High ankle sprain: sonographic demonstration of a posterior inferior tibiofibular ligament avulsion

Abstract

Syndesmotic injuries, also referred as high ankle sprains, may cause significant ankle instability and chronic pain. Ultrasound (US) is a well-proven imaging modality to evaluate the ligaments of the ankle, due to its high spatial resolution and the possibility to perform dynamic examinations. However, considering the syndesmosis complex, the sonographic appearance of the posterior inferior tibiofibular ligament (PITFL) is not well described in the pertinent literature and, to the best of our knowledge, we found no report of PITFL avulsion demonstrated at US, as in the case presented.

Introduction

Ankle injuries are common and may result in ligament(s) disruption.

Traumas involving the syndesmosis of the distal tibiofibular joint are known as high ankle sprains, resulting from high-energy injuries, typically in sportsmen. These injuries may cause significant ankle instability and chronic pain; therefore, a correct diagnosis is important to provide adequate treatment [1].

Ultrasound (US) imaging is widely used for the evaluation of ankle ligaments, [2, 3]; however, there are only a few papers regarding the normal ultrasonographic appearance of the posterior inferior tibiofibular ligament (PITFL) [4–6], and to the best of our knowledge, there are no reports in literature regarding injuries of this particular ligament depicted at US imaging. We report a case of traumatic PITFL avulsion in an amateur soccer player, demonstrated during a sonographic examination of the ankle.

Case report

A 32-year-old man referred to our clinic for pain and ankle instability after a trauma, occurred 20 days before, during a soccer match. Using an ankle orthosis, the patient was able to perform common daily activities (i.e., walking, working).

US examination was performed with a Toshiba Aplio 500 using a linear multifrequency transducer operating at 5–14 MHz multifrequency probe. The relevant structures of the ankle which may be involved in a trauma, including tendons, joint recesses, ligaments, and retinacula were systematically checked [2, 3, 7].

The tibiotalar joint was distended by an anechoic fluid. There were no remarkable tendon alterations. Medially, the deltoid ligament appeared normo-echoic. Laterally, the anterior talofibular ligament was thickened, reflecting a partial tear. A similar appearance was depicted for the anterior inferior tibiofibular ligament AITFL. The calcaneofibular ligament was regular. Posteriorly, a small bony avulsion at the tibial insertion of the PITFL was demonstrated (Fig. 1). The fragment measured approximately 3 mm. Hyperemia at Doppler evaluation was also present (Fig. 1c). Compression over the posterior aspect of the distal tibiofibular joint reproduced the symptoms complained by the patient.

Fig. 1.

Avulsion of the posterior inferior tibiofibular ligament (PITFL). a and b Sagittal and axial-oblique sonograms at the level of the distal tibiofibular joint. Note an avulsed fragment (arrow), with posterior acoustic shadowing, in proximity to the tibial insertion of the PITFL (asterisk). c Sagittal Doppler sonogram demonstrates hyperemia near the fragment. d Computed tomography 3D schematic drawing of the injury. Positions of the probe (black rectangles) over the posterior aspect of the distal tibiofibular joint. Fib indicates the fibula, Tib tibia

The patient, an amateur soccer player, preferred not to perform a radiographic study of the ankle, which was advised. A conservative approach (i.e., rest, managing of sport loads coupled with using of ankle orthosis) was planned with good clinical outcomes at 3 months.

Discussion

The distal tibiofibular joint is a syndesmosis formed by two bones—the tibia and the fibula—linked by the AITFL, the PITFL, and the interosseous ligament; the latter can be considered the distal continuation of the interosseous membrane [8]. This anatomical architecture/arrangement provides stability to the tibiofibular mortise during the physiological movements of hinge and glide [9].

The PITFL is formed by two components, the superficial one originates at the posterior edge of the lateral malleolus and directs to the posterior tibial tubercle in a proximal and medial direction, and the authors usually refer to it as the proper PITFL; the deep component (also called the transverse ligament) originates in the proximal area of the malleolar fossa and directs to the posterior edge of the tibia [8].

Syndesmotic injuries are usually caused by excessive external ankle rotation, or combination of ankle dorsiflexion and adduction or abduction of the foot [1].

In high ankle sprains, commonly the first involved ligament is the AITFL, then the interosseous membrane can be injured, then the PITFL, which is infrequently damaged. As the PITFL is a strong ligament, excessive stress forces may result in a posterior malleolus avulsion, as in our case [1, 10].

US has been demonstrated as an effective imaging modality for the evaluation of patients with ankle sprain [11]. Scanning protocols that describe in details (e.g., position of the patient, position of the probe) how to perform a correct visualization of the AITFL are well described in the pertinent literature [2, 3]. Furthermore, specific dynamic maneuvers can be performed, under the ultrasound guidance, to tension the ligament structure (i.e., ultrasound-guided stress test) and increase the diagnostic accuracy as regards the partial/complete tears [4, 12]. Some authors have shown also the potentiality of US examination in detecting the echo-structure of the interosseous membrane in normal and pathological cases [13].

To evaluate, during the US examination, the superficial component of the PITFL we suggest a posterior approach with the patient in a prone position. The probe is placed, in a transverse plane, at the posterior tip of the distal fibula; then, the medial edge of the transducer is cranially rotated (i.e., to obtain an angle of 30°–45°) until the lateral process of the tibia is depicted, thus revealing the proper PITFL ligament, as a fibrillar structure. To improve the US visibility of the ligament visualization a large amount of gel, gentle pressure with the probe and the dorsiflexion of the ankle may be needed, to tension the ligament, similarly to the AITFL. The deep component (transverse ligament) is cone-shaped and it is located deeper and inferior; it is more difficult to clearly visualize this component because it usually appears hypoechoic due to anisotropy.

When a ligament avulsion is present, US can accurately demonstrate and measure the hyperechoic avulsed fragment, usually with posterior acoustic shadowing, associated with surrounding hyperemia in the acute and subacute stages at color Doppler imaging. Of note, pressure (i.e., sono-palpation) in the region typically can elicit local pain [14].

The main limitation of the present report is the lack of correlation with other imaging modalities. Moreover, further studies are necessary to confirm US capabilities in depicting PITFL injuries.

Since our patient was not a professional soccer player, he was able to walk and the symptoms progressively improved, he preferred a conservative treatment and not have other imaging studies. In literature, there is debate regarding conservative vs surgical approaches for syndesmosis injuries. Generally, conservative treatment can be proposed except for high-grade injury, with severe joint instability [1]. Fractures are often treated surgically, but it seems that a conservative approach can be suggested for cases with small fragments, like our patient [15].

In conclusion, the standard radiological examination should remain the first imaging modality in case of ankle trauma, especially if a fracture is clinically suspected; but US should be considered a valuable complementary exam to promptly evaluate the peri-articular soft tissues like tendons, ligaments and vessels [2, 16]. We suggest to evaluate the PITFL at least in patients with a history of high ankle sprain and generally in patients with ankle injury referring for posterior tibiofibular pain like our patient; moreover, since the PITFL is rarely injured alone [1], it should also be scanned in patients in which abnormalities of the AITFL are demonstrated. Magnetic resonance imaging (MRI) is an accurate modality to demonstrate distal tibiofibular syndesmosis injurie. [9]. MRI can also show associated findings, such as osteochondral lesions, which may be not evident at US, bone marrow edema, and assess tibiofibular joint congruity [17]. MRI is not routinely requested for the evaluation of high ankle sprain; it is useful in particular in patients with instability and persistent symptoms, especially for an eventual pre-operative planning; or when the diagnosis is still uncertain after radiographic and US studies.

Funding

No funding was received.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Informed consent

Informed consent was obtained from all individual participants included in the study.