Gait ground reaction force characteristics of low back pain patients with pronated foot and able-bodied individuals with and without foot pronation
Introduction
Although low back pain (LBP) attracts clinical attention due to its high prevalence (Trainor and Wiesel, 2002), its etiology is still unknown (Castro-Méndez et al., 2013). However, authors have identified risk factors leading to LBP. Biomechanical abnormalities, including stiffness of the joints and muscles of the lumbar spine, asymmetrical spinal loading induced by poor postural muscle function (Barwick et al., 2012, Chuter and de Jonge, 2012), abnormal foot structure such as flat feet, ankle instability, and excessive pronation (Bird and Payne, 1999, Botte, 1981) are among the factors highly linked with mechanical LBP.
There is an interaction between the mechanical abnormalities of the lower limb and the lower back segments (Bird and Payne, 1999, Botte, 1981). Throughout the gait cycle, excessive foot pronation results in altered alignments of the tibia (Levinger et al., 2012), femur (Souza et al., 2010), pelvis (Khamis and Yizhar, 2007), and lumbar spine (Bird et al., 2003, Khamis and Yizhar, 2007, Pinto et al., 2008), that lead to LBP.
Conversely, postural muscle weakness in the lower back (Barwick et al., 2012, Chuter and de Jonge, 2012), and mechanical LBP are associated with limited range of motion in the ankle as well as an increased navicular drop (Brantingham et al., 2007). This makes it difficult to conclude if foot abnormalities are the cause or consequences of LBP. However, it is widely believed that abnormal mechanical conditions of the lower limbs are highly linked with functional and mechanical LBP (Bird and Payne, 1999, Botte, 1981, Kendall et al., 2014).
Among the foot abnormalities, excessive foot pronation has received much clinical attention due to its high incidence (Castro-Méndez et al., 2013, Khamis and Yizhar, 2007, Pinto et al., 2008). Pronation or supination of the foot induced by the application of lateral or medial wedge cause internal or external rotation of tibia and femur, respectively (Duval et al., 2010, Pinto et al., 2008). Internal rotation of the tibia and femur that induce an anterior pelvis tilt (Betsch et al., 2012, Khamis and Yizhar, 2007), result in abnormal lower limb kinematics (Kendall et al., 2014, Müller et al., 2015, Seay et al., 2011), ground reaction forces (GRF) (Shum et al., 2007), muscle activities (Hanada et al., 2011, van der Hulst et al., 2010), and free moments (Bolgla et al., 2008, Li et al., 2001) during gait leading to LBP (Cambron et al., 2011).
The free moment corresponds to the torque about the vertical axis exerted on the foot and acting at the center of pressure (Holden and Cavanagh, 1991). It is assumed that during running, the shock forces transferred to the lumbar spine in individuals with pronated feet are higher than that in those with supinated feet (Kendall et al., 2014). In many LBP clinics, the treatment of foot abnormalities to improve gait pattern (Willy et al., 2012) is recommended as a part of rehabilitation protocol. However, recent reviews concluded that the link between LBP and foot attitude, particularly excessive pronation, has not been well documented (Kendall et al., 2014). To our knowledge, the kinematics and kinetics characteristics during walking of LBP patients with pronated feet have not previously been addressed. Many studies were carried out by normal individuals fitted with a wedge to induce a pronated foot anomaly (Betsch et al., 2012, Duval et al., 2010, Khamis and Yizhar, 2007, Ntousis et al., 2013, Pinto et al., 2008). Their conclusion can be difficult to apply to LBP subjects with pronated feet.
The objective of this study was to investigate the effects of excessive foot pronation on the GRF components in LBP patients during shod walking. This study helps to understand the interaction between LBP and foot pronation on altered biomechanics of walking. It is hypothesized that a) GRF components are altered in pronated foot subjects without LBP, b) the alteration of the GRF components on LBP patients with pronated foot is greater than that in pronated foot subjects without LBP.
Section snippets
Subjects
In this study, one control group (C), a group of subjects with pronated feet only (PF), and another group with pronated feet and LBP (PF+LBP), including 15 male subjects in each group, were studied. A prior statistical power analysis program (G*power) revealed that for a statistical power of 0.80 at an effect size of 0.80 with an alpha level of 0.05 a sample size of at least 13 subjects was required (Faul et al., 2007).
A subject was included in C group if he was between 20 to 30 years old, was
Results
The average walking speed, stance phase and step length were not significantly different between groups (Table 2). Fig. 2 illustrates GRF components of a control subject in a single trial for the three orientations. GRF variables for all groups are presented in Table 3. GRF amplitudes in Fz, Fy, and Fx (except for FxPO) were similar between C and PF groups (p>0.05). The FxPO in PF group was about 80% greater than that in CG (p=0.000). The PF+LBP group displayed greater FzHC and FzPO by 6% (p
Discussion
It was hypothesized that a) foot pronation affects GRF components during walking, and b) the alteration of the GRF components on LBP patients with pronated foot is greater than that in pronated foot subjects without LBP.
This study is the first to identify that FxPO amplitude and TTP of FzHC, FxHC, FyHC, as well as the propulsion impulse in PF group were significantly higher than those in C group. This proves the first hypothesis of this study and reveals that, the foot pronation alters the GRF
Conclusions
In subjects with foot pronation without LBP, vertical and posterior-anterior GRF were normal; but, lateral-medial GRF in push-off phase was altered. In LBP patients with pronated foot, the vertical GRF during heel contact and push-off, loading rate, and the adductor free moments were higher than those in pronated foot subjects without LBP. Whether these altered variable are the cause of LBP need to be assessed in further studies.
It is recommended to include gait parameters measurements in the
Conflict of interest statement
All authors declare no conflict of interests regarding the publication of this manuscript.
Acknowledgments
Authors gratefully thank Dr Ali Saleh, radiologist, for his valuable assistance. We also gratefully thank patients for their participation in this study. Authors did not receive any financial support for this study.
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