Increased unilateral foot pronation affects lower limbs and pelvic biomechanics during walking
Introduction
Increased foot pronation causes biomechanical changes at the lower limbs, which may result in musculoskeletal injuries at the proximal joints [1], [2]. Previous study had shown that inadequate forefoot alignment at ground contact could produce large pronation torques that result in increased magnitude and duration of pronation during walking [3]. Following this rationale, Souza et al. [4] demonstrated that walking using lateral wedges under the forefoot increases rearfoot eversion and shank and hip internal rotation angles during the stance phase. Our work builds on these insights by examining the effects of increased unilateral foot pronation on knee and hip transverse plane moments and pelvic kinematics, since previous studies have demonstrated the occurrence of asymmetries in foot pronation in young [5] and elderly people [6].
The pelvic motion is dependent on the interaction of the lower limbs [7]. Therefore, it is logical to hypothesize that increased unilateral foot pronation may also influence the biomechanics of the opposite lower limb. Research had demonstrated that during quiet standing, foot pronation increases pelvic ipsilateral drop [8]. If that coupling mechanism remains true for walking, unilateral foot pronation may increase pelvic drop and consequently increases contralateral knee adduction moment [9], which is associated with knee ostearthritis progression [10]. In addition, unilateral foot pronation had been associated to low back pain [6], which reinforces the need to understand the biomechanical effects of unilateral foot pronation.
In order to investigate the effects of foot pronation during walking, different strategies have been implemented on shoes [11], foot orthoses [12] and sandals [13]. Specifically for studies using segmented foot models, the use of sandals seems to be more appropriate, since it was demonstrated that markers placed on shoes overestimate foot segments motion [14]. Regardless of the method chosen, it is usual to make assumptions about the effects of increased foot pronation based on a small set of biomechanical variables, such as the ipsilateral knee adduction moment [15]. However, considering that the influence of increased unilateral foot pronation on pelvic kinematics may also affect the biomechanics of the contralateral lower limb [16], more information about the effects of increased unilateral foot pronation on the mechanics of the lower limbs is necessary.
Therefore, the purpose of this study was to investigate the effects of increased unilateral foot pronation on the biomechanics of the lower limbs during the stance phase of walking. We hypothesized that increased foot pronation will increase ipsilateral lower limb internal rotation angles and ipsilateral pelvic drop and reduce internal rotation moments of the ipsilateral knee and hip. In addition, hip and knee adduction moments of the contralateral lower limb were expected to increase during early stance.
Section snippets
Participants
Sample size was determined as the number of participants necessary to reach a statistical power of 80%, with a significance level of 0.05, considering an expected moderate effect size (d = 0.6) [17]. Twenty-two healthy subjects (10 females, 12 males) with an average age, mass and height of 25 years (SD 4.5), 71.7 kg (SD 11.3) and 175 cm (SD 8), respectively, participated in the study. The inclusion criterion was no history of surgery or injuries to the lower limbs or to the lumbar-pelvic complex in
Gait speed and forefoot eversion
The control, ipsilateral side inclined and contralateral side inclined conditions showed an average gait speed of 1.44 m/s (SD 0.15), 1.45 m/s (SD 0.16) and 1.45 m/s (SD 0.16), respectively, and these differences were not statistically significant (p = 0.69). Wearing the wedged sandal increased forefoot eversion by 5.27° (SD 0.42) throughout stance phase (p < 0.001) when compared to the flat sandal.
Gait variables
The results of ANOVA demonstrated 11 PCs that were significantly different between the three conditions:
Discussion
This study demonstrated that unilateral increased foot pronation affects the biomechanics of the lower limbs during walking. The increased shank and femur internal rotation angles and decreased knee and hip internal rotation moments caused by the wedged sandal supports the existence of the coupling mechanism between rearfoot eversion and lower limb internal rotation [4], [13]. In addition, the increased pelvic ipsilateral drop supports the hypothesis that increased foot pronation dynamically
Conflicts of interest
We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.
Acknowledgements
The authors are thankful to the Brazilian Government Funding Agencies CAPES and FAPEMIG, grant number PPM00454-13, for financial support. The authors are also thankful to Amy Morton for her contribution during data collection.
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