Musculoskeletal Ultrasound of the Ankle and Foot

Ultrasound examination of the foot and ankle is clinically useful because most structures are superficial and easily visualized with ultrasound. Ultrasound assists in establishing the diagnosis when symptoms are localized. Unlike MRI, a focused foot or ankle ultrasound examination can be performed efficiently and quickly. It is advised, however, that the sonographer perform a complete examination of all structures to establish familiarity with the region and develop an efficient technique. The opportunity to compare with the asymptomatic side is another advantage offered by ultrasound. The sonographer performs the musculoskeletal ultrasound examination of the foot and ankle with the patient supine or prone on the examination table. Gentle manipulation of the ankle into dorsiflexion, plantarflexion, eversion, or inversion offers better visualization of some structures, as discussed later. A higher-frequency transducer (>10 MHz) allows better visualization of the superficial structures. Transducers with a small footprint (eg, ‘‘hockey-stick’’ probe) can also be useful for evaluating small structures near the bony prominences of the medial or lateral malleolus. ANTERIOR ANKLE Evaluation of the ankle may be performed with the patient supine on the table with the knee slightly flexed and the foot free to allow manipulation during scanning. Place the transducer in the sagittal plane to visualize the anterior recess of the tibiotalar joint distal to the tibia. The anterior fat pad lies anterior to the talar neck, between the talar head and dome. Scan medial to lateral to examine the full extent of the talar dome. The anterior aspect of the ankle joint is assessed in the sagittal plane for synovitis or joint effusion. The hyperechoic joint capsule is seen superficial to the anterior distal tibia and hypoechoic cartilage of the talar dome. The anterior fat pad lies superficial to the joint capsule and can be displaced in the presence of increased joint fluid. In