Stiffness control in posterior-type plastic ankle-foot orthoses: effect of ankle trimline. Part 1: A device for measuring ankle moment

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

BACKGROUND

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.

OBJECTIVES

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.

STUDY DESIGN

Experimental and computational study.

METHODS

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.

RESULTS AND CONCLUSIONS

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.

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.

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.

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.

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.

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.

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.

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

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

Biomechanical response to ankle-foot orthosis stiffness during running

BACKGROUND

The Intrepid Dynamic Exoskeletal Orthosis (IDEO) is an ankle-foot orthosis developed to address the high rates of delayed amputation in the military. Its use has enabled many wounded Service Members to run again. During running, stiffness is thought to influence an orthosis' energy storage and return mechanical properties. This study examined the effect of orthosis stiffness on running biomechanics in patients with lower limb impairments who had undergone unilateral limb salvage.

METHODS

Ten patients with lower limb impairments underwent gait analysis at a self-selected running velocity. 1. Nominal (clinically-prescribed), 2. Stiff (20% stiffer than nominal), and 3. Compliant (20% less stiff than nominal) ankle-foot orthosis stiffnesses were tested.

FINDINGS

Ankle joint stiffness was greatest in the stiffest strut and lowest in the compliant strut, however ankle mechanical work remained unchanged. Speed, stride length, cycle time, joint angles, moments, powers, and ground reaction forces were not significantly different among stiffness conditions. Ankle joint kinematics and ankle, knee and hip kinetics were different between limbs. Ankle power, in particular, was lower in the injured limb.

INTERPRETATION

Ankle-foot orthosis stiffness affected ankle joint stiffness but did not influence other biomechanical parameters of running in individuals with unilateral limb salvage. Foot strike asymmetries may have influenced the kinetics of running. Therefore, a range of stiffness may be clinically appropriate when prescribing ankle-foot orthoses for active individuals with limb salvage.

Mechanism and design analysis of articulated ankle foot orthoses for drop-foot

Robotic technologies are being employed increasingly in the treatment of lower limb disabilities. Individuals suffering from stroke and other neurological disorders often experience inadequate dorsiflexion during swing phase of the gait cycle due to dorsiflexor muscle weakness. This type of pathological gait, mostly known as drop-foot gait, has two major complications, foot-slap during loading response and toe-drag during swing. Ankle foot orthotic (AFO) devices are mostly prescribed to resolve these complications. Existing AFOs are designed with or without articulated joint with various motion control elements like springs, dampers, four-bar mechanism, series elastic actuator, and so forth. This paper examines various AFO designs for drop-foot, discusses the mechanism, and identifies limitations and remaining design challenges. Along with two commercially available AFOs some designs possess promising prospective to be used as daily-wear device. However, the design and mechanism of AFO must ensure compactness, light weight, low noise, and high efficiency. These entailments present significant engineering challenges to develop a new design with wide consumer adoption.

Effects of joint alignment and type on mechanical properties of thermoplastic articulated ankle-foot orthosis

BACKGROUND

Articulated or hinged ankle-foot orthosis (AFO) allow more range of motion. However, quantitative investigation on articulated AFO is still sparse.

OBJECTIVE

The objective of the study was to quantitatively investigate effects of alignment and joint types on mechanical properties of the thermoplastic articulated AFO.

STUDY DESIGN

Tamarack dorsiflexion assist flexure joints with three durometers (75, 85 and 95) and free motion joint were tested. The AFO joint was aligned with the center of the motor shaft (surrogate ankle joint), 10 mm superior, inferior, anterior and posterior with respect to the motor shaft center.

METHODS

The AFO was passively moved from 20° plantar flexion to 15° dorsiflexion at a speed of 10°/s using a motorized device. Mechanical properties including index of hysteresis, passive resistance torque and quasi-static stiffness (at neutral, 5°, 10° and 15° in plantar flexion) were quantified.

RESULTS

Significant effects of joint types and joint alignment on the mechanical properties of an articulated thermoplastic AFO were revealed. Specifically, center alignment showed minimum resistance and stiffness while anterior and posterior alignment showed significantly higher resistance and stiffness. The dorsiflexion assist torques at neutral position ranged from 0.69 ± 0.09 to 1.88 ± 0.10 Nm.

CONCLUSIONS

Anterior and posterior alignment should be avoided as much as possible.

CLINICAL RELEVANCE

The current study suggested that anterior and posterior alignment be avoided as much as possible in clinical practice due to potential skin irritation and increase in stress around the ankle joint.

Development of a method for fabricating polypropylene non-articulated dorsiflexion assist ankle foot orthoses with predetermined stiffness

BACKGROUND

A non-articulated plantarflexion resist ankle foot orthosis (AFO), commonly known as a posterior leaf spring AFO, is indicated for patients with motor impairment to the dorsiflexors. The AFO is often custom molded to a patient's lower limb anatomy and fabricated from polypropylene. There are no established guidelines for fabricating this type of AFO with predetermined stiffness of the ankle region for normal walking speeds. Therefore an AFO may not meet the biomechanical needs of the patient.

OBJECTIVES

Quantify the biomechanical ankle stiffness requirement for an individual with complete dorsiflexor impairment and develop a method for fabricating an AFO with ankle stiffness to meet that requirement.

STUDY DESIGN

Experimental, bench research.

METHODS

The literature on sagittal biomechanics of non-pathological adults was reviewed to derive the stiffness of the ankle during loading response. Computer models of 144 AFOs were created with geometric variations to account for differences in human anthropometrics. Computer-based finite element analysis was employed to determine the stiffness and safety factor of the models.

RESULTS

Stiffness of the AFOs ranged from 0.04 to 1.8 Nm/deg. This ample range is expected to account for the stiffness required for most adults with complete dorsiflexor impairment. At 5° deflection the factor of safety (ratio of strength to stress) ranged from 2.8 to 9.1. A computer program was generated that computes AFO stiffness from user-input variables of AFO geometry. The stiffness is compared to a theoretically appropriate stiffness based on the patient mass. The geometric variables can be modified until there is a close match, resulting in AFO design specification that is appropriate for the patient.

CONCLUSION

Through validation on human subjects, this method may benefit patient outcomes in clinical practice by avoiding the current uncertainty surrounding AFO performance and reducing the labor and time involved in rectifying a custom AFO post-fabrication.

CLINICAL RELEVANCE

This method provides an avenue for improving patient outcomes by avoiding the current uncertainty surrounding non-articulated plantarflexion resist ankle foot orthosis performance. The ability to quantify the biomechanical ankle stiffness requirement for an individual with complete dorsiflexor impairment provides insight into how other AFO types should be designed as well.

Design of an automated device to measure sagittal plane stiffness of an articulated ankle-foot orthosis

The purpose of this study was to design a new automated stiffness measurement device which could perform a simultaneous measurement of both dorsi- and plantarflexion angles and the corresponding resistive torque around the rotational centre of an articulated ankle-foot orthosis (AAFO). This was achieved by controlling angular velocities and range of motion in the sagittal plane. The device consisted of a hydraulic servo fatigue testing machine, a torque meter, a potentiometer, a rotary plate and an upright supporter to enable an AAFO to be attached to the device via a surrogate shank. The accuracy of the device in reproducing the range of motion and angular velocity was within 4% and 1% respectively in the range of motion of 30° (15° plantarflexion to 15° dorsiflexion) at the angular velocity of 10°/s, while that in the measurement of AAFO torque was within 8% at the 0° position. The device should prove useful to assist an orthotist or a manufacturer to quantify the stiffness of an AAFO and inform its clinical use.

A systematic review to determine best practice reporting guidelines for AFO interventions in studies involving children with cerebral palsy

Studies which have examined the effects of ankle-foot orthoses (AFOs) on children with cerebral palsy (CP) often report insufficient detail about the participants, devices and testing protocols. The aim of this systematic review was to evaluate the level and quality of detail reported about these factors in order to generate best practice guidelines for reporting of future studies. A systematic search of the literature was conducted to identify studies which examined any outcome measure relating to AFO use in children with CP. A customized checklist was developed for data extraction and quality assessment. There was substantial variability in the level and quality of detail reported across the 41-paper yield. Many papers reported insufficient detail to allow synthesis of outcomes across studies. The findings of this review have been used to generate guidelines for best practice of reporting for AFO intervention studies. It is important to ensure homogeneity of gait pattern in a subject sample or to subdivide a sample to investigate the possibility that heterogeneity affected results. It is also important to describe the orthosis in sufficient detail that the device can be accurately replicated because differences in designs have been shown to affect outcomes. These guidelines will help researchers provide more systematic and detailed reports and thereby permit future reviewers to more accurately assess both the reporting and quality of orthotic interventions, and will facilitate synthesis of literature to enhance the evidence base.

A new method for evaluating ankle foot orthosis characteristics: BRUCE

The mechanical characteristics of ankle foot orthoses (AFOs), such as the stiffness and neutral angle around the ankle and metatarsal-phalangeal (MTP) joints, are rarely quantified. Paradoxically, it is expected that these characteristics determine the function of the AFO in pathological gait. Therefore a device to determine these AFO characteristics named BRUCE was designed based on multidisciplinary consensus. The design is based on a replicated human leg that is manually driven and continuously registers joint configuration and force exerted by the AFO onto the device. From this information, neutral angles and stiffnesses around the ankle and MTP joints are determined using a linear fit. The reliability of the stiffnesses and neutral angles was studied by repeatedly measuring the mechanical characteristics of four different AFOs, and evaluating the inter-session, intra-session, and inter-observer errors. The reliability study revealed that ankle and MTP stiffness could be measured with very high reliability (ICC=0.98-1.00). Ankle and MTP neutral angles showed reasonable reliability (ICC=0.79-0.92). Measurement error in the neutral angles could mainly be attributed to the difference in testers. With a fixed tester excellent reliability was obtained (ICC=0.99-0.99). The results derived using BRUCE can help to gain insight into the role of the mechanical characteristics of AFOs in correcting pathological gait. Objective information of AFO characteristics is expected to lead to a better founded prescription of AFOs, resulting in optimal functional benefit for the patient.

Development of an ankle-foot orthosis with an oil damper

The purpose of the present study was to develop an ankle-foot orthosis (AFO) that satisfies the requirements for an AFO for patients with hemiplegia as determined in a previous study. An oil damper has been introduced as an assistive device. The oil damper provides a resistive moment to plantar flexion of the ankle joint during initial stance on the paretic side. This function improves the insufficient eccentric contraction of the dorsiflexors. The magnitude of the resistive moment generated by this newly developed AFO can be changed easily to adjust its properties in accordance with the requirements of each patient. The mechanical properties of the AFO were measured, and the results showed that the AFO generated a sufficient resistive moment. Hemiplegic gaits with various types of AFOs were assessed, and it was found that the properties of the AFO affected the movements of the ankle, the knee, and the hip joints. The effects of the resistive moment on the alignment of the shank to the floor during initial stance are also discussed. Based on the results of this study, it is concluded that adjustability will be an essential feature for future AFOs.

Assessment of the non-linear behaviour of plastic ankle foot orthoses by the finite element method

The stiffness characteristics of plastic ankle foot orthoses (AFOs) are studied through finite element modelling and stress analysis. Particular attention is given to the modelling and prediction of non-linear AFO behaviour, which has been frequently observed in previous experimental studies but not fully addressed analytically. Both large deformation effects and material non-linearity are included in the formulation and their individual influence on results assessed. The finite element program is subsequently applied to the simulation of a series of tests designed to investigate the relation between AFO trimline location and stiffness for moderate and large rotations. Through careful consideration and identification of key modelling parameters, the developed finite element solution proves to be a reliable and effective alternative means of assessing variations of a typical plastic AFO design so that particular patient requirements could be met, in the long term.

Test apparatus for the measurement of the flexibility of ankle-foot orthoses in planes other than the loaded plane

Previous publications have reported on the flexibility of ankle-foot orthoses (AFO) only in the same plane as the applied load. This paper reports on a test apparatus developed to detect the flexibility of an AFO in 5 degrees of freedom when subjected to a plantar/dorsiflexion moment, a medial/lateral moment or a torque. A moment applied to an AFO in one plane induces angulation and translation in all planes.