Ankle-foot orthoses that restrict dorsiflexion improve walking in polio survivors with calf muscle weakness
Introduction
Individuals who were affected by polio at young age often have lasting pareses of their lower extremities. Although the severity of paresis and the muscles involved vary largely between polio survivors, the calf muscles are frequently affected [1], [2]. These muscles play an important role in providing ankle and knee stability during single limb support in walking [3]. If calf muscle strength is insufficient and ankle range of motion is not reduced due to muscle shortening, tibia advancement is accelerated, ankle dorsiflexion is abrupt and/or excessive, and, accordingly, knee flexion in stance is increased [1], [4].
To prevent accelerated tibia inclination and provide weight-bearing stability, patients may change their gait, essentially by avoiding their center of pressure (CoP) to progress anterior of the ankle joint in order to diminish the external dorsiflexion moment at the ankle joint [3], [5]. As a result, the limb is loaded in a more extended position, which can cause joint pain from the accumulated effects of repeated impact [6]. Calf muscle weakness can also induce overuse symptoms such as muscle pain and cramps, and/or, fatigue due to an increased walking energy cost [2], [7]. In combination with dorsal flexor weakness, the risk of tripping or falling may increase [8].
To reduce gait-related problems, polio survivors with calf muscle weakness can be provided with an ankle-foot orthosis that restricts ankle dorsiflexion in stance (DR-AFO), thereby allowing the CoP to shift forward without excessive ankle dorsiflexion [1], [6], [9]. There are two types of DR-AFOs that can do this, a hinged DR-AFO and a posterior leaf spring DR-AFO. The hinged DR-AFO restricts dorsiflexion through a joint with a stop, while allowing free plantarflexion. In the posterior leaf spring DR-AFO, both plantarflexion and dorsiflexion are restricted by the stiffness level of the spring. Beneficial effects of DR-AFOs have been reported in patients with spinal cord injury, myelomeningocele, MS, and stroke [10], [11], [12], [13], [14], although only one study investigated biomechanical effects, as well as functional effects [10]. Studying both these effects is needed to establish DR-AFO efficacy [15], which has not been previously investigated in polio survivors. Because differences in disease characteristics may affect treatment outcome, establishing the efficacy of DR-AFOs in polio is warranted.
The purpose of this study was to investigate the effect of DR-AFOs in polio survivors with calf muscle weakness on different levels of functioning, including gait biomechanics, walking energy cost, speed, and perceived walking ability, compared to walking with shoes only.
Section snippets
Study population
A consecutive series of sixteen polio survivors with paretic calf muscles due to poliomyelitis, who were provided with a DR-AFO during a visit to the outpatient clinic, participated in this study. Inclusion criteria were (a) residual paresis of the plantarflexor muscles due to poliomyelitis (i.e., a MRC score <5 and/or unable to perform ≥3heel rises) as confirmed by the rehabilitation specialist, (b) ability to walk for at least six minutes continuously, (c) a prescription of a DR-AFO at least
Results
Baseline patient and DR-AFO characteristics are shown in Table 1 for each of the 16 patients. Four patients had a posterior leaf spring DR-AFO, 12 had a hinged DR-AFO. Three patients did not use their hinged DR-AFO.
One patient could not complete the shoes-only measurement due to an unrelated illness. This patient only completed the questionnaires about perceived walking ability. Due to technical issues, shoes-only and DR-AFO kinematic and kinetic data from one patient and shoes-only kinetic
Discussion
This is the first study that investigated the effect of DR-AFOs on different levels of functioning in polio survivors with calf muscle weakness. Compared to walking with shoes only, we found improvements with wearing the DR-AFO at the ICF component of ‘body functions and structures’ for forward CoP progression and sagittal ankle and knee kinematics during stance, and at the ICF component of ‘activities and participation’ for gait speed and stride length. Furthermore, the patients' perceived
Conclusion
We demonstrated that in polio survivors with calf muscle weakness, DR-AFOs significantly improved gait biomechanics, speed, and perceived walking ability compared to waking with shoes-only. Moreover, they reduced walking energy cost to nearly significant levels. These findings support the use of DR-AFOs as a treatment option to maintain or improve functional abilities in these patients. Nevertheless, DR-AFO efficacy seemed to vary between patients and may be related to orthosis settings and the
Conflicts of interest
All authors declare that they have no conflict of interests with this publication.
Acknowledgements
We would like to thank C.H.M. van Schie, N.M. Otterman and M.A.N. Siebrecht for their contribution in data collection.
Appendix A. Supplementary material
The purposely-designed questionnaire on perceived walking ability can be found as online supplementary material.
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