The effect of ankle–foot orthosis plantarflexion stiffness on ankle and knee joint kinematics and kinetics during first and second rockers of gait in individuals with stroke

Abstract

Background Stiffness of an ankle-foot orthosis plays an important role in improving gait in patients with a history of stroke. To address this, the aim of this case series study was to determine the effect of increasing plantarflexion stiffness of an ankle-foot orthosis on the sagittal ankle and knee joint angle and moment during the first and second rockers of gait. Methods Gait data were collected in 5 subjects with stroke at a self-selected walking speed under two plantarflexion stiffness conditions (0.4 Nm/deg and 1.3 Nm/deg) using a stiffness-adjustable experimental ankle-foot orthosis on a Bertec split-belt fully instrumented treadmill in a 3-dimensional motion analysis laboratory. Findings By increasing the plantarflexion stiffness of the ankle-foot orthosis, peak plantarfexion angle of the ankle was reduced and peak dorsiflexion moment was generally increased in the first rocker as hypothesized. Two subjects demonstrated increases in both peak knee flexion angle and peak knee extension moment in the second rocker as hypothesized. The two subjects exhibited minimum contractility during active plantarflexion, while the other three subjects could actively plantarflex their ankle joint. Interpretation It was suggested that those with the decreased ability to actively plantarflex their ankle could not overcome excessive plantarflexion stiffness at initial contact of gait, and as a result exhibited compensation strategies at the knee joint. Providing excessively stiff ankle-foot orthoses might put added stress on the extensor muscles of the knee joint, potentially creating fatigue and future pathologies in some patients with stroke.

The effect of changing plantarflexion resistive moment of an articulated ankle–foot orthosis on ankle and knee joint angles and moments while walking in patients post stroke

“…We also speculated that the increases in the flexion angles in (e) the initial knee joint angle was linked to the decreases in (f) the peak knee extension angle. These results strongly suggest that the AFOs would affect kinematics and kinetics of the knee joint in patients with stroke, and would reinforce the findings of the previous studies (Kobayashi et al, 2013; Singer et al, 2014). …”

“…These results suggest an important relationship between these kinematic/kinetic parameters and the plantarflexion resistive moment of the AFO. Our previous work were either case series (Singer et al, 2014) or focused only on kinematics (Kobayashi et al, 2011a, 2013) using somewhat bulky experimental AFOs. This study is novel and important because both kinematic and kinetic parameters demonstrated statistically significant effects due to changes in the plantarflexion resistive moments using the new and compact articulated AFO in a group of 10 individuals post stroke.…”

“…It has been suggested that varying the plantarflexion resistive moment of articulated AFOs will affect kinematics and kinetics of lower-limb joints while walking in patients with stroke (Singer et al, 2014; Yamamoto et al, 2013). These studies implied the importance of tuning the plantarflexion resistive moments for individual patients.…”

The Effects of Varying Ankle Foot Orthosis Stiffness on Gait in Children with Spastic Cerebral Palsy Who Walk with Excessive Knee Flexion

“…The efficacy of spring-like AFOs to improve gait is however partly dependent on their stiffness. This has been shown in simulation models [ 19 ], as well as in studies in healthy adults [ 21 ] and in adult patient populations [ 23 – 28 ], where results indicated that changing the AFO stiffness significantly affected knee and ankle kinematics and kinetics, as well as walking energy cost. Results also indicated that the reduction in walking energy cost could be improved by choosing the appropriate AFO stiffness [ 26 ].…”

Description of orthotic properties and effects evaluation of ankle-foot orthoses in non-spastic calf muscle weakness

“…Differences in orthotic properties, such as ankle and footplate stiffness, footplate length and mass, may explain the variation in effectiveness (15,18). Although, these mechanical properties have been evaluated in small clinical studies of patients with lower limb salvage (19), stroke (20,21) and cerebral palsy (22), the few studies evaluating AFOs in non-spastic neuromuscular disorders did not specify the mechanical properties of the investigated AFOs (12,23). Consequently, there is a lack of evidence-based guidelines to select the most effective AFO to improve gait in this population, and choices in current practice are based on the preferences of the prescribing physician or orthotist (12).…”