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Biomechanical effects of foot orthoses during walking
The Foot 17 (2007) 143–153
Biomechanical effects of foot orthoses during walking Alex Stacoff a,∗ , In`es Kramers-de Quervain a,b , Markus Dettwyler a , Peter Wolf a , Renate List a , Thomas Ukelo a , Edgar St¨ussi a a
Institute for Biomechanics, ETH Zurich, 8093 Zurich, Switzerland b Schulthess Clinic, Zurich, Switzerland
Received 26 June 2006; received in revised form 24 January 2007; accepted 6 February 2007
Abstract The purpose of this study was to quantify kinetic and kinematic effects during the stance phase of walking using three different foot orthoses. All test subjects were measured under five test conditions with 10 repetitions each. The test conditions included: neutral orthosis (tested twice) and three different orthoses (posting, molding and posting combined, proprioceptive). Whereas most previous studies rely on healthy subjects to describe effects of orthoses during gait, the present study used eight patients (all pes valgus). Standard gait analysis was used with force plates (KISTLER) and an optoelectric measuring system (VICON). The results show that the combined molding and posting foot orthosis significantly reduced eversion and eversion moments during walking compared to a posting type and a proprioceptive orthosis in several test parameters. EMG measurements with fine wire electrodes on three of the test subjects revealed that the activity pattern of the tibialis posterior muscle can considerably change between subjects but may not be used to explain apparent individual effects. The results suggest that for subjects with pes valgus a combined molding and posting orthoses reduces eversion best and that individual variations may be due to subject dependent proprioception, internal foot mechanics and/or a combination of both. © 2007 Elsevier Ltd. All rights reserved. Keywords: Lower extremity; Shoe inserts; Orthoses; Tibia
1. 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 [1–3]. Traditionally they have been applied in clinical environments treating patients with severe gait problems [4–8]. 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 [9–12]. 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 ∗ Corresponding author at: ETH Zurich, Institute for Biomechanics, Hoenggerberg HCI E 365.1, 8093 Zurich, Switzerland. Tel.: +41 1 633 62 18; fax: +41 1 633 11 24. E-mail address: [email protected] (A. Stacoff).
0958-2592/$ – see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.foot.2007.02.004
positive outcome results may be due to mechanical and/or proprioceptive mechanisms [13–15]. Recent biomechanical literature suggests that orthoses can produce kinematic, kinetic and muscle activity changes, findings which are mainly based on healthy subjects [16–21]. 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 [23–25]. 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
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Table 1 Test subjects and their comfort rating of the orthoses Test persons
Age
Height (cm)
Weight (kg)
Ranking of orthoses
Order of testing
P Q Ra Sa Ta Ua Va W
67 67 69 40 49 38 25 24
155 151 166 166 171 185 173 189
88.0 77.6 92.4 64.4 113.9 74.8 57.8 64.2
O2 > O3 > O1 O2 > O3 > O1 O2 > O3 > O1 O2 > O3 = O1 O1 > O2 > O3 O3 > O2 > O1 O2 > O3 > O1 O3 > O2 > O1
NA, O3, O2, O1, NB NA, O1, O3, O2, NB NA, O3, O2, O1, NB NA, O3, O1, O2, NB NA, O3, O2, O1, NB NA, O1, O2, O3, NB NA, O1, O3, O2, NB NA, O3, O2, O1, NB
Abbreviations: NA, O1, O2, O3, NB refer to Fig. 2. a Indicates the subjects with fine wire electrodes.
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.
bination with the test sandals (Table 1 and Fig. 1). Written consent was given by all participants. 2.2. Orthoses, test sandals and test set-up A standardized test shoe (a “Finn comfort” sandal) with a flat sole (Hassfurt, Germany) was used which allowed easy replacement of the orthoses as an entire inlay between test conditions without removing the foot markers (Fig. 2). The test sequence started for all subjects with the neutral orthoses NA (“N” for neutral and “A” for the first test) to set the baseline for all other test conditions. The next three orthotic conditions were randomly selected. Condition 5 was identical to NA (denoted NB) which allowed identification of possible changes between beginning and end of testing. For each test condition 8–10 walking trials of the right foot were registered, thus, each subject walked 50 times. Podiatrist A constructed “posting” orthoses with a medial post supporting the calcaneus at the sustentaculum tali (Fig. 2 and Table 2). The orthotic was made with two layers, a harder lower (Asker C 70–80) and a softer upper layer (Asker C 40–45). Podiatrist B formed “molding and posting” orthoses consisting of one hard layer with Asker C 70–80 supporting the foot medially and laterally. The proprioceptive orthosis of podiatrist C was thought to stimulate the plantar surface of the foot and thus, the leg muscles inserting there with a total of four elevations: two 3 mm of around 10 cm2 areas at
2. Methods 2.1. 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 com-
Fig. 1. Test sandals with the neutral type of orthosis (NA or NB).
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Fig. 2. Orthoses used in the investigation: NA/NB show the inlay with no support; O1: posting orthosis; O2: combined molding and posting orthosis; O3: proprioceptive orthosis. Shaded areas indicate support.
the midfoot, and two 2 mm of about 20 cm2 areas under the metatarsal heads II–V and toes II–V, respectively (Fig. 2). The tests were performed at the Institute for Biomechanics at the ETH Z¨urich, Switzerland [32,33]. The available gait analysis system allows collection of kinematic, kinetic and EMG data simultaneously while the test subjects walk over a 25 m walkway. After testing, the test subjects gave their individual ranking with respect to preference of the three test orthoses (Table 1). 2.3. Kinematic tests Motion capture was performed with a 7 camera Vicon System 370 (Oxford metrics, UK). The foot and shank segment were each redundantly equipped forming a cluster of 5 markers each (diameter 10 mm; Fig. 3). The foot markers were placed over the matatarsals I and V, medial and lateral calacaneus, and navicular. The shank markers were positioned at the medial and lateral malleolus, head of fibula, tibial tuberosity, and anterior surface of the tibia midway between tuberosity and the malleoli. Thus, the foot and shank segment were made as large as possible to improve angular accuracy. The time dependent spatial location and orientation of the foot and shank segment was determined with a least-squares cluster fit routine (using singular value decomposition after Gander and Hrebicek [34]). Thus, foot and shank were regarded as two rigid segments. The ankle joint was modelled as a ball-
Fig. 3. Marker-set on the foot and shank and definition of coordinate system [35].
and-socket joint with the definition of a subject specific ankle joint center computed from loaded plantar-dorsiflexion and eversion-inversion movements using an optimization routine [35]. The test variables were determined for each test condition and subject (Table 3). 2.4. Kinetic tests and inverse dynamics Force data was collected from a Kistler 9281B force platform (Kistler, Winterthur, Switzerland). All kinetic data was normalized to 100% stance phase using a threshold at 2% bodyweight. Tibia torsional moments were computed about reference axes which all went through the determined joint center. The underlying coordinate system was fixed to the shank segment and the reference axes moved with this segment. The directions of the reference axes were identified as, firstly, the direction from the determined joint center to the marker on the tibial tuberosity (about z-direction), sec-
Table 2 Orthoses and test conditions of the present study Orthosis
Type
Description
NA O1 O2 O3 NB
Neutral Orthosis 1: posting Orthosis 2: molding and posting Orthosis 3: proprioceptive Neutral
2 mm thick inlay, no support, first test Medial posting support, podiatrist A Medial posting combined with molding technique, podiatrist B With four proprioceptive areas, podiatrist C 2 mm thick inlay, no support, second test
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Table 3 Definitions of the study variables Definition of Variables (◦ )
Movement Frontal plane TdInv MaxEv RomEv MaxInv RomInv Transversal plane TdTar MaxTir RomTir MaxTar RomTar Moment (Nm) Frontal plane TdMInv MaxMEv Mev MaxMInv Minv Transversal plane TdMTar MaxMTir Mtir MaxMTar Mtar
Inverted position of foot at touchdown Maximum eversion after touchdown Range of motion between TdInv and MaxEv Maximum inversion during take off Range of motion between MaxEv and MaxInv Externally rotated position of tibia relative to calcaneus at touchdown Maximum internal tibial rotation relative to calcaneus after touchdown Range of motion between TdTar and MaxTir Maximum external tibial rotation relative to calcaneus during take off Range of motion between MaxTir and MaxTar
Inversion moment at touchdown Maximum eversion moment after touchdown Difference between TdMInv and MaxMEv Maximum inversion moment during take off Difference between MaxMInv and MaxMEv
2. Maximum eversion (MaxEv), the range of eversion (RomEv) and the respective moments (MaxMEv and Mev) would be reduced between touchdown and midstance; 3. Maximum internal tibial rotation (MaxTir), the range of internal tibial rotation (RomTir) and the respective moments (MaxMTir and Mtir) would be reduced between touchdown and mistance; 4. Maximum external tibial rotation (MaxTar), the range of external tibial rotation (RomTar) and the respective moments (MaxMTar and MTar) would be reduced between midstance and take off; 5. Maximum inversion (MaxInv), the range of inversion (RomInv) and the respective moments (MaxMInv and Minv) would be reduced between midstance and take off. For the statistical analyses an ANOVA was applied for the comparison of the test variables of all five test conditions. In order to test significant differences between the test conditions a post-hoc after Bonferroni was applied. In order to test possible changes during testing the test variables of condition 1 (NA) were compared to those of condition 5 (NB) using the same procedure. 2.5. Wire EMG
External tibial rotation moment at touchdown Maximum internal tibial rotation moment after touchdown Difference between TdMTar and MaxMTir Maximum external tibial rotation moment during take off Difference between MaxMTar and MaxMTir
ondly, as the direction from the medial to the lateral malleolus (about x-direction), and, thirdly, as the direction of the cross product between the former two (about y-direction; Fig. 3). These three directions did not necessarily form a mutually orthogonal triple set, but the deviations from it were small. 2.4.1. Analysis of kinematic and kinetic data Since all eight test subjects were diagnosed as pes valgus the expected effect of the medially placed orthoses was to see a reduction of the eversion variables between the touchdown of the foot and midstance (Fig. 4 and hypothesis 2 below), whereas at the instant of touchdown no changes were expected (hypothesis 1). A further expectation was that due to the coupling mechanism at the ankle, the internal rotation about its longitudinal axes would be reduced with orthoses (hypothesis 3). During take off it was thought that the orthotic effect would continue and consequently reduce inversion and external tibial rotation (hypothesis 4 and 5). Thus, with respect to the neutral test condition, the hypotheses to be tested were (definitions see Table 3): 1. Foot and tibia position and moment at touchdown (TdInv, TdTar and TdMInv, TdMTar) would not be altered;
Out of the eight test subjects five consented to have fine wire electrodes set into their tibialis posterior muscle (Table 1). The wire electrodes were set according to the technique described by Basmajian [36] into tibialis posterior muscle using a 75 m thin silver wire. The electrodes were bipolar, teflon coated, insulation 140 m thick, thread through a 23 gauge needle and sterilized. At the wire ends the insulation was removed over about 1 mm and bent 180◦ at the tip of the needle in different lengths. This should ensure that the ends would not make contact and would remain in the muscle after insertion and retraction of the needle. The wire ends were fixed on the skin with tape (Fig. 5), the wires connected to the preamplifiers. Muscle function was tested with a muscle stimulation device (Compex Inc., Springfield, VA, USA) using very low stimulations. Foot inversion was observed when the electrodes were set in the tibialis posterior muscle and toe flexion when the flexor digitorum longus muscle was stimulated between 2 and 8 mA. The removal of the wires was done by pulling, all wires came out intact. The raw EMG signal was amplified with a differential pre-amplifier. A telemetry unit carried on the subjects back (Glonner Telemetry, Zettl, Karlsruhe, Germany) transmitted the data which was imported into the Vicon measuring system as an analogue input. The EMG raw data was first filtered (Butterworth 3rd order) with a 10–500 Hz band filter according to the recommendations of De Luca [37]. Then, the signals were rectified, and “integrated” with a moving average window of 50 ms. Maximum voluntary contraction was used as a reference indicating 100% activation. The time axis was normalized to one gait cycle equalling 100%; the plots
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Fig. 4. Definition of study variables and typical curves of one subject showing the repeatability of within one test condition. The curves show calcaneal eversion–inversion relative to the tibia (top row) and internal–external tibial rotation relative to the calcaneus. For the definition of the test variables see also Table 3. A = RomEV, B = RomInv, C = Mev, D = Minv, E = RomTir, F = RomTar, G = Mtir, and H = Mtar.
show the individual median curves of the five test conditions of three test subjects (Fig. 6). 3. Results 3.1. General results in the frontal plane
Fig. 5. Setting of the wire electrode for the tibialis posterior muscle.
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 reduced eversion (MaxEv and RomEv) as well as eversion moments (MaxMEv and Mev) compared to all other test conditions. Largest eversion (MaxEv and RomEv) was found with O1. Between midstance and take off the inversion variables (MaxInv, RomInv, MaxMInv, Minv) showed no significant changes.
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3.3. Individual results The entire time needed for each subject to perform all 50 tests was between 60 and 90 min. During this test time individual changes could have taken place which is addressed in this subsection under (i) possible effects of the order of testing, (ii) changes between test condition NA and NB, and (iii) possible changes in muscle activity of tibialis posterior muscle activity.
Fig. 6. Tibialis posterior activity measured with fine wire of three test subjects all showing significant kinematic and kinetic differences between the two neutral conditions NA and NB (Table 5). Each test condition is represented by the median curve of 8–10 repetitions. TD = touchdown; TO = take off.
3.2. General results in the transverse plane At touchdown, no significant differences in the test variables were found. Between touchdown and midstance only O2 was significantly reduced versus O3 in MaxMTir of all the variables related to internal tibial rotation. Between midstance and take off the external tibial rotation variable RomTar was largest in O1 compared to NA, O2, and NB; O2 was significantly smaller than O3. Between test condition NA and NB no significant differences over all test subjects were found. That means that on average the subjects showed no changes between the beginning and the end of testing. In order to verify this for each individual, the statistical procedures were also applied for NA and NB for each of the test subjects separately (see Section 3.3).
(i) Possible effects of order of testing: the order of testing for the orthosis was set randomly (Table 1) and the possible effects were controlled for each of the eight subjects individually. It was found that eversion with O2 was reduced whether it was tested first, second or third. Thus, the order of testing did not affect the test results. (ii) Changes between the test condition NA and NB: the individual comparison of all test variables comparing condition NA and NB is shown in Table 5. It is evident that over time, i.e. between the first test (NA) and the last test (NB) different individual changes took place. Four subjects (P, R, V, W) showed several significant test variables decreasing between NA and NB; three subjects (Q, T, U) showed an increase in various test variables and one subject (S) no changes. Furthermore, the subjects with fine wire electrodes (denoted “e” in Table 5) showed no common pattern (e.g. increase and/or decrease), thus, a possible argument that the wire would produce a common effect cannot be supported. Hence, although the general comparison between NA and NB showed no significant results (see Sections 3.1 and 3.2), individual differences were apparent. However, these individual differences could neither be explained by the order of testing nor by the setting of the wire electrodes (see (i)). (iii) Possible changes in tibialis posterior muscle activity: measurements with fine wires can be disturbed or disrupted during testing of more than 1 h. In the present study two subjects (S and T) showed a disrupted or noisy EMG signal; as a consequence, valid EMG measurements over all test conditions were available for three test subjects only (Table 5 and Fig. 6). Fig. 6 shows that no systematic changes of EMG activity of the tibialis posterior muscle was apparent although the subjects showed several significant differences (Table 5) between condition NA and NB: subject R (8 significant variables NA > NB) showed a decrease in EMG activity between NA and NB, subject U (6 significant variables NA < NB) an increase, and subject V (7 significant variables NA > NB and 2 NA < NB) showed no activity changes. Thus, tibialis posterior muscle activity cannot be used as an explanation why these subjects showed alterations in the test variables between the condition NA and NB. Furthermore, Fig. 5 shows different strategies in the use of the tibialis posterior muscle: R and U use it throughout
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Table 4 Mean values and standard deviation of test variables of all 8 test subjects All subjects
Neutral A
Orthosis 1
Orthosis 2
Orthosis 3
Neutral B
(◦ )
Movement Frontal plane TdInv1 MaxEv2 RomEv3 MaxInv RomInv Transversal plane TdTar MaxTir RomTir MaxTar RomTar4 Moment (Nm) Frontal plane TdMInv MaxMEv5 Mev6 MaxMInv Minv Transversal plane TdMTar MaxMTir7 Mtir MaxMTar Mtar
4.2 4.0 8.3 8.9 13.0
± ± ± ± ±
2.9 2.2 3.0 4.8 4.7
4.6 5.5 10.1 8.0 13.6
± ± ± ± ±
2.4e 1.7a,e,f,g 2.4a,e 4.8 5.3
6.0 2.2 8.3 9.4 11.6
± ± ± ± ±
2.7b 1.9b,h,i 2.2h 4.3 4.4
0.9 6.1 7.1 0.4 6.5
± ± ± ± ±
5.9 4.6 3.3 5.0 2.2
0.2 6.4 6.6 0.7 7.2
± ± ± ± ±
6.0 4.5 2.8 4.4 1.2a,e,g
1.1 5.9 7.0 0.1 6.0
± ± ± ± ±
0.8 8.0 8.8 15.3 23.3
± ± ± ± ±
0.9 4.6 4.5 10.2 12.1
0.9 7.6 8.5 15.1 22.8
± ± ± ± ±
0.7 3.7 3.5a 9.3 9.8
0.7 6.7 7.4 18.0 24.7
0.4 4.1 4.5 11.0 15.2
± ± ± ± ±
0.4 1.9 2.0 6.4 5.7
0.5 3.9 4.4 11.3 15.2
± ± ± ± ±
0.4 1.3 1.5 5.3 4.9
0.4 3.5 3.9 12.0 15.5
1*** 1 b*** 1 e*** 2*** 2 a*** 2 b*** 2 e*** 2 f*** 2 g*** 2 h*** 2 i*** 3*** 3 a** 3 e***
5.0 4.6 9.6 8.1 12.7
± ± ± ± ±
3.4 2.1 3.1 3.9 4.3
4.7 4.5 9.2 8.0 12.4
± ± ± ± ±
2.1 1.5 2.4 4.2 4.7
6.4 4.6 2.8 4.2 1.8h
0.3 6.5 6.9 0.3 6.8
± ± ± ± ±
6.1 4.5 2.7 4.5 1.9
0.8 6.2 6.9 0.3 6.5
± ± ± ± ±
6.1 4.3 2.8 4.4 1.3
± ± ± ± ±
0.8 3.6h 3.2h,i 11.0 10.9
0.8 8.9 9.7 15.1 23.9
± ± ± ± ±
0.6 4.4 4.3 9.1 10.4
0.9 8.5 9.4 15.7 24.2
± ± ± ± ±
0.8 4.8 4.4 10.2 11.7
± ± ± ± ±
0.4 1.2h 1.4 5.3 4.9
0.4 4.1 4.5 10.9 15.0
± ± ± ± ±
0.4 1.6 1.9 6.1 5.4
0.4 4.0 4.4 11.2 15.3
± ± ± ± ±
0.4 1.7 2.0 5.9 5.2
3 h** 4*** 4 a*** 4 e*** 4 g** 4 h** 5*** 5 h*** 6*** 6 b* 6 h*** 6 i** 7* 7 h*
Indices 1 to 7 indicate significant differences over all five test conditions using the ANOVA. Letters a to j indicate significant differences between test conditions using a post-hoc test. a: comparison between O1 and NA. b: comparison between O2 and NA. c: comparison between O3 and NA. d: comparison between NA and NB. e: comparison between O1 and O2. f: comparison between O1 and O3. g: comparison between O1 and NB. h: comparison between O2 and O3. i: comparison between O2 and NB. j: comparison between O3 and NB. * p-value under 0.100. ** p-value under 0.050. *** p-value under 0.010.
the entire stance phase, V mainly between touchdown and midstance.
4. Discussion 4.1. Limitations of the study Foot and shank were each modelled as rigid segments, a simplification which has been shown to have limited valid-
ity 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 influenced by forefoot movements; it is likely that pure rearfoot movements would have been smaller. However, there are two arguments which reduce the impact of this limitation on the results of the present study: first, the
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Table 5 Individual comparison of the test variables of the test condition NA minus NB
A positive value indicates NA > NB, a negative value NA < NB. The following abbreviations are used: *p-value under 0.100. **p-value under 0.050. ***p-value under 0.010. e Subjects with wire-electrodes set into the tibialis posterior muscle. Shading parts: subjects with undisturbed EMG-signals (graphs see Fig. 6).
results presented are all based on intra-subject comparisons and thus, the assumption that forefoot–rearfoot movements (and skin movement artefacts) remained similar during all test conditions within the same subject seems acceptable. Secondly, although forefoot–rearfoot movements are known to be considerable during running [40] not much knowledge is available with respect to forefoot–rearfoot movements during walking [39]. This enhances the difficulty to judge upon the effect of forefoot movements on the rearfoot data. In conclusion, although the true bone movements could not be quantified in this study it was felt that the test set-up allowed to describe individual orthotic effects during walking for each of the eight test subjects. 4.2. General results Since all test subjects had a pathological pes valgus the common goal of the three podiatrists was to construct orthoses which would reduce eversion (and thus, the variables related to it, see Table 3). It is interesting to note however, that the effects of the three orthoses differed considerably. Common to all orthoses was that at touchdown no differences were apparent with the exception of the molding and posting (O2) which showed a significant increase of inversion (TdInv). Thus, with O2 the feet were moved into a slight inversion position which was 1–2◦ larger than with the other orthoses. Thus, hypothesis 1 was accepted for all test conditions, except for O2. Frontal plane: between touchdown and midstance several test variables indicated that the molding and posting orthosis O2 showed a significant decrease in eversion movement and moment compared to all the other test conditions and a decrease in the internal tibia moment. It is possible that the more inverted position of O2 at touchdown may have helped
to produce this result, although the reduction of eversion was larger then the enhanced inversion, as described above. Eversion of the proprioceptive orthosis (O3) was reduced relative to the posting orthosis (O1), which in turn was enhanced relative to NA and NB. Thus, hypothesis 2 was accepted for O2, in part for O3, but not for O1. This means that the molding and posting orthosis was found to have the most prominent eversion reducing effect on the test subjects. Interestingly, five of the eight test subjects preferred the molding and posting orthoses above the other two (Table 1) which coincided nicely with the test results. The proprioceptive orthosis had some effect (compared to O1), indicating that the surface texture can alter the biomechanics of the foot during walking, a finding which is in agreement with Nurse et al. [41]. The posting orthosis O1 failed to be better than the neutral conditions NA and NB which may have to do with its construction (see below). These finding are in contrast to Mundermann et al. [18] who found that the posting orthosis had most effects on eversion compared to a molding and a combined molding and posting orthoses. One possible explanation of this discrepancy is a different orthotic construction. The posting orthoses of the present study was made of two layers, the upper being relatively soft (see Section 2.2) compared to the relatively hard material of the combined molding and posting orthosis. This indicates that material hardness may be a factor which needs to be considered when studying orthotic effects on study variables such as maximum eversion and eversion moments. Generally, the order of magnitude eversion reduction of the two studies are comparable; however, since Mundermann et al. [18] tested during running (opposed to walking in the present study), their values were generally larger. Further studies that support the present findings show a reduction of maximum eversion of around 3◦ with
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insoles during walking and running [42,43]. Schmalz et al. [44] showed similar graphs and a comparable reduction of the frontal plane maximum moment (variable Mev) during walking when accounting for the different units used (Nm versus Nm/kg). Transverse plane: still between touchdown and midstance, but now in the transverse plane, maximum tibia internal moment (MaxMTir) was reduced significantly only with the combined molding and posting (O2), thus, hypothesis 3 was accepted for O2, but not for O1 and O3. Mundermann et al. [18,22] found the same effect with the posting orthoses which may also be explained with the different orthotic hardnesses used in the two studies (see above). Nester et al. [20] found an even larger reduction with the use of medial wedges (3◦ ) compared to the present study (less than 1◦ in MaxTir). During the second half of stance phase (midstance to take off) almost no orthotic effects were found in the present study: only O1 was enhanced in external tibial rotation (RomTar), hence hypothesis 4 and 5 were rejected, except for O1. The difference between O1 and the other two orthoses of this study is that it only supports medially and posteriorly. Thus, the anterior and lateral support of O2 and O3 may have helped to reduce the external tibial rotation during the second half of the stance phase. Generally, the test orthoses of the present study worked mainly during the first phase (touchdown to midstance) where the foot is loaded and not after the heel rises towards take off. This can be interpreted as a mechanical orthotic effect and is in agreement with Mundermann et al. [18,22] who stated that orthotic effects are mainly present in the first half of stance phase (eversion). That is in contrast to Nester et al. [20] and the result of the posting orthosis O1 where an increase in external tibial rotation of 1–2◦ was found (in RomTar). 4.3. Individual results The comparison of the individual results was found to be contradictory: on the one hand, eversion was significantly reduced in all subjects with the molding and posting orthosis O2. But on the other hand, the test variables found with the first test (NA) compared to the last test (NB) showed unsystematic individual differences (Table 5). When searching for possible explanations, neither the order of testing nor a systematic change of the tibialis posterior muscle activity can be used as an argument (see Section 3.3). Two suggestions are proposed with respect to these differences: (a) proprioception and (b) internal foot mechanics. (a) Proprioception at the sole of the foot: some authors have indicated that the sensory feedback at the sole of the foot can vary considerably between individuals even within the normal population [15,27]. It has also been reported that it changes with age [28]. Thus, it is possible that during testing different proprioceptive effects across the test subjects took place between NA and NB leading to this unsystematic result. Currently, little is known about
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proprioceptive effects of inserts and orthoses [41] and how it can contribute to control gait [23]. It is suggested that in future studies the neutral orthosis should not only be tested at the beginning and end but as a reference between each test condition. (b) Internal foot mechanics: in vitro foot research [45] and in vivo approaches using stereophotogrammetry [46] and MRI [47] and bone pins [48] have shown that considerable individual differences are apparent with respect to bony movements in the midfoot and the tarsus. Thus, it is possible that although externally no differences in foot movements were apparent, considerable foot internal movement differences may occur. Consequently, one given orthosis applied to several subjects may result in a variation of internal bony movements. This may be a research challenge for further studies. 5. Conclusions The test subjects of the present study all had pes valgus in need for medially applied orthosis showing the following results: • 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. • The current results suggest that changes in kinematic and kinetic variables may be due to construction differences of the orthoses as well as their hardness and surface texture. • The results show further that individual non-systematic effects can take place during test duration of more than an hour. EMG measurements with fine wire electrodes on a subset of the test subjects revealed that the activity pattern of the tibialis posterior muscle may not be used as an explanation for the apparent individual effects. It was concluded that for subjects with pes valgus a combined molding and posting orthosis reduces eversion best and that individual variations may be due to subject dependent proprioception, internal foot mechanics and/or a combination of both. 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 (Eidgen¨ossische Sport Kommission); Swiss Life Foundation,
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Z¨urich, Switzerland and Synos Foundation, M¨unsingenBern, 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; L. Hoffman, Numo Systems, 8953 Dietikon, orthoses O2; H.M. Heierling, 7260 Davos, orthoses O3.
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[20] Nester CJ, van der Linden ML, Bowker P. Effect of foot orthoses on the kinematics and kinetics of normal walking gait. Gait Posture 2003;17:180–7. [21] Nigg BM, Wakeling JM. Impact forces and muscle tuning: a new paradigm. Exerc Sport Sci Rev 2001;29:37–41. [22] Mundermann A, Nigg BM, Humble N, Stefanyshyn D. Consistent immediate effects of foot orthoses on comfort and lower extremity kinematics, kinetics, and muscle activity. J Appl Biomech 2004;20:74– 84. [23] Sorensen KL, Hollands MA, Patla E. The effects of human ankle muscle vibration on posture and balance during adaptive locomotion. Exp Brain Res 2002;143:24–34. [24] Sinkjaer T, Andersen JB, Larsen B. Soleus stretch reflex modulation during gait in humans. J Neurophysiol 1996;76:1112–20. [25] van Wezel BM, Ottenhoff FAM, Duysens J. Dynamic control of location-specific information in tactile cutaneus reflexes from the foot during walking. J Neurosci 1997;17:3804–14. [26] Mazzaro N, Grey MJ, Sinkjaer T. Contribution of afferent feedback to the soleus muscle activity during human locomotion. J Neurophysiol 2005;93:167–77. [27] Kekoni J, Hamalainen H, Rautio J, Tukeva T. Mechanical sensibility of the sole of the foot determined with vibratory stimuli of varying frequency. Exp Brain Res 1989;78:419–24. [28] Mold JW, Vesely SK, Keyl BA, Schenk JB, Roberts M. The prevalence, predictors, and consequences of peripheral sensory neuropathy in older patients. J Am Board Fam Pract 2004;17:309–18. [29] Perry J. Gait analysis, normal and pathological function. Thorofare, NJ: Slack Inc.; 1992. [30] O’Connor KM, Hamill J. The role of selected extrinsic foot muscles during running. Clin Biomech (Bristol, Avon) 2004;19:71–7. [31] Rattanaprasert U, Smith R, Sullivan M, Gilleard W. Three-dimensional kinematics of the forefoot, rearfoot, and leg without the function of tibialis posterior in comparison with normals during stance phase of walking. Clin Biomech (Bristol, Avon) 1999;14:14–23. [32] Kramers-de Quervain IA, St¨ussi E, M¨uller R, Drobny T, Munzinger U, Gschwend N. Quantitative gait analysis after bilateral total knee arthroplasty with two different systems within each subject. J Arthroplasty 1997;12:168–79. [33] Stacoff A, Diezi C, Luder G, Stussi E, Kramers-de Quervain IA. Ground reaction forces on stairs: effects of stair inclination and age. Gait Posture 2005;21:24–38. [34] Gander W, Hrebicek J. Solving problems in scientific computing using Maple and Matlab, chapter 23: least squares fit of point clouds. Springer; 1997. [35] Dettwyler M. Biomechanische Untersuchungen und Modellierungen am menschlichen oberen Sprunggelenk im Hinblick auf Arthroplasiken. Zurich: ETH Zurich; 2005. [36] Basmajian JV. Muscles alive, their functions revealed by electromyography. Baltimore: Williams and Wilkins; 1978. [37] De Luca CJ. The use of surface electromyography in biomechanics. J Appl Biomech 1997;13:135–63. [38] Reinschmidt C, vandenBogert AJ, Lundberg A, Nigg BM, Murphy N, Stacoff A, et al. Tibiofemoral and tibiocalcaneal motion during walking: external vs. skeletal markers. Gait Posture 1997;6:98– 109. [39] Hunt AE, Smith RM, Torode M, Keenan AM. Inter-segment foot motion and ground reaction forces over the stance phase of walking. Clin Biomech (Bristol, Avon) 2001;16:592–600. [40] Stacoff A, Kalin X, Stussi E. The effects of shoes on the torsion and rearfoot motion in running. Med Sci Sports Exerc 1991;23:482– 90. [41] Nurse MA, Hulliger M, Wakeling JM, Nigg BM, Stefanyshyn DJ. Changing the texture of footwear can alter gait patterns. J Electromyogr Kinesiol 2005;15:496–506. [42] Nigg BM, Khan AR, Fisher V, Stefanyshyn D. Effect of shoe insert construction on foot and leg movement. Med Sci Sports Exerc 1998;30:550–5.
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Biomechanical effects of foot orthoses during walking Alex Stacoff a,∗ , In`es Kramers-de Quervain a,b , Markus Dettwyler a , Peter Wolf a , Renate List a , Thomas Ukelo a , Edgar St¨ussi a a
Institute for Biomechanics, ETH Zurich, 8093 Zurich, Switzerland b Schulthess Clinic, Zurich, Switzerland
Received 26 June 2006; received in revised form 24 January 2007; accepted 6 February 2007
Abstract The purpose of this study was to quantify kinetic and kinematic effects during the stance phase of walking using three different foot orthoses. All test subjects were measured under five test conditions with 10 repetitions each. The test conditions included: neutral orthosis (tested twice) and three different orthoses (posting, molding and posting combined, proprioceptive). Whereas most previous studies rely on healthy subjects to describe effects of orthoses during gait, the present study used eight patients (all pes valgus). Standard gait analysis was used with force plates (KISTLER) and an optoelectric measuring system (VICON). The results show that the combined molding and posting foot orthosis significantly reduced eversion and eversion moments during walking compared to a posting type and a proprioceptive orthosis in several test parameters. EMG measurements with fine wire electrodes on three of the test subjects revealed that the activity pattern of the tibialis posterior muscle can considerably change between subjects but may not be used to explain apparent individual effects. The results suggest that for subjects with pes valgus a combined molding and posting orthoses reduces eversion best and that individual variations may be due to subject dependent proprioception, internal foot mechanics and/or a combination of both. © 2007 Elsevier Ltd. All rights reserved. Keywords: Lower extremity; Shoe inserts; Orthoses; Tibia
1. 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 [1–3]. Traditionally they have been applied in clinical environments treating patients with severe gait problems [4–8]. 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 [9–12]. 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 ∗ Corresponding author at: ETH Zurich, Institute for Biomechanics, Hoenggerberg HCI E 365.1, 8093 Zurich, Switzerland. Tel.: +41 1 633 62 18; fax: +41 1 633 11 24. E-mail address: [email protected] (A. Stacoff).
0958-2592/$ – see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.foot.2007.02.004
positive outcome results may be due to mechanical and/or proprioceptive mechanisms [13–15]. Recent biomechanical literature suggests that orthoses can produce kinematic, kinetic and muscle activity changes, findings which are mainly based on healthy subjects [16–21]. 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 [23–25]. 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
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Table 1 Test subjects and their comfort rating of the orthoses Test persons
Age
Height (cm)
Weight (kg)
Ranking of orthoses
Order of testing
P Q Ra Sa Ta Ua Va W
67 67 69 40 49 38 25 24
155 151 166 166 171 185 173 189
88.0 77.6 92.4 64.4 113.9 74.8 57.8 64.2
O2 > O3 > O1 O2 > O3 > O1 O2 > O3 > O1 O2 > O3 = O1 O1 > O2 > O3 O3 > O2 > O1 O2 > O3 > O1 O3 > O2 > O1
NA, O3, O2, O1, NB NA, O1, O3, O2, NB NA, O3, O2, O1, NB NA, O3, O1, O2, NB NA, O3, O2, O1, NB NA, O1, O2, O3, NB NA, O1, O3, O2, NB NA, O3, O2, O1, NB
Abbreviations: NA, O1, O2, O3, NB refer to Fig. 2. a Indicates the subjects with fine wire electrodes.
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.
bination with the test sandals (Table 1 and Fig. 1). Written consent was given by all participants. 2.2. Orthoses, test sandals and test set-up A standardized test shoe (a “Finn comfort” sandal) with a flat sole (Hassfurt, Germany) was used which allowed easy replacement of the orthoses as an entire inlay between test conditions without removing the foot markers (Fig. 2). The test sequence started for all subjects with the neutral orthoses NA (“N” for neutral and “A” for the first test) to set the baseline for all other test conditions. The next three orthotic conditions were randomly selected. Condition 5 was identical to NA (denoted NB) which allowed identification of possible changes between beginning and end of testing. For each test condition 8–10 walking trials of the right foot were registered, thus, each subject walked 50 times. Podiatrist A constructed “posting” orthoses with a medial post supporting the calcaneus at the sustentaculum tali (Fig. 2 and Table 2). The orthotic was made with two layers, a harder lower (Asker C 70–80) and a softer upper layer (Asker C 40–45). Podiatrist B formed “molding and posting” orthoses consisting of one hard layer with Asker C 70–80 supporting the foot medially and laterally. The proprioceptive orthosis of podiatrist C was thought to stimulate the plantar surface of the foot and thus, the leg muscles inserting there with a total of four elevations: two 3 mm of around 10 cm2 areas at
2. Methods 2.1. 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 com-
Fig. 1. Test sandals with the neutral type of orthosis (NA or NB).
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Fig. 2. Orthoses used in the investigation: NA/NB show the inlay with no support; O1: posting orthosis; O2: combined molding and posting orthosis; O3: proprioceptive orthosis. Shaded areas indicate support.
the midfoot, and two 2 mm of about 20 cm2 areas under the metatarsal heads II–V and toes II–V, respectively (Fig. 2). The tests were performed at the Institute for Biomechanics at the ETH Z¨urich, Switzerland [32,33]. The available gait analysis system allows collection of kinematic, kinetic and EMG data simultaneously while the test subjects walk over a 25 m walkway. After testing, the test subjects gave their individual ranking with respect to preference of the three test orthoses (Table 1). 2.3. Kinematic tests Motion capture was performed with a 7 camera Vicon System 370 (Oxford metrics, UK). The foot and shank segment were each redundantly equipped forming a cluster of 5 markers each (diameter 10 mm; Fig. 3). The foot markers were placed over the matatarsals I and V, medial and lateral calacaneus, and navicular. The shank markers were positioned at the medial and lateral malleolus, head of fibula, tibial tuberosity, and anterior surface of the tibia midway between tuberosity and the malleoli. Thus, the foot and shank segment were made as large as possible to improve angular accuracy. The time dependent spatial location and orientation of the foot and shank segment was determined with a least-squares cluster fit routine (using singular value decomposition after Gander and Hrebicek [34]). Thus, foot and shank were regarded as two rigid segments. The ankle joint was modelled as a ball-
Fig. 3. Marker-set on the foot and shank and definition of coordinate system [35].
and-socket joint with the definition of a subject specific ankle joint center computed from loaded plantar-dorsiflexion and eversion-inversion movements using an optimization routine [35]. The test variables were determined for each test condition and subject (Table 3). 2.4. Kinetic tests and inverse dynamics Force data was collected from a Kistler 9281B force platform (Kistler, Winterthur, Switzerland). All kinetic data was normalized to 100% stance phase using a threshold at 2% bodyweight. Tibia torsional moments were computed about reference axes which all went through the determined joint center. The underlying coordinate system was fixed to the shank segment and the reference axes moved with this segment. The directions of the reference axes were identified as, firstly, the direction from the determined joint center to the marker on the tibial tuberosity (about z-direction), sec-
Table 2 Orthoses and test conditions of the present study Orthosis
Type
Description
NA O1 O2 O3 NB
Neutral Orthosis 1: posting Orthosis 2: molding and posting Orthosis 3: proprioceptive Neutral
2 mm thick inlay, no support, first test Medial posting support, podiatrist A Medial posting combined with molding technique, podiatrist B With four proprioceptive areas, podiatrist C 2 mm thick inlay, no support, second test
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Table 3 Definitions of the study variables Definition of Variables (◦ )
Movement Frontal plane TdInv MaxEv RomEv MaxInv RomInv Transversal plane TdTar MaxTir RomTir MaxTar RomTar Moment (Nm) Frontal plane TdMInv MaxMEv Mev MaxMInv Minv Transversal plane TdMTar MaxMTir Mtir MaxMTar Mtar
Inverted position of foot at touchdown Maximum eversion after touchdown Range of motion between TdInv and MaxEv Maximum inversion during take off Range of motion between MaxEv and MaxInv Externally rotated position of tibia relative to calcaneus at touchdown Maximum internal tibial rotation relative to calcaneus after touchdown Range of motion between TdTar and MaxTir Maximum external tibial rotation relative to calcaneus during take off Range of motion between MaxTir and MaxTar
Inversion moment at touchdown Maximum eversion moment after touchdown Difference between TdMInv and MaxMEv Maximum inversion moment during take off Difference between MaxMInv and MaxMEv
2. Maximum eversion (MaxEv), the range of eversion (RomEv) and the respective moments (MaxMEv and Mev) would be reduced between touchdown and midstance; 3. Maximum internal tibial rotation (MaxTir), the range of internal tibial rotation (RomTir) and the respective moments (MaxMTir and Mtir) would be reduced between touchdown and mistance; 4. Maximum external tibial rotation (MaxTar), the range of external tibial rotation (RomTar) and the respective moments (MaxMTar and MTar) would be reduced between midstance and take off; 5. Maximum inversion (MaxInv), the range of inversion (RomInv) and the respective moments (MaxMInv and Minv) would be reduced between midstance and take off. For the statistical analyses an ANOVA was applied for the comparison of the test variables of all five test conditions. In order to test significant differences between the test conditions a post-hoc after Bonferroni was applied. In order to test possible changes during testing the test variables of condition 1 (NA) were compared to those of condition 5 (NB) using the same procedure. 2.5. Wire EMG
External tibial rotation moment at touchdown Maximum internal tibial rotation moment after touchdown Difference between TdMTar and MaxMTir Maximum external tibial rotation moment during take off Difference between MaxMTar and MaxMTir
ondly, as the direction from the medial to the lateral malleolus (about x-direction), and, thirdly, as the direction of the cross product between the former two (about y-direction; Fig. 3). These three directions did not necessarily form a mutually orthogonal triple set, but the deviations from it were small. 2.4.1. Analysis of kinematic and kinetic data Since all eight test subjects were diagnosed as pes valgus the expected effect of the medially placed orthoses was to see a reduction of the eversion variables between the touchdown of the foot and midstance (Fig. 4 and hypothesis 2 below), whereas at the instant of touchdown no changes were expected (hypothesis 1). A further expectation was that due to the coupling mechanism at the ankle, the internal rotation about its longitudinal axes would be reduced with orthoses (hypothesis 3). During take off it was thought that the orthotic effect would continue and consequently reduce inversion and external tibial rotation (hypothesis 4 and 5). Thus, with respect to the neutral test condition, the hypotheses to be tested were (definitions see Table 3): 1. Foot and tibia position and moment at touchdown (TdInv, TdTar and TdMInv, TdMTar) would not be altered;
Out of the eight test subjects five consented to have fine wire electrodes set into their tibialis posterior muscle (Table 1). The wire electrodes were set according to the technique described by Basmajian [36] into tibialis posterior muscle using a 75 m thin silver wire. The electrodes were bipolar, teflon coated, insulation 140 m thick, thread through a 23 gauge needle and sterilized. At the wire ends the insulation was removed over about 1 mm and bent 180◦ at the tip of the needle in different lengths. This should ensure that the ends would not make contact and would remain in the muscle after insertion and retraction of the needle. The wire ends were fixed on the skin with tape (Fig. 5), the wires connected to the preamplifiers. Muscle function was tested with a muscle stimulation device (Compex Inc., Springfield, VA, USA) using very low stimulations. Foot inversion was observed when the electrodes were set in the tibialis posterior muscle and toe flexion when the flexor digitorum longus muscle was stimulated between 2 and 8 mA. The removal of the wires was done by pulling, all wires came out intact. The raw EMG signal was amplified with a differential pre-amplifier. A telemetry unit carried on the subjects back (Glonner Telemetry, Zettl, Karlsruhe, Germany) transmitted the data which was imported into the Vicon measuring system as an analogue input. The EMG raw data was first filtered (Butterworth 3rd order) with a 10–500 Hz band filter according to the recommendations of De Luca [37]. Then, the signals were rectified, and “integrated” with a moving average window of 50 ms. Maximum voluntary contraction was used as a reference indicating 100% activation. The time axis was normalized to one gait cycle equalling 100%; the plots
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Fig. 4. Definition of study variables and typical curves of one subject showing the repeatability of within one test condition. The curves show calcaneal eversion–inversion relative to the tibia (top row) and internal–external tibial rotation relative to the calcaneus. For the definition of the test variables see also Table 3. A = RomEV, B = RomInv, C = Mev, D = Minv, E = RomTir, F = RomTar, G = Mtir, and H = Mtar.
show the individual median curves of the five test conditions of three test subjects (Fig. 6). 3. Results 3.1. General results in the frontal plane
Fig. 5. Setting of the wire electrode for the tibialis posterior muscle.
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 reduced eversion (MaxEv and RomEv) as well as eversion moments (MaxMEv and Mev) compared to all other test conditions. Largest eversion (MaxEv and RomEv) was found with O1. Between midstance and take off the inversion variables (MaxInv, RomInv, MaxMInv, Minv) showed no significant changes.
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3.3. Individual results The entire time needed for each subject to perform all 50 tests was between 60 and 90 min. During this test time individual changes could have taken place which is addressed in this subsection under (i) possible effects of the order of testing, (ii) changes between test condition NA and NB, and (iii) possible changes in muscle activity of tibialis posterior muscle activity.
Fig. 6. Tibialis posterior activity measured with fine wire of three test subjects all showing significant kinematic and kinetic differences between the two neutral conditions NA and NB (Table 5). Each test condition is represented by the median curve of 8–10 repetitions. TD = touchdown; TO = take off.
3.2. General results in the transverse plane At touchdown, no significant differences in the test variables were found. Between touchdown and midstance only O2 was significantly reduced versus O3 in MaxMTir of all the variables related to internal tibial rotation. Between midstance and take off the external tibial rotation variable RomTar was largest in O1 compared to NA, O2, and NB; O2 was significantly smaller than O3. Between test condition NA and NB no significant differences over all test subjects were found. That means that on average the subjects showed no changes between the beginning and the end of testing. In order to verify this for each individual, the statistical procedures were also applied for NA and NB for each of the test subjects separately (see Section 3.3).
(i) Possible effects of order of testing: the order of testing for the orthosis was set randomly (Table 1) and the possible effects were controlled for each of the eight subjects individually. It was found that eversion with O2 was reduced whether it was tested first, second or third. Thus, the order of testing did not affect the test results. (ii) Changes between the test condition NA and NB: the individual comparison of all test variables comparing condition NA and NB is shown in Table 5. It is evident that over time, i.e. between the first test (NA) and the last test (NB) different individual changes took place. Four subjects (P, R, V, W) showed several significant test variables decreasing between NA and NB; three subjects (Q, T, U) showed an increase in various test variables and one subject (S) no changes. Furthermore, the subjects with fine wire electrodes (denoted “e” in Table 5) showed no common pattern (e.g. increase and/or decrease), thus, a possible argument that the wire would produce a common effect cannot be supported. Hence, although the general comparison between NA and NB showed no significant results (see Sections 3.1 and 3.2), individual differences were apparent. However, these individual differences could neither be explained by the order of testing nor by the setting of the wire electrodes (see (i)). (iii) Possible changes in tibialis posterior muscle activity: measurements with fine wires can be disturbed or disrupted during testing of more than 1 h. In the present study two subjects (S and T) showed a disrupted or noisy EMG signal; as a consequence, valid EMG measurements over all test conditions were available for three test subjects only (Table 5 and Fig. 6). Fig. 6 shows that no systematic changes of EMG activity of the tibialis posterior muscle was apparent although the subjects showed several significant differences (Table 5) between condition NA and NB: subject R (8 significant variables NA > NB) showed a decrease in EMG activity between NA and NB, subject U (6 significant variables NA < NB) an increase, and subject V (7 significant variables NA > NB and 2 NA < NB) showed no activity changes. Thus, tibialis posterior muscle activity cannot be used as an explanation why these subjects showed alterations in the test variables between the condition NA and NB. Furthermore, Fig. 5 shows different strategies in the use of the tibialis posterior muscle: R and U use it throughout
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Table 4 Mean values and standard deviation of test variables of all 8 test subjects All subjects
Neutral A
Orthosis 1
Orthosis 2
Orthosis 3
Neutral B
(◦ )
Movement Frontal plane TdInv1 MaxEv2 RomEv3 MaxInv RomInv Transversal plane TdTar MaxTir RomTir MaxTar RomTar4 Moment (Nm) Frontal plane TdMInv MaxMEv5 Mev6 MaxMInv Minv Transversal plane TdMTar MaxMTir7 Mtir MaxMTar Mtar
4.2 4.0 8.3 8.9 13.0
± ± ± ± ±
2.9 2.2 3.0 4.8 4.7
4.6 5.5 10.1 8.0 13.6
± ± ± ± ±
2.4e 1.7a,e,f,g 2.4a,e 4.8 5.3
6.0 2.2 8.3 9.4 11.6
± ± ± ± ±
2.7b 1.9b,h,i 2.2h 4.3 4.4
0.9 6.1 7.1 0.4 6.5
± ± ± ± ±
5.9 4.6 3.3 5.0 2.2
0.2 6.4 6.6 0.7 7.2
± ± ± ± ±
6.0 4.5 2.8 4.4 1.2a,e,g
1.1 5.9 7.0 0.1 6.0
± ± ± ± ±
0.8 8.0 8.8 15.3 23.3
± ± ± ± ±
0.9 4.6 4.5 10.2 12.1
0.9 7.6 8.5 15.1 22.8
± ± ± ± ±
0.7 3.7 3.5a 9.3 9.8
0.7 6.7 7.4 18.0 24.7
0.4 4.1 4.5 11.0 15.2
± ± ± ± ±
0.4 1.9 2.0 6.4 5.7
0.5 3.9 4.4 11.3 15.2
± ± ± ± ±
0.4 1.3 1.5 5.3 4.9
0.4 3.5 3.9 12.0 15.5
1*** 1 b*** 1 e*** 2*** 2 a*** 2 b*** 2 e*** 2 f*** 2 g*** 2 h*** 2 i*** 3*** 3 a** 3 e***
5.0 4.6 9.6 8.1 12.7
± ± ± ± ±
3.4 2.1 3.1 3.9 4.3
4.7 4.5 9.2 8.0 12.4
± ± ± ± ±
2.1 1.5 2.4 4.2 4.7
6.4 4.6 2.8 4.2 1.8h
0.3 6.5 6.9 0.3 6.8
± ± ± ± ±
6.1 4.5 2.7 4.5 1.9
0.8 6.2 6.9 0.3 6.5
± ± ± ± ±
6.1 4.3 2.8 4.4 1.3
± ± ± ± ±
0.8 3.6h 3.2h,i 11.0 10.9
0.8 8.9 9.7 15.1 23.9
± ± ± ± ±
0.6 4.4 4.3 9.1 10.4
0.9 8.5 9.4 15.7 24.2
± ± ± ± ±
0.8 4.8 4.4 10.2 11.7
± ± ± ± ±
0.4 1.2h 1.4 5.3 4.9
0.4 4.1 4.5 10.9 15.0
± ± ± ± ±
0.4 1.6 1.9 6.1 5.4
0.4 4.0 4.4 11.2 15.3
± ± ± ± ±
0.4 1.7 2.0 5.9 5.2
3 h** 4*** 4 a*** 4 e*** 4 g** 4 h** 5*** 5 h*** 6*** 6 b* 6 h*** 6 i** 7* 7 h*
Indices 1 to 7 indicate significant differences over all five test conditions using the ANOVA. Letters a to j indicate significant differences between test conditions using a post-hoc test. a: comparison between O1 and NA. b: comparison between O2 and NA. c: comparison between O3 and NA. d: comparison between NA and NB. e: comparison between O1 and O2. f: comparison between O1 and O3. g: comparison between O1 and NB. h: comparison between O2 and O3. i: comparison between O2 and NB. j: comparison between O3 and NB. * p-value under 0.100. ** p-value under 0.050. *** p-value under 0.010.
the entire stance phase, V mainly between touchdown and midstance.
4. Discussion 4.1. Limitations of the study Foot and shank were each modelled as rigid segments, a simplification which has been shown to have limited valid-
ity 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 influenced by forefoot movements; it is likely that pure rearfoot movements would have been smaller. However, there are two arguments which reduce the impact of this limitation on the results of the present study: first, the
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Table 5 Individual comparison of the test variables of the test condition NA minus NB
A positive value indicates NA > NB, a negative value NA < NB. The following abbreviations are used: *p-value under 0.100. **p-value under 0.050. ***p-value under 0.010. e Subjects with wire-electrodes set into the tibialis posterior muscle. Shading parts: subjects with undisturbed EMG-signals (graphs see Fig. 6).
results presented are all based on intra-subject comparisons and thus, the assumption that forefoot–rearfoot movements (and skin movement artefacts) remained similar during all test conditions within the same subject seems acceptable. Secondly, although forefoot–rearfoot movements are known to be considerable during running [40] not much knowledge is available with respect to forefoot–rearfoot movements during walking [39]. This enhances the difficulty to judge upon the effect of forefoot movements on the rearfoot data. In conclusion, although the true bone movements could not be quantified in this study it was felt that the test set-up allowed to describe individual orthotic effects during walking for each of the eight test subjects. 4.2. General results Since all test subjects had a pathological pes valgus the common goal of the three podiatrists was to construct orthoses which would reduce eversion (and thus, the variables related to it, see Table 3). It is interesting to note however, that the effects of the three orthoses differed considerably. Common to all orthoses was that at touchdown no differences were apparent with the exception of the molding and posting (O2) which showed a significant increase of inversion (TdInv). Thus, with O2 the feet were moved into a slight inversion position which was 1–2◦ larger than with the other orthoses. Thus, hypothesis 1 was accepted for all test conditions, except for O2. Frontal plane: between touchdown and midstance several test variables indicated that the molding and posting orthosis O2 showed a significant decrease in eversion movement and moment compared to all the other test conditions and a decrease in the internal tibia moment. It is possible that the more inverted position of O2 at touchdown may have helped
to produce this result, although the reduction of eversion was larger then the enhanced inversion, as described above. Eversion of the proprioceptive orthosis (O3) was reduced relative to the posting orthosis (O1), which in turn was enhanced relative to NA and NB. Thus, hypothesis 2 was accepted for O2, in part for O3, but not for O1. This means that the molding and posting orthosis was found to have the most prominent eversion reducing effect on the test subjects. Interestingly, five of the eight test subjects preferred the molding and posting orthoses above the other two (Table 1) which coincided nicely with the test results. The proprioceptive orthosis had some effect (compared to O1), indicating that the surface texture can alter the biomechanics of the foot during walking, a finding which is in agreement with Nurse et al. [41]. The posting orthosis O1 failed to be better than the neutral conditions NA and NB which may have to do with its construction (see below). These finding are in contrast to Mundermann et al. [18] who found that the posting orthosis had most effects on eversion compared to a molding and a combined molding and posting orthoses. One possible explanation of this discrepancy is a different orthotic construction. The posting orthoses of the present study was made of two layers, the upper being relatively soft (see Section 2.2) compared to the relatively hard material of the combined molding and posting orthosis. This indicates that material hardness may be a factor which needs to be considered when studying orthotic effects on study variables such as maximum eversion and eversion moments. Generally, the order of magnitude eversion reduction of the two studies are comparable; however, since Mundermann et al. [18] tested during running (opposed to walking in the present study), their values were generally larger. Further studies that support the present findings show a reduction of maximum eversion of around 3◦ with
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insoles during walking and running [42,43]. Schmalz et al. [44] showed similar graphs and a comparable reduction of the frontal plane maximum moment (variable Mev) during walking when accounting for the different units used (Nm versus Nm/kg). Transverse plane: still between touchdown and midstance, but now in the transverse plane, maximum tibia internal moment (MaxMTir) was reduced significantly only with the combined molding and posting (O2), thus, hypothesis 3 was accepted for O2, but not for O1 and O3. Mundermann et al. [18,22] found the same effect with the posting orthoses which may also be explained with the different orthotic hardnesses used in the two studies (see above). Nester et al. [20] found an even larger reduction with the use of medial wedges (3◦ ) compared to the present study (less than 1◦ in MaxTir). During the second half of stance phase (midstance to take off) almost no orthotic effects were found in the present study: only O1 was enhanced in external tibial rotation (RomTar), hence hypothesis 4 and 5 were rejected, except for O1. The difference between O1 and the other two orthoses of this study is that it only supports medially and posteriorly. Thus, the anterior and lateral support of O2 and O3 may have helped to reduce the external tibial rotation during the second half of the stance phase. Generally, the test orthoses of the present study worked mainly during the first phase (touchdown to midstance) where the foot is loaded and not after the heel rises towards take off. This can be interpreted as a mechanical orthotic effect and is in agreement with Mundermann et al. [18,22] who stated that orthotic effects are mainly present in the first half of stance phase (eversion). That is in contrast to Nester et al. [20] and the result of the posting orthosis O1 where an increase in external tibial rotation of 1–2◦ was found (in RomTar). 4.3. Individual results The comparison of the individual results was found to be contradictory: on the one hand, eversion was significantly reduced in all subjects with the molding and posting orthosis O2. But on the other hand, the test variables found with the first test (NA) compared to the last test (NB) showed unsystematic individual differences (Table 5). When searching for possible explanations, neither the order of testing nor a systematic change of the tibialis posterior muscle activity can be used as an argument (see Section 3.3). Two suggestions are proposed with respect to these differences: (a) proprioception and (b) internal foot mechanics. (a) Proprioception at the sole of the foot: some authors have indicated that the sensory feedback at the sole of the foot can vary considerably between individuals even within the normal population [15,27]. It has also been reported that it changes with age [28]. Thus, it is possible that during testing different proprioceptive effects across the test subjects took place between NA and NB leading to this unsystematic result. Currently, little is known about
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proprioceptive effects of inserts and orthoses [41] and how it can contribute to control gait [23]. It is suggested that in future studies the neutral orthosis should not only be tested at the beginning and end but as a reference between each test condition. (b) Internal foot mechanics: in vitro foot research [45] and in vivo approaches using stereophotogrammetry [46] and MRI [47] and bone pins [48] have shown that considerable individual differences are apparent with respect to bony movements in the midfoot and the tarsus. Thus, it is possible that although externally no differences in foot movements were apparent, considerable foot internal movement differences may occur. Consequently, one given orthosis applied to several subjects may result in a variation of internal bony movements. This may be a research challenge for further studies. 5. Conclusions The test subjects of the present study all had pes valgus in need for medially applied orthosis showing the following results: • 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. • The current results suggest that changes in kinematic and kinetic variables may be due to construction differences of the orthoses as well as their hardness and surface texture. • The results show further that individual non-systematic effects can take place during test duration of more than an hour. EMG measurements with fine wire electrodes on a subset of the test subjects revealed that the activity pattern of the tibialis posterior muscle may not be used as an explanation for the apparent individual effects. It was concluded that for subjects with pes valgus a combined molding and posting orthosis reduces eversion best and that individual variations may be due to subject dependent proprioception, internal foot mechanics and/or a combination of both. 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 (Eidgen¨ossische Sport Kommission); Swiss Life Foundation,
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Z¨urich, Switzerland and Synos Foundation, M¨unsingenBern, 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; L. Hoffman, Numo Systems, 8953 Dietikon, orthoses O2; H.M. Heierling, 7260 Davos, orthoses O3.
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