Abstract
BackgroundIn people with calf muscle weakness, the stiffness of dorsal leaf spring ankle–foot orthoses (DLS-AFO) needs to be individualized to maximize its effect on walking. Orthotic suppliers may recommend a certain stiffness based on body weight and activity level. However, it is unknown whether these recommendations are sufficient to yield the optimal stiffness for the individual. Therefore, we assessed whether the stiffness following the supplier’s recommendation of the Carbon Ankle7 (CA7) dorsal leaf matched the experimentally optimized AFO stiffness.MethodsThirty-four persons with calf muscle weakness were included and provided a new DLS-AFO of which the stiffness could be varied by changing the CA7® (Ottobock, Duderstadt, Germany) dorsal leaf. For five different stiffness levels, including the supplier recommended stiffness, gait biomechanics, walking energy cost and speed were assessed. Based on these measures, the individual experimentally optimal AFO stiffness was selected.ResultsIn only 8 of 34 (23%) participants, the supplier recommended stiffness matched the experimentally optimized AFO stiffness, the latter being on average 1.2 ± 1.3 Nm/degree more flexible. The DLS-AFO with an experimentally optimized stiffness resulted in a significantly lower walking energy cost (− 0.21 ± 0.26 J/kg/m, p < 0.001) and a higher speed (+ 0.02 m/s, p = 0.003). Additionally, a larger ankle range of motion (+ 1.3 ± 0.3 degrees, p < 0.001) and higher ankle power (+ 0.16 ± 0.04 W/kg, p < 0.001) were found with the experimentally optimized stiffness compared to the supplier recommended stiffness.ConclusionsIn people with calf muscle weakness, current supplier’s recommendations for the CA7 stiffness level result in the provision of DLS-AFOs that are too stiff and only achieve 80% of the reduction in energy cost achieved with an individual optimized stiffness. It is recommended to experimentally optimize the CA7 stiffness in people with calf muscle weakness in order to maximize treatment outcomes.Trial registration Nederlands Trial Register 5170. Registration date: May 7th 2015. http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=5170.
Highlights
Persons with neuromuscular disorders like Charcot– Marie–Tooth disease and poliomyelitis often exhibit weakness of their calf muscles
AFO ankle–foot orthosis, kg kilogram, green indicates that the experimental optimized and recommendation matched, while warmer colors indicate a larger difference in stiffness between the experimental optimized and recommended stiffness five participants it was above 5 Nm/degree (Table 2)
In this study in persons with calf muscle weakness, we demonstrated that the supplier’s recommendation for the Carbon Ankle7 (CA7) stiffness level results in the provision of dorsal leaf spring ankle–foot orthoses (DLS-AFO) that are stiffer and less effective compared to DLS-AFOs with a CA7 stiffness level that is individually optimized based on walking energy costs and 3D gait measurements
Summary
Persons with neuromuscular disorders like Charcot– Marie–Tooth disease and poliomyelitis often exhibit weakness of their calf muscles. Waterval et al J NeuroEngineering Rehabil (2021) 18:97 changes the gait pattern, and typically leads to excessive ankle dorsiflexion, persistent knee flexion and reduced ankle push-off power during stance [1, 2] These gait deviations lower walking speed and elevate walking energy cost by − 30% and + 60%, respectively [1, 3]. To improve walking in persons with calf muscle weakness, dorsal leaf spring ankle–foot orthoses (DLS-AFOs) can be provided with the aim to restrict the ankle dorsiflexion angle by providing an external plantar flexion moment. This external moment is proportional to the bending and stiffness of the leaf spring [3,4,5]. We assessed whether the stiffness following the supplier’s rec‐ ommendation of the Carbon Ankle (CA7) dorsal leaf matched the experimentally optimized AFO stiffness
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