Automatic knee flexion in lower limb orthoses

Abstract

Introduction1 KAFOs (knee-ankle-foot orthoses) are prescribed to paraplegic patients with low level spinal cord injury and with good control of the trunk muscles. According to approximate data from AACD (Associação de Assistência à Criança Deficiente -Association for the Assistance of Handicapped Children), among the patients that could use lower limb orthoses, the rejection rate is as high as 95%; the majority of the patients opts for wheelchair locomotion. The most important reasons for such a rejection rate are the excessive effort demanded from the patients to walk and the lack of aesthetics of the resulting gait. These factors are caused, to a great extent, by the fact that orthoses force the whole gait to be performed with the knee in full extension. The literature presented in the next section suggests the importance of improving the gait with orthoses by implementing automatic knee flexion.This article describes the development of a new device capable of providing knee flexion for orthoses during the swing phase of the gait. In order to produce a light and energy-saving system, we exploit the natural dynamics of the gait. We propose a system whose main actuator is a spring that flexes the knee joint at the beginning of the swing phase. After the knee flexion, the spring is decoupled and the knee reaches its extended position in an entirely passive way. As far as we know, this is an original strategy that leads to an energy-saving gait by reducing the compensation mechanisms required during the gait with conventional orthosis. Our strategy seems to be a viable alternative to the so-called hybrid orthoses, recently proposed in the literature (Gharooni, Heller and Tokhi, 2000; Durfee and Rivard, 2005), which rely on the use of functional electrical stimulation (FES) and present important limitations such as rapid muscle fatigue, high complexity and difficult motion control.A two-degrees-of-freedom model of the lower limb was used to simulate the swing phase, to design the device, and to study the sensitivity of the system behavior to perturbations in the parameters of the orthosis and lower limb. A prototype was built and tests with a single patient were performed. The analysis performed through simulations and tests with a patient has demonstrated the potential of the proposed strategy in improving traditional KAFOs and has shown the need of further improvements of the device. Literature Review Importance of Knee Flexion during GaitIn normal walking, knee flexion during the swing phase leads to foot clearance, that is, the foot does not touch the ground during the swing phase. In the absence of knee flexion, subjects have to compensate by either hiking the pelvis, or by circumducting the leg, or by vaulting on the contralateral limb (Perry, 1992). These strategies are, however, less efficient than flexing the knee. Indeed, Abdulhadi et al. (1996) showed an increase of 20% in oxygen consumption when the knee joint of a person with normal gait is immobilized. Allard et al. (1997) showed that the vertical o...

Modeling and Design of ANFIS Dynamic Sliding Mode Controller for a Knee Orthosis of Hemiplegia

“…Knee-ankle-foot orthoses are frequently employed to help hemiplegic patients correct their gait. Ackermann and Cozman [7] used a spring at the patient's knee joint to generate the necessary knee extension at the end of the swing phase. Energy stored in the spring was also used to create knee flexion at the start of the swing phase.…”

“…The effect of the orthosis on the knee joint during the swing phase was not considered by Ackermann and Cozman [7]. Also, a spring was used at the knee joint to create knee and hip flexion.…”

A novel robotic knee device with stance control and its kinematic weight optimization for rehabilitation

“…His actuation system aimed to produce an impedance-controlled gait rehabilitation robot for treadmill training. Similarly, Ackermann 15 and Sulzer 16 developed a powered knee orthosis that can provide knee flexion torque in the swing phase to compensate for the gait abnormality known as stiff-knee gait (SKG). But even though both knee actuation systems produce high torque with small impedance, they are limited to treadmill-training applications since the actuators must be located on a fixed base.…”