Ultrasound assessment of lateral ankle ligament alterations and correlation with clinical tests in acute ankle sprain: A prospective cross-sectional study

INTRODUCTION

Acute ankle ligament injuries represent a prevalent category of musculoskeletal injuries frequently observed in clinical practice.^[1,2] It accounts for approximately 10–30% of sports-related orthopedic emergency visits.^[3] It commonly involves the lateral collateral ligament (LCL) complex in 85% of cases.^[4,5] LCL complex comprises of the anterior talofibular ligament (ATFL), calcaneofibular ligament (CFL), and posterior talofibular ligament (PTFL).^[6,7] It typically occurs due to an inversion mechanism involving plantarflexion of the foot. The ATFL is recognized as the most vulnerable ligament in the ankle, making it particularly susceptible to injury.^[8,9] In addition, the anterior inferior tibiofibular ligament (AITFL) is another structure that frequently sustains injury. It is the most vulnerable syndesmotic ligament to be injured when exposed to axial rotation.^[1] An acute ankle sprain can be effectively managed through conservative treatment methods; however, in cases where chronic ankle instability develops, surgical intervention is often regarded as the definitive course of action.^[10] The preliminary evaluation of an ankle injury encompasses a series of clinical assessments specifically targeted at the ankle joint. The comprehensive nature of ligamentous injury following an acute ankle sprain is frequently not accurately delineated through clinical evaluation methods due to factors such as pain, swelling, and the risk of additional injury.^[1] Consequently, ultrasonography is employed as a tool for the initial assessment of ligamentous injuries. Musculoskeletal ultrasound (USG) is a cost-effective and readily available imaging modality that can be performed at the bedside. In addition, USG is a real-time, dynamic imaging study that helps accurately diagnose ligamentous injuries, focusing on the point of maximum tenderness adjacent to any avulsion fracture at the ligament attachment site.^[4,9] The basis of musculoskeletal USG in acute ankle sprain is that the ankle ligament thickness is symmetrical in two healthy limbs without previous injuries. Few studies have demonstrated quantifiable differences in ankle ligament thickness between uninjured and injured limbs; however, most have only investigated chronic injuries (>12 weeks post-injury). In our study, we aim to compare the alterations in ankle ligament thickness, fibrillary pattern, and echogenicity between the injured and uninjured contralateral limbs using ultrasound following an acute ankle sprain of <2 weeks’ duration.

MATERIAL AND METHODS

A prospective, single-center, cross-sectional observational study was conducted over 18 months (January 2023 to June 2024) at a tertiary care center in North India, with prior approval from the Institutional Ethics Committee of Indira Gandhi Medical College and Hospital, Shimla {No. HFW (MC-II) B (12) ETHICS/2023/11317/Dated January 01, 2023}. Written informed consent was obtained from all participants enrolled in the study before their participation. The inclusion criteria were patients presenting in the orthopedic department with an acute ankle injury of <2 weeks’ duration with no history of previous ankle trauma. The cases were the injured limbs, and the controls were the contralateral uninjured limbs of these patients. Complete ligament tears were excluded as they could distort ligament thickness measurements. The other exclusion criteria included previous self-reported history of ankle sprain/injury, ankle surgery, pregnancy, diabetes, and medical history of connective tissue diseases such as Ehlers–Danlos syndrome and Marfan syndrome.

All patients underwent a clinical assessment by an orthopedic specialist with more than 3 years of experience. An X-ray of the injured foot was done to exclude a fracture. The physical assessments encompassed the anterior drawer test to evaluate the ATFL, the crossed leg test to assess the AITFL, and the talar tilt test to examine the integrity of the CFL.

The anterior drawer test is a conventional physical examination method used to assess ankle instability. The primary objective of this assessment is to evaluate the integrity of the ATFL by analyzing the anterior translation of the talus beneath the tibia in the sagittal plane. An observable increase in the anterior translation of the talus on the affected side, in comparison to the unaffected side, serves as an indicator of a positive test result. The crossed leg test involves the patient sitting in a chair, positioning the middle to distal one-third of the leg to be evaluated across the knee of the contralateral leg. The patient then exerts a gentle downward force on the knee of the affected leg. Pain in the ankle, especially in the region of the distal tibiofibular joint, constitutes a positive result. This finding may suggest a potential syndesmotic injury of AITFL. The talar tilt test is a widely utilized physical examination technique in clinical practice to assess the integrity of the CFL. This test evaluates CFL integrity by simultaneously assessing the talocrural and subtalar joints, although it carries the risk of overestimating ankle joint laxity. The examiner observes the talus for excessive tilting or “tilting” on the fibula. The test is typically performed on both ankles for comparison.^[2,11]

Sonography of the three ankle ligaments of the injured and uninjured limbs was performed on the same day. Ultrasonography was performed on a Samsung RS80 EVO machine using a high-frequency linear probe (10–13 MHz) or a hockey stick probe (8–18 MHz). Patients were examined while lying on their backs, with their knees bent at a 90° angle. A single consultant radiologist, having 11 years of experience in musculoskeletal ultrasound, and blinded to the clinical test results, conducted the sonographic assessment of the ATFL, AITFL, and CFL complex along the longitudinal axis. The ATFL [Figure 1] originates from the anterior rim of the lateral malleolus of the fibula and inserts into the lateral aspect of the talus at the talar neck. During an ankle inversion, this ligament is most commonly strained. The AITFL [Figure 2] is positioned between the anterior aspect of the distal fibula and the anterior part of the tibia, playing a crucial role in stabilizing the inferior tibiofibular joint. It usually measures <2 mm in width. The CFL [Figure 3] represents the central portion of the LCL and measures approximately 2 mm in width, characterized by its notable strength and length.^[12] This ligament extends from the distal aspect of the lateral malleolus to the lateral surface of the calcaneus. It becomes taut when the ankle is dorsiflexed. The USG parameters that were studied included the thickness at the midsubstance of the ligament from the outer edge to the outer edge of the ligament, fibrillar pattern, and echogenicity of these ligaments of the injured and the uninjured contralateral limb.

Close

Figure 1:

Ultrasound of the anterior talofibular ligament (ATFL) (arrow) was performed by placing the transducer in the transverse plane (longitudinal to the ATFL) anterior to the tip of the lateral malleolus. Tal: Talus, Fib: Fibula

Export to PPT

Close

Figure 2:

Ultrasound of the anterior inferior tibiofibular ligament (AITFL) (arrow) was performed by placing the transducer over the AITFL in the axial plane, about 1 cm proximal to the joint line, with 5–10° passive dorsal flexion. Tib: Tibia, Fib: Fibula

Export to PPT

Close

Figure 3:

Ultrasound of the calcaneofibular ligament (CFL) (arrow) was performed by placing the transducer along the frontal plane from the lateral malleolus to the lateral aspect of the calcaneum (longitudinal to the CFL).

Export to PPT

RESULTS

In the current study, 50 patients were enrolled, with an age range of 13–48 years and a mean age of 30.5 ± 8.5 years. Most patients belonged to the 21–30-year age group (40%). Of these, 58% were male, and 42% were female. In the comparison of ankle ligament thickness of uninjured limbs between male and female patients, the thickness of only AITFL was statistically significant [Table 1]. Furthermore, 58% of the patients had left limb injuries, and 42% had right limb injuries. A comparison of the average thickness of the ATFL, AITFL, and CFL between the uninjured and injured limbs was conducted, revealing a statistically significant difference in the thickness of the ATFL and AITFL with a P < 0.001 [Table 2]. There was an increase of >20% in the thickness of these ligaments in the injured limb from ligaments in the uninjured limb. The ATFL was the most commonly injured ligament in our study, accounting for 92% of cases, followed by AITFL and CFL, which accounted for 46% and 28%, respectively [Table 3]. As far as the number of ligament injuries in the same patient was concerned, there were 25 (50%) patients with single ligament injury [Figure 4], 17 (34%) patients with double ligament injury [Figures 5 and 6] and 8 (16%) patients with triple ligament injury [Figure 7]. ATFL was the most common single ligament injury, and the combined injury of ATFL and AITFL was the most common double ligament injury. All 25 patients with complex ligament injuries (double or triple ligament injuries) showed an injury to the ATFL in common [Table 4].

Close

Figure 4:

A 37-year-old female with a right ankle sprain and single ligament injury. Sonographic grayscale image shows (a) thickened right anterior talofibular ligament (ATFL) with loss of fibrillar pattern and peri ligamentous fluid, (b) normal left ATFL, (c) normal right anterior inferior tibiofibular ligament (AITFL), (d) normal left AITFL, (e) normal right calcaneofibular ligament (CFL), (f) normal left CFL.

Export to PPT

Close

Figure 5:

A 25-year-old female with a right ankle sprain and double ligament injury. Sonographic grayscale image shows (a) thickened right anterior talofibular ligament (ATFL), (b) normal left ATFL, (c) thickened right anterior inferior tibiofibular ligament (AITFL) with loss of fibrillar pattern and hypoechoic appearance of the ligament, (d) normal left AITFL, (e) normal right calcaneofibular ligament (CFL), (f) normal left CFL.

Export to PPT

Close

Figure 6:

A 13-year-old male with a right ankle sprain and double ligament injury. Sonographic grayscale image shows (a) thickened right anterior talofibular ligament (ATFL) with loss of fibrillar pattern and hypoechoic appearance of the ligament, (b) normal left ATFL, (c) thickened right anterior inferior tibiofibular ligament (AITFL) with loss of fibrillar pattern and hypoechoic appearance of the ligament, (d) normal left AITFL, (e) normal right calcaneofibular ligament (CFL), (f) normal left CFL.

Export to PPT

Close

Figure 7:

A 32-year-old woman with a right ankle sprain and triple ligament injury. Sonographic grayscale image shows (a) thickened right anterior talofibular ligament (ATFL) with loss of fibrillar pattern and hypoechoic appearance of the ligament, (b) normal left ATFL, (c) thickened right anterior inferior tibiofibular ligament (AITFL), (d) normal left AITFL, (e) thickened right calcaneofibular ligament (CFL) with loss of fibrillar pattern and hypoechoic appearance of the ligament, (f) normal left CFL.

Export to PPT

The echogenicity and the disruption of the fibrillar pattern of the injured ligaments were also compared with the uninjured ligaments. The ATFL fibrillar pattern was lost in 38 patients, the AITFL fibrillar pattern was lost in 20 patients, and the CFL fibrillar pattern was lost in 10 patients, with a significant P < 0.001, therefore signifying that the ligaments showing loss of fibrillar pattern were acutely injured. The ATFL was hypoechoic in 36 patients, AITFL was hypoechoic in 18 patients, and CFL was hypoechoic in 7 patients, with a P < 0.001, which was again statistically significant, thereby signifying that the ligaments showing a hypoechoic appearance on USG were acutely injured [Supplementary Table 1].

Clinical tests were also performed to assess ligament injuries (ATFL, AITFL, and CFL) in injured and uninjured limbs before sonography. The anterior drawer test, when conducted on the injured limb, was positive in 44 patients and negative in 6 out of 50, suggesting that 44 patients had ATFL injuries. The crossed leg test, when conducted on the injured limb, was positive in eight cases, suggesting an AITFL injury. The talar tilt test was positive in two cases of injured limbs, suggesting CFL injury [Supplementary Table 2]. The anterior drawer test was positive in 44 out of 46 patients, with significantly thickened ATFL on USG, as indicated by a P < 0.01. This finding suggests that patients with a positive anterior drawer test had acutely injured ATFL. The crossed leg test was positive in eight patients out of 23 patients with significantly thickened AITFL on USG, yielding an insignificant P = 0.39. This suggests that, compared to ultrasound, the crossed leg test was not able to accurately identify the acutely injured AITFL. The talar tilt test was positive in 2 out of 14 patients who had significantly thickened CFL on USG, with an insignificant P = 0.07, which also raises questions about the accuracy of the talar tilt test in accurately identifying the acutely injured CFL [Supplementary Table 3].

DISCUSSION

An acute ankle sprain represents one of the most prevalent musculoskeletal injuries, particularly among athletes. This injury entails damage to the ligaments that provide stability to the ankle joint, including the lateral ligament complex, the medial deltoid ligament, and the syndesmotic ligament. The lateral ligament complex is the most commonly affected area in ankle injuries. It consists of three ligaments: The ATFL, the CFL, and the PTFL. Together, these ligaments form the LCL structure. The ligaments that are most frequently injured in ankle sprains are the ATFL, the AITFL, and the CFL. Approximately 70% of lateral ankle sprains involve the ATFL, which is the weakest ligament in the lateral ligament complex and, therefore, the most commonly injured.^[8] The most common mechanism of injury involves a combination of ankle inversion and adduction with the foot in plantar flexion, leading to injury of the lateral ligamentous complex.^[5] Seventy percent of individuals who suffer from ankle sprains experience prolonged recurrent symptoms, which can ultimately lead to chronic ankle instability.^[14] It can also lead to osteoarthritis of the ankle joint, increased risk of falls, and adverse psychological effects. An acute ankle sprain can be managed conservatively through rest, ice, compression, and elevation of the limb (RICE), as well as analgesics, anti-inflammatory medications, bracing, and immobilization. Among these interventions, exercise and bracing are highly recommended during the rehabilitation process.^[15] Once chronic ankle instability sets in, a surgical procedure such as anatomical repair or reconstruction of the ATFL, AITFL, or CFL is required for its treatment.^[10] An accurate diagnosis and appropriate initial treatment of acute ankle sprains are essential to mitigate the risk of long-term complications.

The physical manual tests typically performed are the anterior drawer test for the ATFL, the crossed leg test for the AITFL, and the talar tilt test for the CFL.^[16] While acute ankle sprains are typically diagnosed through clinical examination, accurately determining the extent and range of ligament injury during the acute phase of injury is challenging due to pain and swelling. The diagnostic accuracy, reliability, and validity of physical examination tests for assessing ankle instability are notably limited.^[17] This limitation may result in suboptimal management and treatment, thereby increasing the likelihood of recurrent sprains and adversely affecting the repair and recovery process.

Ultrasound (USG) is the primary imaging tool for assessing injuries and is preferred over other modalities like magnetic resonance imaging (MRI) due to its availability, cost-effectiveness, and ability to provide high spatial and contrast resolution images. Real-time dynamic maneuvers can be performed during the ultrasound examination, enhancing the visibility of the ligaments. In addition, ultrasound can be used for follow-up assessments during the rehabilitation process.

While MRI can directly visualize ankle ligaments and detect injuries, it has certain limitations. MRI is often more expensive, time-consuming, and not as readily available as ultrasound, and it has limited spatial resolution.^[18] Patients with metallic implants are not suitable candidates for MRI scans due to safety concerns. In addition, the internal structure of ligaments is poorly visualized in MRI imaging because ligaments contain a limited number of mobile hydrogen protons, leading to minimal or even undetectable signals. Furthermore, MRI is a static imaging technique, which does not allow for dynamic movements of the ankle to assess various ligaments effectively.^[1]

Ligaments can be assessed through ultrasound to determine if they are injured and to classify the injury as either a partial or complete tear. In the case of a complete acute ankle ligament tear, the ligament will be discontinuous across the joint, resulting in an increased distance between the origin and insertion points of the ligament.^[19] The most consistent finding observed on ultrasound in acute partial ligament tears is known as “ligament thickening.” This thickening can be identified by visually comparing the ligament in question with the corresponding ligament in the uninjured opposite limb. The thickening of the ligament occurs due to increased cellularity and fluid accumulation within the ligament tissue, as well as disorganized remodeling.^[1] Other sonographic findings that may be observed in the case of an acute partial ankle ligament tear include ligament hypoechogenicity, a heterogeneous fibrillar pattern, irregularities in the ligament borders, disruption of the surrounding soft tissues, bony irregularities at the ligament enthesis, and the possibility of avulsion fractures.^[9] Musculoskeletal ultrasound (USG) is an effective tool for detecting early ligament injuries. However, its clinical use has been limited due to the lack of formal training in its implementation. When used correctly, USG can enhance diagnostic accuracy and reduce the time to treatment, ultimately improving patient satisfaction.^[20,21]

The diagnostic accuracy of ultrasound (USG) for diagnosing injuries to the ATFL was reported to be 91% in a study conducted by Oae et al.,^[22] 95.2% in research by Hua et al.,^[23] and 84.2% according to the findings of Cheng et al.^[24] In 2016, Cho et al. conducted a study in which they identified the presence of both laxity and waviness of the ATFL on stress ultrasound in all cases examined, indicating a prevalence of 100% within their sample. They concluded that stress ultrasound may serve as a valuable tool in diagnosing chronic ankle instability.^[25]

George et al.^[26] established a moderate positive correlation between clinical assessments and ultrasound grading of the ATFL and CEL, evidenced by Spearman’s correlation coefficient values of 0.58 and 0.66, respectively. The clinical grading of the anterior drawer test demonstrated a sensitivity of 59.1%, while ultrasound grading achieved a specificity of 100.0%. Furthermore, the clinical grading of the talar tilt test exhibited a sensitivity of 54.5%, while ultrasound grading consistently maintained a specificity of 100.0%.

Hosseinian et al.^[27] demonstrated that ultrasonography was an effective complementary tool for the initial evaluation of ankle injuries. Conversely, clinical tests are not sufficiently reliable to exclude ankle ligament injuries. In their study, the anterior drawer test demonstrated a sensitivity of 81% and a specificity of 80% in the identification of ATFL injuries. Ultrasonography demonstrated exceptional performance in clinical evaluation, achieving a sensitivity and specificity of 100% in distinguishing between a normal ATFL and a ligament that has sustained a tear or sprain, as evidenced by a kappa value of 1.

In our study, an injury to the ATFL was the most commonly observed ligamentous injury associated with acute ankle sprains. Among the 50 cases analyzed, we identified 21 cases (42%) of isolated ATFL injuries. In cases of double ligamentous injury, ATFL injuries were present in 12 instances, occurring alongside injury to the AITFL in 11 cases (22%) and to the CFL in one case (2%). In addition, we noted eight cases (16%) of triple ligamentous injuries. This finding aligns with the study conducted by Song et al.,^[4] which also reported that ATFL injury was the most prevalent.

CONCLUSION

Our study found that patients with acute ankle sprains exhibited a significant increase in the thickness of the injured ligaments, as evaluated using ultrasonography, compared to the uninjured ligaments of the opposite limb. In addition to the increased ligament thickness, we observed a loss of the normal fibrillar pattern and a hypoechoic appearance in the injured ligaments. Among clinical tests, the anterior drawer test showed the highest correlation with USG findings, particularly for ATFL injuries. When we compared the ultrasonographic findings to clinical tests, it became clear that ultrasound was more effective for detecting acute ligament injuries. Hence, ultrasonographic evaluation can be utilized for the early diagnosis of acute ligament injuries, enabling prompt treatment and reducing complications associated with delayed diagnosis and treatment.