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The influence of foot posture on dorsiflexion range of motion and postural control in those with chronic ankle instability
Clinical Biomechanics 38 (2016) 63–67
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Clinical Biomechanics journal homepage: www.elsevier.com/locate/clinbiomech
The influence of foot posture on dorsiflexion range of motion and postural control in those with chronic ankle instability☆ Kathleen K. Hogan MSAT, ATC a, Cameron J. Powden PhD, ATC b,⁎, Matthew C. Hoch PhD, ATC c a b c
School of Physical Therapy and Athletic Training, Old Dominion University, 1121 Health Sciences Building, Norfolk, VA 23529, United States Department of Applied Medicine and Rehabilitation, Indiana State University, Arena B83, 401 North 4th Street, Terre Haute, IN 47809, United States School of Physical Therapy and Athletic Training, Old Dominion University, 3120 Health Sciences Building, Norfolk, VA 23529, United States
a r t i c l e
i n f o
Article history: Received 14 December 2015 Accepted 21 August 2016 Keywords: Chronic ankle instability Foot posture Postural control Dorsiflexion
a b s t r a c t Background: To investigate the effect of foot posture on postural control and dorsiflexion range of motion in individuals with chronic ankle instability. Methods: The study employed a cross-sectional, single-blinded design. Twenty-one individuals with self-reported chronic ankle instability (male = 5; age = 23.76(4.18)years; height = 169.27(11.46)cm; weight = 73.65(13.37)kg; number of past ankle sprains = 4.71(4.10); episode of giving way = 17.00(18.20); Cumberland Ankle Instability Score = 18.24(4.52); Ankle Instability Index = 5.86(1.39)) participated. The foot posture index was used to categorize subjects into pronated (n = 8; Foot Posture Index = 7.50(0.93)) and neutral (n = 13; Foot Posture Index = 3.08(1.93)) groups. The dependent variables of dorsiflexion ROM and dynamic and static postural control were collected for both groups at a single session. Findings: There were no significant differences in dorsiflexion range of motion between groups (p = 0.22) or any of the eyes open time-to-boundary variables (p N 0.13). The pronated group had significantly less dynamic postural control than the neutral group as assessed by the anterior direction of the Star Excursion Balance Test (p b 0.04). However, the pronated group had significantly higher time-to-boundary values than the neutral group for all eyes closed time-to-boundary variables (p ≤ 0.05), which indicates better eyes closed static postural control. Interpretation: Foot posture had a significant effect on dynamic postural control and eyes closed static postural control in individuals with chronic ankle instability. These findings suggest that foot posture may influence postural control in those with chronic ankle instability. © 2016 Elsevier Ltd. All rights reserved.
1. Introduction Lateral ankle sprains are among the most common injuries sustained by physically active populations (Beynnon et al., 2001; Hootman et al., 2007). Injury epidemiology studies have determined that approximately 12 ankle sprains occur per 1000 exposures to sport related activity (Doherty et al., 2014). Additionally, ankle sprains represent 15% to 44% of all injuries reported in collegiate and high school athletics, respectively (Agel et al., 2007; Kannus and Renstrom, 1991). Ankle sprains can create immediate as well as long-term disability that can affect recreational and occupational activity (Hiller et al., 2012; Verhagen et al., 1995). Up to 70% of those who sustain an ankle sprain will experience lingering symptoms of pain, swelling, ankle instability, and repetitive
☆ Acknowledgements: There were no funding sources or help outside of the authors on this project. ⁎ Corresponding author. E-mail addresses: [email protected] (K.K. Hogan), [email protected] (C.J. Powden), [email protected] (M.C. Hoch).
http://dx.doi.org/10.1016/j.clinbiomech.2016.08.010 0268-0033/© 2016 Elsevier Ltd. All rights reserved.
ankle sprains (Anandacoomarasamy and Barnsley, 2005). These recurrent symptoms are the primary characteristics of a condition known as chronic ankle instability (CAI) (Hertel, 2002). CAI has been associated with several contributing factors, which are broadly categorized as mechanical or functional impairments (Hertel, 2000). Several mechanical impairments; such as arthrokinematic restrictions, commonly manifest clinically as decreased dorsiflexion range of motion (ROM) (Hoch et al., 2012b). The functional impairments detected in individuals with CAI are alterations in proprioception and neuromuscular control (Hertel, 2002). The functional impairments associated with CAI commonly present as deficits in postural control (Arnold et al., 2009). In those with CAI, decreased dorsiflexion ROM has been shown to negatively affect gait, dynamic postural control, and landing suggesting there is an interaction between mechanical and functional impairments for many individuals (Drewes et al., 2009; Hoch et al., 2011). Although people with CAI commonly exhibit dorsiflexion and postural control deficits, it is unclear if there are additional factors that may influence these insufficiencies. There is evidence to suggest foot posture may influence several of the postural control and dorsiflexion ROM measurements used to
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examine individuals with CAI (Cote et al., 2005; Hertel et al., 2002; Tsai et al., 2006). Recent studies have demonstrated that healthy individuals with varying foot postures display differences in static and dynamic postural control (Cote et al., 2005; Hertel et al., 2002; Tsai et al., 2006). These differences in postural control may be due to variances in somatosensory feedback associated with different foot postures. Foot posture may also influence weight-bearing dorsiflexion ROM because of the involvement of the entire foot and ankle complex when performing this measurement (Burns, 2005). Currently there has been no published research that has examined the effect of foot posture on postural control or dorsiflexion ROM in individuals with CAI. It is important to investigate the role of foot posture on these measures because it could influence how we interpret these outcomes and plan rehabilitation for people with CAI. Therefore, the purpose of this study was to investigate the effect of foot posture on postural control and dorsiflexion ROM in individuals with CAI. It was hypothesized that deviations in foot posture would influence postural control and dorsiflexion ROM in individuals with CAI.
2. Methods 2.1. Design This study employed a blinded, cross-sectional design. The independent variable was foot posture and the dependent variables were dorsiflexion ROM, dynamic postural control, and static postural control. The Foot Posture Index-6 (FPI) categorized participants into the pronated or neutral groups. Dorsiflexion ROM was measured through the Weight-Bearing Lunge Test (WBLT). Dynamic postural control was measured using the anterior reach of the Star Excursion Balance Test (SEBT-ANT). Single-limb stance static postural control was measured using instrumented measures of center of pressure known as time-toboundary (TTB).
2.2. Subjects A convenience sample of twenty-one subjects was recruited through word of mouth and flyers around a large public university. All subjects provided written informed consent in compliance with the University's institutional review board. Subjects were included if they were between 18 and 45 years of age, had a history of ≥1 significant ankle sprain, had ≥2 episodes of giving way in the past three months, answered “yes” to ≥ 6 questions on the Ankle Instability Instrument (AII) (Redmond et al., 2006), ≤26 on the Cumberland Ankle Instability Tool (CAIT) (Hiller et al., 2006), and ≥15 on the Godin Leisure-Time Exercise Questionnaire (Godin and Shephard, 1985; Gribble et al., 2014). Subjects were excluded if they had an ankle sprain within the past six months, lower extremity injury within the past six months, lower extremity surgery, or had any health conditions known to affect balance. If a subject had bilateral CAI, the ankle with the lower CAIT score was included. After inclusion, the FPI categorized 13 subjects into the neutral group and eight into the pronated group (Table 1).
Table 1 Means and standard deviations of subject characteristics.
FPI Males/Females Age (years) Height (cm) Weight (kg) “Yes” on AII Previous ankles sprains CAIT GLEQ
Neutral (n = 13)
Pronated (n = 8)
p-Value
3.08 (1.93) 3/10 24.85 (4.78) 168.13 (10.07) 73.69 (13.99) 6.0 (1.53) 5.69 (4.94) 17.85 (5.15) 71.15 (54.08)
7.50 (0.93) 2/6 22.00 (2.27) 171.13 (13.96) 73.60 (13.25) 5.63 (1.19) 3.13 (1.25) 18.88 (3.52) 66.50 (25.43)
– – 0.13 0.57 0.99 0.56 0.17 0.63 0.82
FPI = Foot Posture Index; AII = Ankle Instability tool; CAIT = Cumberland Ankle Instability Instrument; GLEQ = Godin Leisure time-Exercise Questionnaire.
2.4. Foot posture A single FPI assessment with the subject standing in a relaxed double limb stance was used to assess foot posture. This technique has demonstrated excellent intra-rater reliability (ICC = 0.90) (Cornwall et al., 2008). The FPI is a scoring system that measures foot posture using a multifactorial approach. It incorporates the following six criteria: talar head palpation, supra and infra lateral malleolar curvature, calcaneal frontal plane position, prominence in the region of the talonavicular joint, congruence of the medial longitudinal arch, and abduction/adduction of the forefoot on the rearfoot which are scored individually (Cornwall et al., 2008; Redmond et al., 2006). Each of these criteria were scored individually based on a 5 point likert-type scale ranging from − 2 to 2 which are summed for a total score between 12 and − 12 (Redmond et al., 2006). Total scores are typically categorized into 5 categories: normal, 0 to + 5; pronated (+ 6 to + 9), highly pronated (+10 and above), supinated (−1 to −4), and highly supinated (−5 to −12) (Redmond, 1998). For this study, subjects were more broadly categorized into 3 categories: normal (0 to + 5), pronated (+ 6 to + 12), and supinated (− 1 to − 12). We chose to use a broad classification system due to the exploratory nature of this investigation. 2.5. Weight-bearing dorsiflexion ROM The WBLT was used to assess maximum weight-bearing dorsiflexion ROM (Fig. 1). This test has demonstrated excellent inter-rater reliability (ICC = 0.99) (Bennell et al., 1998). The WBLT involves subjects performing a modified knee to wall lunge. Each subject performed three practice trials followed by three trials recorded for analysis. During each trial, subjects were instructed to lunge forward until their knee contacted the wall while the heel remained in contact with the floor. Subjects were permitted to place their non-test limb in any comfortable position while having their hands lightly against the wall in front of them for balance. All subjects started with their great toe on a tape measure about three centimeters from the wall and were incrementally progressed further along the tape measure until their heel lifted or their knee did not contact the wall. Therefore, maximal dorsiflexion was considered the furthest point at which the subject was able to make knee contact with the wall while keeping their heel in contact with the ground. These methods were adapted from previous studies (Hoch, 2011).
2.3. Procedures 2.6. Dynamic postural control All data were collected during a single session. After inclusion was determined, a single investigator completed the FPI on the involved limb. Following foot posture assessment, dorsiflexion ROM, dynamic postural control, and static postural control were collected in a counterbalanced order. The investigator assessing foot posture was blinded to all other measures, while the investigators collecting dorsiflexion ROM and postural control measures were blinded to the group assignments throughout the study.
The SEBT-ANT was used to assess dynamic postural control and has demonstrated excellent inter-rater reliability (ICC = 0.88) (Gribble et al., 2013). Subjects performed four practice trials and three collection trials of SEBT-ANT. The SEBT-ANT was measured in centimeters by a tape measure secured to the floor. Foot length was measured on the involved limb and the second toe was placed on the tape measure at half the length of the foot. This position was recorded in the event the foot
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Fig. 1. The Weight-Bearing Lunge Test.
needed to be repositioned. Subjects were instructed to use the uninvolved leg to reach as far as possible along the tape measure, lightly tap the tape measure with their foot and then to return to the double limb stance position. A trial was discarded and repeated if their hands did not remain on their hips, weight was shifted to the reaching leg, the position of the stance foot was not maintained, their heel was not kept in contact with the floor, or if they did not maintain balanced during the full trial. The three collection trials were normalized to leg length (measured from the ASIS to the distal aspect of the medial malleolus) and averaged for analysis (Gribble et al., 2013). These procedures were based on previously described methods (Gribble et al., 2013). 2.7. Static postural control Single-limb stance static postural control was assessed using an Accusway Plus forceplate (AMTI; Watertown, MA) interfaced with a laptop using Balance Clinic software (AMTI; Watertown, MA). The width and length of the involved foot was measured to center the foot on the forceplate. Subjects completed one practice trial and three recorded trials for 10 s with their eyes open and closed. Subjects were instructed to stand as still as possible in a single limb stance position with their hands on their hips and the uninvolved limb at 45° of hip and knee flexion (Fig. 2). If subjects were unable to maintain the testing position, stepped down with the uninvolved limb, made contact between limbs, talked, or opened their eyes during an eyes closed trial the trial was discarded and repeated. All trials were sampled at 50 Hz. Center of pressure (COP) data points were calculated for anterior-posterior (AP) and medial-lateral (ML) directions. COP data along with the foot dimensions for each subject were used to calculate TTB measures using a custom MATLAB code (Version R2012a, MathWorks Inc., Natick, MA) based on previously described methods (Hertel and OlmstedKramer, 2007). TTB was analyzed as the mean of TTB minima (TTBmean) and the standard deviation of TTB minima (TTB-SD) in the AP
Fig. 2. Single-Limb Balance Task for Time-To-Boundary Calculation.
and ML directions (Hertel and Olmsted-Kramer, 2007). TTB-mean represents the estimated time a person has to make a postural correction before they reach the edge of their base of support. A greater TBBmean indicates that an individual has more to time to make a postural correction. TTB-SD is thought to refer to the number of strategies available to an individual to maintain their balance within their base of support. Theoretically, a higher SD of TTB would indicate that the individual has more available strategies to maintain their base of support which signifies a less constrained sensorimotor system (Hertel and OlmstedKramer, 2007).
2.8. Statistical analysis Due to the small sample size and non-normal distribution of the data, non-parametrics were used to describe and analyze the data. Descriptive statistics were calculated using median and interquartile range (IQR). Separate, Mann-Whitney U tests were used to examine each dependent variable for group differences. Alpha was set at a-priori p ≤ 0.05 for all analyses. Effect sizes (ES) were also calculated using the formula, r ¼ √zN , proposed by Cohen (1998). This was completed by
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using the associated Mann-Whitney U z value to calculate r. Positive effect sizes indicated greater postural control or dorsiflexion ROM and were interpreted as large (0.5), medium (0.3), and small (0.1) (Cohen, 1998). 3. Results There were no significant group differences between any demographic or inclusionary instruments (p N 0.05). No significant group differences were identified for the WBLT (p = 0.22, ES = 0.27) or the eyes open TTB variables: TTB-mean AP (p = 0.19, ES = −0.28), TTB-mean ML (p = 0.17, ES = − 0.33), TTB-SD AP (p = 0.35, ES = − 0.21) and TTB-SD ML (p = 0.17, ES = −0.30). The neutral group exhibited significantly greater dynamic postural control on the SEBT-ANT (p = 0.04, ES = 0.46) whereas the pronated group demonstrated significantly greater static postural control with eyes closed TTB-mean AP (p = 0.02, ES = −0.51), TTB-mean ML (p = 0.05, ES = −0.43), TTB-SD AP (p = 0.05, ES = −0.43), and TTB-SD ML (p = 0.04, ES = −0.44). Medians, IQR, and effect sizes are presented in Tables 2, 3, and 4. 4. Discussion The main finding of this study was that foot posture had an effect on static and dynamic postural control but does not influence weight-bearing dorsiflexion ROM in individuals with CAI. These findings partially support our hypothesis that foot posture influences postural control and dorsiflexion ROM in individuals with CAI. Individuals in the pronated group had significantly better static postural control in the eyes closed condition compared to the neutral group (ES b −0.43). In contrast, the pronated group displayed poorer dynamic postural control compared to the neutral group (ES = 0.46). Overall, these findings suggest that foot posture may influence postural control in those with CAI, however, further research is needed to confirm the extent of this association. This study did not identify a statistically significant difference in maximal weight-bearing dorsiflexion ROM between people in the neutral and pronated groups. Currently, there is little evidence that has explored differences in weight-bearing dorsiflexion ROM related to foot posture. A recent study determined that compared to a neutral group, supinators displayed shorter lunge distances while pronators displayed greater lunge distances on the WBLT (Burns, 2005). These results contradict the current study, which could be the result of different methods of categorizing foot posture and because healthy subjects were the population of interest. However, the previous study (Burns, 2005) had low power in the pronator group (n = 5), thus a true representation of dorsiflexion ROM in pronators may not have been captured. In the current study, the median WBLT values were comparable to values previously reported for CAI participants in the literature; however, it should be noted there was 3 cm median difference between groups. Furthermore, there was a much larger dispersion of values in the neutral group, which may have detracted from the ability to detect group differences. Therefore, more evidence is needed to determine how deviations in foot posture affect dorsiflexion ROM in people with CAI as well as other populations. Despite the lack of group differences in weight-bearing dorsiflexion, foot posture had a significant effect on dynamic postural control. The neutral group displayed significantly larger normalized reach distances on the SEBT-ANT, which indicated better dynamic postural control in
Table 3 Median ± Interquartile Ranges, p-values, and effect size for eyes open TTB measures. Variable
Neutral
Pronated
p-Value
Effect Size
TTB-mean AP (s) TTB-mean ML (s) TTB-SD AP (s) TTB-SD ML (s)
4.67 (2.35) 1.50 (0.72) 2.78 (1.32) 1.08 (1.16)
5.29 (2.05) 1.80 (1.09) 3.53 (1.99) 1.40 (1.06)
0.19 0.13 0.35 0.17
-0.28 -0.33 -0.21 -0.30
comparison to the pronator group. This was also supported by a medium effect size. The median difference between groups was 6% of normalized reach distance which is likely not only statistically significant but clinically relevant due this difference being greater than the error associated with the test reported as 1.56% (Hoch et al., 2012a). It was previously determined that healthy people with a pronated foot posture had significantly larger SEBT-ANT reach distances than people with a neutral posture (Cote et al., 2005). The contradictory results may be because the navicular drop test was used to classify foot posture and because the study focused on healthy subjects. Therefore, it is possible that effect of foot posture on dynamic postural control may be condition specific. The pronator group exhibited significantly greater TTB-mean values and TTB-SD values during the eyes closed condition when compared to the neutral group. These greater TTB-values indicate that the pronator group had significantly greater static postural control. Group differences in the eyes closed condition were accompanied by medium to large effect sizes (−0.43 to −0.51) indicating these are likely clinically relevant differences. Despite the differences exhibited in the eyes closed condition, there were no significant differences between groups for the eyes open condition indicating there is a unique interaction between foot posture, vision, and somatosensory input from the plantar surface. Previous research regarding the influence of foot posture on static postural control has provided mixed results. However, a recent study identified decreases in medial longitudinal arch height were accompanied by greater TTB values in the ML direction (Cobb et al., 2014). These researchers concluded that people with a pronated foot posture could have a sensorimotor advantage. In people with a pronated foot posture, decreased medial longitudinal arch height and midfoot hypermobility may allow more skin contact with the ground and added cutaneous receptor contact with the environment. This increase in contact area may allow more sensory information to be incorporated into strategies for making postural corrections, which could explain the better static postural control among the pronated group. The ability to have more sensory information may be particularly advantageous in the eyes closed condition because the reliance on somatosensory input may be increased in the presence of the loss of vision. This study demonstrated that foot posture may contribute to the assessment of both static and dynamic postural control within people with CAI. Therefore, addressing foot posture from both a functional and mechanical perspective may enhance the rehabilitation outcomes for these individuals (Mulligan and Cook, 2013; Sesma et al., 2008). Functionally, short foot exercises target the intrinsic muscle of the medial longitudinal arch as to improve the dynamic support of the foot (Mulligan and Cook, 2013). A four week short foot exercise program has demonstrated efficacy to increase arch height, a modification of foot posture, as well as improve dynamic postural control (Mulligan
Table 4 Median ± Interquartile Ranges, p-values, and effect size for eyes closed TTB measures. Table 2 Median ± Interquartile Ranges and p-values for WBLT and SEBT-ANT.
Variable
Variable
Neutral
Pronated
p-Value
Effect Size
WBLT (cm) SEBT-ANT (%)
10.60 (7.38) 0.75 (0.6)
7.52 (2.63) 0.69 (0.10)
0.22 0.04⁎
0.27 0.46
⁎ Denotes significant differences between neutral and pronated groups (p ≤ 0.05).
TTB-mean AP (s) TTB-mean ML (s) TTB-SD AP (s) TTB-SD ML (s)
Neutral 1.83 (0.56) 0.53 (0.14) 1.25 (0.51) 0.39 (0.22)
Pronated
p-Value
Effect size
2.54 (0.57) 0.84 (0.28) 1.59 (0.71) 0.76 (0.51)
0.02⁎ 0.05⁎ 0.05⁎ 0.04⁎
-0.51 -0.43 -0.43 -0.44
⁎ Denotes significant differences between neutral and pronated groups (p ≤ 0.05).
K.K. Hogan et al. / Clinical Biomechanics 38 (2016) 63–67
and Cook, 2013). Mechanically, foot orthotics can be utilized to artificially increase and support arch height (Sesma et al., 2008). A recent critically appraised topic determined that there is moderate evidence that orthotic interventions can improve postural control (Gabriner et al., 2015) in people with CAI. Collectively, the aforementioned studies strengthen the notion that foot posture and postural control are likely connected. Furthermore, the postural control may be clinically modified through various foot posture interventions. These findings indicate that there may be a need for clinicians and researchers to measure foot posture when assessing postural control in individuals with CAI. This study is limited because we chose to combine foot posture subgroups, did not include pronated foot types in our analysis, and due to the relatively small sample size obtained which could lead to the incidence of type 1 error. Future research should incorporate a larger sample and include the original foot posture subgroups described by Redmond (1998). Additionally, this study was retrospective which does not permit causal links to be established between any of the measures included in this study and the development or progression of CAI. Prospective studies which include interventions to alter foot posture may provide additional insight into strategies for addressing CAI. Furthermore, prospective investigations regarding the efficacy of targeted foot posture interventions should be completed to further the link between foot posture modification and subsequent postural control changes as to further the available treatment modalities for those with CAI. Conflict of interest statement There were no conflicts of interest. Acknowledgments There are no acknowledgments to be made. References Agel, J., Palmieri-Smith, R.M., Dick, R., Wojtys, E.M., Marshall, S.W., 2007. Descriptive epidemiology of collegiate women's volleyball injuries: National Collegiate Athletic Association Injury Surveillance System, 1988–1989 through 2003–2004. J. Athl. Train. 42, 295–302. Anandacoomarasamy, A., Barnsley, L., 2005. Long term outcomes of inversion ankle injuries. Br. J. Sports Med. 39, e14 (discussion e14). Arnold, B.L., De La Motte, S., Linens, S., Ross, S.E., 2009. Ankle instability is associated with balance impairments: a meta-analysis. Med. Sci. Sports Exerc. 4, 1048–1062. Bennell, K.L., Talbot, R.C., Wajswelner, H., Techovanich, W., Kelly, D.H., Hall, A.J., 1998. Intra-rater and inter-rater reliability of a weight-bearing lunge measure of ankle dorsiflexion. Aust. J. Physiother. 44, 175–180. Beynnon, B.D., Renstrom, P.A., Alosa, D.M., Baumhauer, J.F., Vacek, P.M., 2001. Ankle ligament injury risk factors: a prospective study of college athletes. J. Orthop. Res. 19, 213–220. Burns, J.C.J., 2005. Weight bearing ankle dorsiflexion range of motion in idiopathic pes cavus compared to normal and pes planus feet. Foot 15, 91–94. Cobb, S.C., Bazett-Jones, D.M., Joshi, M.N., Earl-Boehm, J.E., James, C.R., 2014. The relationship among foot posture, core and lower extremity muscle function, and postural stability. J. Athl. Train. 49, 173–180. Cohen, J., 1998. Statistical Power Analysis for the Behavioral Sciences. 2nd ed. Lawrence Erlbaum, Hillsdale,NJ.
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Clinical Biomechanics journal homepage: www.elsevier.com/locate/clinbiomech
The influence of foot posture on dorsiflexion range of motion and postural control in those with chronic ankle instability☆ Kathleen K. Hogan MSAT, ATC a, Cameron J. Powden PhD, ATC b,⁎, Matthew C. Hoch PhD, ATC c a b c
School of Physical Therapy and Athletic Training, Old Dominion University, 1121 Health Sciences Building, Norfolk, VA 23529, United States Department of Applied Medicine and Rehabilitation, Indiana State University, Arena B83, 401 North 4th Street, Terre Haute, IN 47809, United States School of Physical Therapy and Athletic Training, Old Dominion University, 3120 Health Sciences Building, Norfolk, VA 23529, United States
a r t i c l e
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Article history: Received 14 December 2015 Accepted 21 August 2016 Keywords: Chronic ankle instability Foot posture Postural control Dorsiflexion
a b s t r a c t Background: To investigate the effect of foot posture on postural control and dorsiflexion range of motion in individuals with chronic ankle instability. Methods: The study employed a cross-sectional, single-blinded design. Twenty-one individuals with self-reported chronic ankle instability (male = 5; age = 23.76(4.18)years; height = 169.27(11.46)cm; weight = 73.65(13.37)kg; number of past ankle sprains = 4.71(4.10); episode of giving way = 17.00(18.20); Cumberland Ankle Instability Score = 18.24(4.52); Ankle Instability Index = 5.86(1.39)) participated. The foot posture index was used to categorize subjects into pronated (n = 8; Foot Posture Index = 7.50(0.93)) and neutral (n = 13; Foot Posture Index = 3.08(1.93)) groups. The dependent variables of dorsiflexion ROM and dynamic and static postural control were collected for both groups at a single session. Findings: There were no significant differences in dorsiflexion range of motion between groups (p = 0.22) or any of the eyes open time-to-boundary variables (p N 0.13). The pronated group had significantly less dynamic postural control than the neutral group as assessed by the anterior direction of the Star Excursion Balance Test (p b 0.04). However, the pronated group had significantly higher time-to-boundary values than the neutral group for all eyes closed time-to-boundary variables (p ≤ 0.05), which indicates better eyes closed static postural control. Interpretation: Foot posture had a significant effect on dynamic postural control and eyes closed static postural control in individuals with chronic ankle instability. These findings suggest that foot posture may influence postural control in those with chronic ankle instability. © 2016 Elsevier Ltd. All rights reserved.
1. Introduction Lateral ankle sprains are among the most common injuries sustained by physically active populations (Beynnon et al., 2001; Hootman et al., 2007). Injury epidemiology studies have determined that approximately 12 ankle sprains occur per 1000 exposures to sport related activity (Doherty et al., 2014). Additionally, ankle sprains represent 15% to 44% of all injuries reported in collegiate and high school athletics, respectively (Agel et al., 2007; Kannus and Renstrom, 1991). Ankle sprains can create immediate as well as long-term disability that can affect recreational and occupational activity (Hiller et al., 2012; Verhagen et al., 1995). Up to 70% of those who sustain an ankle sprain will experience lingering symptoms of pain, swelling, ankle instability, and repetitive
☆ Acknowledgements: There were no funding sources or help outside of the authors on this project. ⁎ Corresponding author. E-mail addresses: [email protected] (K.K. Hogan), [email protected] (C.J. Powden), [email protected] (M.C. Hoch).
http://dx.doi.org/10.1016/j.clinbiomech.2016.08.010 0268-0033/© 2016 Elsevier Ltd. All rights reserved.
ankle sprains (Anandacoomarasamy and Barnsley, 2005). These recurrent symptoms are the primary characteristics of a condition known as chronic ankle instability (CAI) (Hertel, 2002). CAI has been associated with several contributing factors, which are broadly categorized as mechanical or functional impairments (Hertel, 2000). Several mechanical impairments; such as arthrokinematic restrictions, commonly manifest clinically as decreased dorsiflexion range of motion (ROM) (Hoch et al., 2012b). The functional impairments detected in individuals with CAI are alterations in proprioception and neuromuscular control (Hertel, 2002). The functional impairments associated with CAI commonly present as deficits in postural control (Arnold et al., 2009). In those with CAI, decreased dorsiflexion ROM has been shown to negatively affect gait, dynamic postural control, and landing suggesting there is an interaction between mechanical and functional impairments for many individuals (Drewes et al., 2009; Hoch et al., 2011). Although people with CAI commonly exhibit dorsiflexion and postural control deficits, it is unclear if there are additional factors that may influence these insufficiencies. There is evidence to suggest foot posture may influence several of the postural control and dorsiflexion ROM measurements used to
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examine individuals with CAI (Cote et al., 2005; Hertel et al., 2002; Tsai et al., 2006). Recent studies have demonstrated that healthy individuals with varying foot postures display differences in static and dynamic postural control (Cote et al., 2005; Hertel et al., 2002; Tsai et al., 2006). These differences in postural control may be due to variances in somatosensory feedback associated with different foot postures. Foot posture may also influence weight-bearing dorsiflexion ROM because of the involvement of the entire foot and ankle complex when performing this measurement (Burns, 2005). Currently there has been no published research that has examined the effect of foot posture on postural control or dorsiflexion ROM in individuals with CAI. It is important to investigate the role of foot posture on these measures because it could influence how we interpret these outcomes and plan rehabilitation for people with CAI. Therefore, the purpose of this study was to investigate the effect of foot posture on postural control and dorsiflexion ROM in individuals with CAI. It was hypothesized that deviations in foot posture would influence postural control and dorsiflexion ROM in individuals with CAI.
2. Methods 2.1. Design This study employed a blinded, cross-sectional design. The independent variable was foot posture and the dependent variables were dorsiflexion ROM, dynamic postural control, and static postural control. The Foot Posture Index-6 (FPI) categorized participants into the pronated or neutral groups. Dorsiflexion ROM was measured through the Weight-Bearing Lunge Test (WBLT). Dynamic postural control was measured using the anterior reach of the Star Excursion Balance Test (SEBT-ANT). Single-limb stance static postural control was measured using instrumented measures of center of pressure known as time-toboundary (TTB).
2.2. Subjects A convenience sample of twenty-one subjects was recruited through word of mouth and flyers around a large public university. All subjects provided written informed consent in compliance with the University's institutional review board. Subjects were included if they were between 18 and 45 years of age, had a history of ≥1 significant ankle sprain, had ≥2 episodes of giving way in the past three months, answered “yes” to ≥ 6 questions on the Ankle Instability Instrument (AII) (Redmond et al., 2006), ≤26 on the Cumberland Ankle Instability Tool (CAIT) (Hiller et al., 2006), and ≥15 on the Godin Leisure-Time Exercise Questionnaire (Godin and Shephard, 1985; Gribble et al., 2014). Subjects were excluded if they had an ankle sprain within the past six months, lower extremity injury within the past six months, lower extremity surgery, or had any health conditions known to affect balance. If a subject had bilateral CAI, the ankle with the lower CAIT score was included. After inclusion, the FPI categorized 13 subjects into the neutral group and eight into the pronated group (Table 1).
Table 1 Means and standard deviations of subject characteristics.
FPI Males/Females Age (years) Height (cm) Weight (kg) “Yes” on AII Previous ankles sprains CAIT GLEQ
Neutral (n = 13)
Pronated (n = 8)
p-Value
3.08 (1.93) 3/10 24.85 (4.78) 168.13 (10.07) 73.69 (13.99) 6.0 (1.53) 5.69 (4.94) 17.85 (5.15) 71.15 (54.08)
7.50 (0.93) 2/6 22.00 (2.27) 171.13 (13.96) 73.60 (13.25) 5.63 (1.19) 3.13 (1.25) 18.88 (3.52) 66.50 (25.43)
– – 0.13 0.57 0.99 0.56 0.17 0.63 0.82
FPI = Foot Posture Index; AII = Ankle Instability tool; CAIT = Cumberland Ankle Instability Instrument; GLEQ = Godin Leisure time-Exercise Questionnaire.
2.4. Foot posture A single FPI assessment with the subject standing in a relaxed double limb stance was used to assess foot posture. This technique has demonstrated excellent intra-rater reliability (ICC = 0.90) (Cornwall et al., 2008). The FPI is a scoring system that measures foot posture using a multifactorial approach. It incorporates the following six criteria: talar head palpation, supra and infra lateral malleolar curvature, calcaneal frontal plane position, prominence in the region of the talonavicular joint, congruence of the medial longitudinal arch, and abduction/adduction of the forefoot on the rearfoot which are scored individually (Cornwall et al., 2008; Redmond et al., 2006). Each of these criteria were scored individually based on a 5 point likert-type scale ranging from − 2 to 2 which are summed for a total score between 12 and − 12 (Redmond et al., 2006). Total scores are typically categorized into 5 categories: normal, 0 to + 5; pronated (+ 6 to + 9), highly pronated (+10 and above), supinated (−1 to −4), and highly supinated (−5 to −12) (Redmond, 1998). For this study, subjects were more broadly categorized into 3 categories: normal (0 to + 5), pronated (+ 6 to + 12), and supinated (− 1 to − 12). We chose to use a broad classification system due to the exploratory nature of this investigation. 2.5. Weight-bearing dorsiflexion ROM The WBLT was used to assess maximum weight-bearing dorsiflexion ROM (Fig. 1). This test has demonstrated excellent inter-rater reliability (ICC = 0.99) (Bennell et al., 1998). The WBLT involves subjects performing a modified knee to wall lunge. Each subject performed three practice trials followed by three trials recorded for analysis. During each trial, subjects were instructed to lunge forward until their knee contacted the wall while the heel remained in contact with the floor. Subjects were permitted to place their non-test limb in any comfortable position while having their hands lightly against the wall in front of them for balance. All subjects started with their great toe on a tape measure about three centimeters from the wall and were incrementally progressed further along the tape measure until their heel lifted or their knee did not contact the wall. Therefore, maximal dorsiflexion was considered the furthest point at which the subject was able to make knee contact with the wall while keeping their heel in contact with the ground. These methods were adapted from previous studies (Hoch, 2011).
2.3. Procedures 2.6. Dynamic postural control All data were collected during a single session. After inclusion was determined, a single investigator completed the FPI on the involved limb. Following foot posture assessment, dorsiflexion ROM, dynamic postural control, and static postural control were collected in a counterbalanced order. The investigator assessing foot posture was blinded to all other measures, while the investigators collecting dorsiflexion ROM and postural control measures were blinded to the group assignments throughout the study.
The SEBT-ANT was used to assess dynamic postural control and has demonstrated excellent inter-rater reliability (ICC = 0.88) (Gribble et al., 2013). Subjects performed four practice trials and three collection trials of SEBT-ANT. The SEBT-ANT was measured in centimeters by a tape measure secured to the floor. Foot length was measured on the involved limb and the second toe was placed on the tape measure at half the length of the foot. This position was recorded in the event the foot
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Fig. 1. The Weight-Bearing Lunge Test.
needed to be repositioned. Subjects were instructed to use the uninvolved leg to reach as far as possible along the tape measure, lightly tap the tape measure with their foot and then to return to the double limb stance position. A trial was discarded and repeated if their hands did not remain on their hips, weight was shifted to the reaching leg, the position of the stance foot was not maintained, their heel was not kept in contact with the floor, or if they did not maintain balanced during the full trial. The three collection trials were normalized to leg length (measured from the ASIS to the distal aspect of the medial malleolus) and averaged for analysis (Gribble et al., 2013). These procedures were based on previously described methods (Gribble et al., 2013). 2.7. Static postural control Single-limb stance static postural control was assessed using an Accusway Plus forceplate (AMTI; Watertown, MA) interfaced with a laptop using Balance Clinic software (AMTI; Watertown, MA). The width and length of the involved foot was measured to center the foot on the forceplate. Subjects completed one practice trial and three recorded trials for 10 s with their eyes open and closed. Subjects were instructed to stand as still as possible in a single limb stance position with their hands on their hips and the uninvolved limb at 45° of hip and knee flexion (Fig. 2). If subjects were unable to maintain the testing position, stepped down with the uninvolved limb, made contact between limbs, talked, or opened their eyes during an eyes closed trial the trial was discarded and repeated. All trials were sampled at 50 Hz. Center of pressure (COP) data points were calculated for anterior-posterior (AP) and medial-lateral (ML) directions. COP data along with the foot dimensions for each subject were used to calculate TTB measures using a custom MATLAB code (Version R2012a, MathWorks Inc., Natick, MA) based on previously described methods (Hertel and OlmstedKramer, 2007). TTB was analyzed as the mean of TTB minima (TTBmean) and the standard deviation of TTB minima (TTB-SD) in the AP
Fig. 2. Single-Limb Balance Task for Time-To-Boundary Calculation.
and ML directions (Hertel and Olmsted-Kramer, 2007). TTB-mean represents the estimated time a person has to make a postural correction before they reach the edge of their base of support. A greater TBBmean indicates that an individual has more to time to make a postural correction. TTB-SD is thought to refer to the number of strategies available to an individual to maintain their balance within their base of support. Theoretically, a higher SD of TTB would indicate that the individual has more available strategies to maintain their base of support which signifies a less constrained sensorimotor system (Hertel and OlmstedKramer, 2007).
2.8. Statistical analysis Due to the small sample size and non-normal distribution of the data, non-parametrics were used to describe and analyze the data. Descriptive statistics were calculated using median and interquartile range (IQR). Separate, Mann-Whitney U tests were used to examine each dependent variable for group differences. Alpha was set at a-priori p ≤ 0.05 for all analyses. Effect sizes (ES) were also calculated using the formula, r ¼ √zN , proposed by Cohen (1998). This was completed by
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using the associated Mann-Whitney U z value to calculate r. Positive effect sizes indicated greater postural control or dorsiflexion ROM and were interpreted as large (0.5), medium (0.3), and small (0.1) (Cohen, 1998). 3. Results There were no significant group differences between any demographic or inclusionary instruments (p N 0.05). No significant group differences were identified for the WBLT (p = 0.22, ES = 0.27) or the eyes open TTB variables: TTB-mean AP (p = 0.19, ES = −0.28), TTB-mean ML (p = 0.17, ES = − 0.33), TTB-SD AP (p = 0.35, ES = − 0.21) and TTB-SD ML (p = 0.17, ES = −0.30). The neutral group exhibited significantly greater dynamic postural control on the SEBT-ANT (p = 0.04, ES = 0.46) whereas the pronated group demonstrated significantly greater static postural control with eyes closed TTB-mean AP (p = 0.02, ES = −0.51), TTB-mean ML (p = 0.05, ES = −0.43), TTB-SD AP (p = 0.05, ES = −0.43), and TTB-SD ML (p = 0.04, ES = −0.44). Medians, IQR, and effect sizes are presented in Tables 2, 3, and 4. 4. Discussion The main finding of this study was that foot posture had an effect on static and dynamic postural control but does not influence weight-bearing dorsiflexion ROM in individuals with CAI. These findings partially support our hypothesis that foot posture influences postural control and dorsiflexion ROM in individuals with CAI. Individuals in the pronated group had significantly better static postural control in the eyes closed condition compared to the neutral group (ES b −0.43). In contrast, the pronated group displayed poorer dynamic postural control compared to the neutral group (ES = 0.46). Overall, these findings suggest that foot posture may influence postural control in those with CAI, however, further research is needed to confirm the extent of this association. This study did not identify a statistically significant difference in maximal weight-bearing dorsiflexion ROM between people in the neutral and pronated groups. Currently, there is little evidence that has explored differences in weight-bearing dorsiflexion ROM related to foot posture. A recent study determined that compared to a neutral group, supinators displayed shorter lunge distances while pronators displayed greater lunge distances on the WBLT (Burns, 2005). These results contradict the current study, which could be the result of different methods of categorizing foot posture and because healthy subjects were the population of interest. However, the previous study (Burns, 2005) had low power in the pronator group (n = 5), thus a true representation of dorsiflexion ROM in pronators may not have been captured. In the current study, the median WBLT values were comparable to values previously reported for CAI participants in the literature; however, it should be noted there was 3 cm median difference between groups. Furthermore, there was a much larger dispersion of values in the neutral group, which may have detracted from the ability to detect group differences. Therefore, more evidence is needed to determine how deviations in foot posture affect dorsiflexion ROM in people with CAI as well as other populations. Despite the lack of group differences in weight-bearing dorsiflexion, foot posture had a significant effect on dynamic postural control. The neutral group displayed significantly larger normalized reach distances on the SEBT-ANT, which indicated better dynamic postural control in
Table 3 Median ± Interquartile Ranges, p-values, and effect size for eyes open TTB measures. Variable
Neutral
Pronated
p-Value
Effect Size
TTB-mean AP (s) TTB-mean ML (s) TTB-SD AP (s) TTB-SD ML (s)
4.67 (2.35) 1.50 (0.72) 2.78 (1.32) 1.08 (1.16)
5.29 (2.05) 1.80 (1.09) 3.53 (1.99) 1.40 (1.06)
0.19 0.13 0.35 0.17
-0.28 -0.33 -0.21 -0.30
comparison to the pronator group. This was also supported by a medium effect size. The median difference between groups was 6% of normalized reach distance which is likely not only statistically significant but clinically relevant due this difference being greater than the error associated with the test reported as 1.56% (Hoch et al., 2012a). It was previously determined that healthy people with a pronated foot posture had significantly larger SEBT-ANT reach distances than people with a neutral posture (Cote et al., 2005). The contradictory results may be because the navicular drop test was used to classify foot posture and because the study focused on healthy subjects. Therefore, it is possible that effect of foot posture on dynamic postural control may be condition specific. The pronator group exhibited significantly greater TTB-mean values and TTB-SD values during the eyes closed condition when compared to the neutral group. These greater TTB-values indicate that the pronator group had significantly greater static postural control. Group differences in the eyes closed condition were accompanied by medium to large effect sizes (−0.43 to −0.51) indicating these are likely clinically relevant differences. Despite the differences exhibited in the eyes closed condition, there were no significant differences between groups for the eyes open condition indicating there is a unique interaction between foot posture, vision, and somatosensory input from the plantar surface. Previous research regarding the influence of foot posture on static postural control has provided mixed results. However, a recent study identified decreases in medial longitudinal arch height were accompanied by greater TTB values in the ML direction (Cobb et al., 2014). These researchers concluded that people with a pronated foot posture could have a sensorimotor advantage. In people with a pronated foot posture, decreased medial longitudinal arch height and midfoot hypermobility may allow more skin contact with the ground and added cutaneous receptor contact with the environment. This increase in contact area may allow more sensory information to be incorporated into strategies for making postural corrections, which could explain the better static postural control among the pronated group. The ability to have more sensory information may be particularly advantageous in the eyes closed condition because the reliance on somatosensory input may be increased in the presence of the loss of vision. This study demonstrated that foot posture may contribute to the assessment of both static and dynamic postural control within people with CAI. Therefore, addressing foot posture from both a functional and mechanical perspective may enhance the rehabilitation outcomes for these individuals (Mulligan and Cook, 2013; Sesma et al., 2008). Functionally, short foot exercises target the intrinsic muscle of the medial longitudinal arch as to improve the dynamic support of the foot (Mulligan and Cook, 2013). A four week short foot exercise program has demonstrated efficacy to increase arch height, a modification of foot posture, as well as improve dynamic postural control (Mulligan
Table 4 Median ± Interquartile Ranges, p-values, and effect size for eyes closed TTB measures. Table 2 Median ± Interquartile Ranges and p-values for WBLT and SEBT-ANT.
Variable
Variable
Neutral
Pronated
p-Value
Effect Size
WBLT (cm) SEBT-ANT (%)
10.60 (7.38) 0.75 (0.6)
7.52 (2.63) 0.69 (0.10)
0.22 0.04⁎
0.27 0.46
⁎ Denotes significant differences between neutral and pronated groups (p ≤ 0.05).
TTB-mean AP (s) TTB-mean ML (s) TTB-SD AP (s) TTB-SD ML (s)
Neutral 1.83 (0.56) 0.53 (0.14) 1.25 (0.51) 0.39 (0.22)
Pronated
p-Value
Effect size
2.54 (0.57) 0.84 (0.28) 1.59 (0.71) 0.76 (0.51)
0.02⁎ 0.05⁎ 0.05⁎ 0.04⁎
-0.51 -0.43 -0.43 -0.44
⁎ Denotes significant differences between neutral and pronated groups (p ≤ 0.05).
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and Cook, 2013). Mechanically, foot orthotics can be utilized to artificially increase and support arch height (Sesma et al., 2008). A recent critically appraised topic determined that there is moderate evidence that orthotic interventions can improve postural control (Gabriner et al., 2015) in people with CAI. Collectively, the aforementioned studies strengthen the notion that foot posture and postural control are likely connected. Furthermore, the postural control may be clinically modified through various foot posture interventions. These findings indicate that there may be a need for clinicians and researchers to measure foot posture when assessing postural control in individuals with CAI. This study is limited because we chose to combine foot posture subgroups, did not include pronated foot types in our analysis, and due to the relatively small sample size obtained which could lead to the incidence of type 1 error. Future research should incorporate a larger sample and include the original foot posture subgroups described by Redmond (1998). Additionally, this study was retrospective which does not permit causal links to be established between any of the measures included in this study and the development or progression of CAI. Prospective studies which include interventions to alter foot posture may provide additional insight into strategies for addressing CAI. Furthermore, prospective investigations regarding the efficacy of targeted foot posture interventions should be completed to further the link between foot posture modification and subsequent postural control changes as to further the available treatment modalities for those with CAI. Conflict of interest statement There were no conflicts of interest. Acknowledgments There are no acknowledgments to be made. References Agel, J., Palmieri-Smith, R.M., Dick, R., Wojtys, E.M., Marshall, S.W., 2007. Descriptive epidemiology of collegiate women's volleyball injuries: National Collegiate Athletic Association Injury Surveillance System, 1988–1989 through 2003–2004. J. Athl. Train. 42, 295–302. Anandacoomarasamy, A., Barnsley, L., 2005. Long term outcomes of inversion ankle injuries. Br. J. Sports Med. 39, e14 (discussion e14). Arnold, B.L., De La Motte, S., Linens, S., Ross, S.E., 2009. Ankle instability is associated with balance impairments: a meta-analysis. Med. Sci. Sports Exerc. 4, 1048–1062. Bennell, K.L., Talbot, R.C., Wajswelner, H., Techovanich, W., Kelly, D.H., Hall, A.J., 1998. Intra-rater and inter-rater reliability of a weight-bearing lunge measure of ankle dorsiflexion. Aust. J. Physiother. 44, 175–180. Beynnon, B.D., Renstrom, P.A., Alosa, D.M., Baumhauer, J.F., Vacek, P.M., 2001. Ankle ligament injury risk factors: a prospective study of college athletes. J. Orthop. Res. 19, 213–220. Burns, J.C.J., 2005. Weight bearing ankle dorsiflexion range of motion in idiopathic pes cavus compared to normal and pes planus feet. Foot 15, 91–94. Cobb, S.C., Bazett-Jones, D.M., Joshi, M.N., Earl-Boehm, J.E., James, C.R., 2014. The relationship among foot posture, core and lower extremity muscle function, and postural stability. J. Athl. Train. 49, 173–180. Cohen, J., 1998. Statistical Power Analysis for the Behavioral Sciences. 2nd ed. Lawrence Erlbaum, Hillsdale,NJ.
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