Correlations of strength, proprioception, and dynamic balance to the Cumberland Ankle Instability Tool Score among patients with chronic ankle instability: a cross-sectional study

Abstract

Background

The Cumberland Ankle Instability Tool (CAIT) is used to screen patients with chronic ankle instability (CAI) and to quantify the severity of ankle instability. Neuromuscular deficits are common in CAI, including proprioception, strength, and balance issues. The relationship between CAIT scores and neuromuscular factors is unclear. The purpose of this study was to investigate the correlation between ankle instability and ankle muscle strength, proprioception, and dynamic balance.

Methods

Thirty-four individuals with chronic ankle instability were included in this study. The participants’ CAIT scores, muscle strength (isokinetic) and proprioception in plantarflexion (PF), dorsiflexion (DF), inversion (IV), and eversion (EV), and dynamic balance (Star Excursion Balance Test in anterior, posteromedial, and posterolateral directions) were assessed. Bivariate correlations were used to determine the relationship between CAIT scores and ankle muscle strength, proprioception, and dynamic balance.

Results

In terms of muscle strength, ankle PF (r = 0.378, 95%CI: 0.046–0.635, P = 0.027) and IV (r = 0.527, 95%CI: 0.233–0.736, P = 0.001) strength were positively correlated with CAIT Score, whereas ankle DF and EV strength had no significant correlation with CAIT Score. In terms of proprioception, ankle IV proprioception (r = -0.340, 95%CI: -0.608–0.002, P = 0.027) was negatively correlated with CAIT Score, while ankle PF, DF, and EV proprioception had no significant correlation with CAIT Score. In terms of dynamic balance, the SEBT posteromedial (r = 0.444, 95%CI: 0.124–0.680, P = 0.001) was positively correlated with CAIT Score. The SEBT anterior and posterolateral were not significantly correlated with the CAIT Score.

Conclusion

This study found that increasing ankle plantarflexion and inversion muscle strength, improving dynamic balance in the posteromedial direction, and decreasing ankle inversion proprioceptive thresholds may help improve the subjective stability of CAI. This provides data support for targeted ankle neuromuscular function rehabilitation training for patients.

Trial registration

Chinese Clinical Trial Registry ChiCTR2100044089. Registered on 10 March 2021.

Introduction

Chronic ankle instability (CAI) is defined by the International Ankle Consortium as the persistence of symptoms following a significant ankle sprain, characterized by recurrent ankle sprains, feelings of ankle instability, and episodes of giving way occurring at least twice in the past 6 months [1]. The study found that the prevalence of chronic ankle instability, is about 25% in active individuals, and among those with a history of ankle sprain, it is approximately 46% [2]. Patients with CAI experience motor-behavioral impairments, including deficiencies in muscle strength and physical activities, and alterations in movement patterns, which can negatively impact their quality of life and increase the risk of early onset osteoarthritis [3,4,5,6]. Therefore, screening and assessment of patients with chronic ankle instability (CAI) are essential in a clinical setting to accurately determine the severity of the injury, tailor an effective treatment plan, and track improvements over time. Clinical measurements provide objective data that help refine treatment approaches, improve joint stability, and reduce the risk of further injury.

The Cumberland Ankle Instability Tool (CAIT) is a valid and reliable measure widely used in clinical practice to screen patients for CAI and to quantify the severity of ankle instability [7,8,9]. The CAIT consists of 9-item questionnaire totaling 30 points, with lower scores indicating that the patient has more ankle instability and more severe dysfunction. The International Ankle Consortium (IAC) has used the CAIT score as a validated tool for assessing and quantifying ankle instability in patients with CAI and has used a CAIT score of < 24 as an inclusion criterion for ankle instability [1]. Although the CAIT score is effective in screening patients for the presence of CAI and quantifying the degree of ankle instability, this measurement tool is largely based on subjective cognitive feedback from the patient and lacks a link to the patient’s actual ankle functional deficits [10]. Therefore, clarifying the association between CAIT scores and clinical ankle neuromuscular function factors in patients with chronic ankle instability could help to develop and implement more targeted clinical measures to improve patients’ ankle instability after screening.

Significant neuromuscular deficits have been observed in muscle strength, proprioception, and dynamic balance among individuals with CAI [11,12,13,14,15]. Patients with CAI have medial and lateral ankle muscle atrophy with decreased ankle muscle strength [16]. Lateral ankle ligament injuries might impair the ankle joint somatosensory and motor cortex, leading to abnormal biomechanical patterns and an increased risk of ankle instability and re-injury [17]. Compared to healthy individuals and the uninjured limb, the injured limb of CAI patients showed a dynamic postural deficit with significantly reduced dynamic extension ability in the Star Excursion Balance Test [18].

Although previous literature has suggested that individual neuromuscular function factors may be associated with CAI, the relationship between CAIT-reported ankle instability and these multiple factors remains unclear. Given the complex, multifactorial nature of CAI, multiple correlation analyses are necessary to better understand how these various factors—such as muscle strength, proprioception, and dynamic balance—interact and contribute to ankle instability. This approach allows for a more comprehensive assessment of the relative contributions of each factor and helps identify potential targets for intervention. Previous study has shown significant positive correlation between the self-reported ankle instability CAIT score and normalized hip abductor strength on the affected side in females was found in one previous study [19]. Another study also suggested that ankle inversion proprioception during landing may be important for CAI rehabilitation, as proprioceptive performance using the Ankle Inversion Discrimination Apparatus for Landing (AIDAL) was significantly correlated with the severity of CAIT functional ankle instability scores [20]. However, to our knowledge, there is still a gap in the current works of literature regarding the relationship between CAIT score and strength, proprioception, and dynamic balance among patients with CAI. Understanding the association between the ankle instability and neuromuscular function factors may help to provide more targeted and effective rehabilitation treatments for patients with CAI.

Therefore, the purpose of this study was to investigate the correlation between CAIT self-reported degree of ankle instability and ankle muscle strength, proprioception, and dynamic balance among patients with CAI. We hypothesized that the degree of CAIT self-reported ankle instability would be significantly correlated with ankle muscle strength, proprioception, and dynamic balance.

Methods

Participants

An a priori power analysis (using G*Power version 3.1) indicated that at least 32 participants are required to achieve a statistical power of 0.80 at an alpha level of 0.05, based on a previous report that showed a correlation of r = 0.43 between SEBT and CAIT among young CAI participants (aged 27 ± 7.92 years) [21].

A total of 37 patients with unilateral CAI were recruited in this study by distributing leaflets and e-mails on the local university campus, in Jinan, Shandong. The inclusion criteria are as follows: (1) The age range of participants is between 18 and 25 years old [22]; (2) participants had experienced at least one severe ankle sprain within the 12 months prior to the study, characterized by pain, swelling, and activity limitation for at least one day, and requiring protection, immobilization, or activity limitation during weight-bearing activities for at least 24 h [23]; (3) CAIT score must be <24 [23]; (4) participants had at least two episodes of giving way in the 6 months prior to this experiment [23]. The exclusion criteria are as follows: (1) Participants are currently involved in any ankle-related rehabilitation activities [24]; (2) positive results of talar tilt and anterior drawer test [22, 24]. (3) injuries such as fractures or surgical procedures to the lower extremity, as well as other muscular, joint, or neurological conditions that impact lower limb function [23]. (4) cognitive, vestibular, and visual dysfunction due to neurological and vestibular disorders [24].

After initial screening for inclusion and exclusion criteria, a total of 34 eligible participants signed an informed consent form prior to the experiment (Table 1). In the informed consent process, led by the principal researchers, a comprehensive explanation of the study’s aims, procedures, potential risks, benefits, and data confidentiality was provided. Participants retained the right to withdraw at any stage and were requested to consent to data usage in case of withdrawal. Additionally, permission was sought to share pertinent data with participating universities or regulatory bodies. Subjects were required to complete a questionnaire on personal and medical history, which could be obtained upon request from the corresponding author. This study was approved by the ethics committee of Shandong Sport University (No.2021005).

Table 1 Demographic characteristics mean and standard deviation

Protocol

The CAIT scores, history of ankle sprain, and experience of giving way were recorded before the tests. The CAIT was used to complete the assessment of stability. All eligible participants had their affected limbs tested for muscle strength with an isokinetic machine, proprioception on a testing platform, and dynamic balance using a Y balance test. (Fig. 1), with muscle strength measured last to avoid fatigue.

Fig. 1

Test illustrations. (A) Strength test. (B) Proprioception test. (C) Dynamic balance test

Self-reported instability

The CAIT was used to complete the assessment of self-reported instability, which is a 9-item questionnaire that scores ankle instability on a scale of 0-30 [7]. Lower scores indicate greater ankle instability. The IAC used a CAIT score of < 24 as an inclusion criterion for ankle instability [1].

Strength test

The ankle plantarflexion, dorsiflexion, inversion, and eversion strength on the injured side were assessed using a strength testing system (IsoMed 2000, D & R Ferstl GmbH, Germany), which demonstrated strong consistency in measuring ankle-related muscle movements (Intraclass Correlation Value, ICC = 0.77–0.98) [25]. In ankle plantarflexion and dorsiflexion test section, participants lay supine with their lower extremities fully extended on a dynamometer. A lap belt was used to secure their trunk, pelvis, and thighs to the seat. The dynamometer’s foot adapter was fixed to the participant’s foot in a matching position, with the ankle in a neutral position. All participants were instructed to perform three trials of maximal exertion dorsal/plantarflexion of the ankle at an angular speed of 30°/s for each direction on injured side, with a minimum of 2 min rest between trials. The test data will be corrected for the influence of the gravity-effect torque by applying static gravitational correction. In ankle inversion and eversion test section, the participant sits on the seat of the dynamometer. The tibia shall be horizontal to the ground. Set the dynamometer head and test seat to 80° and 45° respectively. Adjust the position of the safety valve to ensure participant safety and prevent excessive joint movement. All participants were instructed to perform three trials of maximal exertion inversion and eversion of the ankle at an angular speed of 30°/s for each direction on injured side, with a minimum of 2 min rest between trials. The lower velocity of 30◦/s was chosen because it is used to indicate maximum voluntary contraction [26].

Proprioception test

The ankle proprioception during ankle dorsal/plantarflexion, inversion, and eversion of the injured side were assessed by ankle passive detection sense with ankle joint proprioception testing device (Sunny, AP-II, China), which has good test-retest reliability (ICC = 0.74–0.94) [27].

The device consists of an operating panel and a test pedal. During the test, participants wore eye masks and noise-cancelling headphones and sat in their seats with their feet on the test pedals to minimize the influence of the external environment and to focus their attention on the feet part. The test pedal is driven by a motor for passive movement at 0.4°/s in the plantarflexion, dorsiflexion, inversion, and eversion directions. The operator performed the test in a random direction on the operating panel, and the participant stopped the pedal movement as soon as he/she felt the passive movement of the ankle joint. The angle of passive movement of the ankle joint was recorded as the threshold of joint movement, and the participants were asked to say the direction of passive movement, and each direction was repeated three times and the average value was taken for analysis.

Dynamic balance test

The dynamic balance was assessed in anterior, posteromedial, and posterolateral direction using the Star Excursion Balance Test (SEBT). The SEBT has been shown to have good test-retest reliability, the ICC for all directions ranged from 0.88 to 0.96 [28]. Each participant was given verbal and visual test explanations and instructed to practice in different directions before the formal test. The participant’s injured leg was used as the support leg for single leg bracing and the non-injured leg was used as the extension leg. During the assessment, subjects were asked to be barefoot. To minimize measurement error, a standardized foot position was used where the injured lower limb was placed as the stance foot in the center of the star so that the malleoli was in the center of the star. Subjects were asked to perform a single-legged deep squat with the supporting leg while keeping their hands on their hips. During the single-leg stance, participants slowly reached the extended leg as far as they could along the anterior, posteromedial, or posterolateral directions. The maximum reach distance in each direction was measured using a tape measure. The test data was normalized to the length of the participant’s leg and averaged over three tests in each direction.

Statistical analyses

All data analyses were performed with SPSS 25.0 (IBM Corp., Armonk, NY, USA) software. Descriptive statistics are expressed as mean ± standard deviation. All outcome variables were tested for normality using Shapiro-Wilk tests. Bivariate correlation analyses were performed using Pearson correlation for data that conformed to a normal distribution and Spearman correlation for data that were non-normally distributed. The thresholds for correlation coefficient were as follows: 0–0.1 (trivial), > 0.1–0.3 (weak), > 0.3–0.5 (moderate), and > 0.5 (strong) [29]. The level of significance was set at P < 0.05.

Results

Descriptive characteristics of all outcome variables, including strength, proprioception, and dynamic balance, are shown in Table 2 with mean, standard deviation, maximum and minimum values.

Table 2 Descriptive characteristics of outcome variables

The statistical results of the bivariate correlation analysis of CAIT Score with ankle strength are shown in Fig. 2. The results show that ankle plantarflexion (moderate, r = 0.378, 95%CI: 0.046–0.635, P = 0.027), inversion (strong, r = 0.527, 95%CI: 0.233–0.736, P = 0.001) strength were positively correlated with CAIT Score. However, ankle dorsiflexion, eversion strength were not significantly correlated with CAIT.

Fig. 2

The relationship between CAIT and ankle plantarflexion (A), dorsiflexion (B), inversion (C), and eversion (D) strength. Each point represents an individual subject (n = 34)

The statistical results of the bivariate correlation analysis of CAIT Score with ankle proprioception are shown in Fig. 3. The results show that only ankle inversion proprioception (moderate, r = -0.340, 95%CI: -0.608–0.002, P = 0.027) was negatively correlated with CAIT Score. However, ankle plantarflexion, dorsiflexion, and eversion proprioception were not significantly correlated with CAIT.

Fig. 3

The relationship between CAIT and ankle plantarflexion (A), dorsiflexion (B), inversion (C), and eversion (D) proprioception. Each point represents an individual subject (n = 34)

The statistical results of the bivariate correlation analysis of CAIT with dynamic balance are shown in Fig. 4. The results show that SEBT posteromedial (moderate, r = 0.444, 95%CI: 0.124–0.680, P = 0.009) was positively correlated with CAIT. However, SEBT anterior, and SEBT posterolateral were not significantly correlated with CAIT.

Fig. 4

The relationship CAIT and anterior (A), posteromedial (B), and posterolateral (C) direction dynamic balance. Each point represents an individual subject (n = 34)

Discussion

This study investigated the relationship between CAIT scores and ankle muscle strength, proprioception and dynamic balance using bivariate correlation analysis. The findings partially supported our hypothesis, indicating a significantly positive correlation between CAIT scores and dorsiflexion, inversion muscle strength, and posterior medial dynamic balance ability. Additionally, a significant negative correlation was observed with inversion proprioception.

Ankle muscle strength deficits are considered to be one of the most important causes of ankle instability [30]. The results of present study showed that both ankle plantarflexion and inversion muscle strengths were significantly correlated with CAIT scores. Although another previous study concluded that ankle plantarflexion and eversion strengths were not significantly correlated with ankle stability [31], the conflict may be due to differences in methods adoption of muscle strength measurement (previous studies used hand-held dynamometers). We found a significant positive correlation between CAIT scores and plantarflexion muscle strength, which is consistent with the previous studies [32]. This means that individuals with better plantarflexion strength of the foot scored higher on the CAIT test, and that a limited strength of plantarflexion may lead to reduced resistance of the foot to torsional movements, further might increasing the risk of ankle sprain injuries [33]. A study of CAIT-screened patients with CAI versus a healthy population in terms of isokinetic muscle strength found that plantarflexion maximal muscle strength was significantly lower in the CAI group than in the healthy control group [34]. Another study found plantarflexion torque deficits in functional ankle instability, and eccentric plantarflexion strength may be an important factor in functional ankle stability [35]. The above findings suggest that improving ankle plantarflexion strength may contribute to addressing functional ankle instability, providing additional context to the conclusions of our study. Our results also showed that CAIT scores were significantly positive correlated with inversion muscle strength. Inversion muscle strength refers to the strength of the muscle groups associated with inversion movements of the foot, and individuals with higher CAIT scores may have better inversion muscle strength. A previous study in a population of 103 patients with unilateral CAI found significant positive correlations between isokinetic muscle strength in inversion and the single leg balance test, the single heel raise test, and the lateral step test, suggesting that more attention should be given to developing ankle inversion muscle strength in the maintenance of dynamic and static balance [36]. Previous studies have indicated that an Eversion/Inversion ratio greater than 1.0 at an angular velocity of 120°/s increases the chance of ankle injury in basketball players [37]. Above our findings further suggest that more attention should be paid to ankle plantarflexion and inversion muscle strength in clinical rehabilitation to improve CAIT scores and enhance ankle stability more effectively.

Our findings indicated a significant negative correlation between CAIT scores and inversion proprioception. The lower CAIT score, which suggests greater self-reported ankle instability, correlated with higher inversion proprioception thresholds, indicating reduced sensitivity to inversion movements. This means that people who report higher instability have more difficulty detecting motion in the direction of inversion in proprioception. The correlation between inversion proprioception and CAIT scores is consistent with some studies [20]. So, the inversion proprioception might be the important factor for self-reported degree of ankle instability. However, another study was inconsistent with our findings and concluded that CAIT scores were not significantly correlated with inversion proprioception [38]. Differences in proprioceptive testing may explain the contradiction between the inversion proprioceptive results observed when completing different tasks [39, 40]. Central nervous system reorganization, particularly within the motor cortex, is the likely underlying mechanism for persisting neuromuscular deficits following peripheral joint injury [41]. Ligament injuries result in damage to proprioceptive nerve endings, which affects position, movement, force, and vibration senses [17, 42, 43]. The larger passive detection sense threshold is also positive associated with poorer sports performance and a higher risk of ankle sports injuries [30, 44]. Individuals with accurately perceive their inversion status may be more likely to be able to control ankle posture and motion, thereby reducing the risk of injury. Our findings support that ankle inversion proprioception is one of the keys to effectively improving CAIT scores, and that ankle inversion proprioception should be incorporated into screening and rehabilitation programs.

Our results also showed that there was a significant positive correlation between dynamic balance ability in the posteromedial direction and CAIT scores. Previous studies have shown that dynamic balance in the posteromedial direction of the SEBT is highly representative of the performance of all 8 components of the test in limbs differentiated with and without CAI, which is consistent with our findings [45]. Previous studies have shown that, compared to strength training, balance training can effectively improve CAIT scores and dynamic balance in the posteromedial and posterolateral directions in SEBT [46]. Postural control is a dynamic skill with two main goals—postural orientation and equilibrium—relying on sensory input from the somatosensory, vestibular, and visual systems, with their importance varying by task and environment [47]. The pre-motor areas, basal ganglia, and cerebellum play key roles in coordinating and controlling movement [48]. In individuals with chronic ankle instability, the resting motor threshold of the fibularis longus is higher bilaterally, suggesting that greater stimulation is needed to excite cortical neurons, potentially impairing motor command generation for the target muscle [49]. When postural control is compromised, an individual’s ability to manage dynamic balance, anticipate destabilizing forces, and adapt strategies may directly affect their perception of ankle instability, even if the ankle’s mechanical integrity is not significantly impaired. Overall, our findings emphasize the importance of CAIT and SEBT in assessing ankle stability, and that the combined use of CAIT and SEBT allows for a more comprehensive assessment of a patient’s ankle stability and provides a basis for further research and clinical application.

This study has several limitations. Firstly, the small sample size of our study is subject to random error and individual outliers or extreme values, which increases the error and uncertainty of the study. Second, the age of our participants was 22.47 ± 2.36, and the age factor has a greater impact on ankle muscle strength, proprioception, and dynamic balance, so this may affect the scope of application of our findings, especially in the elderly population of CAI patients. Thirdly, the passive proprioceptive assessment was used in this study, so the proprioceptive results in this study were limited to passive proprioception, while the results of active proprioception of the ankle may be different. Finally, we consider the potential for self-reporting bias as a limitation in our study. Despite this, we believe that the data collected provides valuable insights. However, it is important to note that the cross-sectional and correlational design of this study limits our ability to draw definitive conclusions about whether targeting these parameters can improve CAIT scores. Future research with longitudinal or experimental designs is needed to establish effective rehabilitation strategies for CAI patients.

Conclusion

There were significant positive correlations between CAIT scores and ankle plantarflexion, inversion muscle strength, and dynamic balance in the posteromedial direction, and significant negative correlations with inversion proprioception threshold. Therefore, further research with experimental designs is needed to establish effective rehabilitation methods for these indicators.