The extra-articular anatomy in this region was discussed in Chapter 5, but certain anatomic structures and landmarks are important to emphasize here (Fig. 14-1A, B). The lateral malleolus is routinely palpable and is the key to identifying the posterior facet of the subtalar joint. The sinus tarsi is also usually palpable, although it can be filled with large amounts of adipose tissue.⁷ Inversion and eversion of the foot may be helpful in palpating the sinus tarsi. In addition, the lateral talar dome can be palpated as the anterolateral portion slides out from under the distal tibia as the ankle is taken from dorsiflexion into plantar flexion.

Posterior to the lateral malleolus lies the sural nerve, lesser saphenous vein, and peroneal tendons (Fig. 14-2). The sural nerve is usually 2 cm posterior and 2 cm inferior to the lateral malleolus. The peroneal tendons pass along the posterior surface of the distal fibula and are tightly held in the fibular groove by the superior peroneal retinaculum. The lateral ankle ligaments include the anterior talofibular ligament, the calcaneofibular ligament, and the posterior talofibular ligament. The anterior talofibular ligament is a broad, thin ligament with the most inferior margin superior to the posterior facet of the subtalar joint. The calcaneofibular ligament courses deep to the peroneal tendons in an oblique fashion from the tip of the fibula toward the most posterior portion of the calcaneus. As it crosses the subtalar joint, it also stabilizes this joint, and a steep surface can be expected arthroscopically. The posterior talofibular ligament is also superior and forms a roof over the subtalar joint. The posterior portion of the subtalar joint is very close to the posterior ankle joint, and as the talus tapers, the posterior talofibular ligament is just proximal to the posterior subtalar joint line.

Palpation of surface landmarks on the medial side of the foot begins with the articulation of the talar head and the navicular, felt as the forefoot is inverted and everted. The sustentaculum tali is palpated one fingerbreadth beneath the tip of the medial malleolus. The posterior portion of the subtalar joint is more difficult to palpate because of its deep position and the fact that it is covered by the Achilles, the flexor hallucis longus, and the joint capsule. The os trigo-num is present in 2.7% to 7.7% of people unilaterally.⁸

The subtalar joint may be divided into anterior and posterior articulations, separated by the sinus tarsi and the tarsal
canal. The anterior subtalar joint (talocalcaneal navicular joint) is formed by the anterior aspect of the talus, the posterior surface of the navicular, the anterior portion of the calcaneus, and the calcaneonavicular (spring) ligament-fibrocartilage complex (Figs. 14-3 and 14-4).⁹ The anterior articulation is separated from the posterior articulation by the tarsal canal. The tarsal canal is formed by a sulcus in the undersurface of the talus and the superior surface of the calcaneus, and laterally, the opening is termed the sinus tarsi. The borders of the tarsal canal include the anterior portion of the posterior subtalar joint capsule, which forms the posterior boundary of this canal. The anterior boundary is the posterior portion of the talocalcaneal navicular joint capsule. There is a 45° angle of orientation of the long axis of the sinus tarsi to the lateral aspect of the calcaneus. According to Cahill, the tarsal canal is about 10 to 15 mm high, 3 to 5 mm wide, and 15 to 20 mm long.¹⁰ It gives attachments to the medial root of the inferior extensor retinaculum, the cervical ligament, the ligament in the tarsal canal (interosseous talocalcaneal ligament), and fatty tissue and blood vessels (Fig. 14-5A-C). This is discussed later in the chapter.

The posterior talocalcaneal or posterior subtalar joint is formed by the posterior calcaneal facet on the inferior surface of the talus and the corresponding posterior talar facet on the calcaneus (see Fig. 14-4). The posterior facet of the calcaneus is convex, and the posterior facet of the inferior surface of the talus is concave. This is shaped much like a saddle joint, and the motion is that of a “mitered hinge.” Its long axis is obliquely located about 40° to the midline of
the foot, and its joint capsule is reinforced laterally by the lateral talocalcaneal ligament and calcaneofibular ligament and in line with the synovium.

There is much debate over the ligamentous support of the subtalar joint. One of the first detailed descriptions of the anatomy of the contents of the sinus tarsi and tarsal canal was by Wood Jones in 1944.⁴ Since then, several papers have discussed these ligaments. The last description in 1952 determined that the cervical ligament was the strongest bond between the talus and the calcaneus.¹¹ Cahill described the presence of three lateral roots for the inferior extensor retinaculum and emphasized that the retinaculum consisted of two layers, one superficial and one deep to the extensor tendons.⁵ In 1978, Schmidt defined five distinct ligaments within the sinus tarsi and canal.¹² Viladot and associates in 1984 divided the ligaments into peripheral or central.⁶ Subsequently, Harper categorized the supporting structures into superficial, intermediate, and deep layers¹³ (Table 14-1). Stephens and Sammarco described the stabilizing role of the lateral ligament complex around the subtalar joint.¹⁴ Jotoku et al. and Lui have also studied ligaments of the subtalar joint.¹⁵, ¹⁶ In addition, Tochigi et al. and Ringleb et al. have described the importance of the interosseous calcaneal ligament and have shown it is the greatest contributor to subtalar joint stability.¹⁷, ¹⁸

Our dissections have concurred with Harper’s work, dividing the supporting structures into three layers. The superficial or peripheral layer includes (Fig. 14-6A, B).