Scan the anterior aspect of the joint in the sagittal plane to visualize the anterior recess. Identify the distal tibia, the talar head, and the talar dome in between them with its thin anechoic cartilage. The joint capsule extends as a hyperechoic line between the distal tibia and the talar head. Immediately deep to the capsule is the intra-articular fat pad, which is triangular shaped, like a wide arrowhead pointing posteroinferiorly into the joint space. Sweep medially and laterally to visualize the surface of the talar dome, exploring for effusion or osteochondral defects. Rotate the transducer 90° to the axial plane. Position it slightly inferior to the distal tibia, and identify the tendons of the tibialis anterior, extensor hallucis longus, and extensor digitorum longus muscles. Identify and avoid the anterior tibial artery and deep fibular nerve (Fig. 7.1).

Patient positioning: Lay the patient supine, knee flexed with foot flat. Alternatively, the ankle can rest off the end of the table with the foot passively plantar flexed.

Probe positioning: Position the transducer so that the center of the screen is in between the extensor hallucis longus and tibialis anterior, and then rotate back to the sagittal plane for the injection (Fig. 7.2a).

Markings: Identify the dorsalis pedis artery, deep fibular nerve, tibialis anterior tendon, and extensor hallucis longus tendon.

Needle position: Enter in-plane and maintain a relatively steep angle to avoid scraping the talar dome, which can sometimes appear contiguous with an overlying effusion.

Safety considerations: Avoid the dorsalis pedis artery, deep fibular nerve, tibialis anterior tendon, and extensor hallucis longus tendon.

Pearls:

Equipment needed:

The subtalar joint is comprised of three articulations between the talus and the calcaneus. The anterior facet is located above the anteromedial corner of the calcaneus, the middle facet is located medially, and the posterior facet is located posteriorly. The anterior and middle facets are contiguous and together comprise the anterior subtalar articulation [9, 10]. The current literature only focuses on the posterior articulation, perhaps because it is the largest of the three and presumably bears the majority of the weight across the joint. In one study blind injection using an anterolateral approach resulted in a 27 % rate of extravasation into the surrounding structures in an unpredictable distribution [9]. The posterolateral approach was found to be superior (91.2 % vs. 67.6 %) [10]. A study comparing ultrasound-guided anterolateral, posterolateral, and posteromedial approaches resulted in 100 % accuracy for all three methods, with rates of extravasation 25, 25, and 8.3 %, respectively [11]. Furthermore, using dynamic ultrasound may allow a smoother needle trajectory, minimizing contact with surrounding structures [12].

Ankle sprains have been found to account for 15–40 % of all athletic injuries [13–15]. The medial ligament is composed of the posterior tibiotalar, tibiocalcaneal, tibionavicular, and anterior talotibial ligaments. The complex is stronger, more stable, and less commonly injured than the lateral ligaments. It is a major contributor to ankle stability during weight bearing and is the primary limiter of lateral talar shift and talar external rotation. External rotation fractures at the lateral malleolus are associated with medial ligament injuries. Local swelling, tenderness, and ecchymosis have been shown to be unreliable in establishing a diagnosis. MRI is useful for visualization of ligament irregularity but is unable to demonstrate instability. A 2004 study found the most commonly used radiographic finding for deltoid ligament rupture and medial ankle instability (the medial clear space) to be unreliable [16]. In a prospective study of 12 patients with supination external rotation injuries, ultrasound accurately diagnosed acute deltoid ligament rupture with a sensitivity and specificity of 100 % [8]. No current evidence supports the use of local injections for medial ligament injuries. However, emerging studies seem promising for the eventual development of an appropriate injectate.

The lateral ligament complex consists of the anterior talofibular ligament (ATFL), the calcaneofibular ligament (CFL), and the posterior talofibular ligament (PTFL) [17, 18]. In one study, point tenderness over the ATFL and CFL correlated with ligament rupture 52 and 72 % of the time, respectively. 71 % of patients with a positive anterior drawer sign, 68 % of patients with a positive talar tilt, 70 % of patients with ≥4 cm of swelling under the lateral malleolus, and 91 % of patients with such swelling in combination with point tenderness were shown to have lateral ligamentous injury [19]. Ultrasound has been shown to have the diagnostic accuracy of 95 % for ATFL tears and 90 % for CFL tears (Table 7.2) [17, 18].

The retrocalcaneal bursa is located immediately superior and deep to the distal insertion of the Achilles tendon on the posterior calcaneus. Ultrasound has been shown to accurately visualize the bursa and guide targeted intervention [20]. One study suggests that merely visualizing the bursa on ultrasound suggests pathology [22]. An anterior to posterior diameter greater than 2.5 mm is generally considered abnormal [15]. The Achilles (retro-Achilles/subcutaneous calcaneal) bursa is larger and located superficial to the Achilles tendon at the same level. Any evidence of fluid here on ultrasound is pathologic.

Ultrasound is useful in identifying small tears, partial ruptures, retrocalcaneal bursitis, and chronic tendinosis [24–26]. Corticosteroid injection is generally not recommended due to the risk of rupture; however, in the setting of acute and/or chronic inflammation, corticosteroid injection to the surrounding paratenon sheath can alleviate symptoms. If symptoms become chronic, dry needling and injection of reparative substances are potential interventions (Table 7.3) [27].