Preliminary study using shear wave elastography to evaluate anterior talofibular ligament stiffness in chronic ankle instability

Abstract

Introduction:

Anterior talofibular ligament injury is the most common type in chronic ankle instability patients. While initial injuries are often treated conservatively, some patients still require surgery. Shear wave elastography provides quantitative, accurate assessment of ligament damage, offering an objective basis for surgical planning and rehabilitation monitoring.

Method:

Shear wave elastography quantified shear wave velocity of bilateral anterior talofibular ligaments in neutral and stressed positions in 30 chronic ankle instability patients’ group and 60 healthy controls’ group. Functional assessments included the Cumberland Ankle Instability Tool, American Orthopaedic Foot & Ankle Society scale, Foot and Ankle Ability Measure for Activities of Daily Living and Foot and Ankle Ability Measure for Sports (FAAM-S) and Visual Analogue Scale for pain.

Results:

Inter-observer and test–retest reliability for anterior talofibular ligament shear wave velocity were excellent (neutral position: intraclass correlation coefficient = 0.87, 0.93; stressed position: intraclass correlation coefficient = 0.89, 0.96). Shear wave velocity showed no significant differences by gender, age or body mass index. Chronic ankle instability patients had significantly higher shear wave velocity in affected anterior talofibular ligaments (neutral/stressed, p < 0.001) versus healthy controls; unaffected sides showed no difference. Affected ankles scored significantly worse on Cumberland Ankle Instability Tool, Foot and Ankle Ability Measure for Activities of Daily Living, Ankle Ability Measure for Sports, American Orthopaedic Foot & Ankle Society and Visual Analogue Scale (p < 0.001). Shear wave velocity in affected anterior talofibular ligaments (both positions) positively correlated with pain intensity (neutral: r = 0.488, p = 0.004; stressed: r = 0.514, p = 0.004). Neutral-position shear wave velocity negatively correlated with Foot and Ankle Ability Measure for Activities of Daily Living (r = −0.457, p = 0.011), but not with Ankle Ability Measure for Sports, American Orthopaedic Foot & Ankle Society or Cumberland Ankle Instability Tool scores.

Conclusion:

Shear wave elastography noninvasively, conveniently and accurately assesses anterior talofibular ligament quality in chronic ankle instability patients, providing an objective approach for surgical decision-making and rehabilitation monitoring.

Introduction

Chronic ankle instability (CAI) ¹ results from lateral collateral ligament injury due to ankle sprain, primarily involving the anterior talofibular ligament (ATFL) with contusion or partial tear but no complete rupture. In total, 20%–40% of patients experience ankle pain, giving-way episodes, reduced athletic performance, recurrent sprains and even early osteoarthritis, significantly impairing daily activities and work capacity. ² While conservative management is standard for acute ATFL injuries, ³ 10%–30% of patients require surgical ligament repair or reconstruction after failed conservative treatment. Surgical selection depends on ligament injury severity, type, number, patient weight and activity level. ⁴ Thus, accurate ATFL assessment is critical.

Current CAI ligament evaluation methods include self-reported scales, imaging and clinical examination.^5,6 Imaging modalities encompass magnetic resonance imaging (MRI), stress radiography and ultrasound (US). MRI evaluates ATFL integrity and associated injuries, showing ligament thickening and wavy morphology in CAI. However, MRI has high sensitivity but low specificity for ATFL injury, lacks dynamic assessment, and is time-consuming and costly. Stress radiography diagnoses ATFL injury when the tibiotalar tilt angle exceeds,^5,7 but it is technically demanding, indirectly assesses ligaments and involves radiation exposure. US dynamically evaluates ligament continuity, thickness and echotexture changes in periarticular soft tissues. ⁸ Although highly sensitive (comparable to MRI), US cannot characterise tissue composition or biomechanical properties. Timely assessment of ligament healing and inflammation directly impacts clinical decision-making, necessitating novel CAI evaluation methods.

Shear wave ultrasound elastography (SWE) is a recently developed technology that quantifies tissue stiffness by generating transverse shear waves. It provides real-time colour-coded elasticity mapping and quantitative analysis of soft tissue elasticity. ⁹ While previously studied in hepatic, thyroid and breast applications,^10–12 SWE remains underutilised in musculoskeletal systems. Chen et al. ¹³ reported lower ATFL elasticity on injured versus uninjured sides in acute/subacute groups but not in chronic cases. Liu et al. ¹⁴ observed increased ATFL thickness in previously sprained ankles versus controls. Chen et al. ⁷ demonstrated reduced shear wave velocity (SWV) in ruptured versus intact Achilles tendons. By quantifying biomechanical properties, SWE offers insights into tissue composition and has gained clinical interest.

This study aims to evaluate ATFL stiffness in CAI patients using SWE and analyse its correlation with Cumberland Ankle Instability Tool (CAIT), Foot and Ankle Ability Measure (FAAM), American Orthopaedic Foot & Ankle Society (AOFAS) and Visual Analogue Scale (VAS) scores, thereby assessing SWE’s diagnostic value in ligament pathology.

Methods

Subjects

Thirty CAI patients (21 male, 9 female) treated at the Department of Sports Medicine, First Affiliated Hospital of Kunming Medical University from November 2021 to November 2022 were enrolled. Sixty healthy volunteers (30 male, 30 female) served as controls. Ethical approval was obtained before commencement of this project, and all participants voluntarily joined the trial and signed informed consent forms. Inclusion Criteria include: (1) met CAI diagnostic criteria; ¹⁵ (2) unilateral involvement; (3) aged 18–60 years; (4) no acute ankle sprain within 3 months; (5) failed 6-month conservative treatment; (6) prior US or MRI confirmed ATFL injury (contusion/partial tear without complete rupture) and (7) normal foot/ankle osseous structures. Exclusion criteria include (1) poorly visualised ATFL on ultrasound; (2) ankle injury (e.g. fracture/sprain) within 3 months; (3) history of major lower-limb surgery or trauma and (4) major memonths or autoimmune diseases.

Equipment

A Siemens ACUSON Sequoia digital colour Doppler US system (USA) equipped with SWE technology was used. A high-frequency linear array transducer (4–10 MHz) was employed.

Methods

Positioning

Participants were seated with the healthy knee flexed to approximately 90°, the limb placed in a semi-arc position, and the lateral foot facing the examiner.

Scanning planes

SWV was measured along the ATFL long axis (longitudinal plane) in two positions: (1) neutral (relaxed) position and (2) 25° plantarflexion-inversion (stressed position) (Figure 1).

Figure 1.

ATFL measurement positions: (a) neutral position and (b) stressed position.

SWE protocol

The transducer identified bony landmarks (fibular head, talus) to locate ATFL, ensuring perpendicular beam alignment-mode image was optimised (time-gain compensation, focus, depth) without probe pressure. SWE mode was activated (dual display: left = B-mode, right = electrogram) when images stabilised. A 20 × 10 mm measurement box was set with a 3-mm region of interest (ROI). SWV was recorded after pressing ‘Update’ after image stabilisation. Three consecutive SWV measurements per position per ankle were averaged (Figures 2 and 3).

Figure 2.

SWE of ATFL in a healthy 26-year-old male. (a) Neutral position: SWV = 2.21 m/s; (b) stressed position: SWV = 3.01 m/s. White arrows indicate ATFL; LM: lateral malleolus.

Figure 3.

SWE of affected ATFL in a 26-year-old male CAI patient. (a) Neutral position: SWV = 3.33 m/s; (b) stressed position: SWV = 4.20 m/s. White arrows indicate ATFL; LM: lateral malleolus.

Inter-observer reliability assessment

Two musculoskeletal sonographers (A and B) with ⩾5 years’ experience (including ⩾2 years in SWE) performed reliability testing. Forty ankles from 20 randomly selected healthy controls (HCs; 10 male, 10 female) were assessed. Both operators quantified ATFL identically. Operator A repeated measurements after 1 week. Three measurements (2-minute intervals, adequate rest between tests) were averaged per session. Participants rested 30 minutes post-assessment. Data were blinded to operators to ensure validity.

Questionnaire survey and pain intensity scale

1. CAIT: a 10-item standardised questionnaire assessing ankle instability symptoms (pain, mobility, dysfunction). Scores range 0–30 (higher = better stability).

2. FAAM: self-reported scale evaluating functional recovery,^16,17 comprising: FAAM Activities of Daily Living (FAAM-ADL): 21 items (max 84) and FAAM Sports (FAAM-S): 8 items (max 32). Higher scores indicate better function.

3. OFAS Scale: standardised instrument assessing pain, function, alignment and satisfaction. ¹⁸ Higher scores denote less impairment.

4. VAS: 10 cm line (0 = ‘no pain’ to 10 = ‘worst imaginable pain’) quantifying subjective pain intensity.

Statistical analysis

Data were analysed using SPSS 26.0. Normally distributed variables are expressed as mean ± SD; non-normal as median (interquartile range (IQR)). Group comparisons used independent t-tests (normal) or Mann–Whitney U-tests (non-normal). Categorical data analysed with chi-square tests. Spearman’s correlation assessed relationships. The significance is p < 0.05. Inter-operator (A vs. B) and intra-operator (A test–retest) reliability determined by intraclass correlation coefficient (ICC): >0.90 = excellent; 0.75–0.90 = good; 0.55–0.74 = moderate and <0.55 = poor. Standard error of measurement (SEM) and minimal detectable change (MDC) were calculated.

Results

Inter- and intra-observer reliability

SWE demonstrated excellent intra-observer reliability for ATFL SWV: Neutral position: ICC = 0.93 (95% confidence interval (CI) = 0.88-0.97), SEM < 0.06 m/s, MDC < 0.17 m/s and stressed position: ICC = 0.96 (95% CI = 0.92-0.98), SEM < 0.07 m/s, MDC < 0.19 m/s.

Good inter-observer reliability was observed: neutral position: ICC = 0.87 (95% CI = 0.76-0.93), SEM < 0.06 m/s, MDC < 0.17 m/s and stressed position: ICC = 0.89 (95% CI = 0.81-0.95), SEM < 0.07 m/s, MDC < 0.19 m/s (Table 1).

Table 1.

Inter-rater reliability and test–retest reliability of ATFL at different body positions in the healthy group.

	ATFL (neutral)			ATFL (stressed)
	$\overline{x}$ ± s (m/s)	SEM	MDC	$\overline{x}$ ± s (m/s)	SEM	MDC
Test A1	1.98 ± 0.39	0.06	0.17	3.22 ± 0.43	0.07	0.19
Test B	2.31 ± 0.36	0.06	0.17	3.31 ± 0.43	0.07	0.18
Test A2	2.18 ± 0.38	0.06	0.17	3.18 ± 0.41	0.06	0.19
ICCA1A2 (95% CI)	0.93 (0.88-0.97)			0.96 (0.92-0.98)
ICCA1B (95% CI)	0.87 (0.76-0.93)			0.89 (0.81-0.95)

ICC: intraclass correlation coefficient; CI: confidence interval; SEM (m/s): standard error of measurement; MDC (m/s): minimal detectable change; A1B: inter-rater reliability; A1A2: test-retest reliability.

Baseline characteristics

No significant differences existed between CAI patients and HCs in gender, age or body mass index (BMI) (all p > 0.05, Table 2).

Table 2.

Comparison of general clinical data between healthy group and CAI group.

	CAI group (n = 30)	Healthy group (n = 60)	χ2/Z	p
Age (years)	32.00 (11)	32.00 (22.00)	-0.468	0.640
Gender (male/female)	21/7	30/30	3.258	0.071
BMI (kg/m2)	21.31 (3.06)	21.15 (4.12)	-1.083	0.279

IQR for non-normally distributed variables. p < 0.05 indicates the statistical significance.

Gender effects on SWV

SWV showed no gender-based differences in either group at neutral/stressed positions (all p > 0.05, Tables 3 and 4).

Table 3.

The effect of gender on the SWV of ATFL in the healthy group (unit m/s).

	SWV value (m/s)		t/Z	p
	Male	Female
Right-neutral	2.10 (0.81)	2.06 (0.55)	-0.089	0.929
Right-stressed	3.21 (0.45)	3.17 (0.51)	-0.059	0.953
Left-neutral	2.16 ± 0.34	2.13 ± 0.43	-0.263	0.794
Left-stressed	3.06 (0.48)	3.15 (0.50)	-1.139	0.255

Mean ± SD for normally distributed variables; IQR for non-normally distributed variables. p < 0.05 indicates statistical significance.

Table 4.

The influence of gender on the SWV value of ATFL in CAI group (unit m/s).

	SWV value (m/s)		t/Z	p
	male	female
The neutral position of the affected side	2.72 ± 0.37	2.59 ± 0.33	0.940	0.355
The stressed position of the affected side	3.54 (0.90)	3.61 (0.85)	-0.475	0.657

Mean ± SD for normally distributed variables; IQR for non-normally distributed variables. p < 0.05 indicates the statistical significance.

Age/BMI correlations with SWV

Neither age nor BMI correlated with SWV in HCs (bilateral ankles) or CAI patients (affected ankles) at either position (all p > 0.05, Tables 5 and 6).

Table 5.

Correlation analysis of age and BMI with SWV of ATFL in healthy group.

			SWE value (left-stressed)	SWE value (right-neutral)	SWE value (eight-stressed)
Age	r(P)	0.070 (0.597)	-0.057 (0.663)	-0.087 (0.507)	0.012 (0.930)
BMI	r(P)	0.018 (0.892)	-0.030 (0.819)	-0.122 (0.352)	0.096 (0.467)

p < 0.05 indicates the statistical significance.

Table 6.

Correlation analysis between age and BMI in CAI group and SWV of ATFL on the affected side.

		SWE value (the neutral position of the affected side)	SWE value (the stressed position of the affected side)
Age	r(P)	0.130 (0.495)	0.057 (0.763)
BMI	r(P)	0.179 (0.344)	0.188 (0.320)

p < 0.05 indicates the statistical significance.

SWV comparisons

Affected ATFLs in CAI group exhibited higher SWV than unaffected sides at both positions (p < 0.001, Table 7).

Table 7.

The difference of SWV values of ATFL between the affected side and the healthy side in CAI group.

	SWV value of the affected side (m/s)	SWV value of the healthy side (m/s)	t/Z	p
The neutral position	2.80 (0.59)	2.08 (0.55)	-3.990	<0.001
The stressed position	3.68 ± 0.50	3.18 ± 0.26	4.872	<0.001

p < 0.05 indicates the statistical significance.

Affected ATFL SWV in CAI group exceeded HCs’ values at both positions (p < 0.001, Table 8).

Table 8.

Differences in SWV values between the affected side of CAI group and the healthy group.

	SWV value of the affected side in CAI group (m/s)	SWV value of healthy group (m/s)	Z	p
The neutral position	2.80 (0.59)	2.10 (0.67)	-5.985	<0.001
The stressed position	3.55 (0.93)	3.17 (0.47)	-4.626	<0.001

IQR for non-normally distributed variables. p < 0.05 indicates the statistical significance.

Functional score comparisons in CAI group

Affected ankles showed significantly lower CAIT, FAAM, AOFAS and VAS scores versus unaffected sides (p < 0.001, Table 9).

Table 9.

Comparison of each score scale between the affected side and the healthy side of the ankle joint in CAI group.

	The affected side	Health side	Z	p
FAAM Daily Activity Score	65.48 (21.13)	100.00 (1.19)	-4.785	<0.001
FAAM sports score	50.00 (25.75)	100.00 (0.78)	-4.519	<0.001
AOFAS score	53.00 (9.25)	100.00 (0.00)	-4.789	<0.001
CAIT score	15.00 (7.25)	30.00 (1.00)	-4.791	<0.001
VAS score	5.00 (1.00)	0.00 (0.00)	-4842	<0.001

IQR for non-normally distributed variables. p < 0.05 indicates the statistical significance.

SWV-functional score correlations in affected ankles

In the neutral position, there was a positive correlation with pain intensity (r = 0.488, p = 0.006) and a negative correlation with FAAM-ADL (r = −0.457, p = 0.011). No correlations with FAAM Sports (FAAM-S), AOFAS or CAIT. Stressed position: Positive correlation with pain intensity (r = 0.514, p = 0.004). No correlations with FAAM-ADL, FAAM-S, AOFAS or CAIT (Table 10).

Table 10.

Correlation analysis between CAI ankle joint affected side and each rating scale.

		FAAM daily activity score	FAAM physical activity score	AOFAS score	CAIT score	VAS score
The neutral position	r	-0.457*	-0.131	-0.238	-0.164	0.488**
	(P)	(0.011)	(0.489)	(0.206)	(0.385)	(0.006)
The stressed position	r	-0.274	0.034	0.011	-0.304	0.514**
	(P)	(0.143)	(0.860)	(0.954)	(0.103)	(0.004)

^*At the 0.05 level (two-tailed), the correlation is significant.

^**At the 0.01 level (two-tailed), the correlation is significant.

Discussion

CAI is a chronic sports injury primarily characterised by damage to the ATFL. Most patients experience mild symptoms such as joint swelling, pain and numbness. However, some develop significant structural and functional abnormalities of the ankle joint following recurrent sprains, leading to restricted movement that severely impacts daily activities and work. ² Clinically, conservative treatment is often adopted for asymptomatic patients with early ATFL injury. If conservative management fails, anatomical ligament repair or reconstruction surgery becomes necessary, requiring precise assessment of the ligament injury type, number, severity and healing potential to select the appropriate surgical technique. ⁴

Current conventional assessment methods have limitations. Self-assessment questionnaires are susceptible to patient subjectivity, while imaging techniques like US, MRI and stress radiography primarily evaluate ligament morphology.^5,6 SWE, however, can quantitatively and dynamically reflect tissue elasticity and biomechanical properties in real time. This allows for accurate assessment of ligament injury severity and healing potential, providing clinicians with a clear understanding of the injury specifics to guide surgical decision-making. ¹⁹ Post-surgery and rehabilitation, SWE enables comprehensive evaluation of ATFL recovery by comparing results with pre-operative and interim rehabilitation assessments, determining if rehabilitation goals are met and guiding subsequent treatment and functional recovery. As SWE does not require probe pressure, it reduces operator dependence and demonstrates good reliability and reproducibility. In this study, intra-rater reliability for ATFL assessment was excellent in both the neutral position (ICC = 0.93) and stressed position (ICC = 0.96). Inter-rater reliability was also good (ICC = 0.87 in neutral, ICC = 0.89 in stressed). These findings indicate that SWE provides a reliable and reproducible assessment of ATFL elasticity, establishing it as a credible and feasible method for real-time quantitative evaluation of ATFL injury in CAI patients.

Our results show that gender has no significant effect on ATFL elasticity values, and age and BMI show no correlation with ATFL elasticity, which is generally consistent with previous findings. Hotfiel et al. ²⁰ evaluated the ATFL in 32 women and 28 men, finding no significant differences in elasticity values based on gender or side (left/right). While some studies on muscles and tendons suggest gender effects on elasticity, findings vary. For instance, Bedewi et al. ²¹ reported significant differences in shear wave elasticity values between left and right scalenus medius muscles, but not for the scalenus anterior, with no influence from gender or BMI. Liu et al. ²² found no statistically significant difference in relaxed gastrocnemius elasticity among different age groups in healthy subjects, but under stress, the elasticity in the elderly group (>55 years) was significantly higher than in children (<16 years) and middle-aged adults (30–40 years). Therefore, further research is warranted to confirm potential influencing factors on ligament elasticity.

Ligaments are highly organised, dense fibrous connective tissues. Following injury, healing occurs via scar formation. Normal ligaments consist mainly of type I collagen, while healed ligaments exhibit increased collagen fibre density over time, ultimately leading to altered elasticity and ligament thickening. ²³ Our results demonstrate that SWE-derived SWV values in the affected ATFL of CAI patients were significantly higher than those in the asymptomatic side and the HC group, regardless of whether the ligament was in a neutral or stressed position. Furthermore, the affected ATFL’s elasticity was higher in the stressed position compared to the neutral position. Previous literature indicates increased ligament elasticity in chronic injuries, although no prior studies specifically investigated SWE for ATFL assessment in CAI patients. Wu et al. ²⁴ compared the elasticity of the Coracohumeral Ligament (CHL) in 30 healthy subjects and 20 patients with chronic frozen shoulder. They found higher CHL elasticity in the stressed position across all subjects (p < 0.01). Patients showed higher CHL thickness and elasticity on the affected side compared to the asymptomatic side, while healthy subjects exhibited no significant difference in CHL elasticity between dominant and non-dominant shoulders. Thus, SWE can accurately quantify increased stiffness in chronically injured ligaments, muscles and tendons under various pathological conditions.

This study compared CAIT, FAAM, AOFAS and VAS scores between the affected and asymptomatic sides in CAI patients. Scores were significantly lower on the affected side, aligning with previous research. ²⁵ Correlation analysis between these scores and ATFL elasticity revealed: a negative correlation between neutral-position SWV in the affected ATFL and FAAM Activities of Daily Living (ADL) score (r = −0.458, p = 0.011); a positive correlation between neutral-position SWV and pain intensity (r = 0.438, p = 0.016) and a positive correlation between stressed-position SWV and pain intensity (r = 0.521, p = 0.003). Adal et al. ²⁶ demonstrated a positive correlation between VAS pain scores and ankle instability, potentially due to altered biomechanics between the talus and ankle joint in unstable ankles, leading to imbalanced loading and degenerative changes in the medial ankle cartilage of CAI patients. No significant correlations were found between affected ATFL SWV and FAAM Sports score, AOFAS score or CAIT score, possibly due to the multifactorial nature of these scales and the limited sample size for elasticity measurements. Future studies should further explore the correlation between SWE and clinical diagnostic scores in CAI to assess their combined value in early screening or treatment monitoring.

In this study, we utilised SWE to objectively assess and analyse ATFL injury in CAI patients, comparing them with HCs. We innovatively incorporated potential confounding factors (age, gender, BMI) and performed correlation analysis with commonly used CAI assessment scales. This preliminary investigation explored the quantitative assessment and influencing factors of SWE for ATFL injury in CAI. Key findings include SWE demonstrated high inter-rater and intra-rater reliability; ATFL SWV was significantly higher in the stressed position than in the neutral position; SWV in the affected ATFL of CAI patients was significantly increased compared to the asymptomatic side and HCs and affected ATFL SWV correlated positively with VAS pain scores. These results suggest SWE is a highly reliable and promising tool for evaluating ATFL injury in CAI patients. However, limitations exist; this was a single-centre study with a relatively small sample size; it focused solely on ATFL injury, excluding other lateral ligaments; patients were not stratified by chronicity, functional/mechanical instability or symptom duration, potentially obscuring their effects on ATFL stiffness. Future large-scale, multi-centre studies incorporating more patient data (demographics, injury duration/type, surgical details, assessment scores, SWE data) are needed to identify independent risk factors for CAI development and progression. Building predictive models could assist clinicians in more accurately assessing CAI severity, selecting optimal treatments and guiding long-term patient management.

Conclusion

In summary, SWE is a practical, rapid, non-invasive and reproducible US technique capable of accurately assessing ATFL changes under different conditions, thereby objectively evaluating ligament biomechanics. The ATFL elasticity values measured in healthy adults in this study provide reference data for future research and offer clinical value in diagnosing ligament injuries and monitoring recovery. Furthermore, integrating SWE with clinical assessment scales provides a comprehensive understanding of ligament status, offering a scientific basis for determining and adjusting treatment strategies.