Biomechanical effects of foot orthoses during walking
Introduction
Foot orthoses date back to the 19th century and have been industrially produced since the turn of the 20th century, both in America and Europe [1], [2], [3]. Traditionally they have been applied in clinical environments treating patients with severe gait problems [4], [5], [6], [7], [8]. Outcome studies report 70–80% positive results in runners with the use of medially placed orthoses with differing material properties and shape of the orthoses [9], [10], [11], [12]. The remaining 20–30% of these patients showed unsatisfactory results with no indication what the possible reasons for this outcome might be.
Current opinion is that biomechanical effects produced by orthoses are not clearly understood. It has been suggested that positive outcome results may be due to mechanical and/or proprioceptive mechanisms [13], [14], [15]. Recent biomechanical literature suggests that orthoses can produce kinematic, kinetic and muscle activity changes, findings which are mainly based on healthy subjects [16], [17], [18], [19], [20], [21]. Mundermann et al. [22] found that different types of orthoses have different effects, the posting orthoses would work better to decrease maximum foot eversion and the molding type would work better to decrease maximum tibia rotation; it was concluded that with a combination (molding and posting) the positive effects of the molding would override the posting orthotic effects. On the other hand, little is known how proprioception may contribute to the control of gait [23], [24], [25]. Mazzaro et al. [26] suggested that “continuous contribution of afferent feedback to muscle activity automatically adjusts the muscle activation level to meet external demands of the walking surface”. One main limitation of the understanding of this feedback is the substantial difference in sensory thresholds on the plantar surface of the foot even within the normal population [15], [27] and the changes of this threshold with age, respectively [28]. Thus, subjects with different sensitivity levels on the plantar surface of the foot may have an inherently different muscle activation pattern [14]. In summary, orthotic effects may not only depend of the type (posting, molding, or a combination), but also on their surface texture to stimulate the sensory feedback (proprioceptive orthosis); furthermore, biomechanical investigations are often performed on healthy test subjects and not on patients.
In order to gain more insight about muscle activation patterns at the lower leg, EMG signals of various leg muscles during gait have been recorded in various studies [13], [22], [29]. However, most of these studies used surface electrodes which cannot be applied to deeper muscles such as the tibialis posterior or flexor digitorum communis muscles. Particularly, the tibialis posterior muscle has been reported to play an important role during the stance phase of walking hereby controlling eversion [30] and maintaining the medial longitudinal arch of the foot [31].
There is very little knowledge on biomechanical effects of different foot orthoses of patients during walking. Hence, the purpose of this study was to quantify kinematic and kinetic effects at the foot and leg during the stance phase of walking using (i) a posted, (ii) a combination of molded and posted and (iii) a proprioceptive foot orthosis.
Additionally, in selected patients of the study the EMG activity of the tibialis posterior muscle was evaluated using fine wire electrodes.
Section snippets
Subjects
The eight patients of the present study visited their physician on their own due to foot problems and were referred to one of three podiatrists who participated in the study. All eight test subjects were described to have a pes valgus, i.e. to have a permanent eversion of the rearfoot combined with a lowering of the plantar arch. All subjects agreed to see the other two podiatrists for the other two orthoses. Thus, each subject was fitted with three different orthoses which they used in
General results in the frontal plane
At touchdown, one inversion variable (TdInv) showed an increased mean value for orthosis 2 (O2) compared with NA and O1, all other inversion variables showed no significant differences (Table 4); thus, except for O2, no changes were apparent over all test conditions. Between touchdown and midstance the four variables related to eversion (MaxEv, RomEv, MaxMEv, Mev) showed several significant differences between the five test conditions. Post-hoc testing revealed that O2 showed significantly
Limitations of the study
Foot and shank were each modelled as rigid segments, a simplification which has been shown to have limited validity mostly due to skin movement artefacts [38] and relative movement between various foot segments [39]. However, the resolution of the optoelectric system that was available for testing did not allow describing the rearfoot only, thus the five foot markers needed to be set on the forefoot as well as the rearfoot (see Section 2). This had the disadvantage that the present data was
Conclusions
The test subjects of the present study all had pes valgus in need for medially applied orthosis showing the following results:
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Combined molding and posting foot orthosis (O2) significantly reduced eversion and eversion moments during walking compared to a posting (O1) and a proprioceptive orthosis (O3). Eversion of the proprioceptive orthosis was reduced relative to the posting orthosis which showed an increase of external tibial rotation during take off.
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The current results suggest that changes
Conflict of interest
There are no financial and personal relationships with other people or organisations that inappropriately influenced or biased the authors work.
Acknowledgements
The authors are grateful for the support of the ESK (Eidgenössische Sport Kommission); Swiss Life Foundation, Zürich, Switzerland and Synos Foundation, Münsingen-Bern, Switzerland for their support of this investigation. Many thanks go also to Dr. med. H.P. Hofmann for the support during testing, H. Strebel, T. Bichsel and M. Sieber for their help during the data analysis of the present work and to the three podiatrists in Switzerland: H.J. Rombach (eidg. Dipl. OSM) 8752 Schlieren, orthoses O1;
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