The use of MRI in pre-operative evaluation of anterior talofibular ligament in chronic ankle instability

Article focus

In cases where surgery is considered for symptomatic chronic ankle instability (CAI), it is imperative not only to detect injured lesions but also to document the extent of ligament tear and the quantity of residual ligamentous tissue.

This study aimed to evaluate the applicability of MRI for the quantitative assessment of anterior talofibular ligaments (ATFLs) in symptomatic CAI.

Key messages

On pre-operative MRI, ATFLs were abnormal in all 39 cases and classified as ten ‘thickened’ and 29 ‘thin or absent’.

In all cases pre-operatively categorised as ‘thickened’, residual ligaments were thick enough to be advanced, as observed during surgery, and graft replacement was not required. In the remaining cases, we were unable to detect bulky or normal residual tissue, and reconstruction had to be performed.

MRI is valuable as a pre-operative assessment tool that can provide the quantitative information of ATFLs in CAI patients.

Strengths and limitations

This study is based on the experience of a single surgeon.

Stress radiography was performed under general anaesthesia immediately prior to surgery.

Small numbers were involved in this study.

Introduction

Acute lateral ankle ligament lesions are the most common injuries sustained in sports and recreational activities.^1,2 Although most of these injuries can be treated successfully with conservative treatment, the development of chronic ankle instability (CAI), characterised by the occurrence of repetitive ankle sprains and persistence of symptoms after the initial injury, is not uncommon.^3-5 Increased ligamentous laxity is one of the main causes of residual symptoms after ankle sprains, and failure of appropriate conservative management is an indication for surgical treatment.^6,7 The anterior talofibular ligament (ATFL) is the main lateral stabiliser of the ankle joint and is most commonly affected first, followed by the calcaneofibular ligament (CFL) and the posterior talofibular ligament (PTFL).^8,9 In cases where surgery is considered for symptomatic CAI, it is imperative not only to detect injured lesions but also to document the extent of ligament tear and the quantity of residual ligamentous tissue, as anatomic repair is recommended when the quality of the ruptured ligaments permits, and anatomic reconstruction should be performed when ligaments are attenuated.^10,11 Although various imaging techniques such as stress radiography and MRI have been used for diagnosis,^12-15 few studies have examined the sensitivities of evaluation methods in providing information about residual ligamentous tissue.¹⁶

In this study, we pre-operatively assessed injured ATFLs in symptomatic CAI patients by MRI and stress radiography under general anaesthesia. Using surgical findings as the gold standard, we evaluated the use of these two methods as pre-operative assessment tools. We hypothesised that pre-operative MRI can quantitatively evaluate injured ATFLs, and is useful in surgical planning.

Patients and Methods

Pre-operative MRI evaluation

On T2-weighted images, maximum diameters of the ATFLs were measured and classified into three categories based on a previously published method¹⁷ with modifications: ‘normal’, diameter = 1.0 to 3.2 mm; ‘thickened’, diameter > 3.2 mm; ‘thin or absent’, diameter < 1.0 mm (Fig. 1). Cases in which the continuity of the ATFL could not be confirmed were classified as ‘absent’.

Figs. 1a - 1c

Axial T2-weighted images showing typical ATFL findings (white arrows). T and F denote tibia and fibula, respectively, the MRI evaluation was undertaken pre-operatively, and maximum diameters of the anterior talofibular ligaments (ATFLs) were measured.

Surgical findings

ATFLs were evaluated and classified into two categories during surgery: ‘thickened’, an obvious thickened ligament; ‘thin or absent’, a maximum diameter of < 1.0 mm or when the path of the ligamentous tissue from the anterior aspect of the distal fibula at the malleolar fossa level to the neck of the talus was undetectable (Fig. 2).

Figs. 2a - 2b

Photographs showing the typical intra-operative appearance of injured anterior talofibular ligaments (ATFLs), either a) ‘thickened’ or b) ‘thin or absent’.

Results

ATFLs in all patients were abnormal at surgery. ‘Thickened’ and ‘thin or absent’ ATFLs were observed in ten and 29 cases, respectively (Table I).

There were no gender- or age-related differences between the two groups. The time between initial injury and surgery was significantly different in the two groups (thickened, 2.3 years (sd 2.2); thin or absent, 6.4 years (sd 6.1), p = 0.006).

Stress radiography and surgical findings

The mean talar tilt was 14.4 (sd 6.3°) (Table II, Fig 3). Comparison of the two groups categorised by surgical findings revealed a significant difference (thickened, 11.2 (sd 4.8°); thin or absent, 15.5 (sd 6.4°); p = 0.037). The angle of talar tilt did not have a significant effect on categorisation based on surgical findings using the logistic regression analysis (odds ratio: 0.872; p = 0.072), and a clear cut-off angle, which would allow discrimination between ‘thickened’ and ‘thin or absent’ patients, was not identified (Fig. 3); p = 0.037). The angle of talar tilt did not have a significant effect on categorisation based on surgical findings using the logistic regression analysis (odds ratio: 0.872; p = 0.072), and a clear cut-off angle, which would allow discrimination between ‘thickened’ and ‘thin or absent’ patients, was not identified (Fig. 3). The angle of talar tilt did not have a significant effect on categorisation based on surgical findings using the logistic regression analysis (odds ratio: 0.872; p = 0.072), and a clear cut-off angle, which would allow discrimination between ‘thickened’ and ‘thin or absent’ patients, was not identified (Fig. 3), and a clear cut-off angle, which would allow discrimination between ‘thickened’ and ‘thin or absent’ patients, was not identified (Fig. 3).

Fig. 3

Stress radiography data distribution for surgically-established anterior talofibular ligament (ATFL) categories. Angles of talar tilt were significantly different in the two surgically-established groups (thickened, 11.2 (sd 4.8°); thin or absent, 15.5 (sd 6.4°); p = 0.037). A clear cut-off angle was not identified.

Discussion

CAI not only limits physical activity, but also leads to an increased risk of osteoarthritis, and patients with severe disability often need surgical treatment to restore mechanical stability.^5,19,20 Although various imaging methods, such as stress radiography, MRI, computed tomography, and ultrasonography, are available to facilitate precise diagnosis, the first two methods are most frequently used.^7,21

The anterior drawer test and talar tilt stress radiographs are commonly used in the clinical setting.^18,22However, these measurements correlate poorly with the degree of ligamentous disruption due to large individual variations.^15,17,23Some patients have bilateral ankle sprains, which render comparison with the contralateral side unreliable. Furthermore, some investigators claim that radiographic stress tests cause pain and muscle spasms that restrict movement unless the joint is anaesthetised.^14,15,18 To overcome these problems, both stress radiographs in the present study were obtained under general anaesthesia in the operating room and a side-by-side comparison was not performed. The mean angle of talar tilt was smaller in those patients with a thickened ATFL than in those whose ATFL was thin or absent. However, a clear cut-off angle, which would allow discrimination between thickened and thin or absent, was not identified. These data are consistent with previous reports.^12,23

MRI is commonly used as a less invasive technique for diagnosing acute lateral ankle ligament injury.^15,23,24However, its use in CAI is controversial.^12,14,17Cardone et al¹⁷ examined 43 CAI patients and developed a set of diagnostic criteria in MRI for abnormalities of the ankle ligament. After comparing the results of stress radiography in 23 patients, they concluded that MRI is more useful than stress radiography for identifying injured ligaments. Chandnani et al¹² compared the efficacy of conventional MRI, MR arthrography, and stress radiography in 17 CAI patients and found that MRI has a sensitivity of 50% in the diagnosis of ATFL and CFL tears, which is similar to that of stress radiography. Oae et al¹⁴ performed stress radiography, ultrasonography, MRI, and arthroscopy in 15 cases of chronic ankle sprains. Using arthroscopic results as the gold standard, both MRI and stress radiography yielded 93% accuracy in ATFL injury diagnoses. The discrepancy between these two results may be due to the lack of common diagnostic criteria in MRI findings for ankle ligament injury, as well as differences in imaging protocols. In our study, maximum diameters of the ATFLs were measured from T2-weighted axial images in the neutral ankle position, as described by Cardone et al.¹⁷ This protocol generates reproducible images, allowing objective evaluation of injured ligaments. In all of our cases, residual ATFLs were diagnosed as abnormal by pre-operative MRI and confirmed during surgery. The accuracy of ATFL injury diagnosis was higher or equal to those previously reported.^12,14,17

Several studies have correlated imaging findings with surgical findings in CAI.^12,14,16,17 However, to the best of our knowledge, this is the first report to examine the use of MRI in the quantitative evaluation of residual ligamentous tissues in CAI patients. In this study, patients were categorised into three groups according to maximum diameters of residual ATFLs measured by pre-operative MRI. In all cases pre-operatively categorised as thickened, residual ligaments were thick enough to be advanced, as observed during surgery, and graft replacement was not required. In the remaining cases, we were unable to detect bulky or normal residual tissue, and reconstruction had to be performed.²⁵ Retrospectively, surgical procedures can be chosen according to the extent of residual ligamentous tissues predicted by pre-operative MRI. As the reconstruction procedure requires graft preparation, accurate pre-operative planning has substantial merit. In our study, the quantity of ATFLs were well evaluated. However, MRI evaluation of the quality of ligaments is difficult, partially due to the lack of a standard evaluation method. This is an issue to be addressed in future studies.

In conclusion, our results show that MRI is capable of quantitatively evaluating the injured ATFL. We believe that pre-operative MRI is useful as an adjunct to stress radiography in surgical planning.