The interosseous tibiofibular ligament and anterior and posterior inferior tibio-fibular ligaments comprise the distal syndesmosis . On axial MR images, the medial margin of the distal fibula can be used as an anatomic reference. When the medial margin of the distal fibula appears flat, the ligaments in view are the anterior and posterior tibiofibular ligaments (Fig. 6). The tibiofib-ular ligaments demonstrate an oblique course and may be seen on multiple
sequential axial images. The inferior margin of the posterior tibiofibular ligament forms an articular labrum for the lateral ridge of the trochlea of the talus  (Fig. 7). Some authors describe this deep, inferior component of the posterior tibiofibular ligament as a separate ligament called the transverse tibiofibular ligament , while others conclude that it cannot be considered as a separate ligament . Injury to the syndesmosis occurs most commonly as a result of external rotation or hyperdorsiflexion . Imaging findings in the acute setting include edema of the syndesmosis, with or without disruption of the ligaments (Fig. 8), and in the chronic setting, disruption or remodeling of the syndesmosis without edema . Associated injuries are common, most commonly anterior talofibular ligament injury . Patients with ankle sprains tend to have longer recovery times if the syndesmosis is injured .
On axial MR images, when the medial margin of the distal fibula is curved because of indentation at the malleolar fossa, the ligaments in view are the anterior and posterior talofibular ligaments (Fig. 9). The posterior talofibular ligament demonstrates an inhomogeneous appearance, correlating at anatomic dissection with areas of normal fat between ligament fibers . The calcaneo-fibular ligament extends from the fibular tip, deep to the peroneal tendons, to the posterolateral calcaneus (Fig. 10). The anterior talofibular ligament is the most commonly injured ankle ligament [21,24]. The calcaneofibular ligament is also commonly injured, while injury to the posterior talofibular ligament is uncommon . The imaging findings of an injured ligament include complete or partial discontinuity, increased signal intensity within the ligament, or irregularity or waviness of the ligament (Fig. 11) . A biomechanical study demonstrated an association of calcaneofibular ligament disruption (Fig. 12) with subtalar joint instability, whereas ankle joint instability was seen only after
Fig. 7. Axial FSE image demonstrates the deep, inferior portion of the posterior tibiofibular ligament (transverse tibiofibular ligament). This ligament forms a labrum for the lateral ridge of the trochlea of the talus.
Fig. 9. Axial image demonstrates the anterior (white arrow) and posterior (black arrow) talofibular ligaments. Inhomogeneous appearance of the posterior talofibular ligament is because of normal fat between ligament fibers .
the anterior talofibular ligament was also disrupted . Approximately 80% to 85% of ankle sprains are treated conservatively with functional rehabilitation, while surgery is generally reserved for those with recurrent instability or reinjury . Methods of surgical repair include reattaching the torn ligament to the lateral malleolus or talus , or reconstructing the ligament with a tendon graft, most commonly the peroneus brevis tendon [27,28]. Even in cases with associated chondral defects, lateral ligament reconstruction decreases pain and instability .
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