The subtalar joint, also known as the talocalcaneal joint, is a synovial joint of the foot, that occurs between the talus and the calcaneus with the talus that is oriented slightly obliquely on the anterior surface of the calcaneus. The two bones articulate at two different sites (i.e. one anteriorly and one posteriorly). The anterior talocalcaneal joint is a convex area of the talus that fits on a concave surface of the calcaneus. The posterior talocalcaneal joint is formed by a concave surface of the talus and a convex surface of the calcaneus.
The subtalar joint contributes to the dorsiflexion of the ankle. Three articulating facets (anterior, middle and posterior) are present between the talus and the calcaneus. The sustentaculum tali forms the floor of middle facet, and the anterior facet articulates with the head of the talus, and sits lateral and congruent to the middle facet. The posterior facet is the largest of the three, and separated from the others by the tarsal canal. The most relevant actions done by the joint are inversion and eversion of the foot. The subtalar joint can also be considered a combination of the anatomic subtalar joint discussed above, and the talocalcaneal part of the talocalcaneonavicular joint. When both those joints are accounted together, it allows for pronation and supination to occur.
The subtalar joint is frequently involved in arthritis and, particularly in patients with previous sprains, secondary osteoarthritis can also occur. Symptoms of subtalar joint arthritis include pain, loss of motion through the joint's range of motion, and difficulty walking on uneven surfaces.
Among the imaging techniques that are appropriate for the assessment of the subtalar joint, ultrasound (US) has been increasingly used over the last years. Indeed it is able to image different abnormalities, including both inflammatory and structural changes, and it is helpful in guiding local procedures that can be easily and safely performed with optimal patient's tolerance.
The US scanning technique is quite complex, and the whole joint area should be scanned in the longitudinal (sagittal or coronal) plane with pathology that should be confirmed in the orthogonal (perpendicular) plane. By using a standardised scanning technique and agreed definitions of pathology, US allows an optimal assessment of inflammatory and structural abnormalities, thus filling the gap between clinical and radiographic evaluations of the subtalar joint.
Disclosure of Interest None declared