all AFOs were clamped with the calf shell in a fixed vertical component and the foot section in a rotating plate. Each AFO was tested for 3 trials, loading the foot plate 30 Nm towards dorsiflexion and 20 Nm towards plantarflexion. Torque-angle graphs were plotted and deflection and stiffness compared descriptively across AFOs. Average deflection of AFOs was UK: 3.42±0.83° and USA: 4.81±1.05°. Average stiffness of AFOs was UK: 14.34±3.34 Nm/° and USA: 10.30±1.92 Nm/°. All tested AFOs deflected only a few degrees in either direction (range: 2.59° to 6.02°), providing the first information reported for the stiffness of rigid pediatric non-articulated AFOs. Overall, the UK AFOs were stiffer and deflected less than the USA study AFOs. AFO design features should be carefully considered as they likely influence sagittal plane stiffness and deflection under load.

Design and evaluation of the SMApp: A stiffness measurement apparatus for ankle–foot orthoses

Ankle–foot orthoses (AFOs) are braces worn by individuals with gait impairments to support ankle motion. AFO rotational stiffness is a key mechanical property that affects gait biomechanics. However, it is unclear how design choices affect AFO stiffness and what specific stiffness ranges impact gait. This stems largely from the absence of commercial devices or established guidelines for measuring AFO stiffness. This paper details the design of the AFO Stiffness Measurement Apparatus (SMApp). The SMApp is a non-destructive, automated system that measures torque and angle as an AFO is moved through a range of motion at a set speed. Using the derived torque–angle curve, we can calculate rotational stiffness, neutral angle and hysteresis of any AFO for speeds up to 37 deg/s. The repeatability of the SMApp was evaluated between and within two operators and three testing sessions using three AFOs cycled 10 times through flexion and extension. We also measured the stiffness of three different AFOs with the SMApp and another published system in a comparative case study. The SMApp had excellent reliability with high intraclass correlation coefficients (ICC ≥0.97) for all measured AFO properties. The standard error of measurement (SEM) and minimum detectable difference (MDD) were comparable to published parameters from other devices for stiffness (SEM ¡ 0.32 N m/°, MDD ¡ 0.88 N m/°) and neutral angle (SEM ¡ 0.30°, MDD ¡ 0.84°). In comparison to a previously described, reliable manual stiffness measurement device, the SMApp measurements had similar stiffness, but different neutral angle values for one of three AFOs. The SMApp can be utilized in future studies for AFO material fatigue testing, to validate finite element models, and to evaluate speed effects on AFO properties.

The effect of rotational speed on ankle-foot orthosis properties

Ankle–foot orthoses (AFOs) are devices that support ankle motion. An AFO’s sagittal plane rotational stiffness can affect gait kinematics. Because AFOs are often made from viscoelastic materials, their properties may vary at different walking speeds. The influence of rotational speed on AFO properties has not been thoroughly investigated. Therefore, the purpose of this study was to determine the impact of rotational speed on AFO stiffness about the ankle. We tested a sample of one thermoplastic off-the-shelf AFO and two 3-D printed carbon fiber enforced nylon AFOs. Each AFO’s dynamic resistance torque was measured as it was flexed at five speeds (5-100 °/s) using a custom-built measurement apparatus. We compared loading stiffness, neutral angle, and energy dissipation parameters for each AFO across speeds. Parameter values were generally greater at higher speeds. These effects were statistically significant for all AFOs (p≤0.002). However, differences in AFO stiffness and neutral angle across speeds were quite small (<0.6 Nm/° and <2.2 °). Changes in the thermoplastic AFO’s stiffness were lower than the minimum detectable difference. Energy dissipation, as indicated by hysteresis area, increased by up to 6.3 J (about 250%) at the highest speed. This demonstrates that AFO flexion speed can influence the properties of different AFOs over the range typically achieved in human walking. Future work should assess whether the observed small variations of stiffness and neutral angle have a clinically meaningful impact on user performance, as well as explore effects of angular speed on a variety of AFO materials and designs.

Effect of Ankle-Foot Orthosis Stiffness on Muscle Force During Gait Through Mechanical Testing and Gait Simulation

Mechanical testing and gait measurement for ankle-foot orthosis (AFO) are crucial for determining the AFO stiffness magnitude in an individual. However, information on the effect of the stiffness magnitude on the muscle force during gait is limited. This study aimed to investigate the relationship between the AFO stiffness and ankle muscle force during gait. The AFO stiffness was mechanically tested using a six-axis robot arm. The stiffness magnitude was adjusted using different spring constants. Five stiffness conditions were set for each plantarflexion resistive (PFR) and dorsiflexion resistive (DFR) function. The effect of the PFR and DFR on the ankle muscle force during gait were determined using musculoskeletal and AFO models. Tibialis anterior (TA) and triceps surae (TS) muscle forces were calculated through gait simulation. The angle-moment relationships display hysteresis loops for each condition. One of the PFR and DFR conditions differed significantly from the others (for all, p <; 0.05). In order of lower stiffness, the each PFR contribution ratio to the peak TA muscle force normalized in the no-stiffness condition was 8.4%, 10.8%, 11.3%, 13.5%, and 15.3%; while the each DFR contribution ratio to the peak TS muscle force was 16.2%, 20.9%, 25.3%, 29.8%, and 30.5%, respectively. Through mechanical testing as well as gait simulation, it was demonstrated that the magnitude of the AFO stiffness decreased the required ankle muscle force during gait. This study can contribute to more effective gait rehabilitation using AFO as well as AFO fabrication with customized stiffness for individual gait function.

Additive Manufacturing of Ankle-Foot Orthosis with Predefined Ankle Stiffness—A Case Report

ABSTRACT Introduction The success of orthotic interventions depends on how well an individual patient's needs are identified and addressed. In this prospective study, we addressed the following question: Is it possible to additively manufacture an ankle-foot orthosis (AFO) with predefined ankle stiffness that would decrease excessive plantarflexion in the dropfoot gait? Materials and Methods A child with unilateral drop foot was recruited for this study and took part in three gait assessments. In the first gait assessment, the “optimal” AFO stiffness was determined using a hinged AFO with adjustable ankle stiffness. A leaf-spring-type AFO with predefined optimal ankle stiffness was then virtually designed and additively manufactured. The impact of this orthosis on the patient's gait before and after 6 weeks of acclimatization period was evaluated in the second and the third gait assessments, respectively. Results A hinged orthosis with an ankle stiffness of 0.009 N·m·deg−1·kg−1 was deemed to be the optimal for the study patient. The ankle stiffness of the additively manufactured AFO was 0.008 N·m·deg−1·kg−1. This orthosis decreased patient's excessive plantarflexion, but its impact was moderately inferior compared with that of the optimal hinged orthosis. Conclusions Despite having the same ankle stiffness, hinged AFO and leaf-spring AFO did not produce the same gait pattern. Therefore, to prescribe an optimal AFO, a better understanding of subject-AFO interaction in walking is needed.

Effects of Varying Plantarflexion Stiffness of Ankle-Foot Orthosis on Achilles Tendon and Propulsion Force During Gait.

An ankle-foot orthosis (AFO) with a plantarflexion resistance function, improves post-stroke gait. An AFO with a plantarflexion resistance function not only affects the first rocker function and the weight acceptance but also the late stance phase. Achilles tendon extension is important for ankle joint function and for forward propulsion during the late stance phase; however, the effect of an AFO with a plantarflexion resistance function on the Achilles tendon is unclear. The purpose of this study was to investigate the effect of plantarflexion resistance on the extension of the Achilles tendon and the forward-propulsive force. Herein, 10 healthy adult males participated who walked under three different conditions: a no-AFO condition and two AFO conditions that had different levels of plantarflexion resistance (P1 and P2). The stiffness value of the P1 and P2 conditions was 0.56 and 1.47 Nm/°, respectively. A three-dimensional (3D) motion analysis system and a musculoskeletal model were used to assess the tendon-length change, the ground reaction force, kinematics, and kinetics data. The change in Achilles tendon length was significantly lower in the P1 and P2 conditions than the no-AFO condition. Furthermore, changes in the length of the Achilles tendon significantly decreased in the P2 condition when compared with that in the P1 condition. The peak anterior ground reaction force was significantly lower in the P2 condition than the no-AFO condition. These results suggest that excessive assist provided by an AFO prevents efficient gait by decreasing both the forward-propulsive force and tendon function.

Design and evaluation of a modularized ankle-foot orthosis with quick release mechanism.

Ankle foot orthosis (AFO) stiffness affects ankle range of motion but can also provide energy storage and return to improve mobility. To perform multiple activities during the day, a person may want to change their AFO stiffness to meet their activity's demand. Carrying multiple AFOs and changing AFOs is inconvenient and could discourage users from engaging in multiple activities. This project will develop a new quick-release mechanism (QRM) that allows users to easily change posterior strut elements to change AFO stiffness. The QRM attaches to the AFO and requires no tools to operate. The proposed QRM includes a quick-release key, weight-bearing pin, receptacle anchor, and immobilization pin. A prototype was modelled with SolidWorks and simulated with SolidWorks Simulation. The QRM was designed to have no mechanical failure during intense activities such as downhill walking and jogging. Unlike a solid screw connection, the QRM needed an additional part to eliminate unsecured motion related to clearance between the quick release key and receptacle anchor. Mechanical test results and measurement data proved no deformation on each part after mechanical testing.Clinical Relevance- The quick release AFO has the potential to improve user's activities range by tuning from stiffness free mode to high stiffness mode.

Development of a Decision Support System for Ankle-Foot Orthosis (AFO) Design Based on Lumped Parameter Models for Human Locomotion Prediction

This work aims to develop a decision support system (DSS) to help orthotic clinicians design AFOs to correct pathological gait patterns that result from various nerve impairments. The DSS utilizes lumped parameter models to predict key joint angles, step length, and swing and stance durations based on anthropometric data, impairment and AFO design. The predicted gait patterns by DSS were in general agreement with data from available literature. In the presented drop foot example, the DSS shows that increasing AFO stiffness would result in increased stride duration on both sides; proper AFO stiffness may result in increased stride length on both sides comparing with stride length for pathological gait without AFO. The DSS can be used by clinicians to suggest proper AFO’s mechanical properties, such as stiffness and range of motion, to help improve abnormal gait patterns resulting from underlying nerve impairments.

A study on the efficacy of AFO stiffness prescriptions

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.

Stiffness modification of two ankle-foot orthosis types to optimize gait in individuals with non-spastic calf muscle weakness \u2013 a proof-of-concept study

BackgroundTo reduce gait problems in individuals with non-spastic calf muscle weakness, spring-like ankle-foot orthoses (AFOs) are often applied, but they are not individually optimized to treatment outcome. The aim of this proof-of-concept study was to evaluate the effects of modifying the stiffness for two spring-like AFO types with shoes-only as reference on gait outcomes in three individuals with calf muscle weakness due to polio.MethodsWe assessed 3D gait biomechanics, walking speed and walking energy cost for shoes-only and five stiffness conditions of a dorsal-leaf-spring AFO and a spring-hinged AFO. Outcomes were compared between stiffness conditions in the two AFOs and three subjects.ResultsMaximum ankle dorsiflexion angle decreased with increasing stiffness in both AFOs (up to 6–8°) and all subjects. Maximum knee extension angle changed little between stiffness conditions, however different responses between the AFOs and subjects were observed compared to shoes-only. Walking speed remained unchanged across conditions. For walking energy cost, we found fairly large differences across stiffness conditions with both AFOs and between subjects (range 3–15%).ConclusionsModifying AFO stiffness in individuals with non-spastic calf muscle weakness resulted in substantial differences in ankle biomechanics and walking energy cost with no effect on speed. Our results provide proof-of-concept that individually optimizing AFO stiffness can clinically beneficially improve gait performance.

Trunk Movements Should be Considered When Optimizing Ankle-Foot Orthosis Stiffness in Children with Cerebral Palsy

To investigate whether varying Ankle-Foot Orthosis (AFO) stiffness leads to changes in trunk movements, and whether these changes are related to the walking energy cost.