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The evaluation of rotational lateral ankle laxity in gravity stress position by ultrasonography: normative value in uninjured ankles

BMC Musculoskeletal Disorders volume 25, Article number: 764 (2024) Cite this article

Abstract

Background

The evaluation of lateral ankle laxity remains challenging when diagnosing chronic lateral ankle instability (CLAI). Several studies have reported that internal rotation of the talus as an indicator of rotational lateral ankle laxity (RLAL) increases in patients with CLAI. However, there is no established method for detecting and evaluating the RLAL. This study aimed to report a novel method for evaluating the RLAL in the gravity stress position by measuring the talofibular distance (TFD) using ultrasonography (US) and show the normative value of the TFD.

Methods

The TFDs in the subjects with healthy ankles were prospectively measured 10 mm distal to the ankle joint in the neutral ankle position and gravity stress position using US. The differences in the TFD between the two ankle positions were evaluated. The differences in the TFD by gender and ankle laterality were also evaluated.

Results

A total of 52 healthy ankles of 28 subjects (mean age, 24.0 ± 1.6; male/female, 12/16) were finally included. There was a significant difference in the TFD between the neutral ankle position (6.9 ± 0.9 mm) and gravity stress position (9.0 ± 0.9 mm) (p < 0.001). The mean difference in the TFD between the two ankle positions was 2.1 ± 0.6 mm. There were no significant differences in the TFD by gender and ankle laterality.

Conclusions

The present study reported a novel US method for evaluating RLAL by applying gravity stress and the normative value of the TFD.

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Background

Lateral ankle sprain (LAS) is one of the most common musculoskeletal disorders in the general population as well as in the athletic population [1,2,3]. If left untreated or not properly treated, 20–74% of patients with LAS develop chronic lateral ankle instability (CLAI) [4, 5]. CLAI is clinically diagnosed based on the patient’s history, physical examination findings, and imaging findings. However, the evaluation of lateral ankle laxity remains challenging for orthopaedic surgeons [3, 6]. Previous studies did not use standardized methods for evaluating lateral ankle laxity pre- or post-operatively, resulting in non-standardized diagnoses, surgical indications, and definitions of failure after CLAI surgery [6, 7]. Therefore, further advancements in imaging modalities to detect and assess lateral ankle laxity are required.

Previous studies have reported that internal rotation of the talus as an indicator of rotational lateral ankle laxity (RLAL) increases in patients with CLAI, mainly because of anterior talofibular ligament (ATFL) insufficiency [8,9,10,11,12,13,14]. Li et al. reported that the internal rotation of the talus assessed by magnetic resonance imaging (MRI) significantly decreased after surgery for CLAI [14]. However, in this study, MRI scans were obtained with the patients in the supine position, and dynamic assessment of RLAL was not performed. Some authors reported the usefulness of anterolateral drawer test (ALDT) or reverse ALDT for detecting RLAL [15, 16]. However, these physical examination tests are subjective and affected by the examiner’s experience. There is a lack of studies reporting the methods for evaluating RLAL. Advancements in the assessment of RLAL would lead to the ability to perform a comprehensive evaluation of lateral ankle laxity in patients with CLAI.

The gravity stress view has been shown to be useful and reliable for detecting deltoid ligament insufficiency [17,18,19,20]. The reported advantages of this technique include that the force of gravity is constant without being affected by the examiner’s skill, the patient’s ankle position and muscle activation, or the extent of pain [19, 20]. It was hypothesized that the evaluation of RLAL by applying gravity stress would be useful and reliable. In the gravity stress position, the talus internally rotates with the ankle joint in the natural plantarflexion.

The purpose of this study is to introduce a novel method for evaluating RLAL in the gravity stress position using ultrasonography (US) and report the normative extent of RLAL in uninjured ankles.

Methods

This cross-sectional study was approved by the institutional review board (Approval No. O-0987). All procedures were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and the Declaration of Helsinki of 1975, as revised in 2013.

Study subjects

Healthy young adult volunteers of 20 to 30 years old had been consecutively recruited at a single institute from September 2023. Study participants were contacted at university hospital buildings and several university facilities. All participants provided their written informed consent before participating in this study. The exclusion criteria of this study were as follows: history of ankle sprain and giving way of the ankle, prior surgery to the foot or ankle, presence of foot or ankle pain at the time of examination, ankle osteoarthritis, and inflammatory arthritis. The possibility of recall bias in the history of ankle sprains was also considered [12]. Therefore, to obtain US data from uninjured ankles, participants were also excluded if the absence of ATFL, lax and wavy ATFL, or avulsion fracture of the lateral malleolus was confirmed by US [11, 21].

A total of 52 ankles from 28 subjects were finally included in this study after excluding 4 ankles as follows: a history of ankle surgery (N = 1), absence of ATFL (N = 1), or a lax and wavy ATFL (N = 3). The study included 12 males and 16 females with mean ages of 24.7 ± 2.4 (range, 20–29) years old and 23.3 ± 1.6 (range, 20–27) years old, respectively. The participants’ demographic data are presented in Table 1. Generalized joint laxity (GJL) was assessed using the Beighton score [22].

Table 1 Participant’s demographic data (N = 28)
Full size table

The US evaluation of the RLAL

All US images were captured using an ALOKA ARIETTA 850 US apparatus (FUJIFILM, Tokyo, Japan) with a linear probe (L64 probe; 18 − 5 MHz). The spatial resolution of this US apparatus was as follows: axial resolution, ≤ 0.8 mm; lateral resolution, ≤ 3.0 mm. In this study, to evaluate the internal rotation of the talus as an indicator of RLAL, the talofibular distance (TFD) was measured by US in two different positions: in the neutral ankle position and in the gravity stress position. In the neutral ankle position, the subject was placed in supine position with the ankle joint maintained in a neutral position (Fig. 1-A). In the gravity stress position, the subject was placed in the lateral decubitus position, with the evaluated ankle hanging down from the end of the examination table. In this position, internal rotation of the talus occurs with the ankle joint in the natural plantarflexion owing to gravity stress (Fig. 1-B). When the right ankle was evaluated, US evaluation was performed with the patient in the left lateral decubitus position, which is the opposite of the gravity stress test for evaluating the medial clear space of the ankle joint [17]. The subject was instructed to relax the evaluated ankle when obtaining US pictures. The patient’s hip was kept neutral in abduction/adduction using pillows with the patella facing a wall in order to standardize the method of measurement (Fig. 1-B).

Fig. 1
figure 1

Ankle positions when measuring the talofibular distance by ultrasonography. (A) The neutral ankle position. The patient was placed in the supine position with the ankle joint maintained in a neutral position. Line 1, ankle joint line; Line 2, 10 mm distal from Line 1. (B) The gravity stress position. The patient was placed in the lateral decubitus position with the lateral aspect of the evaluated ankle facing upward. By applying gravity stress, the talus internally rotates with the ankle in the natural plantarflexion

Full size image

In both positions, the ankle joint level was confirmed using US (Fig. 2). The marker was then used to draw two lines: one along the ankle joint line and another 10 mm distal and parallel to the joint line (Fig. 1-A). In this study, the TFD was measured 10 mm distal to the ankle joint level using digital calipers included with the US apparatus (Figs. 3 and 4). In each method, pictures were taken while keeping the TFD centered on the screen. TFD was defined as the linear distance from the fibula to the talus.

Fig. 2
figure 2

Confirmation of the ankle joint level using ultrasonography. By placing the center of the probe at the ankle joint, the ankle joint level can be identified. Ti, tibia; Ta, talus

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Fig. 3
figure 3

Ultrasonographic measurement of the talofibular distance (TFD) in the gravity stress position. In this study, the TFD was measured 10 mm distal to the ankle joint (The red line is the ankle joint level)

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Fig. 4
figure 4

Ultrasonographic measurement of the talofibular distance (TFD) in the neutral ankle position (A) and in the gravity stress position (B). TFD is defined as the linear distance from the fibula to the talus (red arrow). F, fibula; Ta, talus

Full size image

The reliability of the US measurements was confirmed by calculating intraclass correlation coefficients (ICCs). TFDs in the two conditions were measured independently by two senior orthopaedic surgeons to evaluate the inter-rater reliability. An examiner repeated the measurements four weeks later to confirm intra-rater reliability. The mean values obtained by the two examiners were used for data analyses.

Statistical analyses

Data analyses were performed using the SAS software program (JMP Pro, ver. 17.2.0; SAS Institute, Cary, NC, USA). Statistical significance was set at p < 0.05. The results were reported as mean values with standard deviations. The normality of the data distribution was confirmed using the Shapiro-Wilk test. To compare the results between the two ankle positions and the right vs. left side, the paired Student t-test or Wilcoxon rank-sum test was performed. Student t test or the Mann-Whitney U test was conducted to compare continuous data between male and female subjects. ICCs were rated using the Landis’s classification (slight, 0.0-0.20; fair, 0.21–0.40; moderate, 0.41–0.60; substantial, 0.61–0.80; almost perfect, 0.81-1.00) [23]. The sample size was based on previous studies that established reference values for a healthy cohort [24,25,26].

Results

Reliability of the US measurement of the TFD

The intra- and inter-rater reliabilities of US measurements are shown in Table 2. All ICCs were > 0.8, indicating almost perfect agreement.

Table 2 Intra- and inter-rater reliability of US measurement
Full size table

TFD in the neutral ankle and gravity stress positions

The results of TFD in each ankle position are shown in Table 3. The TFDs in the neutral ankle and gravity stress positions were 6.9 ± 0.9 mm and 9.0 ± 0.9 mm, respectively, and there was a statistically significant difference between the two positions (p < 0.001). The mean difference in the TFD between the two ankle positions was 2.1 ± 0.6 mm.

Table 3 Results of talo-fibular distance in each ankle position
Full size table

There was no significant difference by gender in the TFD in the neutral ankle (p = 0.59) and gravity stress (p = 0.50) position. There was also no significant difference by ankle laterality in the TFD in the neutral ankle (p = 0.24) or gravity stress (p = 0.30) position (Table 4).

Table 4 Comparison of bilateral ankles
Full size table

Discussion

The present study reported a novel US method for evaluating RLAL by measuring the TFD while applying gravity stress. As a preliminary study, uninjured ankles from young adult subjects were included to investigate the normative value of the TFD. This US procedure has excellent reliability and can detect RLAL in the healthy ankles. The normative value of the TFD in the gravity stress position was 9.0 ± 0.9 mm, and the TFD increased by 2.1 ± 0.6 mm from the neutral ankle position to the gravity stress position.

The quantitative evaluation of lateral ankle laxity in patients with CLAI remains a challenge [3, 6, 27]. Regarding imaging modalities for detecting lateral ankle laxity, stress radiography, arthrometer, capacitance-type sensor, and stress US have been reported [12, 27,28,29]. However, at present, there is no established modality for assessing lateral ankle laxity, resulting in non-standardized diagnosis of CLAI and criteria for failure after CLAI surgery [6]. Most studies have not objectively evaluated pre- and post-operative lateral ankle laxity in patients with CLAI [7].

Several authors have reported that the internal rotation of the talus increases in ankles with injured lateral ankle ligaments [8,9,10,11,12,13,14]. Dalmau-Pastor et al. have recently demonstrated that sectioning of the ATFL, especially the superior fascicle of the ATFL, caused increased internal rotation and anterior translation of the talus [13]. Additionally, rotational ankle instability is a hot topic [30,31,32]. Rotational ankle instability involves a combination of lesions in the lateral and medial ligamentous complex [32]. Considering that the majority of ankle sprains are LAS [1], it is a common clinical scenario that increased lateral ankle laxity following LAS causes deltoid ligament instability, resulting in rotational ankle instability [30, 31]. Rotational ankle instability is also a risk factor for secondary ankle osteoarthritis [33]. However, at present, there is no useful method reported for evaluating RLAL.

In the presented technique, the talus internally rotates with plantarflexion of the ankle joint by applying gravity stress. The TFD, as an indicator of RLAL, can be reliably and repeatably measured in healthy ankles. In addition, the TFD was not influenced by gender or ankle laterality. Furthermore, US is generally non-invasive, free from exposure to radiation, and non-expensive. Thus, the proposed US method may serve as a promising method for evaluating RLAL. Regarding anterior cruciate ligament injury, methods of detecting rotational knee laxity have been introduced and utilized [34,35,36]. Similar to the knee joint, by introducing and improving the method for evaluating RLAL in patients with CLAI, orthopaedic surgeons will better understand and be able to more effectively consider the biomechanical pathology of CLAI, which would contribute to advancements in the management of CLAI. Future studies, including cadaveric studies, are needed to further clarify whether or not the evaluation of RLAL by applying gravity stress is a reliable method for evaluating RLAL in patients with acute or chronic lateral ankle ligament injuries.

The present study has several limitations. First, this was a cross-sectional study with a small sample size. However, previous studies that established normative findings in healthy subjects had the same sample sizes as our study [24,25,26]. Second, the US procedure generally depends on the examiner’s experience and skill. In this study, almost perfect agreement of the intra- and inter-rater reliabilities was demonstrated using the presented US technique. Third, this study evaluated only a young adult cohort and did not include other age groups. The participant’s age may affect the study findings. Fourth, this study did not evaluate patients with CLAI. However, RLAL in healthy ankles could be detected by applying gravity stress. Future studies, such as cadaveric studies and clinical studies using radiographic evaluation, are needed to confirm that significant differences in the TFD are detected between patients with and without CLAI. Despite these limitations, this is the first study to investigate RLAL in subjects with healthy ankles by using a novel US measurement in the gravity stress position. The study findings would serve as a reference value for RLAL and contribute to advancements in the evaluation of RLAL in patients with CLAI.

Conclusions

This study reported a novel US method for assessing RLAL by measuring the TFD while applying gravity stress. In subjects with healthy ankles, the mean TFD in the gravity stress position was 9.0 mm, which increased by 2.1 mm from the neutral ankle position to the gravity stress position. Future studies are needed to verify the usefulness of the reported procedure when evaluating RLAL in patients with CLAI.

Data availability

All data are available from the corresponding author upon reasonable request.

Abbreviations

LAS:

Lateral ankle sprain

CLAI:

Chronic lateral ankle instability

RLAL:

Rotational lateral ankle laxity

ATFL:

Anterior talofibular ligament

MRI:

Magnetic resonance imaging

ALDT:

Anterolateral drawer test

US:

Ultrasonography

GJL:

Generalized joint laxity

TFD:

Talofibular distance

ICC:

Intraclass correlation coefficient

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Authors and Affiliations

  1. Division of Orthopaedic Surgery, Department of Medicine of Sensory and Motor Organs, Faculty of Medicine, University of Miyazaki, Kihara, Kiyotake, 5200, 889-1692, Miyazaki, Japan

    Takuji Yokoe, Fan Yang, Takuya Tajima & Etsuo Chosa

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Contributions

TY: conception and design, drafting of the article. FY: acquisition and analysis of the data. TT: conception and design. EC: conception and design, supervision of the study. All authors read and approved the final manuscript.

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Correspondence to Takuji Yokoe.

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Ethical approval of this study was obtained from the institutional review board at Miyazaki University Graduate School of Medicine (Approval NO. O-0987). This study was performed in accordance with the Declaration of Helsinki. Written informed consent was obtained from all subjects. Informed consent was obtained from all individual participants included in the study.

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Yokoe, T., Yang, F., Tajima, T. et al. The evaluation of rotational lateral ankle laxity in gravity stress position by ultrasonography: normative value in uninjured ankles. BMC Musculoskelet Disord 25, 764 (2024). https://doi.org/10.1186/s12891-024-07881-5

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BMC Musculoskeletal Disorders

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