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Subtalar joint: want to learn more about it?

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Subtalar joint

Subtalar joint (Articulatio subtalaris)

The subtalar joint (talocalcaneal joint) is anatomically described as the articulation formed between posterior articular surfaces of two tarsal bones; the talus and calcaneus. In the literature, this joint is also referred to as the anatomical subtalar joint or subtalar joint proper

However, in clinical practice, the subtalar joint is considered as a functional unit consisting of the anatomical subtalar (posterior) and talocalcaneonavicular (anterior) joints. In the middle of this functional unit is the conical interosseous tunnel consisting of the tarsal canal and tarsal sinus.

The anatomical subtalar joint is a single synovial articulation formed between the posterior calcaneal articular facet of the talus and the convex posterior articular facet of the calcaneus. These bones are held together by the fibrous capsule, medial talocalcaneal, lateral talocalcaneal, interosseous talocalcaneal and cervical ligaments.

Two principal compound movements occur in this joint; supination and pronation. These movements are affected by several adjacent joints, ligaments and periarticular tendinous tissue.

This article will discuss the anatomy and function of the talocalcaneal joint.

Key facts about the subtalar joint
Type Plane synovial joint; three degrees of freedom
Articular surfaces Posterior calcaneal facet on the posterior part of the inferior surface of the talus; 
Posterior facet on the superior surface of the calcaneus
Ligaments Medial, lateral and posterior talocalcaneal ligaments, interosseous talocalcaneal and cervical ligaments
Innervation Plantar aspect - medial or lateral plantar nerve 
Dorsal aspect - deep fibular nerve
Blood supply Posterior tibial artery, fibular artery
Movements Inversion/eversion, abduction/adduction, plantarflexion/dorsiflexion (gliding and rotation)

Articular surfaces

The anatomical subtalar joint is a synovial articulation between the talus and calcaneus. It consists of two articular facets lined with the hyaline cartilage.

The articular surfaces that comprise this joint involve the concave posterior calcaneal facet on the inferior surface of the talus and the convex posterior talar articular surface on the superior aspect of the calcaneus.

Learn more about the general features of the synovial joints by exploring articles, diagrams, videos and quizzes.

Ligaments and joint capsule

The subtalar joint has one loose joint capsule that envelops the whole joint. Like in other synovial joints, the joint capsule is lined with a synovial membrane. The lateral, medial and posterior thickenings of the joint capsule are the main ligaments that participate in movements of this joint. The subtalar joint capsule attaches to the edges of the articular surfaces as well as to the floor and roof of the tarsal sinus. The tarsal sinus is a narrow passageway located immediately anterior to the subtalar joint, between the talus and calcaneus.

Inside the tarsal sinus, the joint capsules of the subtalar and talocalcaneonavicular joints meet and form the talocalcaneal interosseous ligament.

The lateral talocalcaneal ligament is a flat fibrous band that spans obliquely between the lateral talar process to the lateral calcaneal surface and calcaneofibular ligament. It lies deep to the calcaneofibular ligament.

The medial talocalcaneal ligament spans between the medial aspects of talar tubercle and calcaneus and the posterior aspect of sustentaculum tali. Some of its distal biers blend with the medial deltoid ligament of the ankle joint.

The posterior talocalcaneal ligament is a short band of fibrous tissue that spans from the posterolateral tubercle of the talus to the superomedial aspect of the calcaneus.

The interosseous talocalcaneal ligament is composed of two short and broad fibrous bands located in the tarsal sinus. The deep extension of the inferior extensor retinaculum is situated between these bands of the interosseous ligament. Occupying the central position between the talocalcaneal and talocalcaneonavicular joints, this ligament is associated with the functions of both joints. The primary role of this ligament in the subtalar joint is maintaining stability both at rest and during active movements. Being attached to the talar sulcus and calcaneal sulcus, the interosseous talocalcaneal ligament is taut in pronation of the foot, limiting its movement.

The cervical/anterior talocalcaneal ligament is located lateral to the interosseous ligament and the tarsal sinus. It extends from the superior calcaneal surface to the inferolateral tubercle of the talar neck. This ligament is also taut in pronation.

Cement your memorizing in foot ligaments with this challenging quiz:

Innervation

The plantar aspect of the subtalar joint is innervated by the medial or lateral plantar nerves, while the dorsal aspect receives its innervation from the deep fibular nerve.

Blood supply

Arterial supply for the subtalar joint comes from two arteries; 

Movements

The movements that occur at the subtalar joint are gliding and rotation.The combination of these movements result in pronation and supination; these are considered to be the primary movements in the subtalar joint. They are always accompanied by movements in the talocalcaneonavicular and calcaneocuboid joints which is why these three joints are considered to be one functional unit of the foot.

Supination and pronation can be considered to occur around a single axis that runs anteriorly and superomedially from the posterolateral tubercle of calcaneus to the superomedial aspect of the neck of talus. To be more specific, studies have suggested that the average axis of rotation is orientated 42° upwards and anterior to the transverse plane, and 16° from the sagittal plane.

The long axis of the transverse tarsal joint is (A) inclined 15° superiorly from the transverse plane and (B) inclined 9° from the sagittal plane

Supination is a composite movement which combines inversion, adduction and plantarflexion at these joints. Pronation, on the other hand, is the opposite movement resulting from eversion, abduction and dorsiflexion.
Although these cardinal movements (inversion/eversion, adduction/abduction and plantar/dorsiflexion) will be described individually below, it’s important to emphasize that they always occur synchronously with each other, and never in isolation.

Inversion and eversion, if considered in isolation, occur around a longitudinal axis in the frontal plane and are considered to be the primary movements in the subtalar and transverse tarsal joints. The range of motion at the subtalar joint varies across sources; the RoM in inversion ranges from 25° to 30°, while in eversion it ranges from 5° to 10°. 

Inversion is the movement in which the sole of the foot rotates towards the midline, while the lateral border of the foot is directed inferiorly. Eversion is the movement in which the sole of the foot is laterally orientated while the medial border of the foot is directed inferiorly.

Abduction and adduction (also described as external and internal rotation, respectively) occur around a vertical axis in the transverse plane. In the subtalar joint, since the axis of rotation is roughly halfway between the vertical and longitudinal orthogonal axes, the range of motion for adduction/abduction is usually similar to that mentioned for inversion/eversion. This is subject to interindividual orientation of the axis of rotation for the joint i.e. an inclination less than 42° will result in greater RoM for inversion/eversion, and less adduction/abduction, and while the opposite will occur the closer the axis gets to the long axis of the leg. 

Dorsiflexion and plantarflexion of the subtalar and transverse tarsal joints occur around a mediolateral axis within the sagittal plane. Due to the orientation of the mentioned axis of rotation for the subtalar joint, the RoM for these movements is minor relative to inversion/eversion and abduction/adduction.

The closed packed position of the subtalar joint is supination. The capsular pattern has a limited ROM defined in varus and valgus.

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Muscles acting on the subtalar joint

Subtalar joint: want to learn more about it?

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