The stability of the ankle is provided by bony (talo-crural joint, subtalar joint) and ligamentous structures. The ligamentous structures are important not only because of their "check rein" function but also because they, along with the joint capsule relay proprioceptive information regarding joint function. The anterior talo-fibular ligament, the calcaneo- fibular ligament and the posterior talo- fibular ligament make up the lateral ligament complex. The posterior talo-fibular ligament is difficult to identify with ultrasound but fortunately is rarely injured except in severe trauma. The other 2 ligaments are easily identified. A third ligament which also seen easily with ultrasound is the anterior tibio-fibular ligament and this is injured in high ankle sprains. Other less frequently injured ligaments include the talo-navicular and the talo-calcaneal ligaments.

In the loaded ankle the bony configuration of the joint is mainly responsible for stability but with plantar flexion the ligaments become increasingly important. The peroneal tendons are recruited when the other restraints are injured and this can precipitate peroneal tendinopathy. When the extensor retinaculum is ripped off, subluxation/dislocation of the peroneal tendons creates instability.

The normal appearance of the ligaments, tendons and retinaculum will be demonstrated including surface anatomy, ultrasound technique and landmarks. Dynamic evaluation of the calcaneo-fibular ligament, peroneal tendons and subtalar joint will be discussed. The patterns of injury of the ligaments (acute, chronic and partial) and associated pathology will be demonstrated.