Abstract
BackgroundTo reduce gait problems in individuals with non-spastic calf muscle weakness, spring-like ankle-foot orthoses (AFOs) are often applied, but they are not individually optimized to treatment outcome. The aim of this proof-of-concept study was to evaluate the effects of modifying the stiffness for two spring-like AFO types with shoes-only as reference on gait outcomes in three individuals with calf muscle weakness due to polio.MethodsWe assessed 3D gait biomechanics, walking speed and walking energy cost for shoes-only and five stiffness conditions of a dorsal-leaf-spring AFO and a spring-hinged AFO. Outcomes were compared between stiffness conditions in the two AFOs and three subjects.ResultsMaximum ankle dorsiflexion angle decreased with increasing stiffness in both AFOs (up to 6–8°) and all subjects. Maximum knee extension angle changed little between stiffness conditions, however different responses between the AFOs and subjects were observed compared to shoes-only. Walking speed remained unchanged across conditions. For walking energy cost, we found fairly large differences across stiffness conditions with both AFOs and between subjects (range 3–15%).ConclusionsModifying AFO stiffness in individuals with non-spastic calf muscle weakness resulted in substantial differences in ankle biomechanics and walking energy cost with no effect on speed. Our results provide proof-of-concept that individually optimizing AFO stiffness can clinically beneficially improve gait performance.
Highlights
To reduce gait problems in individuals with non-spastic calf muscle weakness, spring-like ankle-foot orthoses (AFOs) are often applied, but they are not individually optimized to treatment outcome
Gait biomechanics Sagittal plane ankle angle Maximum ankle angle during terminal stance was smaller in almost all stiffness conditions of both AFOs, and for all three subjects when compared to shoes-only, and decreased with increasing stiffness (k1-k5) between 5 and 8° for the dorsal-leaf-spring AFO (DLS-AFO) and between 2 and 6° for the spring-hinged AFO (SH-AFO) (Fig. 3a, Table 3)
Shoes-only1 is performed at the DLS-AFO testing day, Shoes-only2 is performed at the SH-AFO testing day Loading response: 1–10% gait cycle, early stance: 1–20% gait cycle, †: plantar and dorsiflexion angles are relative to the ankle angle at initial contact, §: satisfaction about walking in general when walking on shoes-only and with different AFO stiffness scored on a numeric rating scale (NRS) with 10 as highest satisfaction, *: quotes about the most satisfying condition: subject A: “was just sufficient for my remaining muscle force; it supports, but obstructs not too much”
Summary
To reduce gait problems in individuals with non-spastic calf muscle weakness, spring-like ankle-foot orthoses (AFOs) are often applied, but they are not individually optimized to treatment outcome. In individuals with calf muscle weakness due to neuromuscular disorders, gait is frequently hampered by excessive ankle dorsiflexion and knee flexion during stance, and by reduced ankle push-off [1,2,3,4,5,6]. This leads to gait problems such as instability, and an increased walking energy cost [2, 6, 7], which may affect functioning in daily life [8]. The gait pattern from healthy subjects and subjects with stroke and MS without AFO is different from that in polio, and the aims and effects of the AFO are different and, not transferable
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