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. 2019 Aug 7:12:41.
doi: 10.1186/s13047-019-0348-8. eCollection 2019.

Stiffness modification of two ankle-foot orthosis types to optimize gait in individuals with non-spastic calf muscle weakness - a proof-of-concept study

Hilde E Ploeger  1 , Niels F J Waterval  1 , Frans Nollet  1 , Sicco A Bus  1 , Merel-Anne Brehm  1
Affiliations

Stiffness modification of two ankle-foot orthosis types to optimize gait in individuals with non-spastic calf muscle weakness - a proof-of-concept study

Hilde E Ploeger et al. J Foot Ankle Res. .

Abstract

Background: 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. 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.

Methods: We 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.

Results: Maximum 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%).

Conclusions: Modifying 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.

Keywords: Ankle-foot orthosis; Calf muscle weakness; Gait biomechanics; Neuromuscular disorders; Poliomyelitis; Spring stiffness modification; Walking energy cost.

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Conflict of interest statement

Competing interestsThe authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Computed tomography images of the lower right (R) and left (L) leg of the three subjects
Fig. 2
Fig. 2
Example of the two types of ankle-foot orthoses Left: the dorsal-leaf-spring ankle-foot-orthosis, and right: the spring-hinged ankle-foot-orthosis, both with their five interchangeable springs with different degrees of stiffness.
Fig. 3
Fig. 3
Gait biomechanics. (a) Ankle angles, (b) ankle powers, (c) knee angles of subject A (calf muscle strength MRC 4), subject B (calf muscle strength MRC 4) and subject C (calf muscle strength MRC 0). Shoes-only (1) is performed at the DLS-AFO testing day, Shoes-only (2) is performed at the SH-AFO testing day (subject B had all AFO conditions tested at one day, therefore only one shoes-only condition was performed). Abbreviations: DLS-AFO: dorsal-leaf-spring ankle-foot-orthosis, SH-AFO: spring-hinged ankle-foot-orthosis, k: stiffness in N•m•deg− 1, DF: dorsiflexion, PF: plantarflexion, EX: extension, FL: flexion, Gen: generation, Abs: absorption
Fig. 3
Fig. 3
Gait biomechanics. (a) Ankle angles, (b) ankle powers, (c) knee angles of subject A (calf muscle strength MRC 4), subject B (calf muscle strength MRC 4) and subject C (calf muscle strength MRC 0). Shoes-only (1) is performed at the DLS-AFO testing day, Shoes-only (2) is performed at the SH-AFO testing day (subject B had all AFO conditions tested at one day, therefore only one shoes-only condition was performed). Abbreviations: DLS-AFO: dorsal-leaf-spring ankle-foot-orthosis, SH-AFO: spring-hinged ankle-foot-orthosis, k: stiffness in N•m•deg− 1, DF: dorsiflexion, PF: plantarflexion, EX: extension, FL: flexion, Gen: generation, Abs: absorption
See this image and copyright information in PMC

References

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