Abstract
Keywords
Introduction
Chronic ankle instability (CAI) is defined as a “condition resulting from a significant lateral ankle sprain with greater than 12 months of giving way or subjective instability” [11]. The prevalence of CAI in young adults is estimated around 1.1% in males and 0.7% in females [12]. Long term lateral ankle pain, chronic swelling around ankle region, inability to return to the previous status of functioning and sporting activities are some of the impairments observed [13, 17]. CAI includes mechanical instability caused due to lateral ligament tears and functional instability due to proprioceptive and muscular deficits [13, 20].
Individuals with CAI are also found to have impaired static and dynamic balance [2]. Postural instability or impaired balance is one among the major factors leading to and maintain CAI. Dynamic balance can be measured in those with lower extremity injury using the Star Excursion Balance Test (SEBT) [9]. This test involves unilateral weight bearing on the affected extremity and simultaneous reaching of the other leg in various directions. The greater reach distances indicate better dynamic stability of the tested lower extremity. Stability at hip and pelvis is essential to maintain balance while performing unilateral weight bearing activities [1]. Pelvic stabilization is mostly achieved from gluteal muscle contraction [23], which is found to be important for postural stability while performing the SEBT test [1]. Ambegaonkar et al. have found a positive correlation between maximal isometric hip muscle strength and dynamic balance in collegiate female athletes [1]. Norris et al. reported significant activation of gluteus muscles while performing anterior, posteromedial and medial reach directions of SEBT test [24]. These studies which were done in uninjured populations indicate the role of gluteal muscles in maintaining dynamic balance.
Since impaired balance leads to recurrent ankle sprains in those with CAI, it is essential to know the contributing factors for impaired balance. Previous research has shown gluteal muscle dysfunction post ankle sprain [5, 7]. These studies have found reduced hip abductor strength in CAI and decreased gluteus maxmius activation after an inversion sprain [5, 7]. Numerous studies have found that reduced hip strength can lead to excessive dynamic knee valgus which can increase the risk of lower extremity injuries [6, 27]. There is evidence for the influence of gluteal muscle control on ankle hypermobility and inversion injury [3, 4]. This reduced gluteal muscle strength could also be one of the underlying factors for impaired balance in those with CAI. But there is limited evidence supporting the influence of hip strength deficits directly on the lower extremity balance in CAI. Lack of pelvic stabilization due to gluteal muscle dysfunction in this cohort may impair balance during various functional activities, leading to recurrent ankle sprains. This results in a complex cascade of initial injury, altered muscle function, and impaired balance, re-injury and chronic ankle instability.
However, there is a dearth of literature investigating the relationship between gluteal muscles function and balance in those with CAI. Therefore the objective of the present study is to determine the relationship between maximal isometric gluteal muscle strength and SEBT reach distances. The results of this study will help in developing appropriate muscle strengthening programs in the management of impaired balance in those with CAI.
Methods
The Institutional Ethics Committee of Kasturba hospital, Manipal approved the study. This is a cross-sectional, correlation study conducted from March 2015 to September 2015. The participants were the students of Manipal University, Manipal and recruited through verbal advertisement. Written informed consent was obtained from the participants who agreed to participate in the study.
Participants
The recruitment criteria for the study followed the standard recommendations outlined in Gribble et al. [8]. These were as follows:
Inclusion criteria: History of one significant ankle sprain one year prior A subjective feeling of giving away in the past six months Functional ankle instability (IdFAI) score >11.
Participants were excluded if they exhibited any of the following exclusion criteria: Acute musculoskeletal injury to lower limbs in the past three months History of fracture requiring realignment or any surgeries of the lower extremity.
Measurements
The outcome measures used in the study were maximal isometric gluteus maximus and medius strength and SEBT scores. The maximal isometric strength of gluteal muscles was measured using a handheld dynamometer (Chatillon MSE 100 series) as used in previous research [1]. This method has been shown to be reliable [18, 28]. To measure the gluteus medius strength the participant was positioned in sidelying with the measurement lower extremity on the top. The hips and knees were placed in 45-degree flexion and a pillow was kept in between the legs. The dynamometer was placed just proximal to the lateral malleolus of the leg and the participant was instructed to push the dynamometer in the direction of abduction and external rotation, isometrically against the resistance of the outcome assessor. The gluteus maximus strength was measured by placing the participant in prone with lower extremities below the level of anterior superior iliac spine off the couch and feet placed on the ground. The knee of the testing lower extremity was flexed to 70 degrees and the dynamometer was kept on the distal thigh. The participant was asked to push against the dynamometer in the direction of hip extension while the outcome assessor isometrically resisted the movement. The other foot was supported on the ground. For both the muscles, three repetitions of maximal isometric contractions held for five seconds were performed with one minute rest period between repetitions. The average of the three readings was noted in lbs.
Dynamic balance was measured using a modified Star Excursion Balance Test which measured the anterior, posteromedial (PM) and posterolateral (PL) reach distances [14]. The test was performed as per the standard guidelines. A rigid tape was affixed to the floor with 3 arms meeting at a center point representing the anterior, posteromedial and posterolateral directions of the test. The anterior arm was laid in a straight line while the PM and PL arms were attached 135 degrees to the anterior arm posteriorly in either direction. The participants were made to stand on the affected lower extremity with the heel of the affected leg on the center point of the grid and with hands on the hips. Then the participants were asked to lift and reach with the other extremity (unaffected) as far as they could and touch their toe on each of the 3 arms and return back to the center of the grid. The reach distances were measured in centimeters and normalized to limb length. SEBT test has been shown to have excellent reliability and validity for measuring dynamic balance [9, 19].
Statistical analysis
SPSS version 15 was used for data analysis. The data was checked for normal distribution using Shapiro-Wilk test and Pearson’s Product-Moment Correlation was used to determine the relationship between gluteal muscle strength and SEBT scores. The strength of the correlation coefficient was considered as follows:
0.00–0.25 = little or no relationship;
0.26–0.50 = fair degree of relationship;
0.51–0.75 = moderate to good relationship,
0.76–1.00 = good to excellent relationship [26].
Results
Fifty-four individuals with CAI were screened for the inclusion criteria of which thirty-two individuals were found to be eligible and participated in the study. The mean age of the participants was twenty-four. Other participant demographic information is shown in Table 1. The mean SEBT scores and gluteal muscle strength are shown in the Table 2.
Overall the SEBT composite scores were moderately and positively correlated with gluteus medius and gluteus maximus strength (Table 3). The anterior SEBT score demonstrated a positive correlation with gluteal muscle strength (r = 0.45, p = 0.05 and r = 0.38, p = 0.02). There was a good positive relationship between gluteus medius strength and posteromedial and posterolateral SEBT scores (r = 0.66, p = 0.01 and r = 0.72, p = 0.03 respectively). However, a weak positive correlation was found between gluteus maximus strength and PM and PL SEBT scores (r = 0.25, p = 0.05 and r = 0.30, p = 0.05 respectively).
Discussion
Previous studies have found that there is a reduction of gluteal muscle strength and impaired balance post ankle sprain [2, 7]. In the present study, the authors have found a significant positive relationship between dynamic balance scores as measured by SEBT and maximal isometric gluteal muscle strength in those with CAI. This shows that gluteal muscle strength could be one of the factors responsible for balance deficits observed in CAI.
The positive correlation between the anterior direction of SEBT and gluteus maximus and medius muscles suggest that an individual with CAI with good gluteal strength can have better dynamic stability during unilateral lower extremity anterior reaching activities. While performing the anterior reach in SEBT test Norris et al. have found significant activation of both gluteus maximus and gluteus medius muscles [24]. It can be hypothesized that anterior SEBT reach distances might be a measure of overall gluteal muscle function in these participants [1].
Posteromedial reach distances were moderately positively correlated with the gluteal medius strength which reinforces the hypothesis that gluteus medius contributes to pelvic stability while performing mediolateral activities [23]. The correlation found between reach distances in a posterolateral direction of SEBT and gluteus medius muscle further reinforces this point. However, a weak positive association was found with gluteus maximus strength.
Overall, there is a better correlation noted between gluteus medius strength and balance. This could be due to following reasons: Strong stabilization at the pelvis by this muscle would have minimized the lateral postural sway during unilateral activities and allowed the participants with strong gluteus medius strength to reach farther while maintaining balance on the involved extremity [7, 21]. The lower extremity is a serial linkage of multiple joints where the problem at one joint can be caused or corrected by compensation by the other joints [27]. Foot moments during single leg stance can be influenced and compensated by hip abductor strength [7, 21]. For example, weak hip abductors could not have controlled the excessive inversion moments at ankle occurring due to ankle stability during unilateral stance and thereby not allowing the patients to reach farther distances.
The balance deficit observed in those with CAI may be contributed or maintained by gluteal muscle dysfunction. However, it should be noted that maintaining optimal balance is a process requiring the interaction of proprioceptive, vestibular and visual inputs, joint range of motion and laxity and muscle function [15]. However, only the contribution of the gluteal muscles to balance in those with CAI has been demonstrated in this study. Previous research showed improved balance after 12 weeks of hip strengthening exercise in anterior cruciate ligament reconstruction participants [10]. This is the first study to investigate the relationship between gluteal muscles strength and balance in those with CAI.
Limitations and future recommendations
In the present study, the maximum isometric strength of gluteal muscles was measured. However, during the performance of anterior, PM and PL reaches of SEBT some amount of eccentric control of the gluteal muscles would be required. Since the stance leg was static we assumed isometric gluteal strength would be sufficient enough to control the pelvis during the reaching movement of SEBTs. Also, previous research on those with CAI has shown eccentric strength deficits only in the hip flexor muscles and not in other hip muscle groups [22]. Future studies should try to measure and find the relationship between the eccentric strength of gluteal muscles and reach distances, which may help in understanding the type of gluteal contraction required while performing SEBT test. This study also highlights the need for studies investigating the effects of muscle strengthening, especially gluteal muscles, on balance in CAI.
Clinical implications
The significant correlation between gluteal muscle strength and balance, highlights the need for gluteal muscle assessment in patients with chronic ankle instability. Proximal stability in the hip and pelvis is essential to performing various unilateral weight bearing exercises used in the rehabilitation CAI individuals. Therefore simultaneous gluteal muscles strengthening would improve balance, which reduces the recurrence of injury and thereby improving function and performance in the long term.
Conclusion
The present study found a fair correlation between gluteus maximus strength and balance and a moderate to good relationship between gluteal medius strength and balance. This study signifies the role of the gluteal muscles while performing unilateral activities of the lower extremities in those with CAI. Gluteal muscle evaluation, and subsequent strengthening need to be considered during the rehabilitation of patients with features of CAI. The exact cause and effect relationship might have to be further explored in terms of whether gluteal muscle dysfunction leads to impaired balance or vice versa.
Conflict of interest
The authors have no conflict of interest to report.