Yasushi Akazawa

Development of Shear Type Compact MR Brake for the Intelligent Ankle-Foot Orthosis and Its Control; Research and Development in NEDO for Practical Application of Human Support Robot

A brake in which the magnetorheologic fluid (MRF) is used has a simple structure and good responsibility. Therefore, MR brake is expected to perform a good adaptability for human-coexistence system. Being applied in an ankle-foot orthosis, however, conventional MR brake is too large to fit. Then, in this study we developed a shear-type MR brake with multi layer disks and minute gaps (50 micrometers) to realize compactness and high performance. This paper describes the development of a shear type compact MR brake and a new controllable ankle-foot orthosis with this brake. Furthermore, we design algorithm to control an ankle. We assist gait of a patient by changing a brake force.

Design of a stiffness-adjustable ankle-foot orthosis and its effect on ankle joint kinematics in patients with stroke

Ankle-foot orthoses (AFOs) are commonly prescribed to improve gait. The stiffness of an AFO is central for successful prescription; however, the recommended level of stiffness is currently based on the experience of clinicians. Therefore, the aim of this study was to design an experimental AFO (EAFO) whose stiffness was adjustable using commercially available oil-damper joints, and to demonstrate its potential capability in investigating the effects of altering AFO stiffness on gait. The influence of the EAFO stiffness on ankle joint kinematics in sagittal plane was evaluated in 10 patients with stroke by altering the stiffness of its oil-damper- type orthotic ankle joints using the four levels pre-set and defined by the manufacturer in dorsi- and plantarflexion directions independently. The mean peak plantarflexion angle was reduced by 105%, showing a change from 8.18 (3.14) degrees of plantarflexion to 0.38 (4.17) degrees of dorsiflexion, whilst the mean peak dorsiflexion angle was reduced by 44%, showing a change from 11.46 (5.57) degrees of dorsiflexion to 6.47 (5.23) degrees of dorsiflexion by altering the EAFO stiffness. The EAFO would therefore serve as a convenient tool when investigating the influence of AFO stiffness on gait in both clinical and research settings.

Quantitative measurement of spastic ankle joint stiffness using a manual device: a preliminary study.

Quantitative measurement of ankle joint stiffness following stroke could prove useful in monitoring the progress of a rehabilitation programme. The objective of this study was to design a manual device for use in the clinical setting. Manual measurement of spastic ankle joint stiffness has historically been conducted using hand-held dynamometers or alternative devices, but some difficulties have been reported in controlling the velocity applied to the ankle during the measurement. In this study, a manually operated device was constructed with a footplate, a torquemeter and a potentiometer. It was mechanically designed to rotate around an approximated axis of the ankle joint and to measure ankle joint angular position and its corresponding resistive torque. Two stroke hemiplegic subjects pariticapted in a pilot study. The results suggested that difficulty in controlling the applied velocity might be complemented by presenting torque data as a function of peak angular velocity in each stretching cycle. Moreover, the results demonstrated that the device could potentially apply a wide range of angular velocities and provide potentially useful clinical information. Quantitative data successfully acquired using this method included the approximate ankle angular position, where the velocity-dependent characteristics of stiffness was notably initiated and its corresponding torque and velocity.

The effect of varying the plantarflexion resistance of an ankle-foot orthosis on knee joint kinematics in patients with stroke

Ankle-foot orthoses (AFOs) can improve gait in patients with hemiplegia. However, it is anecdotally known that excessive plantarflexion resistance of an AFO could induce undesired knee flexion at early stance. The aim of this study was to systematically investigate the effect of varying the degrees of plantarflexion resistance of an AFO on knee flexion angles at early stance in five subjects with chronic stroke who demonstrated two clear knee flexion peaks at early stance and swing. Each subject wore an experimental AFO constructed with an oil-damper type ankle joint and was instructed to walk at their self-selected walking speed under five plantarflexion resistance conditions. The sagittal plane ankle and knee joint kinematics and gait speed were analyzed using a 3-D Motion Analysis System. A number of significant differences (P<0.005) in maximum knee flexion angles at early stance amongst different plantarflexion resistance conditions were revealed. The knee flexion angle was 23.80 (3.25) degrees under the free hinge joint condition (condition 1), while that was 26.09 (3.79) degrees under the largest resistance condition (condition 5). It was therefore demonstrated that increasing the plantarflexion resistance of an AFO would induce more knee flexion at early stance phase in patients with stroke.

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&dG (15&dG plantarflexion to 15&dG dorsiflexion) at the angular velocity of 10&dG /s, while that in the measurement of AAFO torque was within 8% at the 0&dG 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.

Correlations between Berg balance scale and gait speed in individuals with stroke wearing ankle–foot orthoses – a pilot study

Abstract Purpose: The Berg balance scale (BBS) is commonly used to assess balancing ability in patients with stroke. The BBS may be a good candidate for clinical assessment prior to orthotic intervention, if it correlates well with outcome measures such as gait speed. The purpose of this study was to investigate the correlation between the BBS measured prior to walking with an ankle-foot orthosis (AFO) and specific temporal-spatial parameters of gait when walking with an AFO donned. Methods: Eight individuals with chronic stroke participated in this study. Balancing ability was assessed using the BBS, while temporal–spatial parameters of gait (gait speed, bilateral step length, stride length and step width) were measured using a three-dimensional motion analysis system. The correlations between the BBS and gait parameters were investigated using a non-parametric Kendall’s Tau (τ) correlation analysis. Results: The BBS showed correlations with gait speed (τ = 0.64, p < 0.05), the step length of the affected side (τ = 0.74, p < 0.05), and the stride length (τ = 0.64, p < 0.05). Conclusions: Assessment of the BBS prior to AFO prescription may potentially help clinicians to estimate the gait speed achievable following orthotic intervention in patients with stroke. Implications for Rehabilitation Assessment of the BBS prior to AFO prescription may help orthotists to estimate the gait speed following an orthotic intervention in patients with stroke. Assessment of the BBS prior to AFO prescription may help orthotists to understand overall balance and postural control abilities in patients with stroke. A larger scale multifactorial analysis is warranted to confirm the results of this pilot study.

Effect of ankle-foot orthoses on the sagittal plane displacement of the center of mass in patients with stroke hemiplegia: a pilot study.

Abstract Background: Ankle-foot orthoses (AFOs) have been reported to have positive effects on the temporal-spatial parameters and kinematics and kinetics of gait in patients with stroke. The center of mass (COM) may be used to represent whole body movement and energy cost in gait, and therefore COM movement would also be positively influenced with use of an appropriate AFO. Objective: To investigate the effect of AFOs on the sagittal plane displacement of the COM in patients with stroke hemiplegia. Methods: Five male subjects with stroke hemiplegia participated in this pilot study. The trajectory of the COM in the sagittal plane, gait speed, bilateral step length, step width, and bilateral stance time were analyzed while participants ambulated under 2 test conditions: with an AFO or with footwear only. The height of the 2 peaks of the vertical displacement of the COM in a gait cycle was subsequently measured and normalized to body height. Statistical analyses were conducted using a nonparametric Friedman test. Results: Gait speed, bilateral step length, and the normalized peak height of the vertical COM trajectory during stance phase on the affected leg all revealed statistically significant increases (P < .05), and step width showed significant decreases (P < .05) under the AFO condition when compared to the footwear-only condition. Conclusions: An AFO may influence the vertical displacement of the COM in patients with stroke hemiplegia. The results of this pilot study therefore suggested that vertical movement of COM could potentially serve as a useful parameter to evaluate the effect of an AFO.

Evaluating the contribution of a neural component of ankle joint resistive torque in patients with stroke using a manual device.

Primary objective: To investigate the methodology using a manual ankle joint resistive torque measurement device to evaluate the contribution of the neural component of ankle joint resistive torque in patients with stroke. Research design: Within-subject comparison to compare the ankle joint resistive torque between fast and slow stretching conditions. Methods and procedures: Ten patients with stroke participated in this study. The incremental ratio of ankle joint resistive torque at the ankle angular position of 5° dorsiflexion under the fast stretching condition in comparison to the slow one was calculated in each patient. Main outcomes and results: A significant increase (p < 0.01) in the ankle joint resistive torque was demonstrated under the fast stretching condition in comparison to the slow one in all patients and the mean ankle joint resistive torque was 4.6 (SD = 1.7) Nm under the slow stretching condition, while it was 8.4 (SD = 4.1) Nm under the fast stretching condition at the ankle angular position of 5° dorsiflexion. The incremental ratio ranged from 9.4–139.3% among the patients. Conclusions: The results of this study demonstrated the potential advantage of the device to evaluate the contribution of the neural component of ankle joint resistive torque.

Development of an Intelligent Prosthetic Ankle Joint (3rd Report, Development of the 2nd Prototype with an Intelligent Prosthetic Ankle Joint and Experimental Evaluations)

It is very important to test the intelligent prosthetic ankle joint in various conditions to ensure the usability of the equipment, however, there are some difficulties to evaluate the performance of the first prototype which is controlled by a bulky system adequately for the inferior mobility of the controlling system. In this paper, a prototype with an intelligent prosthetic ankle joint controlled by a mobile system constructed from a notebook computer and a compact and light control unit was developed to enable testing experiments in various environments. Walking experiments with the prototype was carried out and the usability of the intelligent prosthetic ankle joint was confirmed.

Estimation of Lower Limb Muscle Function from Kinematic Gait Analysis and Muscle Tension Model

This article discusses a biomechanical model-based approach toward estimation of muscle function of lower limb by using planer link model and muscle tension model based on kinematic gait analysis. The muscle tension model uses the relation between isometric tension and strain by Kaufman and others, and the relation between the isotonic tension and velocity by Hatze. A link model of four elements is defined for the sagittal plane motion, and regression model by Hawkins and Hull is employed to relate the joint angles and lengths of eight representative muscles. The optimum lengths of muscles are calculated based on a minimization problem by paying attention to the qualitative EMG pattern during the stance phase. The obtained muscle tension pattern had the typical characteristics in stance phase in the case of muscle with a small index of archtecture. As a case study, the function estimation is carried out for a patient with fibula fracture, and the tension calculated by model-based approach with kinematic data of gait analysis showed the reasonable recovering process consistent with that found in the joint moments. This observation encourages the model-based estimation of muscle tension using kinematic data of gait analysis with model improvement.