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

Abstract

IntroductionRigid Ankle-Foot Orthoses (AFOs) are commonly prescribed to counteract excessive knee flexion during the stance phase of gait in children with cerebral palsy (CP). While rigid AFOs may normalize knee kinematics and kinetics effectively, it has the disadvantage of impeding push-off power. A spring-like AFO may enhance push-off power, which may come at the cost of reducing the knee flexion less effectively. Optimizing this trade-off between enhancing push-off power and normalizing knee flexion in stance is expected to maximize gait efficiency. This study investigated the effects of varying AFO stiffness on gait biomechanics and efficiency in children with CP who walk with excessive knee flexion in stance. Fifteen children with spastic CP (11 boys, 10±2 years) were prescribed with a ventral shell spring-hinged AFO (vAFO). The hinge was set into a rigid, or spring-like setting, using both a stiff and flexible performance. At baseline (i.e. shoes-only) and for each vAFO, a 3D-gait analysis and 6-minute walk test with breath-gas analysis were performed at comfortable speed. Lower limb joint kinematics and kinetics were calculated. From the 6-minute walk test, walking speed and the net energy cost were determined. A generalized estimation equation (p<0.05) was used to analyze the effects of different conditions. Compared to shoes-only, all vAFOs improved the knee angle and net moment similarly. Ankle power generation and work were preserved only by the spring-like vAFOs. All vAFOs decreased the net energy cost compared to shoes-only, but no differences were found between vAFOs, showing that the effects of spring-like vAFOs to promote push-off power did not lead to greater reductions in walking energy cost. These findings suggest that, in this specific group of children with spastic CP, the vAFO stiffness that maximizes gait efficiency is primarily determined by its effect on knee kinematics and kinetics rather than by its effect on push-off power.Trial RegistrationDutch Trial Register NTR3418

An articulated ankle–foot orthosis with adjustable plantarflexion resistance, dorsiflexion resistance and alignment: A pilot study on mechanical properties and effects on stroke hemiparetic gait

“…The peak released ankle power was reduced as the dorsiflexion resistance was increased (Figure 3(d)), which is consistent with findings of a previous study [4]. This result suggests that toe rocker (3 rd rocker) was somewhat impeded due to restriction in ankle rocker (2 nd rocker), shown by reduction in range of motion toward dorsiflexion (Figure 3(b)), resulting from increased dorsiflexion resistance.…”

“…Currently there are some AFO joints available on the market whose mechanical properties are tunable [4, 11]. However, the evidence necessary to maximize the benefit of these AFO joints is still limited.…”

“…The importance of tuning the mechanical properties of an articulated AFO to improve gait in individuals with neuromuscular disorders has been increasingly recognized by researchers and clinicians [2–4]. In non-articulated AFOs, resistance and alignment are usually determined during the fabrication, fitting and adjustment processes which can affect stiffness and support in the planes of control; therefore, errors in the initial resistance or alignment are difficult to change once the AFO has been fabricated.…”

“…There are some AFO joints that are commercially available which allow tuning of mechanical properties constructed with oil-damper [11] or springs [4]. The use of tunable articulated AFOs is expected to be more common in future clinical practice as the benefits of clinical optimization become more evident through research.…”

Contribution of ankle-foot orthosis moment in regulating ankle and knee motions during gait in individuals post-stroke

“…Therefore, it is still unclear how much contribution is needed from the AFO moment to regulate ankle and knee joint motion during gait in these individuals. Quantification of the AFO moment during gait can be performed indirectly by analyzing mechanical property of an AFO on the bench (Kerkum et al, 2015; Yamamoto et al, 1993) or directly by mounting a load cell on a joint (Kobayashi et al, 2016; Yamamoto et al, 2013). Clarifying the AFO moment needed to regulate lower limb joint movement to assist gait in individuals post-stroke could provide valuable AFO design criteria.…”