Design of an Automated Device to Measure Sagittal Plane Stiffness of an Articulated Ankle-Foot Orthosis

Abstract

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 308 (158 plantarflexion to 158 dorsiflexion) at the angular velocity of 108/s, while that in the measurement of AAFO torque was within 8% at the 08 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.

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

“…A precedence study showed that stiffness of the oildamper joint was velocity-dependent and enabled stepless adjustment ranging from 0.5 to 1.4 Nm/deg [8]. However, measurement of AFO stiffness is influenced by various experimental factors [4]. A further study is therefore required to transfer the stiffness values applied by the EAFO to a definitive AFO.…”

“…was measured using a custom-made AFO stiffness measurement device at the angular velocity of 10 deg/s [4]. The results were as follows: designated level 1 (0.32 Nm/deg), level 2 (0.41 Nm/deg), level 3 (0.76 Nm/deg) and level 4 (1.26 Nm/ deg).…”

“…Therefore, a number of attempts to measure its stiffness have been made [4,5]. It has been suggested that the plantarflexion resistive stiffness of an AFO to enable smooth plantarflexion at initial contact is the most important function [6].…”

Design of a manual device to measure ankle joint stiffness and range of motion

“…12 The deformation of an AFO would depend on (1) the thickness and design of the structure, (2) the elastic modulus of the material, (3) the fit and firmness of the limb within, and (4) the constraining characteristics of the shoe. These factors would also affect the motion resistance characteristics of an articulated AFO by altering the degree of coalignment of medial and lateral joint components.…”

A Review on the Control of the Mechanical Properties of Ankle Foot Orthosis for Gait Assistance

“…In the cases where more than one direction is needed, additional oil dampers need to be installed opposite each other [67], as shown in Figure 7a. The output resistance torque can be adjusted by a screw mechanism [68] and it may be classified into several levels [69]. The amount of stiffness in each level is measured beforehand by using a custom-made AFO stiffness measurement device [69].…”