When doing a subatalar arthrodesis, it is important to understand the anatomy in the subtalar joint in order to preserve soft tissue and maintain the blood supply of the talus and calcaneus without further damage. The subtalar joint consists of 3 facets on the dorsal surface of the calcaneus and plantar surface of the talus. The facets are the anterior, middle, and posterior. The anterior and middle facets are convex in nature whereas the posterior facet is generally concave in nature.³

This arthrodesis can be performed arthroscopically by using anterolateral and posterolateral portals. The posterolateral portal is located just lateral to the Achilles tendon. The anterolateral portal is identified as 1 cm distal and 0.5 cm anterior to the tip of the lateral malleolus. A posteromedial portal may be used, but caution must be taken to identify and avoid the tibial nerve and the posterior tibial artery. An accessory portal can be made through the sinus tarsi.⁴

The plantar surface of the body of the talus consists of the posterior calcaneal articular facet, which runs anterolaterally and is concave in nature. This facet articulates with the dorsal surface of the calcaneus known as the posterior talar articular surface. This surface also runs anterolaterally and is convex in nature.⁵

Anterior to the posterior talar articular surface lies a groove named the sulcus calcanei. It joins the sulcus tali, a groove on the talus, to become the canalis tarsi and sinus tarsi. The interosseus talocalcaneal ligament is located within this canal. It is important to try to preserve this ligament, as it does carry some blood supply to the area. Other ligaments such as the bifurcate ligament, the cervical ligament, and the stem of the inferior extensor retinaculum also can be found in this region. They all attach laterally to sulcus calcanei.

The blood supply to the area of the subtalar joint comes from the artery of the sinus tarsi, a branch of the lateral tarsal artery, and the artery of the canalis tarsi, a branch of the posterior tibial artery. The medial side of the body of the talus receives the blood supply from deltoid branches of the canalis tarsi. It is important to preserve the blood supply, as disruption could cause aseptic necrosis.

The subtalar joint is a prominent joint in the foot in that it dictates the movements of the midtarsal joint as well as the forefoot. The 3 articulations between the talus and calcaneus, namely the anterior, middle, and posterior facets, move in unison during motion.⁶ The movements of these articulations are stabilized by ligaments; if any damage occurs to the ligaments the result is abnormal motion at the joint. The joint itself allows for transmission of rotation from the leg and ankle to the distal articulations of the foot, as well as providing for shock absorption during the early part of the stance phase.^7,8

Much controversy exists as to the type of motion that occurs at the subtalar joint. Some⁹ claim a sliding type motion, whereas others such as Hicks¹⁰ describe rotational motion. In recent literature the motion is described more as a screwlike motion with multiaxial motion involving rotations and translations.¹¹ Many experiments have been performed using loading configurations to deduce the motion at the joint. Hicks¹⁰ maintained that the joint motion was the same whether the foot was loaded or unloaded. Leardini and colleagues¹² deduced that subtalar motion occurs when external deviations are applied, but was recovered as soon as the deviations were removed.

The axis of the subtalar joint is another subject of debate. As the joint is put through motion the axis changes its orientation because it is likely that the joint is not fully congruous throughout that motion. Given that the subtalar joint is a diarthrodial joint, Shephard¹³ described the axis of joint rotation to run from anteromediosuperior to posterolateroinferior, passing through the tuberosity of the calcaneus upwards and slightly medial to the neck of the talus forward, crossing the canalis tarsi.

Pathology that leads to degeneration of the subtalar joint and chronic pain may require subtalar joint arthrodesis. Pain and deformity are the most important indications that would lead to isolated subtalar fusion. Rearfoot varus or valgus can be corrected during talocalcaneal fusion.

Posttraumatic arthritis may result from calcaneal or talar fractures, whether the fracture was originally treated conservatively or surgically. Primary talocalcaneal arthritis can also be treated with a fusion. Residual congenital deformities including talipes equinovarus, talocalcaneal coalitions, and calcaneovalgus can eventually lead to arthritis of the subtalar joint. Posterior tibial tendon dysfunction may also lead to a symptomatic subtalar joint.²

The surgeon may opt to primarily fuse an intra-articular comminuted calcaneal fracture. Cartilage damage and inability to reconstruct the posterior facet following a severely comminuted fracture often leads to severe discomfort, decreased quality of life, inability to perform activities of daily living, and the need for eventual subtalar joint arthrodesis. Therefore, the surgeon may opt to save the patient future discomfort and primarily fuse if initial surgical management is chosen. Initial nonsurgical management is often chosen if there is minimal hindfoot deformity followed by subsequent subtalar arthrodesis.

Conservative treatment is the first-line treatment for subtalar joint pain and arthritis. Oral nonsteroidal anti-inflammatories are often attempted first. Sinus tarsi/subtalar joint injections consisting of a mixture of local anesthetic and steroids are helpful in temporarily relieving arthritis pain and inflammation. Bracing and physical therapy are other conservative treatments. When activities of daily living are affected by chronic subtalar joint pain, patients then opt for surgical treatment. Surgeons may attempt arthroscopic treatment before resorting to subtalar joint fusion.

The clinical signs and symptoms of subtalar joint pain are different depending on the etiology. Patients will often complain of pain in the hindfoot and ankle. The nature of the pain is often described as dull and stiff. These individuals will often present with a valgus or varus deformity of the hindfoot. On occasion, a patient may describe the pain as numbness depending on the etiology of the subtalar joint pain.

In addition, a surgeon may also notice swelling of the ankle joints as well as swelling in the entire hindfoot. If there is a history of intra-articular calcaneal fractures, one may notice a decrease in the heel height as well as a widened heel. These patients will often complain of discomfort and difficulty in wearing their shoes. Patients will complain of the pain worsening throughout the day because of this discomfort.

On clinical evaluation, the surgeon may or may not find restriction on range of motion of the ankle joint. Patients with restricted range of motion will often complain of their ankles/foot locking and difficulty walking. In addition, these individuals will complain of muscular pain on the back of their leg and difficulty walking. Therefore, depending on the origin of the subtalar joint pain, its presentation can be very diverse.