Energy cost optimized dorsal leaf ankle-foot-orthoses reduce impact forces on the contralateral leg in people with unilateral plantar flexor weakness

N.F.J Waterval,M.A Brehm,J Harlaar,F Nollet

doi:10.1016/j.gaitpost.2021.11.023

Abstract

BackgroundIn individuals with unilateral plantar flexor weakness, the second peak of the vertical ground reaction force (GRF) is decreased. This leads to a higher ground reaction force, e.g. impact, of the contralateral leg, potentially explaining quadriceps muscle and/or knee joint pain. Energy cost optimized dorsal leaf ankle-foot-orthoses (AFOs) may increase the push-off ground reaction force, which in turn could lead to lower impact forces on the contralateral leg. Research questions1) Are impact forces increased in the contralateral leg of people with unilateral plantar flexor weakness compared to healthy subjects? 2) Do energy cost optimized AFOs reduce impact forces and improve leg impact symmetry compared to walking without AFO in people with unilateral plantar flexor weakness? MethodsNine subjects with unilateral plantar flexor weakness were provided a dorsal leaf AFO with a stiffness primarily optimized for energy cost. Using 3D gait analyses peak vertical GRF during loading response with and without AFO, and the symmetry between the legs in peak GRF were calculated. Peak GRF and symmetry were compared with reference data of 23 healthy subjects. ResultsThe contralateral leg showed a significant higher peak vertical GRF (12.0 ± 0.9 vs 11.2 ± 0.6 N/kg, p = 0.005) compared to healthy reference data. When walking with AFO, the peak vertical GRF of the contralateral leg significantly reduced (from 12.0 ± 0.9 to 11.4 ± 0.7 N/kg, p = 0.017) and symmetry improved compared to no AFO (from 0.93 ± 0.06 to 1.01 ± 0.05, p < 0.001). ConclusionIn subjects with unilateral plantar flexor weakness, impact force on the contralateral leg was increased when compared to healthy subjects and dorsal leaf AFOs optimized for energy cost substantially reduced this force and improved impact symmetry when compared to walking without AFO. This indicates that dorsal leaf AFOs may reduce pain resulting from increased impact forces during gait in the contralateral leg in people with unilateral plantar flexor weakness.

Highlights

Neuromuscular disorders, such as poliomyelitis or peripheral nerve damage, may cause unilateral plantar flexor weakness
Research questions: 1) Are impact forces increased in the contralateral leg of people with unilateral plantar flexor weakness compared to healthy subjects? 2) Do energy cost optimized ankle-foot orthoses (AFOs) reduce impact forces and improve leg impact symmetry compared to walking without AFO in people with unilateral plantar flexor weakness? Methods: Nine subjects with unilateral plantar flexor weakness were provided a dorsal leaf AFO with a stiffness primarily optimized for energy cost
This study demonstrated that the gait pattern of subjects with uni lateral plantar flexor weakness contains risk factors for the development of pain in the contralateral leg due to a higher impact force and increased knee adduction and knee flexion impulses during body weight shift from the affected to the contralateral leg, when compared to healthy subjects

Summary

Introduction

Neuromuscular disorders, such as poliomyelitis or peripheral nerve damage, may cause unilateral plantar flexor weakness. In individuals with unilateral plantar flexor weakness, the second peak of the vertical ground re action force (GRF) is decreased This leads to a higher ground reaction force, e.g. impact, of the contralateral leg, potentially explaining quadriceps muscle and/or knee joint pain. 2) Do energy cost optimized AFOs reduce impact forces and improve leg impact symmetry compared to walking without AFO in people with unilateral plantar flexor weakness? Conclusion: In subjects with unilateral plantar flexor weakness, impact force on the contralateral leg was increased when compared to healthy subjects and dorsal leaf AFOs optimized for energy cost substantially reduced this force and improved impact symmetry when compared to walking without AFO. This indicates that dorsal leaf AFOs may reduce pain resulting from increased impact forces during gait in the contralateral leg in people with unilateral plantar flexor weakness

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