Magnetic resonance imaging-based assessment of lateral ligament injury and soft-tissue swelling in ankle trauma: Correlation and clinical predictive value

INTRODUCTION

Ankle injuries rank among the most common musculoskeletal problems encountered in clinical settings, often resulting from sports, falls, and everyday activities.^[1-3] The lateral ligaments of the ankle, notably the anterior talofibular ligament (ATFL) and the calcaneo-fibular ligament (CFL), are particularly susceptible to injury due to their essential role in stabilizing the ankle during inversion movements.^[4,5] While fractures are easily detected through standard radiographic imaging, assessing soft-tissue injuries, particularly ligament damage, presents a more complex challenge. Soft-tissue swelling is a frequent response to ankle trauma and can be a crucial indicator of underlying ligamentous damage. However, the precise relationship between the degree of swelling and specific ligament injuries has not been extensively studied. Magnetic resonance imaging (MRI) provides detailed views of both bone and soft-tissue structures, making it an invaluable tool for diagnosing ligament injuries and associated soft-tissue changes.^[6]

This study aims to find the relationship between lateral ligament injury and soft-tissue swelling in patients presenting with ankle injuries without fractures, using MRI. Through this study, we aim to identify specific swelling measurements that correlate with high-grade ligamentous injuries. Radiographs have inherent limitations in interpreting soft-tissue injuries such as ligament tears. This underscores the importance of our study, which aims to understand the relationship between soft-tissue swelling and ligamentous injury as shown on MRI and will allow clinicians to make more informed interpretations of swelling on radiographs. Our study aims to enhance clinical decision-making, allowing for more accurate and timely identification of significant ligament injuries, and streamline the pathway to appropriate management and rehabilitation. For example, when a radiograph reveals significant soft-tissue swelling, clinicians can use the thresholds identified in this study to determine whether further imaging, such as MRI, is necessary. Utilizing this information, healthcare providers can better prioritize patients for MRI based on radiographic findings, thereby optimizing resource use. Patients with swelling measurements below the identified thresholds might be managed conservatively without immediate MRI, while those exceeding the thresholds can be fast-tracked for further imaging.

MATERIALS AND METHODS

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All MRIs were evaluated by two musculoskeletal fellowship-trained radiologists, with 20 and 8 years of experience, respectively, in a single setting. The radiologists were blinded to the actual MRI reports and each other’s interpretations. Examples of some of the scans presented to the radiologists are shown in Figures 1 to 4.

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Figure 1:

Proton density fat-suppressed (a) axial and (b) coronal of the left ankle showing thickened edematous anterior talofibular ligament in keeping with high-grade 2 sprain and the measurements of medial and lateral soft-tissue swelling.

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Figure 2

Proton density fat-suppressed (a) axial and (b) coronal of left ankle showing full-thickness tear of the anterior talofibular ligament and thickened, edematous calcaneofibular ligament in keeping with high-grade 2 sprain and the measurements of medial and lateral soft-tissue swelling.

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Figure 3:

Analysis of the medial/lateral malleolar swelling ratio revealed an area under the curve of 0.636 (95% confidence interval : 0.500–0.773), indicating moderate ability to discriminate.

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Figure 4:

Isolated lateral swelling exhibited an area under the curve of 0.842 (95% confidence interval : 0.756–0.927). ROC: Receiver operating curve

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RESULTS

The study included 100 consecutive patients diagnosed with ankle injuries without fractures. The cohort comprised 67 males and 33 females, with an average age of 20.6 years (range: 8–38 years, standard deviation [SD] = 6.1). All patients underwent MRI within 1 week of their injury to minimize variations in the presentation of acute soft-tissue changes. The average thickness of soft tissue around the lateral malleolus was 2.16 mm (range: 1.0–10.0 mm, SD = 1.37 mm), while the medial malleolar thickness averaged 1.69 mm (range: 1.0–6.6 mm, SD = 0.83 mm). The cases were classified into subgroups based on ligament integrity: 66 patients had normal ligaments, 4 patients had isolated ATFL injuries, 1 patient had an isolated CFL injury, 4 patients had isolated AITFL injuries, 3 patients had combined ATFL and AITFL injuries, and 22 patients had combined ATFL and CFL injuries.

Isolated lateral swelling demonstrated the best discriminative ability, with an area under the curve (AUC) of 0.842 (95% CI : 0.756–0.927). A lateral swelling measurement exceeding 2.5 mm was found to be 91% specific and 51% sensitive for predicting high-grade lateral ligamentous injury. A swelling ratio (lateral to medial) >1.6 was 91% sensitive and 55% specific for detecting high-grade lateral ligamentous injury. This ratio was particularly useful in identifying more severe injuries when isolated lateral swelling was ambiguous. The swelling ratio (medial to lateral) had an AUC of 0.636 (95% confidence interval [CI] 0.500–0.773), indicating a moderate ability to discriminate between normal and injured ligaments [Figures 3 and 4].

Statistical analysis revealed a highly significant association between lateral ligamentous injury and both lateral swelling (P < 0.0001) and the swelling ratio (lateral to medial soft-tissue thickness) (P = 0.0001) [Tables 1 and 2]. These findings underscore the clinical relevance of measuring soft-tissue swelling in the evaluation of ankle injuries. Significant differences in swelling were observed between certain ligament injury groups (P = 0.046). The most notable difference was between the normal group and the ATFL + CFL injury group (P = 0.031), indicating that combined injuries result in more pronounced swelling. There was good interobserver reliability with a kappa of 0.8.

DISCUSSION

While the ascendancy of MRI for elucidating the anatomy and pathology linked to soft tissues is an established fact,^[8,9] due to cost and time limitations, it is also important to assess which patients actually require one. Our study aimed to establish a threshold of soft-tissue swelling over the ankle that would serve as a pointer for clinicians to identify patients at risk of ligament injury and allow them to earmark this group of patients for further investigation using MRI. Toward this aim, we have successfully established that this is a fruitful arena where further investigations will provide incrementally supportive outcomes. We found the individual thresholds for medial and lateral malleolar swellings, along with the fact that the swelling ratio can function as a suitable adjunct to identify injured ligaments, and also that these findings are particularly useful in identifying lateral ligament injury.

Our study also established that the likelihood of detecting combined ligament injuries is higher when utilizing this approach. We were unable to find any relevant published research aiming to establish such a correlation.

The lateral ligament complex includes the ATFL, CFL, AITFL, and PTFL, and together these are the most commonly injured ligaments.^[10] Often, injury of one of these is associated with a combined injury in another ligament; therefore, the chances of finding combined ligament injuries are much higher in these.^[11] As elucidated in our results section, our approach would be particularly useful for clinicians to identify this group, as combined injuries result in more pronounced swelling. Moreover, the results of our study demonstrated that both the linear threshold and swelling ratio identified by us are significantly associated with lateral ligament injuries. Conventionally, clinicians tend to recommend a radiograph as the first step in the diagnostic ladder for a patient presenting with an ankle injury, and a majority of patients end up with a radiograph.^[12] In a meta-analysis to establish if clinicians could indeed diagnose ankle injuries solely by clinical tests, the authors concluded that, as of now, there are no tests that are conclusively diagnostic. Hence, investigations are an indispensable component for the management of such a patient.^[13] Typically, radiographs are utilized to rule out the presence of a fracture, and a subsequent MRI is performed depending on the severity and time frame of the symptoms. However, if the radiograph could serve as a tool providing clues to the clinician of the likelihood of a ligament injury, such patients could be prioritized for an MRI and could have a definitive diagnosis sooner rather than later. This lead time cannot be understated because it is a researched fact that patients with ankle injuries who do not receive a timely diagnosis and therapy^[14] or are misdiagnosed often suffer from chronic ankle instability.^[15]

Beyond the acute setting, MRI also plays a pivotal role in the evaluation of chronic ankle instability, where it not only delineates persistent ligamentous laxity but also identifies associated pathologies such as osteochondral lesions and synovial changes that may influence long-term management.^[16] In addition, the spectrum of ankle injuries varies with different sporting activities, and recent literature has highlighted the value of imaging in sport-specific patterns, such as cricket-related ankle trauma, where MRI can help differentiate subtle ligamentous and soft-tissue injuries that may otherwise be underrecognized on conventional radiographs.^[17] Finally, while imaging remains the cornerstone for non-invasive diagnosis, arthroscopy continues to serve as both a diagnostic and therapeutic modality in ankle ligament injuries. It allows direct visualization of intra-articular pathology, facilitates grading of ligament injury severity, and enables simultaneous intervention, thereby complementing the diagnostic performance of MRI.^[18]

Recent advances, including radiomics-based MRI assessment,^[19] combined ultrasonography and MRI evaluation,^[20] and quantitative MRI metrics such as CFL cross-sectional area,^[21] further underscore the evolving role of imaging for predicting ankle ligament injuries and instability.

Despite the strengths of this study, several limitations should be acknowledged. First, the retrospective design inherently limits the control over variables and can introduce selection bias. Although the study included a well-defined cohort of 100 patients, the exclusion of cases with fractures or MRI performed beyond one week of injury may not fully represent the broader spectrum of ankle injuries. The variability in MRI scan parameters, while minimized, could still introduce variability in the soft-tissue measurements. Furthermore, the interpretation of MRI was conducted by only two radiologists, which may limit the generalizability of the findings and the reproducibility of measurements across different settings or radiologists. Furthermore, the study did not account for the potential impact of varying injury mechanisms or patient activities, which could influence swelling patterns and injury severity. In addition, the swelling evolves over time, and measurements obtained on day 1 may differ from those on day 5 or 6. Although all MRIs were performed within one week, we did not stratify by exact day post-injury; this remains a variable that could be addressed in future prospective studies. Finally, data regarding the use of anti-inflammatory medication, corticosteroids, or diuretics in the immediate post-injury period were not consistently available and thus could not be analyzed. Addressing these limitations in future research could help validate and extend the findings of this study. Our study serves as a pilot study for future studies, which can be designed prospectively and can encompass a larger sample size. Further, a validation study documenting the effectiveness of these thresholds in clinical practice can be planned.

CONCLUSION

This study provides valuable insights into the relationship between soft-tissue swelling and lateral ligament injuries in the absence of fractures, using MRI as a diagnostic tool. We established thresholds for soft-tissue swelling that can serve as indicators for identifying patients with a higher likelihood of ligament injuries on radiographs. These thresholds offer a practical approach for clinicians to determine the need for further imaging and prioritize patients based on radiographic findings. This method could enhance diagnostic accuracy and facilitate timely management, potentially improving outcomes for patients with ankle injuries. It allows for rapid identification of patients and helps resolve diagnostic uncertainties regarding the necessity and timing of MRI. However, the study’s limitations, including its retrospective design and reliance on a single imaging modality, highlight the need for further research to validate these findings and explore additional diagnostic approaches. Overall, the results contribute to a better understanding of how soft-tissue swelling correlates with ligament injuries and may support more informed clinical decision-making in managing ankle injuries.