Development of a Testing Apparatus for Structural Stiffness Evaluation of Ankle-Foot Orthoses:

Assessment of Five-Foot Plantar Morphological Pressure Points of Children with Cerebral Palsy Using or Not Dynamic Ankle Foot Orthosis

People with spastic cerebral palsy (CP) often experience a decline in gait function and flexion. The children's posture and hip strategy, which leads to knee flexion, predisposes these children to increased contact area in the medial foot region. This study investigated the use of DAFO (dynamic ankle-foot orthosis) prescribed to patients with cerebral palsy (CP) to determine the plantar pressure distribution with orthosis use. Eight children with spastic CP (age 4-12 years) were classified as Gross Motor Function Classification System (GMFCS) levels I-II with a maximum spasticity level of 3 in their ankle muscles according to the Modified Ashworth Scale. We assessed the plantar distribution by using eight WalkinSense sensors in each trial and exported data from the proprietary software (WalkinSense version 0.96, Tomorrow Options Microelectronics, S.A.). The plantar pressure distribution was conducted under two conditions: only shoes and DAFO with shoes. The activation percentages for sensor number 1 under the 1st metatarsal and sensor number 4 under the lateral edge of the heel were significantly different under the DAFO condition. The 1-point sensor activation percentage significantly decreased, while the 4-point sensor activation percentage increased during DAFO walking. According to our study findings, there was an increase in pressure distribution in the lateral part of the foot during the stance phase in DAFO. DAFO improved the gait cycle and influenced the plantar foot pressure in children with mild cerebral palsy.

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.

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.

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.

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.

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 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.