A new method for evaluating ankle foot orthosis characteristics: BRUCE

Optimizing 3D printed ankle-foot orthoses for patients with stroke: Importance of effective elastic modulus and finite element simulation

Patients with stroke often use ankle-foot orthoses (AFOs) for gait improvement. 3D printing technology has become a popular tool in recent years for the production of AFOs due to its strengths on customization and rapid manufacturing. However, the porosity of the 3D printed materials affects the kinetic features of these orthoses, leading to its lower-strength than solid ones. The effective elastic modulus of 3D printed material was measured following standard test method to obtain the kinetic features precisely in a finite element simulation. This study demonstrated that the porosity of 3D printed samples using 100% fill density was 11% for PLA and 16% for Nylon. As a result, their effective elastic modulus was reduced to 1/3 and 1/12 of fully solid objects, respectively, leading to a lower stiffness of 3D printed orthoses. A fatigue testing platform was built to verify our finite element model, and the findings of the fatigue test were consistent with the analysis of the finite element model. Further, our AFO has been proven to have a lifespan exceeding 200 thousand steps. Our study highlights the significance of determining the actual porosity of 3D printed samples by calculating the effective elastic modulus, which leads to a more precise finite element simulation and enables reliable prediction of the kinetic features of the AFO. Overall, this study provides valuable insights into the production and optimization of 3D printed AFOs for patients with stroke.

Design of a Quasi-Passive Ankle-Foot Orthosis with Customizable, Variable Stiffness

Most commercial ankle-foot orthoses (AFOs) are passive structures that cannot modulate stiffness to assist with a diverse range of activities, such as stairs and ramps. It is sometimes possible to change the stiffness of passive AFOs through reassembly or benchtop adjustment, but they cannot change stiffness during use. Passive AFOs are also limited in their ankle mechanics and cannot replicate a biomimetic, nonlinear torque-angle relationship. Many research labs have developed ankle exoskeletons that show promise as viable alternatives to passive AFOs, but they face challenges with reliability, mass, and cost. Consequently, commercial translation has largely failed to date. Here we introduce the Variable Stiffness Orthosis (VSO), a quasi-passive variable stiffness ankle-foot orthosis that strikes a balance between powered and passive systems, in terms of mass, complexity, and onboard intelligence. The VSO has customizable torque-angle relationships via a cam transmission, and can make step-to-step stiffness adjustments via motorized reconfiguration of a spring support along a lead-screw. In this work, we introduce two versions: a nominal and a stiff prototype, which differ primarily in their mass and available stiffness levels. The available torque-angle relationships are measured on a custom dynamometer and closely match model predictions. The experimental results showed that the prototypes are capable of producing ankle stiffness coefficients between 9 - 330 Nm/rad.

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

BACKGROUND

The 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.

METHOD

The 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.

RESULTS

There 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%].

CONCLUSIONS

This 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.

Standardised classification system for bespoke thermoplastic ankle foot orthoses

PURPOSE

To validate a new classification system for bespoke thermoplastic ankle foot orthoses (AFOs).

METHODS

Inter- and intra-observer reliability study. A classification system based on the design and function of AFOs was created. Sixty-three independent observers classified thirty-six photographs of different AFOs, according to the proposed classification system via an online questionnaire. Approximately two weeks later, the same AFOs were classified again by fifty-three of the same participants. All participants were health care professionals, researchers, or technicians with experience in referring for, prescribing, fitting, reviewing, researching or manufacturing AFOs.

RESULTS

The mean inter- and intra-observer agreement Fleiss' kappa was 0.932 and 0.944, respectively. 98.3% of participants reported that the classification system was very easy or moderately easy to use, with 85.7% reporting they would use the classification system. 90.5% of participants reported that the proposed AFO classification system was clear, with 84% stating it was useful.

CONCLUSION

The proposed classification system for bespoke thermoplastic AFOs, has an excellent inter- and intra-observer agreement. It will reduce the ambiguity of the description of the type of AFOs used in clinical practice and research. Furthermore, it makes reproducible comparisons between groups possible, which are essential for future evaluations of evidence-based orthotic care.

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.

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.

Quantifying alignment bias during the fabrication and fitting of ankle-foot orthoses: A single center study

BACKGROUND

The sagittal plane alignment of ankle-foot orthoses (AFO) and AFO footwear combinations (AFO-FC) has been shown to influence gait outcomes. As such, clinicians often target a particular alignment during the fabricating and fitting of an AFO to maximize outcomes.

RESEARCH QUESTION

How does the alignment of an AFO change during the fabrication and fitting process with respect to the intended, benchmark sagittal plane alignment identified by the consulting orthotist?

STUDY DESIGN

Prospective METHODS: The assessment of AFO alignment was performed using a convenience sample of 125 custom molded AFOs from 68 individuals fabricated at our center (57 bilateral AFOs, 11 unilateral AFOs). The alignment of each AFO was measured at 5 distinct steps during the fabrication and fitting process using a recently validated method to measure AFO neutral angle using differential inclinometers.

RESULTS

Prior to fabrication, the intended, benchmark alignment set by the consulting orthotist was 90 degrees for 92% of AFOs, was between 1 and 7 degrees of dorsiflexion for 7% of AFOs and was 5 degrees of plantarflexion for 1% of AFOs. Repeated measures ANOVA showed that AFO alignment changed between all fabrication and fitting steps. Overall, paired t-tests confirmed that AFO alignment was consistently 2-5 degrees more dorsiflexed than the benchmark alignment. Prior to fitting shoes, 55% of fabricated AFOs measured more than 2 degrees from the benchmark alignment. After fitting shoes, nearly 87% of AFO-FCs were more than 2 degrees from the benchmark alignment.

SIGNIFICANCE

The finding of systematic dorsiflexion bias and changes in AFO alignment throughout the fabrication and fitting process indicates the need to improve AFO fabrication precision. The neutral angle measurement methodology - using differential inclinometers - provides a means to improve this precision by enabling orthotists to precisely quantify and make appropriate adjustments to AFO alignment throughout the entire fabrication and fitting process.

Ankle-foot orthosis with an oil damper versus nonarticulated ankle-foot orthosis in the gait of patients with subacute stroke: a randomized controlled trial

BACKGROUND

Gait improvement in patients with stroke has been examined in terms of use or non-use of an ankle-foot orthosis (AFO), but the effects of different kinds of AFOs remain unclear. In this study, the effect on gait of using an AFO with an oil damper (AFO-OD), which has plantarflexion stiffness without dorsiflexion resistance, was compared with a nonarticulated AFO, which has both dorsiflexion and plantarflexion stiffness, in a randomized controlled trial.

METHODS

Forty-one patients (31 men, 10 women; mean age 58.4 ± 11.3 years) in the subacute phase of stroke were randomly allocated to two groups to undergo gait training for 1 h daily over 2 weeks by physiotherapists while wearing an AFO-OD or a nonarticulated AFO. A motion capture system was utilized to measure shod gait without orthosis at baseline and after training with the allocated AFO. Data analysis focused on the joint kinematics and kinetics, spatial and temporal parameters, ground reaction force, and shank-to-vertical angle. Unpaired t-test or Mann-Whitney U test was performed to clarify the difference in gait with an AFO between the two AFO groups after training, with a significance level of p = 0.05.

RESULTS

Thirty-six patients completed the study (17 in the AFO-OD group and 19 in the nonarticulated AFO group). The ankle joint was more dorsiflexed in single stance (p = 0.008, effect size r = 0.46) and peak ankle power absorption was larger in stance (p = 0.007, r = 0.55) in the AFO-OD group compared with the nonarticulated AFO group. Peak power absorption varied among patients in the AFO-OD group. Increased dorsiflexion angles were also found at initial contact (p = 0.008, r = 1.51), pre-swing (p = 0.045, r = 0.91), and the swing phase (p = 0.045, r = 0.91) in the AFO-OD group. There was no difference in peak plantarflexion moment, ankle power generation, spatial or temporal parameters, ground reaction force, or shank-to-vertical angle between the two groups.

CONCLUSIONS

The results of this study showed that an AFO with plantarflexion stiffness but without dorsiflexion resistance produced greater improvement in ankle joint kinematics and kinetics compared with the nonarticulated AFO, but the results of peak power absorption varied greatly among patients. Trial registration UMIN000028126, Registered 1 August 2017, https://upload.umin.ac.jp/cgi-bin/icdr/ctr_menu_form_reg.cgi?recptno=R000032197.

Design principles, manufacturing and evaluation techniques of custom dynamic ankle-foot orthoses: a review study

Ankle-Foot Orthoses (AFO) can be prescribed to allow drop-foot patients to restore a quasi-normal gait pattern. Standard off-the-shelf AFOs are cost-effective solutions to treat most patients with foot and ankle weakness, but these devices have several limitations, especially in terms of comfort. Therefore, custom AFOs are increasingly adopted to address drop-foot when standard solutions are not adequate. While the solid ones are the most common type of AFO, providing full stability and strong resistance to ankle plantarflexion, passive dynamic AFOs (PD-AFOs) represent the ideal solution for patients with less severe ankle weakness. PD-AFOs have a flexible calf shell, which can bend during the stance phase of walking and absorb energy that can be released to support the limb in the push-off phase. The aim of this review is to assess the state-of-the-art and identify the current limitations of PD-AFOs. An extensive literature review was performed in Google Scholar to identify all studies on custom PD-AFOs. Only those papers reporting on custom PD-AFOs were included in the review. Non peer-reviewed papers, abstract shorter than three pages, lecture notes and thesis dissertations were excluded from the analysis. Particular attention was given to the customization principles and the mechanical and functional tests. For each topic, the main results from all relevant papers are reported and summarized herein. There were 75 papers that corresponded to the search criteria. These were grouped according to the following macro-topics: 16 focusing on scanning technologies and geometry acquisition; 14 on customization criteria; 19 on production techniques; 16 on mechanical testing, and 33 on functional testing. According to the present review, design and production of custom PD-AFOs are becoming increasingly feasible due to advancements in 3D scanning techniques and additive manufacturing. In general, custom PD-AFOs were shown to provide better comfort and improved spatio-temporal parameters with respect to standard solutions. However, no customization principle to adapt PD-AFO stiffness to the patient's degree of ankle impairment or mechanical/functional demand has thus far been proposed.

Energy cost optimized dorsal leaf ankle-foot-orthoses reduce impact forces on the contralateral leg in people with unilateral plantar flexor weakness

BACKGROUND

In individuals with unilateral plantar flexor weakness, the second peak of the vertical ground reaction force (GRF) is decreased. This leads to a higher ground reaction force, e.g. impact, of the contralateral leg, potentially explaining quadriceps muscle and/or knee joint pain. Energy cost optimized dorsal leaf ankle-foot-orthoses (AFOs) may increase the push-off ground reaction force, which in turn could lead to lower impact forces on the contralateral leg.

RESEARCH QUESTIONS

1) Are impact forces increased in the contralateral leg of people with unilateral plantar flexor weakness compared to healthy subjects? 2) Do energy cost optimized AFOs reduce impact forces and improve leg impact symmetry compared to walking without AFO in people with unilateral plantar flexor weakness?

METHODS

Nine subjects with unilateral plantar flexor weakness were provided a dorsal leaf AFO with a stiffness primarily optimized for energy cost. Using 3D gait analyses peak vertical GRF during loading response with and without AFO, and the symmetry between the legs in peak GRF were calculated. Peak GRF and symmetry were compared with reference data of 23 healthy subjects.

RESULTS

The contralateral leg showed a significant higher peak vertical GRF (12.0 ± 0.9 vs 11.2 ± 0.6 N/kg, p = 0.005) compared to healthy reference data. When walking with AFO, the peak vertical GRF of the contralateral leg significantly reduced (from 12.0 ± 0.9 to 11.4 ± 0.7 N/kg, p = 0.017) and symmetry improved compared to no AFO (from 0.93 ± 0.06 to 1.01 ± 0.05, p < 0.001).

CONCLUSION

In subjects with unilateral plantar flexor weakness, impact force on the contralateral leg was increased when compared to healthy subjects and dorsal leaf AFOs optimized for energy cost substantially reduced this force and improved impact symmetry when compared to walking without AFO. This indicates that dorsal leaf AFOs may reduce pain resulting from increased impact forces during gait in the contralateral leg in people with unilateral plantar flexor weakness.

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

INTRODUCTION

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.

MATERIALS AND METHODS

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.

RESULTS

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/°.

CONCLUSIONS

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.

Surrogate lower limb design for ankle-foot orthosis mechanical evaluation

Purpose

This study designs and provides a pilot evaluation of a novel surrogate lower limb (SLL) that provides anatomically realistic three-dimensional (3D) foot motion, based on a literature consensus of passive lower limb motion. This SLL is intended to replace single axis surrogates currently used in mechanical testing of ankle-foot orthoses (AFO).

Material and Methods

The SLL design is inspired by the Rizzoli foot model, with shank, hindfoot, midfoot, forefoot, and toe sections. Ball and socket joints were used between hindfoot-midfoot (HM)-forefoot sections. Forefoot-toes used a hinge joint. Three-dimensional printed nylon, thermoplastic polyurethane (TPU) and polylactic acid (PLA), as well as casted silicone rubber were used to re-create foot components. After fabrication, motion capture was performed to measure rotation using fiducial markers. The SLL was then loaded under both static and cyclic loads representing a 100 kg person walking for 500,000 cycles.

Results

Most joints were within 5° of target angles. The SLL survived static loads representing 1.5 times body weight for both static and cyclical loading.

Conclusions

This SLL moved as designed and survived testing loads, warranting further investigation towards enabling essential mechanical testing for AFO currently on the market, and helping to guide device prescription.

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.

Alternative methods for measuring ankle-foot orthosis alignment in clinical care

BACKGROUND

Changes in gait due to an ankle foot orthosis (AFO) have been shown to be impacted by the sagittal plane alignment of the AFO, but there is variability in practice and lack of consensus as to how this alignment should be measured. The neutral angle is a measure of AFO alignment that has the potential to be used by various specialties that prescribe, provide, and analyze AFOs. Currently, a lack of validated measurement methods prevents the neutral angle from being used in various clinical settings. Two experimental neutral angle measurement methods are proposed to address this shortcoming: a portable low-cost method for use during AFO fabrication and fitting, and a laboratory-based method for use during dynamic three-dimensional gait analysis (3DGA).

RESEARCH QUESTION

What is the concurrent validity of the two experimental neutral angle measurement methods against the gold standard?

METHODS

The gold standard neutral angle measurement (NA_GOLD) was prospectively collected during a static 3DGA trial for 19 pediatric AFOs from 10 individuals. While NA_GOLD was being collected, the neutral angle was simultaneously measured using digital differential inclinometers (NA_INCL). Within the same 3DGA session, the neutral angle was also measured during the swing phase of gait (NA_SWING). The NA_INCL and NA_SWING measurements were compared to NA_GOLD using repeated measures ANOVA, ICC, and bootstrapped errors-in-variables regressions.

RESULTS

Repeated measures ANOVA indicated no differences between measurement methods (p = 0.43) and ICC analysis indicated good absolute agreement (ICC(A-1) = 0.85). Mean absolute deviations between the NA_INCL and NA_SWING with NA_GOLD measurements were 2.4 ° and 1.9 °, with standard deviations of 2.9 ° and 2.7 °, respectively. Maximum observed differences were less than 7 °. The NA_INCL and NA_SWING methods explained 74 % and 81 % of the variance in NA_GOLD, respectively.

SIGNIFICANCE

The concurrent validity of two new neutral angle measurement methods provides alternative means to assess AFO alignment in the clinic.

Understanding the effects of quantitatively prescribing passive-dynamic ankle-foot orthosis bending stiffness for individuals after stroke

BACKGROUND

Passive-dynamic ankle-foot orthosis (PD-AFO) bending stiffness, which assists plantar flexor function, can be prescribed to improve poststroke gait. However, outcomes with PD-AFOs are variable likely because of improper personalization. We implemented a prescription model that objectively personalizes PD-AFO bending stiffness based on each individual's level of plantar flexor weakness (quantitatively prescribed PD-AFO).

OBJECTIVES

To evaluate whether a quantitatively prescribed PD-AFO improves peak paretic plantar flexion moment compared with the original AFO for individuals after stroke and to examine the immediate effects of wearing a quantitatively prescribed PD-AFO.

STUDY DESIGN

This is a repeated-measures study.

METHODS

PD-AFO bending stiffness was personalized for 10 individuals after stroke through the previously developed prescription model. Participants underwent an instrumented gait analysis while wearing their original AFO and the quantitatively prescribed PD-AFO.

RESULTS

Participants' peak paretic plantar flexion moment significantly increased while wearing the quantitatively prescribed PD-AFO compared with the original AFO. In addition, participants showed different levels of improvements in a series of other key biomechanical and walking performance parameters with PD-AFO use. Some participants showed improvements in all parameters, whereas others showed moderate to no improvements.

CONCLUSIONS

Quantitatively prescribed PD-AFO bending stiffness resulted in inconsistent improvements in biomechanical and walking performance parameters, which warrants further investigation. Future work should investigate whether more consistent benefits are seen with faster walking speeds and longer-term PD-AFO use. In addition, future work should conduct larger-scale studies that aim to understand and optimize orthosis-patient matching for all AFO designs/characteristics.

The effects of footplate stiffness on push-off power when walking with posterior leaf spring ankle-foot orthoses

BACKGROUND

Many studies on ankle-foot orthoses investigated the optimal stiffness around the ankle, while the effect of footplate stiffness has been largely ignored. This study investigated the effects of ankle-foot orthosis footplate stiffness on ankle-foot push-off power during walking in able-bodied persons.

METHODS

Twelve healthy participants walked at a fixed speed (1.25 m·s^-1) on an instrumented treadmill in four conditions: shod and with a posterior leaf-spring orthosis with a flexible, stiff or rigid footplate. For each trial, ankle kinematics and kinetics were averaged over one-minute walking. Separate contributions of the ankle joint complex and distal hindfoot to total ankle-foot power and work were calculated using a deformable foot model.

FINDINGS

Peak ankle joint power was significantly higher with the rigid footplate compared to the flexible and stiff footplate and not different from shod walking. The stiff footplate increased peak hindfoot power compared to the flexible and rigid footplate and shod walking. Total ankle-foot power showed a significant increase with increasing footplate stiffness, where walking with the rigid footplate was comparable to shod walking. Similar effects were found for positive mechanical work.

INTERPRETATION

A rigid footplate increases the lever of the foot, resulting in an increased ankle moment and energy storage and release of the orthosis' posterior leaf-spring as reflected in higher ankle joint power. This effect dominates the power generation of the foot, which was highest with the intermediate footplate stiffness. Future studies should focus on how tuning footplate stiffness could contribute to optimizing ankle-foot orthosis efficacy in clinical populations.

Individual stiffness optimization of dorsal leaf spring ankle-foot orthoses in people with calf muscle weakness is superior to standard bodyweight-based recommendations

BACKGROUND

In people with calf muscle weakness, the stiffness of dorsal leaf spring ankle-foot orthoses (DLS-AFO) needs to be individualized to maximize its effect on walking. Orthotic suppliers may recommend a certain stiffness based on body weight and activity level. However, it is unknown whether these recommendations are sufficient to yield the optimal stiffness for the individual. Therefore, we assessed whether the stiffness following the supplier's recommendation of the Carbon Ankle7 (CA7) dorsal leaf matched the experimentally optimized AFO stiffness.

METHODS

Thirty-four persons with calf muscle weakness were included and provided a new DLS-AFO of which the stiffness could be varied by changing the CA7® (Ottobock, Duderstadt, Germany) dorsal leaf. For five different stiffness levels, including the supplier recommended stiffness, gait biomechanics, walking energy cost and speed were assessed. Based on these measures, the individual experimentally optimal AFO stiffness was selected.

RESULTS

In only 8 of 34 (23%) participants, the supplier recommended stiffness matched the experimentally optimized AFO stiffness, the latter being on average 1.2 ± 1.3 Nm/degree more flexible. The DLS-AFO with an experimentally optimized stiffness resulted in a significantly lower walking energy cost (- 0.21 ± 0.26 J/kg/m, p < 0.001) and a higher speed (+ 0.02 m/s, p = 0.003). Additionally, a larger ankle range of motion (+ 1.3 ± 0.3 degrees, p < 0.001) and higher ankle power (+ 0.16 ± 0.04 W/kg, p < 0.001) were found with the experimentally optimized stiffness compared to the supplier recommended stiffness.

CONCLUSIONS

In people with calf muscle weakness, current supplier's recommendations for the CA7 stiffness level result in the provision of DLS-AFOs that are too stiff and only achieve 80% of the reduction in energy cost achieved with an individual optimized stiffness. It is recommended to experimentally optimize the CA7 stiffness in people with calf muscle weakness in order to maximize treatment outcomes. Trial registration Nederlands Trial Register 5170. Registration date: May 7th 2015. http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=5170 .

Effect of a carbon reinforcement for maximizing shoe outsole bending stiffness on plantar pressure and walking comfort in people with diabetes at high risk of foot ulceration

BACKGROUND

Different shoe design features can reduce peak plantar pressure to help prevent foot ulcers in people with diabetes. A carbon reinforcement of the shoe outsole to maximize bending stiffness is commonly applied in footwear practice, but its effect has not been studied to date.

RESEARCH QUESTION

What is the effect of a carbon shoe-outsole reinforcement on peak plantar pressure and walking comfort in people with diabetes at high risk of foot ulceration?

METHODS

In 24 high-risk people with diabetes, in-shoe regional peak pressures were measured during walking at a comfortable speed in two different shoe conditions: an extra-depth diabetes-specific shoe with a non-reinforced outsole and the same type of shoe with a 3-mm-thick full-length carbon reinforcement of the outsole. The same custom-made insole was worn in both shoe conditions. Walking comfort was assessed using a Visual Analogue Scale (0-10, 10 being highest possible comfort).

RESULTS

Significantly lower metatarsal head peak pressures (by a median 10-22 kPa) were found with the reinforced shoe compared to the non-reinforced shoe (p < .001). In >83% of cases with the reinforced shoe and >71% with the non-reinforced shoe metatarsal head peak pressures were <200 kPa. At the hindfoot, peak pressures were significantly higher (by a median 24 kPa) with the reinforced shoe (p = .001). No significant shoe effects were found for the toes. No significant shoe effects were found for walking comfort: median 6.1 for the reinforced shoe versus 5.6 for the non-reinforced shoe.

SIGNIFICANCE

Adding a full-length carbon reinforcement to the outsole of a diabetes-specific shoe significantly reduces peak pressures at the metatarsal heads, where ulcers often occur, in high-risk people with diabetes, and this does not occur at the expense of patient-perceived walking comfort.

The Codivilla Spring: from then to now and beyond

The ankle-foot-orthosis (AFO), originally called Codivilla Spring, is an orthotic device prescribed to the patients with foot drop due to neurological diseases in order to control the range of motion of the ankle joint, to compensate for the muscle weakness/spasticity thus optimizing the gait function. In this paper, a historical revision of the most known and used AFO worldwide from the origin of its name and the first applications at the Rizzoli Orthopedic Institute to the most advanced solutions in use today is covered. Through the critical analysis of historical documents available, the paper reports on the controversy about the true inventor of the Codivilla Spring during the first decades of the twentieth century. Main current adult and child AFOs, in terms of their design and indications are presented. Finally, possible approaches for the selection of the correct orthosis and the individual prescription are discussed in order to manage specific mechanical neuromuscular deficiencies of the subject's ankle-foot complex optimizing walking efficiency.

Effectiveness comparison between carbon spring and hinged ankle-foot orthoses in crouch gait treatment of children with diplegic cerebral palsy: a randomized crossover trial

BACKGROUND

Children with cerebral palsy (CP) often present a loss of effectiveness of the plantarflexors/knee-extensors couple that leads to crouch gait. When treating a child with crouch gait by means of ankle foot orthoses, preserving or restoring push off power is a key issue.

AIM

To compare carbon-fiber spring (Carbon Ankle Seven® = CAFO) and hinged anklefoot orthoses (HAFO) effectiveness in improving functionality and walking ability in children with diplegic CP and crouch gait.

DESIGN

Randomized crossover trial.

SETTING

Hospital center.

POPULATION

Ten children with diplegic CP and crouch gait, 5 males and 5 females, aged 11 (4) years.

METHODS

The gait of each child was evaluated by means of instrumental gait analysis with both CAFO and HAFO, in a randomized order and after a 4-week adaptation period. The primary outcome measure was the change in ankle power generation. As secondary outcome measures, knee joint kinematics, stride length, walking speed, Observational Gait Scale, and preferred orthosis were considered.

RESULTS

The median of the energy produced in stance was superior with CAFO (+2.2 J/kg, IQR 4.7, p=0.006), and the energy absorbed inferior (-3.3 J/kg, IQR 4.3, p=0.011). No statistically significant difference was found for any other parameter. Preference of the children was equally distributed between the two orthoses.

CONCLUSIONS

No evident superiority of CAFO with respect to HAFO was found in improving gait performance of children with CP and crouch gait. Nevertheless, the results suggest the possibility that CAFO permits an energy saving and reduction of the more compromising deficits.

CLINICAL REHABILITATION IMPACT

The final choice of the participants indicates that CAFOs are preferred by older and heavier children, but the preference does not correlate with the performance of the orthoses during gait.

Strength Evaluation and Modification of a 3D Printed Anterior Ankle Foot Orthoses

Ankle foot orthosis (AFO) is widely used to prevent foot drop and improve walking ability for individuals with cerebral palsy and stroke. However, traditional anterior AFO (TAAFO) could only last within months because the bilateral neck of TAAFO was easy to break. Currently, a 3D-printing technique is used to develop assistive devices for rehabilitation. The study aimed to implement the finite element (FE) method to revise the 3D printed AAFO (3DP-AAFO) and evaluate its strength. A 3.2 mm-thickness for the TAAFOs and 3DP-AAFOs were fabricated, respectively. The stiffness of TAAFO and 3DP-AAFO were tested by a material machine and compared to the FE model. In the FE analysis, the thickness of AAFO model was increased at the neck to enhance its strength. A plantarflexion and dorsiflexion moment were respectively subjected to 3DP-AAFO models to undergo stress analysis. Under the mechanical test, the 3DP-AAFO (K = 1.09 Nm/degree) was 7.8 times stiffer than the traditional AAFO (K = 0.14 Nm/degree). The FE results showed that thickening the 3DP-AAFO on the neck up to 4.7 mm could moderate stress concentration and increase the stiffness of the 3DP-AAFO. Therefore, the study concluded that the 3DP-AAFO was stiffer than the traditional AAFO. Increasing the appropriate thickness around neck of 3DP-AAFO could avoid neck fracture as much as possible.

An Unsupervised Data-Driven Model to Classify Gait Patterns in Children with Cerebral Palsy

Ankle and foot orthoses are commonly prescribed to children with cerebral palsy (CP). It is unclear whether 3D gait analysis (3DGA) provides sufficient and reliable information for clinicians to be consistent when prescribing orthoses. Data-driven modeling can probe such questions by revealing non-intuitive relationships between variables such as 3DGA parameters and gait outcomes of orthoses use. The purpose of this study was to (1) develop a data-driven model to classify children with CP according to their gait biomechanics and (2) identify relationships between orthotics types and gait patterns. 3DGA data were acquired from walking trials of 25 typically developed children and 98 children with CP with additional prescribed orthoses. An unsupervised self-organizing map followed by k-means clustering was developed to group different gait patterns based on children's 3DGA. Model inputs were gait variable scores (GVSs) extracted from the gait profile score, measuring root mean square differences from TD children's gait cycle. The model identified five pathological gait patterns with statistical differences in GVSs. Only 43% of children improved their gait pattern when wearing an orthosis. Orthotics prescriptions were variable even in children with similar gait patterns. This study suggests that quantitative data-driven approaches may provide more clarity and specificity to support orthotics prescription.

Modifying ankle foot orthosis stiffness in patients with calf muscle weakness: gait responses on group and individual level

Background

To improve gait, persons with calf muscle weakness can be provided with a dorsal leaf spring ankle foot orthosis (DLS-AFO). These AFOs can store energy during stance and return this energy during push-off, which, in turn, reduces walking energy cost. Simulations indicate that the effect of the DLS-AFO on walking energy cost and gait biomechanics depends on its stiffness and on patient characteristics. We therefore studied the effect of varying DLS-AFO stiffness on reducing walking energy cost, and improving gait biomechanics and AFO generated power in persons with non-spastic calf muscle weakness, and whether the optimal AFO stiffness for maximally reducing walking energy cost varies between persons.

Methods

Thirty-seven individuals with neuromuscular disorders and non-spastic calf muscle weakness were included. Participants were provided with a DLS-AFO of which the stiffness could be varied. For 5 stiffness configurations (ranging from 2.8 to 6.6 Nm/degree), walking energy cost (J/kg/m) was assessed using a 6-min comfortable walk test. Selected gait parameters, e.g. maximal dorsiflexion angle, ankle power, knee angle, knee moment and AFO generated power, were derived from 3D gait analysis.

Results

On group level, no significant effect of DLS-AFO stiffness on reducing walking energy cost was found (p = 0.059, largest difference: 0.14 J/kg/m). The AFO stiffness that reduced energy cost the most varied between persons. The difference in energy cost between the least and most efficient AFO stiffness was on average 10.7%. Regarding gait biomechanics, increasing AFO stiffness significantly decreased maximal ankle dorsiflexion angle (− 1.1 ± 0.1 degrees per 1 Nm/degree, p < 0.001) and peak ankle power (− 0.09 ± 0.01 W/kg, p < 0.001). The reduction in minimal knee angle (− 0.3 ± 0.1 degrees, p = 0.034), and increment in external knee extension moment in stance (− 0.01 ± 0.01 Nm/kg, p = 0.016) were small, although all stiffness’ substantially affected knee angle and knee moment compared to shoes only. No effect of stiffness on AFO generated power was found (p = 0.900).

Conclusions

The optimal efficient DLS-AFO stiffness varied largely between persons with non-spastic calf muscle weakness. Results indicate this is caused by an individual trade-off between ankle angle and ankle power affected differently by AFO stiffness. We therefore recommend that the AFO stiffness should be individually optimized to best improve gait.

Trial registration number

Nederlands Trial Register 5170. Registration date: May 7th 2015. http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=5170

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

Background

To 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.

Methods

We 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.

Results

Maximum 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%).

Conclusions

Modifying 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.

Electronic supplementary material

The online version of this article (10.1186/s13047-019-0348-8) contains supplementary material, which is available to authorized users.

Development of an Ankle-Foot Orthosis That Provides Support for Flaccid Paretic Plantarflexor and Dorsiflexor Muscles

ADJUST, a novel ankle-foot orthosis (AFO) that we have developed, allows the ankle a normal range of motion (ROM) while providing support for flaccid ankle-muscle paresis. It consists of two leaf-spring hinges that independently control plantarflexion and dorsiflexion stiffness. To evaluate whether ADJUST meets the minimum mechanical requirements, we quantified its ankle ROM and stiffness. To evaluate whether it meets the minimum ankle kinematic and kinetic goals for normal gait, a patient with both plantarflexor and dorsiflexor paralysis used it, and his own AFO, to walk. When fitted with stiff springs, ADJUST met all requirements and goals. During the stance and the swing phases, ankle ROM was within the normal range when ADJUST was fitted with stiff springs. Ankle ROM during stance was outside the normal range both with the patient's own AFO and with ADJUST when it was fitted with flexible springs. Power at the ankle met the minimum goal but was lower with ADJUST than with the patient's own AFO. The optimal stiffness configuration that would result in a higher power at the ankle with a normal ankle ROM was not reached for this patient. Walking with ADJUST seems feasible and could be profitable in patients with flaccid ankle muscle paresis.

Computational and experimental evaluation of the mechanical properties of ankle foot orthoses: A literature review

BACKGROUND

Ankle foot orthoses are external medical devices applied around the ankle joint area to provide stability to patients with neurological, muscular, and/or anatomical disabilities, with the aim of restoring a more natural gait pattern.

STUDY DESIGN

This is a literature review.

OBJECTIVES

To provide a description of the experimental and computational methods present in the current literature for evaluating the mechanical properties of the ankle foot orthoses.

METHODS

Different electronic databases were used for searching English-language articles realized from 1990 onward in order to select the newest and most relevant information available.

RESULTS

A total of 46 articles were selected, which describe the different experimental and computational approaches used by research groups worldwide.

CONCLUSION

This review provides information regarding processes adopted for the evaluation of mechanical properties of ankle foot orthoses, in order to both improve their design and gain a deeper understanding of their clinical use. The consensus drawn is that the best approach would be represented by a combination of advanced computational models and experimental techniques, capable of being used to optimally mimic real-life conditions.

CLINICAL RELEVANCE

In literature, several methods are described for the mechanical evaluation of ankle foot orthoses (AFOs); therefore, the goal of this review is to guide the reader to use the best approach in the quantification of the mechanical properties of the AFOs and to help gaining insight in the prescription process.

Ankle-foot orthosis alignment affects running mechanics in individuals with lower limb injuries

BACKGROUND

Individuals with severe lower extremity injuries often require ankle-foot orthoses to return to normal activities. Ankle-foot orthoses alignment is a key consideration during the clinical fitting process and may be particularly important during dynamic activities such as running.

OBJECTIVE

To investigate how 3° changes in sagittal plane ankle-foot orthoses alignment affect running mechanics.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twelve participants with unilateral lower limb injury ran overground and lower extremity running mechanics were assessed. Participants wore their passive-dynamic ankle-foot orthoses in three alignments: clinically fit neutral, 3° plantarflexed from clinically fit neutral, and 3° dorsiflexed from clinically fit neutral.

RESULTS

The 3° changes in sagittal alignment significantly influenced ankle mechanics during running. The plantarflexed alignment significantly decreased the peak ankle plantarflexor moment, peak knee extensor moment, and peak ankle and knee power absorption and generation compared to more dorsiflexed alignments. Alignment also altered footstrike angle, with dorsiflexed alignments associated with a more dorsiflexed footstrike pattern and plantarflexed alignments toward a more plantarflexed footstrike pattern. However, alignment did not influence loading rate.

CONCLUSION

Small changes in ankle-foot orthoses alignment significantly altered running mechanics, including footstrike angle, and knee extensor moments. Understanding how ankle-foot orthoses design parameters affect running mechanics may aid the development of evidence-based prescription guidelines and improve function for ankle-foot orthoses users who perform high-impact activities.

CLINICAL RELEVANCE

Understanding how ankle-foot orthoses alignment impacts biomechanics should be a consideration when fitting passive-dynamic devices for higher impact activities, such as running. Individual running styles, including footstrike patterns, may be affected by small changes in alignment.

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.

Design of a Low Profile, Unpowered Ankle Exoskeleton That Fits Under Clothes: Overcoming Practical Barriers to Widespread Societal Adoption

Here, we present the design of a novel unpowered ankle exoskeleton that is low profile, lightweight, quiet, and low cost to manufacture, intrinsically adapts to different walking speeds, and does not restrict non-sagittal joint motion; while still providing assistive ankle torque that can reduce demands on the biological calf musculature. This paper is an extension of the previously-successful ankle exoskeleton concept by Collins, Wiggin, and Sawicki. We created a device that blends the torque assistance of the prior exoskeleton with the form-factor benefits of clothing. Our design integrates a low profile under-the-foot clutch and a soft conformal shank interface, coupled by an ankle assistance spring that operates in parallel with the user's calf muscles. We fabricated and characterized technical performance of a prototype through benchtop testing and then validated device functionality in two gait analysis case studies. To our knowledge, this is the first ankle plantarflexion assistance exoskeleton that could be feasibly worn under typical daily clothing, without restricting ankle motion, and without components protruding substantially from the shoe, leg, waist, or back. Our new design highlights the potential for performance-enhancing exoskeletons that are inexpensive, unobtrusive, and can be used on a wide scale to benefit a broad range of individuals throughout society, such as the elderly, individuals with impaired plantarflexor muscle strength, or recreational users. In summary, this paper demonstrates how an unpowered ankle exoskeleton could be redesigned to more seamlessly integrate into daily life, while still providing performance benefits for common locomotion tasks.

The impact of ankle-foot orthosis stiffness on gait: A systematic literature review

BACKGROUND

Ankle-foot orthoses (AFOs) are commonly prescribed to provide ankle support during walking. Current prescription standards provide general guidelines for choosing between AFO types, but are limited in terms of guiding specific design parameter choices. These design parameters affect the ankle stiffness of the AFO.

RESEARCH QUESTION

The aim of this review was to investigate the impact of AFO stiffness on walking mechanics.

METHODS

A literature search was conducted using three databases: Pubmed, Engineering Village, and Web of Science.

RESULTS

After applying the exclusion criteria, 25 of 287 potential articles were included. The included papers tested a range of stiffnesses (0.02-8.17 Nm/deg), a variety of populations (e.g. healthy, post-stroke, cerebral palsy) and various gait outcome measures. Ankle kinematics were the most frequently reported measures and the most consistently affected by stiffness variations. Greater stiffnesses generally resulted in reduced peak ankle plantarflexion, dorsiflexion, and total range of motion, as well as increased dorsiflexion at initial contact. At the knee, a few studies reported increased flexion at initial contact, and decreased peak extension and increased peak flexion during stance when stiffness was increased. Stiffness did not affect hip kinetics and there was low evidence for its effects on hip or pelvis kinematics, ankle and knee kinetics, muscle activity, metabolic cost, ground reaction forces and spatiotemporal parameters. There were no generalizable trends for the impact of stiffness on user preference.

SIGNIFICANCE

AFO stiffness is a key factor influencing ankle movement. Clear reporting standards for AFO design parameters, as well as additional high quality research is needed with larger sample sizes and different clinical populations to ascertain the true effect of stiffness on gait.

Ground reaction and solid ankle-foot orthoses are equivalent for the correction of crouch gait in children with cerebral palsy

AIM

To investigate any performance differences between the solid ankle-foot orthosis (SAFO) and ground reaction ankle-foot orthosis (GRAFO) designs for correcting crouch gait in children diagnosed with cerebral palsy (CP).

METHOD

We retrospectively analyzed 147 individuals seen at our center who: (1) were diagnosed with diplegic CP, (2) walked with crouch gait, (3) had bilateral SAFO or GRAFO prescription, and (4) had three-dimensional gait analysis collected for both barefoot and orthosis walking conditions.

RESULTS

Overall, no performance gap was identified between the SAFO and GRAFO groups (p=0.828). A series of bootstrapped stepwise regression analyses indicated that ankle-foot orthosis (AFO) design was not predictive of crouch gait improvements. Improvements in crouch gait were instead shown to be predicted by AFO neutral angle and four patient factors: amount of dorsiflexion in stance, level of knee flexion contracture, age, and severity of crouch.

INTERPRETATION

Our results show that the SAFO and GRAFO designs are equally effective at correcting crouch gait for individuals diagnosed with CP.

WHAT THIS PAPER ADDS

No performance difference was detected between solid ankle-foot orthoses and ground reaction ankle-foot orthoses designs for crouch gait correction. Crouch gait improvement from ankle-foot orthoses (AFO) is influenced by AFO neutral angle. Other factors of influence include: dorsiflexion in stance, level of knee flexion contracture, age, and severity of crouch.

Determination of Ankle and Metatarsophalangeal Stiffness During Walking and Jogging

Forefoot stiffness has been shown to influence joint biomechanics. However, little or no data exist on metatarsophalangeal stiffness. Twenty-four healthy rearfoot strike runners were recruited from a staff and student population at the University of Central Lancashire. Five repetitions of shod, self-selected speed level walking, and jogging were performed. Kinetic and kinematic data were collected using retroreflective markers placed on the lower limb and foot to create a 3-segment foot model using the calibrated anatomical system technique. Ankle and metatarsophalangeal moments and angles were calculated. Stiffness values were calculated using a linear best fit line of moment versus of angle plots. Paired t tests were used to compare values between walking and jogging conditions. Significant differences were seen in ankle range of motion, but not in metatarsophalangeal range of motion. Maximum moments were significantly greater in the ankle during jogging, but these were not significantly different at the metatarsophalangeal joint. Average ankle joint stiffness exhibited significantly lower stiffness when walking compared with jogging. However, the metatarsophalangeal joint exhibited significantly greater stiffness when walking compared with jogging. A greater understanding of forefoot stiffness may inform the development of footwear, prosthetic feet, and orthotic devices, such as ankle foot orthoses for walking and sporting activities.

Shape Memory Ankle-Foot Orthoses

Electrically actuated ankle-foot orthoses (AFOs) were designed and prototyped using shape memory textile composites. Acrylic copolymers were synthesized as the matrix to demonstrate shape memory effects, whereas electrothermal fabrics were embedded to generate uniform heat as a trigger. Superior to conventional polymeric orthoses, shape memory AFOs (SM-AFOs) could be repeatedly programmed at least 20 times with stable shape fixity and recovery. Evidenced by clinical practice, SM-AFOs were effectively actuated at 10 V, allowing the correction of ankle angles with 10° plantarflexion. Ultimately, we envision a smart orthopedic system that can advance progressive rehabilitation with manipulation under safe and convenient conditions.

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.

Effect of different designs of ankle-foot orthoses on gait in patients with stroke: A systematic review

BACKGROUND

Ankle foot orthoses (AFOs) are used to improve the gait of patients with stroke.

RESEARCH QUESTION

The current review aimed at evaluating the efficacy of different designs of AFOs and comparison between them on the gait parameters of individuals with hemiplegic stroke.

METHODS

The search strategy was based on the population intervention comparison outcome (PICO) method. A search was performed in PubMed, ISI Web of Knowledge, Scopus, Science Direct, and Google Scholar databases.

RESULTS

A total of 27 articles were found for the final evaluation. All types of AFOs had positive effects on ankle kinematic in the first rocker and swing phases, but not on knee kinematics in the swing phase, hip kinematics or the third rocker function. All trials, except two, assessed immediate or short-term effects only. The articulated passive AFO compared with the non-articulated passive AFO had better effects on some aspects of the gait of patients with hemiplegia following stroke, more investigations are needed in this regard though.

SIGNIFICANCE

An ankle-foot orthosis can immediately improve the dropped foot in the stance and swing phases. The effects of long-term usage and comparison among the different types of AFOs need to be evaluated.

Assessment of Mechanical Characteristics of Ankle-Foot Orthoses

Recent designs of ankle-foot orthoses (AFOs) have been influenced by the increasing demand for higher function from active individuals. The biomechanical function of the individual and device is dependent upon the underlying mechanical characteristics of the AFO. Prior mechanical testing of AFOs has primarily focused on rotational stiffness to provide insight into expected functional outcomes; mechanical characteristics pertaining to energy storage and release have not yet been investigated. A pseudostatic bench testing method is introduced to characterize compressive stiffness, device deflection, and motion of solid-ankle, anterior floor reaction, posterior leaf spring, and the intrepid dynamic exoskeletal orthosis (IDEO) AFOs. Each of these four AFOs, donned over a surrogate limb, were compressively loaded at different joint angles to simulate the foot-shank orientation during various subphases of stance. In addition to force–displacement measurements, deflection of each AFO strut and rotation of proximal and supramalleolar segments were analyzed. Although similar compressive stiffness values were observed for AFOs designed to reduce ankle motion, the corresponding strut deflection profile differed based on the respective fabrication material. For example, strut deflection of carbon-fiber AFOs resembled column buckling. Expanded clinical test protocols to include quantification of AFO deflection and rotation during subject use may provide additional insight into design and material effects on performance and functional outcomes, such as energy storage and release.

Evaluating the Effects of Ankle-Foot Orthosis Mechanical Property Assumptions on Gait Simulation Muscle Force Results

Musculoskeletal modeling and simulation techniques have been used to gain insights into movement disabilities for many populations, such as ambulatory children with cerebral palsy (CP). The individuals who can benefit from these techniques are often limited to those who can walk without assistive devices, due to challenges in accurately modeling these devices. Specifically, many children with CP require the use of ankle-foot orthoses (AFOs) to improve their walking ability, and modeling these devices is important to understand their role in walking mechanics. The purpose of this study was to quantify the effects of AFO mechanical property assumptions, including rotational stiffness, damping, and equilibrium angle of the ankle and subtalar joints, on the estimation of lower-limb muscle forces during stance for children with CP. We analyzed two walking gait cycles for two children with CP while they were wearing their own prescribed AFOs. We generated 1000-trial Monte Carlo simulations for each of the walking gait cycles, resulting in a total of 4000 walking simulations. We found that AFO mechanical property assumptions influenced the force estimates for all the muscles in the model, with the ankle muscles having the largest resulting variability. Muscle forces were most sensitive to assumptions of AFO ankle and subtalar stiffness, which should therefore be measured when possible. Muscle force estimates were less sensitive to estimates of damping and equilibrium angle. When stiffness measurements are not available, limitations on the accuracy of muscle force estimates for all the muscles in the model, especially the ankle muscles, should be acknowledged.

Do research papers provide enough information on design and material used in ankle foot orthoses for children with cerebral palsy? A systematic review

OBJECTIVES

The purpose of this article is to determine how many of the current peer-reviewed studies of ankle foot or-thoses (AFOs) on children with cerebral palsy (CP) have included adequate details of the design and material of the AFO, to enable the study to be reproduced and outcomes clearly understood.

METHODS

A thorough search of studies published in English was conducted in March 2015, with no restriction on dates, within all major databases using relevant phrases. These searches were then supplemented by tracking all key references from the appropriate articles identified.

STUDY SELECTION

The inclusion criteria were as follows: (1) population - children with CP; (2) intervention - AFOs; and (3) outcome measure. One reviewer extracted data regarding the characteristics of the included studies, with the extracted data checked for accuracy and completeness by a second reviewer. None of the studies reviewed gave adequate details of the AFOs. Only 3.6% (n = 2) of papers tested the stiffness. Many studies (54.5%) did not describe the material used nor the material thickness (72.7 %). None of them gave any clinical justification for the chosen design of AFO.

CONCLUSIONS

There is a clear paucity of detail regarding the design and material used in AFOs on studies involving children with CP. Such a lack of detail has the potential to affect the validity of the reported outcomes, the ability to reproduce the studies and may misinform clinical practice.

A comparison of mechanical properties between different percentage layups of a single-style carbon fibre ankle foot orthosis

BACKGROUND

Currently, a range of 'off-the-shelf' ankle foot orthoses are used in clinical practice, of various functions and designs. Their use relates to immediate control over mild conditions.

OBJECTIVES

To investigate the properties of carbon fibre ankle foot orthoses at different percentage layups and provide a comparison of these through assessment of the (1) elastic properties, (2) deflection about the ankle (including the calculation of stiffness) and (3) failure under compressive forces (dorsiflexion).

STUDY DESIGN

Experimental, bench test.

METHODS

Literature was reviewed to derive a suitable bench test for mechanical testing of ankle foot orthoses. Two universal Instron machines were used to apply the necessary forces. A pilot device was utilised to establish the range of forces appropriate to confirm the setup chosen was effective. Each test was then carried out on nine ankle foot orthoses (3 × 3 different percentage layups).

RESULTS

All nine devices had their elastic properties deduced. Stiffness exhibited greater resistance in tension, with angular deflection being greatest in the 'Lite' set and least in the Rigid. Failure occurred mainly due to fracture, proximally on the strut; however, this was not consistent among the devices.

CONCLUSION

Results confirmed the properties expected of carbon fibre ankle foot orthoses were consistent. This can now be related to functionality and therefore specific device prescription options. Clinical relevance This article attempts to increase the understanding and develop the area of mechanically testing ankle foot orthoses. This was achieved by comparing carbon fibre at different percentage layups on an identical design and their resultant structural properties. This article outlines a clear and simple setup for obtaining repeatable results.

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.

Gastrocnemius operating length with ankle foot orthoses in cerebral palsy

BACKGROUND

Many individuals with cerebral palsy wear ankle foot orthoses during daily life. Orthoses influence joint motion, but how they impact muscle remains unclear. In particular, the gastrocnemius is commonly stiff in cerebral palsy. Understanding whether orthoses stretch or shorten this muscle during daily life may inform orthosis design and rehabilitation.

OBJECTIVES

This study investigated the impact of different ankle foot orthoses on gastrocnemius operating length during walking in children with cerebral palsy.

STUDY DESIGN

Case series, within subject comparison of gastrocnemius operating length while walking barefoot and with two types of ankle foot orthoses.

METHODS

We performed gait analyses for 11 children with cerebral palsy. Each child was fit with two types of orthoses: a dynamic ankle foot orthosis (Cascade dynamic ankle foot orthosis) and an adjustable dynamic response ankle foot orthosis (Ultraflex ankle foot orthosis). Musculoskeletal modeling was used to quantify gastrocnemius musculotendon operating length and velocity with each orthosis.

RESULTS

Walking with ankle foot orthoses could stretch the gastrocnemius more than barefoot walking for some individuals; however, there was significant variability between participants and orthoses. At least one type of orthosis stretched the gastrocnemius during walking for 4/6 and 3/5 of the Gross Motor Functional Classification System Level I and III participants, respectively. AFOs also reduced peak gastrocnemius lengthening velocity compared to barefoot walking for some participants, with greater reductions among the Gross Motor Functional Classification System Level III participants. Changes in gastrocnemius operating length and lengthening velocity were related to changes in ankle and knee kinematics during gait.

CONCLUSION

Ankle foot orthoses impact gastrocnemius operating length during walking and, with proper design, may assist with stretching tight muscles in daily life. Clinical relevance Determining whether ankle foot orthoses stretch tight muscles can inform future orthotic design and potentially provide a platform for integrating therapy into daily life. However, stretching tight muscles must be balanced with other goals of orthoses such as improving gait and preventing bone deformities.

Precision orthotics: optimising ankle foot orthoses to improve gait in patients with neuromuscular diseases; protocol of the PROOF-AFO study, a prospective intervention study

INTRODUCTION

In patients with neuromuscular disorders and subsequent calf muscle weakness, metabolic walking energy cost (EC) is nearly always increased, which may restrict walking activity in daily life. To reduce walking EC, a spring-like ankle-foot-orthosis (AFO) can be prescribed. However, the reduction in EC that can be obtained from these AFOs is stiffness dependent, and it is unknown which AFO stiffness would optimally support calf muscle weakness. The PROOF-AFO study aims to determine the effectiveness of stiffness-optimised AFOs on reducing walking EC, and improving gait biomechanics and walking speed in patients with calf muscle weakness, compared to standard, non-optimised AFOs. A second aim is to build a model to predict optimal AFO stiffness.

METHODS AND ANALYSIS

A prospective intervention study will be conducted. In total, 37 patients with calf muscle weakness who already use an AFO will be recruited. At study entry, participants will receive a new custom-made spring-like AFO of which the stiffness can be varied. For each patient, walking EC (primary outcome), gait biomechanics and walking speed (secondary outcomes) will be assessed for five stiffness configurations and the patient's own (standard) AFO. On the basis of walking EC and gait biomechanics outcomes, the optimal AFO stiffness will be determined. After wearing this optimal AFO for 3 months, walking EC, gait biomechanics and walking speed will be assessed again and compared to the standard AFO.

ETHICS AND DISSEMINATION

The Medical Ethics Committee of the Academic Medical Centre in Amsterdam has approved the study protocol. The study is registered at the Dutch trial register (NTR 5170). The PROOF-AFO study is the first to compare stiffness-optimised AFOs with usual care AFOs in patients with calf muscle weakness. The results will also provide insight into factors that influence optimal AFO stiffness in these patients. The results are necessary for improving orthotic treatment and will be disseminated through international peer-reviewed journals and scientific conferences.

Passive-dynamic ankle-foot orthosis replicates soleus but not gastrocnemius muscle function during stance in gait: Insights for orthosis prescription

BACKGROUND

Passive-dynamic ankle-foot orthosis characteristics, including bending stiffness, should be customized for individuals. However, while conventions for customizing passive-dynamic ankle-foot orthosis characteristics are often described and implemented in clinical practice, there is little evidence to explain their biomechanical rationale.

OBJECTIVES

To develop and combine a model of a customized passive-dynamic ankle-foot orthosis with a healthy musculoskeletal model and use simulation tools to explore the influence of passive-dynamic ankle-foot orthosis bending stiffness on plantar flexor function during gait.

STUDY DESIGN

Dual case study.

METHODS

The customized passive-dynamic ankle-foot orthosis characteristics were integrated into a healthy musculoskeletal model available in OpenSim. Quasi-static forward dynamic simulations tracked experimental gait data under several passive-dynamic ankle-foot orthosis conditions. Predicted muscle activations were calculated through a computed muscle control optimization scheme.

RESULTS

Simulations predicted that the passive-dynamic ankle-foot orthoses substituted for soleus but not gastrocnemius function. Induced acceleration analyses revealed the passive-dynamic ankle-foot orthosis acts like a uniarticular plantar flexor by inducing knee extension accelerations, which are counterproductive to natural knee kinematics in early midstance.

CONCLUSION

These passive-dynamic ankle-foot orthoses can provide plantar flexion moments during mid and late stance to supplement insufficient plantar flexor strength. However, the passive-dynamic ankle-foot orthoses negatively influenced knee kinematics in early midstance.

CLINICAL RELEVANCE

Identifying the role of passive-dynamic ankle-foot orthosis stiffness during gait provides biomechanical rationale for how to customize passive-dynamic ankle-foot orthoses for patients. Furthermore, these findings can be used in the future as the basis for developing objective prescription models to help drive the customization of passive-dynamic ankle-foot orthosis characteristics.

The Effects of Varying Ankle Foot Orthosis Stiffness on Gait in Children with Spastic Cerebral Palsy Who Walk with Excessive Knee Flexion

Introduction

Rigid Ankle-Foot Orthoses (AFOs) are commonly prescribed to counteract excessive knee flexion during the stance phase of gait in children with cerebral palsy (CP). While rigid AFOs may normalize knee kinematics and kinetics effectively, it has the disadvantage of impeding push-off power. A spring-like AFO may enhance push-off power, which may come at the cost of reducing the knee flexion less effectively. Optimizing this trade-off between enhancing push-off power and normalizing knee flexion in stance is expected to maximize gait efficiency. This study investigated the effects of varying AFO stiffness on gait biomechanics and efficiency in children with CP who walk with excessive knee flexion in stance. Fifteen children with spastic CP (11 boys, 10±2 years) were prescribed with a ventral shell spring-hinged AFO (vAFO). The hinge was set into a rigid, or spring-like setting, using both a stiff and flexible performance. At baseline (i.e. shoes-only) and for each vAFO, a 3D-gait analysis and 6-minute walk test with breath-gas analysis were performed at comfortable speed. Lower limb joint kinematics and kinetics were calculated. From the 6-minute walk test, walking speed and the net energy cost were determined. A generalized estimation equation (p<0.05) was used to analyze the effects of different conditions. Compared to shoes-only, all vAFOs improved the knee angle and net moment similarly. Ankle power generation and work were preserved only by the spring-like vAFOs. All vAFOs decreased the net energy cost compared to shoes-only, but no differences were found between vAFOs, showing that the effects of spring-like vAFOs to promote push-off power did not lead to greater reductions in walking energy cost. These findings suggest that, in this specific group of children with spastic CP, the vAFO stiffness that maximizes gait efficiency is primarily determined by its effect on knee kinematics and kinetics rather than by its effect on push-off power.

Trial Registration

Dutch Trial Register NTR3418

The Shank-to-Vertical-Angle as a parameter to evaluate tuning of Ankle-Foot Orthoses

The effectiveness of an Ankle-Foot Orthosis footwear combination (AFO-FC) may be partly dependent on the alignment of the ground reaction force with respect to lower limb joint rotation centers, reflected by joint angles and moments. Adjusting (i.e. tuning) the AFO-FC's properties could affect this alignment, which may be guided by monitoring the Shank-to-Vertical-Angle. This study aimed to investigate whether the Shank-to-Vertical-Angle during walking responds to variations in heel height and footplate stiffness, and if this would reflect changes in joint angles and net moments in healthy adults. Ten subjects walked on an instrumented treadmill and performed six trials while walking with bilateral rigid Ankle-Foot Orthoses. The AFO-FC heel height was increased, aiming to impose a Shank-to-Vertical-Angle of 5°, 11° and 20°, and combined with a flexible or stiff footplate. For each trial, the Shank-to-Vertical-Angle, joint flexion-extension angles and net joint moments of the right leg at midstance were averaged over 25 gait cycles. The Shank-to-Vertical-Angle significantly increased with increasing heel height (p<0.001), resulting in an increase in knee flexion angle and internal knee extensor moment (p<0.001). The stiff footplate reduced the effect of heel height on the internal knee extensor moment (p=0.030), while the internal ankle plantar flexion moment increased (p=0.035). Effects of heel height and footplate stiffness on the hip joint were limited. Our results support the potential to use the Shank-to-Vertical-Angle as a parameter to evaluate AFO-FC tuning, as it is responsive to changes in heel height and reflects concomitant changes in the lower limb angles and moments.

Acclimatization of the gait pattern to wearing an ankle-foot orthosis in children with spastic cerebral palsy

BACKGROUND

Ankle-foot orthoses can be prescribed to improve gait in children with cerebral palsy. Before evaluating the effects of ankle-foot orthoses on gait, a period to adapt or acclimatize is usually applied. It is however unknown whether an acclimatization period is actually needed to reliably evaluate the effect of a new orthosis on gait. This study aimed to investigate whether specific gait parameters in children with cerebral palsy would change within an acclimatization period after being provided with new ankle-foot orthoses.

METHODS

Ten children with cerebral palsy, walking with excessive knee flexion in midstance (8 boys; mean (SD) 10.2 (1.9) years; Gross Motor Function Classification System levels I-II) were provided with ventral shell ankle-foot orthoses. The orthoses were worn in combination with the child's own shoes and tuned, based on ground reaction force alignment with respect to the lower limb joints. Directly after tuning (T0) and four weeks later (T1), 3D-gait analysis was performed using an optoelectronic motion capture system and a force plate. From this assessment, ten spatiotemporal, kinematic and kinetic gait parameters were derived for the most affected leg. Differences in parameters between T0 and T1 were analyzed using paired t-tests or Wilcoxon signed rank tests (P<0.05).

FINDINGS

Over the course of four weeks, no significant differences (P ≥ 0.080) were observed for any investigated parameter.

INTERPRETATION

These results imply that the biomechanical effect of ventral shell ankle-foot orthoses on gait in independent walking children with cerebral palsy is immediately apparent, i.e., there is no further change after acclimatization.