Development of an ankle – foot orthosis with an oil damper

Abstract

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.

Techniques to measure rigidity of ankle-foot orthosis: A review

“…Methods used to achieve the force application and/or measure the subsequent deflection or strain during bench testing included a tensionmeter [4,[9][10][13][14][15][16], a dial gauge [12,[17][18], a strain gauge or a load cell [2,[21][22][23][24]], a forceplate [11], a muscle training machine [25][26], and a mechanical testing machine [5,[27][28][29][30].…”

“…The viscoelastic properties of a human limb would affect the rigidity of an AFO, and the result would have been different if a surrogate limb had been used. A similar device was used to examine mechanical properties of an AFO with an oil-damper joint without a surrogate limb [26]. Use of a muscle training machine would be an attractive alternative to custom-made automated apparatuses in the clinical setting.…”

“…The desirable AFO for patients with hemiplegia was recommended to have an articulated orthotic ankle joint to provide a fair amount of inversion and eversion corrective moment, an initial dorsiflexion angle between 0° and 10°, an adjustable range of motion between 30° of dorsiflexion and 10° of plantar flexion, no plantar flexion assistive moment, and dorsiflexion assistive moment during ankle plantar flexion (5-20 N·m/10 of plantar flexion) [37]. A dorsiflexion assist controlled by spring (DACS) AFO [20] and an AFO with an oil-damper joint [26] were subsequently developed based on these studies and tested for efficacy. These criteria have indicated the ankle joint moments to be expected when a patient is walking with an AFO and should inform the development of appropriate mechanisms to mechanically test AFOs with appropriate loading rates.…”

“…The reported range of angular velocities used in the test is 0.5 /s to 50 /s [4][5]16,[24][25][26]30] (Table). However, angular velocity reportedly does not affect the stiffness of a thermoplastic AFO [11,25].…”

“…One study using a muscle testing apparatus reported no effect on the stiffness (moment vs deflection angle) of various thermoplastic AFOs when tested at different velocities between 5 /s and 50 /s [25], while another study that used a forceplate to test AFOs also reported no effect of the applied velocity on their stiffness [11]. However, an AFO with oildamper joint revealed a velocity-dependent effect in its stiffness [26]. Therefore, testing at different levels of velocity would be required to evaluate an AFO constructed of a material with velocity-dependent properties.…”