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GAIPOS-4450; No. of Pages 5 Gait & Posture xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Gait & Posture journal homepage: www.elsevier.com/locate/gaitpost
Contributing factors to Star Excursion Balance Test performance in individuals with chronic ankle instability Michael L. Gabriner a, Megan N. Houston b,*, Jessica L. Kirby c, Matthew C. Hoch d a
The Steadman Clinic, 181 W. Meadow Dr. Suite 400, Vail, CO 81657, United States Department of Interdisciplinary Health Sciences, A.T. Still University, 5850 E. Still Circle, Mesa, AZ 85206, United States c School of Physical Education, Sport, and Exercise Science, Ball State University, 2000 W University Ave, Muncie, IN 47306, United States d School of Physical Therapy & Athletic Training, Old Dominion University, 102 Health Sciences Annex, Norfolk, VA 23529, United States b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 9 November 2014 Received in revised form 11 March 2015 Accepted 20 March 2015
The purpose of this study was to determine the contributions of strength, dorsiflexion range of motion (DFROM), plantar cutaneous sensation (PCS), and static postural control to Star Excursion Balance Test (SEBT) performance in individuals with chronic ankle instability (CAI). Forty individuals with CAI completed isometric strength, weight-bearing DFROM, PCS, static and dynamic balance assessments. Three separate backward multiple linear regression models were calculated to determine how strength, DFROM, PCS, and static postural control contributed to each reach direction of the SEBT. Explanatory variables included dorsiflexion, inversion, and eversion strength, DFROM, PCS, and time-to-boundary mean minima (TTBMM) and standard deviation (TTBSD) in the medial–lateral (ML) and anterior– posterior (AP) directions. Criterion variables included SEBT-anterior, posteromedial, and posterolateral directions. The strength of each model was determined by the R2-value and Cohen’s f2 effect size. Regression models with an effect size 0.15 were considered clinically relevant. All three SEBT directions produced clinically relevant regression models. DFROM and PCS accounted for 16% of the variance in SEBT-anterior reach (f2 = 0.19, p = 0.04). Eversion strength and TTBMM-ML accounted for 28% of the variance in SEBT-posteromedial reach (f2 = 0.39, p < 0.01). Eversion strength and TTBSD-ML accounted for 14% of the variance in SEBT-posterolateral reach (f2 = 0.16, p = 0.06). DFROM and PCS explained a clinically relevant proportion of the variance associated with SEBT-anterior reach. Eversion strength and TTB ML explained a clinically relevant proportion of the variance in SEBT-posteromedial and posterolateral reach distances. Therefore, rehabilitation strategies should emphasize DFROM, PCS, eversion strength, and static balance to enhance dynamic postural control in patients with CAI. ß 2015 Elsevier B.V. All rights reserved.
Keywords: Ankle sprain Postural balance Sensorimotor feedback
1. Introduction Ankle sprains are common in physically active populations. The incidence of ankle sprains in military and select athletic cohorts can be up to twenty-seven times greater than reported in the general population [1]. Approximately 30% of individuals who suffer an initial lateral ankle sprain develop chronic ankle instability (CAI) [2]. CAI is a condition defined as a history of at
* Corresponding author at: Department of Interdisciplinary Health Sciences, Arizona School of Health Sciences, A.T. Still University, 5850 E. Still Circle, Mesa, AZ 85206, United States. Tel.: +1 480 219 6131. E-mail addresses: [email protected] (M.L. Gabriner), [email protected] (M.N. Houston), [email protected] (J.L. Kirby), [email protected] (M.C. Hoch).
least one ankle sprain resulting in one or more recurrent sprains combined with feelings of joint instability and occasionally pain [3]. CAI has been associated with both short- and long-term sequelae; thus requiring clinicians and researchers to develop a better understanding of the factors that contribute to this condition [3]. Individuals with CAI have commonly displayed dynamic postural control deficits [4]. These deficits have often been identified using a clinical assessment known as the Star Excursion Balance Test (SEBT) [4]. The SEBT requires an individual to establish and maintain a stable base of support during single-limb stance while performing a maximal reach excursion with the contralateral limb [5]. Shorter reach distances are indicative of dynamic postural control deficits which are typically associated with a combination of mechanical or sensorimotor system constraints [6]. To date, contributing factors to SEBT performance
http://dx.doi.org/10.1016/j.gaitpost.2015.03.013 0966-6362/ß 2015 Elsevier B.V. All rights reserved.
Please cite this article in press as: Gabriner ML, et al. Contributing factors to Star Excursion Balance Test performance in individuals with chronic ankle instability. Gait Posture (2015), http://dx.doi.org/10.1016/j.gaitpost.2015.03.013
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in individuals with CAI have not been thoroughly examined. Terada et al. [7] identified dorsiflexion range of motion (DFROM) and self-perceived stiffness as significant contributors to SEBTanterior reach distance; however, range of motion and selfreported outcomes did not significantly influence the other reach directions of the SEBT. CAI has been associated with impairments beyond range of motion and self-reported outcomes suggesting other factors may influence dynamic postural control in these individuals. Identifying impairments that contribute to normalized SEBT performance may provide insight into the dynamic postural control deficits experienced by individuals with CAI. CAI has been associated with a combination of mechanical and functional impairments [3]. Documented impairments include but are not limited to arthrokinematic restrictions [8], pathologic joint laxity [9], and sensorimotor deficits [2]. The sensorimotor impairments associated with CAI range from altered motoneuron pool excitability [10,11] and increased peroneal reaction time [12] to decreased joint reposition acuity [13]. However, many of these deficits may be impractical to collect in clinical settings, or they may not be associated with clear intervention strategies. Conversely, ankle eversion and inversion strength, DFROM, static postural control, and plantar cutaneous sensation (PCS) deficits have been observed in individuals with CAI using common clinical and laboratory assessments and have been successfully addressed through various rehabilitation interventions [14–17]. Examining the contribution of strength, DFROM, static postural control, and PCS to dynamic postural control performance may help identify a core group of modifiable impairments that are important for functional movements in these individuals. Understanding the relationships between SEBT performance and strength, DFROM, static postural control, and PCS may help to elucidate meaningful pathways toward developing evidencebased rehabilitation strategies to address dynamic postural control deficits in individuals with CAI. Therefore, the purpose of this study was to determine the extent to which strength, DFROM, static postural control, and PCS contribute to SEBT performance in individuals with CAI. We hypothesized that SEBT-anterior, posteromedial, and posterolateral reach directions would each have their own unique set of explanatory variables. 2. Methods 2.1. Participants Forty physically active adults (males = 13, females = 27) with self-reported CAI [18] participated in this cross-sectional study (Table 1). Participants were recruited from a large public university over a one-year period. These participants were part of a larger study that examined contributions of functional and mechanical impairments to health-related quality of life in individuals with CAI [19]. Prior to enrollment, all participants provided written
Table 1 Participant characteristics and inclusionary measurements (n = 40). Participant characteristics
Mean SD
Age (years) Height (cm) Mass (kg) Cumberland Ankle Instability Tool Ankle Instability Instrument National Aeronautics and Space Administration Physical Activity Scale Previous ankles sprains Episodes of giving way in the past three months Time since last significant ankle sprain (months)
23.25 4.76 168.84 9.20 72.04 14.36 16.33 4.55 6.60 1.41 6.70 1.71 3.45 1.65 5.88 7.91 23.64 22.75
informed consent which was approved by the University’s Institutional Review Board. Participants were included if they reported a history of one or more ankle sprains, at least two episodes of ‘‘giving way’’ in the last three months, a score 0.700), the variable with the higher correlation coefficient in relation to the criterion variable was entered into the model. Additionally, to account for multicollinearity, variance inflation factors were checked for values >10. To determine the clinical relevance of the final regression models, Cohen’s f2 effect sizes were used to determine the efficacy of the models and interpreted as large (0.35), medium (0.15–0.34), and small (0.02–0.14) [30]. Due to the exploratory nature of this study, regression models with an effect size 0.15 were considered clinically relevant. All data analyses were performed using IBM SPSS Statistics version 21.0. 3. Results Descriptive statistics for the regression variables are displayed in Table 2. The regression models for the SEBT-anterior (R2 = 0.16, p = 0.041, Cohen’s f2 = 0.19), posteromedial (R2 = 0.28, p = 0.002, Cohen’s f2 = 0.39) and posterolateral (R2 = 0.14, p = 0.063, Cohen’s f2 = 0.16) reach directions exceeded the clinically relevant
Fig. 1. Explanatory variables entered into the regression models for each reach direction of the Star Excursion Balance Test. Abbreviations: ANT, anterior; DFROM, dorsiflexion range of motion; PCS, plantar cutaneous sensation; PM, posteromedial; PL, posterolateral; TTBMM-ML, time-to-boundary mean minima-medial-lateral; TTBSD-ML, time-to-boundary standard deviation-medial-lateral. *Denotes a predictor variable included in the final model.
Please cite this article in press as: Gabriner ML, et al. Contributing factors to Star Excursion Balance Test performance in individuals with chronic ankle instability. Gait Posture (2015), http://dx.doi.org/10.1016/j.gaitpost.2015.03.013
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variables contribute to a clinically relevant portion of the variance for posteromedial and posterolateral reach. DFROM and PCS explained 16% of the variance associated with anterior reach distance. Eversion strength and TTBMM-ML explained 28% of the variance associated with posteromedial reach and eversion strength and TTBSD-ML explained 14% of the variance in posterolateral reach. These findings suggest that anterior and posterior reaches of the SEBT likely require different physical demands to perform the task. Our results suggest that the anterior reach of the SEBT may be more affected by mechanical restrictions and sensory deficits at the ankle complex, whereas the posteromedial and posterolateral reach directions relied more on strength and postural control. These results corroborate Terada et al.’s [7] findings that mechanical restrictions at the ankle influence anterior reach but not posteromedial or posterolateral reaches of the SEBT. This may be attributed to the fact that the posterior reaches incorporate multiple planes of motion compared to the anterior reach direction, which is primarily a sagittal plane movement. Furthermore, due to the dynamic nature of the SEBT, variables beyond the ankle complex likely contribute to performance on the test. For example, Robinson and Gribble [31] found that hip and knee range of motion explained a large portion of the variance associated with each reach direction of the SEBT. Therefore, it is important to keep in mind that this study only investigated potential contributors at the ankle complex. The addition of knee and hip strength range of motion, motorneuron pool excitability, peroneal reaction time, joint position sense, isokinetic strength or the myriad of other factors thought to contribute to CAI may have explained a large amount of the unexplained variance for each reach direction investigated in the current study. The posteromedial and posterolateral reach directions of the SEBT were associated with ML balance measures and eversion strength. The regression models built around the posteromedial and posterolateral reach directions demonstrated large (f2 = 0.39) and medium (f2 = 0.16) effects, respectively, which were considered clinically relevant. Therefore, when an individual performs the posteromedial and posterolateral reach directions; they appear to rely on ML static postural stability and eversion strength to complete these tasks. These findings seem logical because the medial and lateral components of these reach directions create postural control perturbations in the ML plane and likely require stabilization from the peroneal muscles. We also know that rehabilitation protocols that target balance and strength impairments have been shown to improve SEBT performance. For example, McKeon et al. [16] identified improvements in TTB ML measures, as well as, SEBT posteromedial and posterolateral reach distances but not anterior reach following dynamic balance training. Thus, reiterating our findings that the anterior direction is constrained by mechanical restrictions more so than sensorimotor deficits. Furthermore, Hale et al. [32] observed reach distance improvements for all directions of the SEBT following a 4week comprehensive rehabilitation program that included balance, isotonic, and range of motion exercises. Exercises included single-limb stances, bipedal calf raises, thera-band resistance in multiple planes, gastrocnemius and soleus stretches and functional tasks. We can speculate that the anterior improvements in the comprehensive program were most likely due to decreased mechanical restrictions, as a result of range of motion exercises. Hence, there is evidence to support that modifying the explanatory variables identified in the current study can improve SEBT performance. The regression model for the anterior reach direction demonstrated a medium effect (f2 = 0.19). The final explanatory variables were DFROM and PCS which aligns with the clinical implications of previous studies [15,32]. While this is the first study to link PCS to
dynamic postural control, the relationship between DFROM and SEBT performance has been previously established in the literature. Following a 2-week joint mobilization intervention, Hoch et al. [15] observed improvements in DFROM and significant improvements in all three SEBT reach directions in people with CAI. Other studies [7,8,33] have identified relationships between weight-bearing DFROM and SEBT-anterior performance in individuals with CAI. Hoch et al. [8] found that DFROM (10.73 3.44 cm) explained 22% of the variance associated with anterior reach distances (76.05 6.26%), while Basnett et al. [33] found that DFROM (41.3 7.98) explained 31% of anterior reach distances (64.4 6.0%). Additionally, Terada et al. [7] identified DFROM (9.08 2.46 cm) and self-reported stiffness as contributors to anterior reach distance (62.23 6.85%), with 35% of the variance explained. While it is unclear why these studies explained more of the variance associated with anterior reach distances than the current study, it could be partly due to subtle differences in the methods used to capture SEBT-anterior reach and DFROM or discrepancies in the inclusion criteria. Based on the descriptive statistics, subjects in this study demonstrated lower DFROM values but greater normalized SEBT-anterior reach distances when compared to the aforementioned studies. However, the other studies required participants to report a level of disability (90%) on the FAAM, whereas, the current study did not set a functional loss requirement for inclusion. Such discrepancies make it difficult to compare results however the International Ankle Consortium’s position statement on selection criteria for CAI research should help to resolve these issues and improve overall research quality. Despite the selection criteria discrepancies, the results of this study continue to support the idea that DFROM and PCS are important factors for achieving maximal anterior reach distances on the SEBT. The results of this study suggest that rehabilitation programs emphasize eversion strength, DFROM, PCS, and static balance exercises to improve SEBT performance in individuals with CAI. Strategies such as strengthening [32], joint mobilizations [15,34], plantar massage [35], and balance training [16,32] can be used to target the impairments identified in this study. Addressing these impairments using evidence-based rehabilitation strategies may help restore functional performance in individuals with CAI. However, it is important to note, that multifaceted rehabilitation strategies are still necessary to account for the potential contributors that have yet to be investigated. It is important to address the limitations associated with this study. The retrospective study design does not allow a causal relationship to be established between the explanatory and criterion variables. Future studies may consider a prospective approach to further investigate predictors of dynamic postural control in individuals with CAI. Additionally in this study, we chose to only include modifiable predictors of SEBT performance that have been well established in previous CAI cohorts. Lastly, ankle strength was measured using a handheld dynamometer, although reliable and clinically replicable, the majority of the strength deficits reported in the CAI literature were detected using isokinetic testing devices. Future research may consider addressing additional impairments such as isokinetic strength, joint position sense, or peroneal reaction time, as well as, the accuracy of the regression models identified in the study. Intervention-based designs should also be carried out to determine if addressing the impairments identified in this study improve dynamic postural control and function over time. 5. Conclusion Our results indicate that DFROM and PCS contribute to SEBTanterior reach and eversion strength and TTB-ML variables contribute to SEBT-posteromedial and posterolateral reaches in individuals with CAI. These findings suggest that anterior and
Please cite this article in press as: Gabriner ML, et al. Contributing factors to Star Excursion Balance Test performance in individuals with chronic ankle instability. Gait Posture (2015), http://dx.doi.org/10.1016/j.gaitpost.2015.03.013
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posterior reaches require different physical demands to successfully complete the task. Therefore, rehabilitation protocols should be tailored to address specific mechanical and functional impairments, including strength, DFROM, PCS, and static postural control, in order to improve dynamic postural control and ultimately function in patients with CAI. Acknowledgements This study was funded by the Mid-Atlantic Athletic Trainers’ Association. Conflict of interest The authors have no conflict of interest to report. References [1] Waterman BR, Owens BD, Davey S, Zacchilli MA, Belmont Jr PJ. The epidemiology of ankle sprains in the United States. J Bone Joint Surg Am 2010;92:2279–84. [2] Hertel J. Sensorimotor deficits with ankle sprains and chronic ankle instability. Clin Sports Med 2008;27:353–70. [3] Hertel J. Functional anatomy, pathomechanics, and pathophysiology of lateral ankle instability. J Athl Train 2002;37:364–75. [4] Arnold BL, De La Motte S, Linens S, Ross SE. Ankle instability is associated with balance impairments: a meta-analysis. Med Sci Sports Exerc 2009;41: 1048–62. [5] Gribble PA, Hertel J, Plisky P. Using the Star Excursion Balance Test to assess dynamic postural-control deficits and outcomes in lower extremity injury: a literature and systematic review. J Athl Train 2012;47:339–57. [6] Hoch MC, Staton GS, McKeon PO. Dorsiflexion range of motion significantly influences dynamic balance. J Sci Med Sport 2011;14:90–2. [7] Terada M, Harkey MS, Wells AM, Pietrosimone BG, Gribble PA. The influence of ankle dorsiflexion and self-reported patient outcomes on dynamic postural control in participants with chronic ankle instability. Gait Posture 2014;40: 193–7. [8] Hoch MC, Staton GS, Medina McKeon JM, Mattacola CG, McKeon PO. Dorsiflexion and dynamic postural control deficits are present in those with chronic ankle instability. J Sci Med Sport 2012;15:574–9. [9] Hubbard TJ, Kramer LC, Denegar CR, Hertel J. Contributing factors to chronic ankle instability. Foot Ankle Int 2007;28(3):343–54. [10] McVey ED, Palmieri RM, Docherty CL, Zinder SM, Ingersoll CD. Arthrogenic muscle inhibition in the leg muscles of subjects exhibiting functional ankle instability. Foot Ankle Int 2005;26(12):1055–61. [11] Sedory EJ, McVey ED, Cross KM, Ingersoll CD, Hertel J. Arthrogenic muscle response of the quadriceps and hamstrings with chronic ankle instability. J Athl Train 2007;42(3):355–60. [12] Hoch MC, Mckeon PO. Peroneal reaction time after ankle sprain: a systematic review and meta-analysis. Med Sci Sports Exerc 2014;46(3):546–56. [13] Munn J, Sullivan SJ, Schneiders AG. Evidence of sensorimotor deficits in functional ankle instability: a systematic review with meta-analysis. J Sci Med Sport 2010;13(1):2–12. [14] Smith BI, Docherty CL, Simon J, Klossner J, Schrader J. Ankle strength and force sense after a progressive, 6-week strength-training program in people with functional ankle instability. J Athl Train 2012;47(3):282–8.
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[15] Hoch MC, Andreatta RD, Mullineaux DR, English RA, Medina McKeon JM, Mattacola CG, et al. Two-week joint mobilization intervention improves selfreported function, range of motion, and dynamic balance in those with chronic ankle instability. J Orthop Res 2012;30:1798–804. [16] McKeon PO, Ingersoll CD, Kerrigan DC, Saliba E, Bennett BC, Hertel J. Balance training improves function and postural control in those with chronic ankle instability. Med Sci Sports Exerc 2008;40:1810–9. [17] Powell MR, Powden CJ, Houston MN, Hoch MC. Plantar cutaneous sensitivity and balance in individuals with and without chronic ankle instability. Clin J Sport Med 2014;24(6):490–6. [18] Gribble PA, Delahunt E, Bleakley CM, et al. Selection criteria for patients with chronic ankle instability in controlled research: a position statement of the International Ankle Consortium. J Athl Train 2014;49(1):121–7. [19] Houston MN, Hoch JM, Gabriner ML, Kirby JL, Hoch MC. Clinical and laboratory measures associated with health-related quality of life in individuals with chronic ankle instability. Phys Ther Sport 2014. pii:S1466-853X(14)00101-1 [Epub ahead of print]. [20] Donahue M, Simon J, Docherty CL. Critical review of self-reported functional ankle instability measures. Foot Ankle Int 2011;32:1140–6. [21] Kelln BM, McKeon PO, Gontkof LM, Hertel J. Hand-held dynamometry: reliability of lower extremity muscle testing in healthy, physically active, young adults. J Sport Rehabil 2008;17:160–70. [22] Vicenzino B, Branjerdporn M, Teys P, Jordan K. Initial changes in posterior talar glide and dorsiflexion of the ankle after mobilization with movement in individuals with recurrent ankle sprain. J Orthop Sports Phys Ther 2006;36: 464–71. [23] Bennell KL, Talbot RC, Wajswelner H, Techovanich W, Kelly DH, Hall AJ. Intrarater and inter-rater reliability of a weight-bearing lunge measure of ankle dorsiflexion. Aus J Physiother 1998;44:175–80. [24] Dyck PJ, O’Brien PC, Kosanke JL, Gillen DA, Karnes JL. A 4, 2, and 1 stepping algorithm for quick and accurate estimation of cutaneous sensation threshold. Neurology 1993;43(8):1508–12. [25] Hertel J, Olmsted-Kramer LC. Deficits in time-to-boundary measures of postural control with chronic ankle instability. Gait Posture 2007;25:33–9. [26] Hoch MC, Mullineaux DR, Andreatta RD, English RA, Medina-McKeon JM, Mattacola CG, et al. Effect of a 2-week joint-mobilization intervention on single-limb balance and ankle arthrokinematics in those with chronic ankle instability. J Sport Rehabil 2014;23:18. [27] Robinson RH, Gribble PA. Support for a reduction in the number of trials needed for the star excursion balance test. Arch Phys Med Rehabil 2008;89: 364–70. [28] Gribble PA, Mitterholzer J, Myers AN. Normalizing considerations for time to stabilization assessment. J Sci Med Sport 2012;15:159–63. [29] Hyong IH, Kim JH. Test of intrarater and interrater reliability for the star excursion balance test. J Phys Ther Sci 2014;26:1139–41. [30] Cohen J. A power primer. Psychol Bull 1992;112:155–9. [31] Robinson R, Gribble P. Kinematic predictors of performance on the Star Excursion Balance Test. J Sport Rehabil 2008;17:347–57. [32] Hale SA, Hertel J, Olmsted-Kramer LC. The effect of a 4-week comprehensive rehabilitation program on postural control and lower extremity function in individuals with chronic ankle instability. J Orthop Sports Phys Ther 2007;37: 303–11. [33] Basnett CR, Hanish MJ, Wheeler TJ, Miriovsky DJ, Danielson EL, Barr JB, et al. Ankle dorsiflexion range of motion influences dynamic balance in individuals with chronic ankle instability. Int J Sports Phys Ther 2013;8:121–8. [34] Hoch MC, McKeon PO. Joint mobilization improves spatiotemporal postural control and range of motion in those with chronic ankle instability. J Orthop Res 2011;29:326–32. [35] LeClaire JE, Wikstrom EA. Massage for postural control in individuals with chronic ankle instability. Athl Train Sports Health Care 2012;4:213–9.
Please cite this article in press as: Gabriner ML, et al. Contributing factors to Star Excursion Balance Test performance in individuals with chronic ankle instability. Gait Posture (2015), http://dx.doi.org/10.1016/j.gaitpost.2015.03.013
GAIPOS-4450; No. of Pages 5 Gait & Posture xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Gait & Posture journal homepage: www.elsevier.com/locate/gaitpost
Contributing factors to Star Excursion Balance Test performance in individuals with chronic ankle instability Michael L. Gabriner a, Megan N. Houston b,*, Jessica L. Kirby c, Matthew C. Hoch d a
The Steadman Clinic, 181 W. Meadow Dr. Suite 400, Vail, CO 81657, United States Department of Interdisciplinary Health Sciences, A.T. Still University, 5850 E. Still Circle, Mesa, AZ 85206, United States c School of Physical Education, Sport, and Exercise Science, Ball State University, 2000 W University Ave, Muncie, IN 47306, United States d School of Physical Therapy & Athletic Training, Old Dominion University, 102 Health Sciences Annex, Norfolk, VA 23529, United States b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 9 November 2014 Received in revised form 11 March 2015 Accepted 20 March 2015
The purpose of this study was to determine the contributions of strength, dorsiflexion range of motion (DFROM), plantar cutaneous sensation (PCS), and static postural control to Star Excursion Balance Test (SEBT) performance in individuals with chronic ankle instability (CAI). Forty individuals with CAI completed isometric strength, weight-bearing DFROM, PCS, static and dynamic balance assessments. Three separate backward multiple linear regression models were calculated to determine how strength, DFROM, PCS, and static postural control contributed to each reach direction of the SEBT. Explanatory variables included dorsiflexion, inversion, and eversion strength, DFROM, PCS, and time-to-boundary mean minima (TTBMM) and standard deviation (TTBSD) in the medial–lateral (ML) and anterior– posterior (AP) directions. Criterion variables included SEBT-anterior, posteromedial, and posterolateral directions. The strength of each model was determined by the R2-value and Cohen’s f2 effect size. Regression models with an effect size 0.15 were considered clinically relevant. All three SEBT directions produced clinically relevant regression models. DFROM and PCS accounted for 16% of the variance in SEBT-anterior reach (f2 = 0.19, p = 0.04). Eversion strength and TTBMM-ML accounted for 28% of the variance in SEBT-posteromedial reach (f2 = 0.39, p < 0.01). Eversion strength and TTBSD-ML accounted for 14% of the variance in SEBT-posterolateral reach (f2 = 0.16, p = 0.06). DFROM and PCS explained a clinically relevant proportion of the variance associated with SEBT-anterior reach. Eversion strength and TTB ML explained a clinically relevant proportion of the variance in SEBT-posteromedial and posterolateral reach distances. Therefore, rehabilitation strategies should emphasize DFROM, PCS, eversion strength, and static balance to enhance dynamic postural control in patients with CAI. ß 2015 Elsevier B.V. All rights reserved.
Keywords: Ankle sprain Postural balance Sensorimotor feedback
1. Introduction Ankle sprains are common in physically active populations. The incidence of ankle sprains in military and select athletic cohorts can be up to twenty-seven times greater than reported in the general population [1]. Approximately 30% of individuals who suffer an initial lateral ankle sprain develop chronic ankle instability (CAI) [2]. CAI is a condition defined as a history of at
* Corresponding author at: Department of Interdisciplinary Health Sciences, Arizona School of Health Sciences, A.T. Still University, 5850 E. Still Circle, Mesa, AZ 85206, United States. Tel.: +1 480 219 6131. E-mail addresses: [email protected] (M.L. Gabriner), [email protected] (M.N. Houston), [email protected] (J.L. Kirby), [email protected] (M.C. Hoch).
least one ankle sprain resulting in one or more recurrent sprains combined with feelings of joint instability and occasionally pain [3]. CAI has been associated with both short- and long-term sequelae; thus requiring clinicians and researchers to develop a better understanding of the factors that contribute to this condition [3]. Individuals with CAI have commonly displayed dynamic postural control deficits [4]. These deficits have often been identified using a clinical assessment known as the Star Excursion Balance Test (SEBT) [4]. The SEBT requires an individual to establish and maintain a stable base of support during single-limb stance while performing a maximal reach excursion with the contralateral limb [5]. Shorter reach distances are indicative of dynamic postural control deficits which are typically associated with a combination of mechanical or sensorimotor system constraints [6]. To date, contributing factors to SEBT performance
http://dx.doi.org/10.1016/j.gaitpost.2015.03.013 0966-6362/ß 2015 Elsevier B.V. All rights reserved.
Please cite this article in press as: Gabriner ML, et al. Contributing factors to Star Excursion Balance Test performance in individuals with chronic ankle instability. Gait Posture (2015), http://dx.doi.org/10.1016/j.gaitpost.2015.03.013
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in individuals with CAI have not been thoroughly examined. Terada et al. [7] identified dorsiflexion range of motion (DFROM) and self-perceived stiffness as significant contributors to SEBTanterior reach distance; however, range of motion and selfreported outcomes did not significantly influence the other reach directions of the SEBT. CAI has been associated with impairments beyond range of motion and self-reported outcomes suggesting other factors may influence dynamic postural control in these individuals. Identifying impairments that contribute to normalized SEBT performance may provide insight into the dynamic postural control deficits experienced by individuals with CAI. CAI has been associated with a combination of mechanical and functional impairments [3]. Documented impairments include but are not limited to arthrokinematic restrictions [8], pathologic joint laxity [9], and sensorimotor deficits [2]. The sensorimotor impairments associated with CAI range from altered motoneuron pool excitability [10,11] and increased peroneal reaction time [12] to decreased joint reposition acuity [13]. However, many of these deficits may be impractical to collect in clinical settings, or they may not be associated with clear intervention strategies. Conversely, ankle eversion and inversion strength, DFROM, static postural control, and plantar cutaneous sensation (PCS) deficits have been observed in individuals with CAI using common clinical and laboratory assessments and have been successfully addressed through various rehabilitation interventions [14–17]. Examining the contribution of strength, DFROM, static postural control, and PCS to dynamic postural control performance may help identify a core group of modifiable impairments that are important for functional movements in these individuals. Understanding the relationships between SEBT performance and strength, DFROM, static postural control, and PCS may help to elucidate meaningful pathways toward developing evidencebased rehabilitation strategies to address dynamic postural control deficits in individuals with CAI. Therefore, the purpose of this study was to determine the extent to which strength, DFROM, static postural control, and PCS contribute to SEBT performance in individuals with CAI. We hypothesized that SEBT-anterior, posteromedial, and posterolateral reach directions would each have their own unique set of explanatory variables. 2. Methods 2.1. Participants Forty physically active adults (males = 13, females = 27) with self-reported CAI [18] participated in this cross-sectional study (Table 1). Participants were recruited from a large public university over a one-year period. These participants were part of a larger study that examined contributions of functional and mechanical impairments to health-related quality of life in individuals with CAI [19]. Prior to enrollment, all participants provided written
Table 1 Participant characteristics and inclusionary measurements (n = 40). Participant characteristics
Mean SD
Age (years) Height (cm) Mass (kg) Cumberland Ankle Instability Tool Ankle Instability Instrument National Aeronautics and Space Administration Physical Activity Scale Previous ankles sprains Episodes of giving way in the past three months Time since last significant ankle sprain (months)
23.25 4.76 168.84 9.20 72.04 14.36 16.33 4.55 6.60 1.41 6.70 1.71 3.45 1.65 5.88 7.91 23.64 22.75
informed consent which was approved by the University’s Institutional Review Board. Participants were included if they reported a history of one or more ankle sprains, at least two episodes of ‘‘giving way’’ in the last three months, a score 0.700), the variable with the higher correlation coefficient in relation to the criterion variable was entered into the model. Additionally, to account for multicollinearity, variance inflation factors were checked for values >10. To determine the clinical relevance of the final regression models, Cohen’s f2 effect sizes were used to determine the efficacy of the models and interpreted as large (0.35), medium (0.15–0.34), and small (0.02–0.14) [30]. Due to the exploratory nature of this study, regression models with an effect size 0.15 were considered clinically relevant. All data analyses were performed using IBM SPSS Statistics version 21.0. 3. Results Descriptive statistics for the regression variables are displayed in Table 2. The regression models for the SEBT-anterior (R2 = 0.16, p = 0.041, Cohen’s f2 = 0.19), posteromedial (R2 = 0.28, p = 0.002, Cohen’s f2 = 0.39) and posterolateral (R2 = 0.14, p = 0.063, Cohen’s f2 = 0.16) reach directions exceeded the clinically relevant
Fig. 1. Explanatory variables entered into the regression models for each reach direction of the Star Excursion Balance Test. Abbreviations: ANT, anterior; DFROM, dorsiflexion range of motion; PCS, plantar cutaneous sensation; PM, posteromedial; PL, posterolateral; TTBMM-ML, time-to-boundary mean minima-medial-lateral; TTBSD-ML, time-to-boundary standard deviation-medial-lateral. *Denotes a predictor variable included in the final model.
Please cite this article in press as: Gabriner ML, et al. Contributing factors to Star Excursion Balance Test performance in individuals with chronic ankle instability. Gait Posture (2015), http://dx.doi.org/10.1016/j.gaitpost.2015.03.013
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variables contribute to a clinically relevant portion of the variance for posteromedial and posterolateral reach. DFROM and PCS explained 16% of the variance associated with anterior reach distance. Eversion strength and TTBMM-ML explained 28% of the variance associated with posteromedial reach and eversion strength and TTBSD-ML explained 14% of the variance in posterolateral reach. These findings suggest that anterior and posterior reaches of the SEBT likely require different physical demands to perform the task. Our results suggest that the anterior reach of the SEBT may be more affected by mechanical restrictions and sensory deficits at the ankle complex, whereas the posteromedial and posterolateral reach directions relied more on strength and postural control. These results corroborate Terada et al.’s [7] findings that mechanical restrictions at the ankle influence anterior reach but not posteromedial or posterolateral reaches of the SEBT. This may be attributed to the fact that the posterior reaches incorporate multiple planes of motion compared to the anterior reach direction, which is primarily a sagittal plane movement. Furthermore, due to the dynamic nature of the SEBT, variables beyond the ankle complex likely contribute to performance on the test. For example, Robinson and Gribble [31] found that hip and knee range of motion explained a large portion of the variance associated with each reach direction of the SEBT. Therefore, it is important to keep in mind that this study only investigated potential contributors at the ankle complex. The addition of knee and hip strength range of motion, motorneuron pool excitability, peroneal reaction time, joint position sense, isokinetic strength or the myriad of other factors thought to contribute to CAI may have explained a large amount of the unexplained variance for each reach direction investigated in the current study. The posteromedial and posterolateral reach directions of the SEBT were associated with ML balance measures and eversion strength. The regression models built around the posteromedial and posterolateral reach directions demonstrated large (f2 = 0.39) and medium (f2 = 0.16) effects, respectively, which were considered clinically relevant. Therefore, when an individual performs the posteromedial and posterolateral reach directions; they appear to rely on ML static postural stability and eversion strength to complete these tasks. These findings seem logical because the medial and lateral components of these reach directions create postural control perturbations in the ML plane and likely require stabilization from the peroneal muscles. We also know that rehabilitation protocols that target balance and strength impairments have been shown to improve SEBT performance. For example, McKeon et al. [16] identified improvements in TTB ML measures, as well as, SEBT posteromedial and posterolateral reach distances but not anterior reach following dynamic balance training. Thus, reiterating our findings that the anterior direction is constrained by mechanical restrictions more so than sensorimotor deficits. Furthermore, Hale et al. [32] observed reach distance improvements for all directions of the SEBT following a 4week comprehensive rehabilitation program that included balance, isotonic, and range of motion exercises. Exercises included single-limb stances, bipedal calf raises, thera-band resistance in multiple planes, gastrocnemius and soleus stretches and functional tasks. We can speculate that the anterior improvements in the comprehensive program were most likely due to decreased mechanical restrictions, as a result of range of motion exercises. Hence, there is evidence to support that modifying the explanatory variables identified in the current study can improve SEBT performance. The regression model for the anterior reach direction demonstrated a medium effect (f2 = 0.19). The final explanatory variables were DFROM and PCS which aligns with the clinical implications of previous studies [15,32]. While this is the first study to link PCS to
dynamic postural control, the relationship between DFROM and SEBT performance has been previously established in the literature. Following a 2-week joint mobilization intervention, Hoch et al. [15] observed improvements in DFROM and significant improvements in all three SEBT reach directions in people with CAI. Other studies [7,8,33] have identified relationships between weight-bearing DFROM and SEBT-anterior performance in individuals with CAI. Hoch et al. [8] found that DFROM (10.73 3.44 cm) explained 22% of the variance associated with anterior reach distances (76.05 6.26%), while Basnett et al. [33] found that DFROM (41.3 7.98) explained 31% of anterior reach distances (64.4 6.0%). Additionally, Terada et al. [7] identified DFROM (9.08 2.46 cm) and self-reported stiffness as contributors to anterior reach distance (62.23 6.85%), with 35% of the variance explained. While it is unclear why these studies explained more of the variance associated with anterior reach distances than the current study, it could be partly due to subtle differences in the methods used to capture SEBT-anterior reach and DFROM or discrepancies in the inclusion criteria. Based on the descriptive statistics, subjects in this study demonstrated lower DFROM values but greater normalized SEBT-anterior reach distances when compared to the aforementioned studies. However, the other studies required participants to report a level of disability (90%) on the FAAM, whereas, the current study did not set a functional loss requirement for inclusion. Such discrepancies make it difficult to compare results however the International Ankle Consortium’s position statement on selection criteria for CAI research should help to resolve these issues and improve overall research quality. Despite the selection criteria discrepancies, the results of this study continue to support the idea that DFROM and PCS are important factors for achieving maximal anterior reach distances on the SEBT. The results of this study suggest that rehabilitation programs emphasize eversion strength, DFROM, PCS, and static balance exercises to improve SEBT performance in individuals with CAI. Strategies such as strengthening [32], joint mobilizations [15,34], plantar massage [35], and balance training [16,32] can be used to target the impairments identified in this study. Addressing these impairments using evidence-based rehabilitation strategies may help restore functional performance in individuals with CAI. However, it is important to note, that multifaceted rehabilitation strategies are still necessary to account for the potential contributors that have yet to be investigated. It is important to address the limitations associated with this study. The retrospective study design does not allow a causal relationship to be established between the explanatory and criterion variables. Future studies may consider a prospective approach to further investigate predictors of dynamic postural control in individuals with CAI. Additionally in this study, we chose to only include modifiable predictors of SEBT performance that have been well established in previous CAI cohorts. Lastly, ankle strength was measured using a handheld dynamometer, although reliable and clinically replicable, the majority of the strength deficits reported in the CAI literature were detected using isokinetic testing devices. Future research may consider addressing additional impairments such as isokinetic strength, joint position sense, or peroneal reaction time, as well as, the accuracy of the regression models identified in the study. Intervention-based designs should also be carried out to determine if addressing the impairments identified in this study improve dynamic postural control and function over time. 5. Conclusion Our results indicate that DFROM and PCS contribute to SEBTanterior reach and eversion strength and TTB-ML variables contribute to SEBT-posteromedial and posterolateral reaches in individuals with CAI. These findings suggest that anterior and
Please cite this article in press as: Gabriner ML, et al. Contributing factors to Star Excursion Balance Test performance in individuals with chronic ankle instability. Gait Posture (2015), http://dx.doi.org/10.1016/j.gaitpost.2015.03.013
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