Subtalar Dislocation: Ligaments Involved, Anatomy, and Recovery

What ligaments are involved in the subtalar dislocation?

Subtalar dislocation primarily involves the rupture or significant compromise of the strong intrinsic ligaments connecting the talus and calcaneus, most notably the interosseous talocalcaneal ligament and the cervical ligament, alongside other capsular and extrinsic talocalcaneal ligaments.

Understanding Subtalar Dislocation

Subtalar dislocation, also known as peritalar dislocation, is a relatively rare but severe injury characterized by the complete displacement of the talus from the calcaneus and navicular bone, while the ankle joint (tibiotalar joint) remains intact. This injury typically results from high-energy trauma, such as falls from height or motor vehicle accidents, often involving extreme inversion or eversion forces applied to a plantarflexed foot. Due to the inherent stability provided by the strong ligaments surrounding the subtalar joint, significant force is required to disrupt its integrity.

Anatomy of the Subtalar Joint

To understand the ligaments involved in a subtalar dislocation, it's crucial to first grasp the anatomy of the subtalar joint itself. This joint, also known as the talocalcaneal joint, is formed by the articulation between the inferior surface of the talus and the superior surface of the calcaneus. It is a complex synovial joint primarily responsible for inversion and eversion movements of the foot, which are essential for adapting to uneven terrain.

• Bones Involved: The primary bones forming the subtalar joint are the talus (superiorly) and the calcaneus (inferiorly). The talus also articulates with the navicular bone anteriorly, forming part of the talonavicular joint, which is often involved in peritalar dislocations.
• Joint Structure: The subtalar joint is functionally composed of three facets: anterior, middle, and posterior, each with its own articular cartilage. These facets are separated by the tarsal sinus laterally and the tarsal canal medially, a crucial space housing vital ligaments.
• Primary Movements: The subtalar joint allows for complex triplanar motion, often simplified into inversion (sole of foot turns inward) and eversion (sole of foot turns outward), which occur around an oblique axis.

Key Ligaments of the Subtalar Joint

The stability of the subtalar joint is heavily reliant on a robust network of intrinsic and extrinsic ligaments. When a subtalar dislocation occurs, these ligaments are stretched, torn, or completely ruptured.

• Interosseous Talocalcaneal Ligament (ITCL): This is arguably the most important intrinsic ligament of the subtalar joint. It is a strong, multi-banded ligament located within the tarsal canal, running obliquely between the sulcus tali (on the talus) and the sulcus calcanei (on the calcaneus). Its fibers are oriented to resist all movements, but particularly inversion and eversion, acting as a crucial pivot and primary stabilizer. Rupture of the ITCL is almost universally present in subtalar dislocations.
• Cervical Ligament: Located in the tarsal sinus, anterior and lateral to the ITCL, the cervical ligament runs from the neck of the talus to the superior surface of the calcaneus. It works synergistically with the ITCL to limit excessive inversion and eversion, especially inversion. Its involvement in subtalar dislocation is also very common.
• Medial Talocalcaneal Ligament: This ligament is part of the deltoid ligament complex, specifically the deep portion. It extends from the medial malleolus of the tibia to the sustentaculum tali of the calcaneus and the medial tubercle of the talus. While primarily an ankle stabilizer, its fibers also contribute to the medial stability of the subtalar joint and can be involved, particularly in lateral subtalar dislocations.
• Lateral Talocalcaneal Ligament: This ligament runs from the lateral process of the talus to the lateral surface of the calcaneus. It is a relatively short and strong ligament that helps reinforce the lateral capsule of the subtalar joint, limiting adduction and inversion. It is commonly injured in medial subtalar dislocations.
• Posterior Talocalcaneal Ligament: Located posteriorly, this ligament connects the posterior process of the talus to the superior surface of the calcaneus. It helps to limit extreme dorsiflexion and plantarflexion of the subtalar joint and can be injured in dislocations.
• Anterior Talocalcaneal Ligament: A less distinct ligament connecting the anterior aspect of the talus to the calcaneus, contributing to anterior stability.
• Capsular Ligaments: The joint capsule surrounding the subtalar joint is reinforced by various thickenings that act as accessory ligaments, contributing to overall stability and often sustaining injury during dislocation.

Ligamentous Involvement in Subtalar Dislocation

The specific ligaments injured depend largely on the mechanism and direction of the dislocation (medial, lateral, anterior, or posterior).

• Medial Subtalar Dislocation (Most Common): This typically results from forced plantarflexion and inversion. In this scenario, the talus displaces medially and often plantarflexes relative to the calcaneus. The ligaments most commonly disrupted are:
  • Lateral Talocalcaneal Ligament
  • Interosseous Talocalcaneal Ligament (ITCL)
  • Cervical Ligament
  • The calcaneofibular ligament (a lateral ankle ligament) may also be involved due to the extreme inversion.
• Lateral Subtalar Dislocation: Less common, usually caused by forced dorsiflexion and eversion. The talus displaces laterally relative to the calcaneus. The ligaments most commonly disrupted are:
  • Medial Talocalcaneal Ligament (part of the deltoid complex)
  • Interosseous Talocalcaneal Ligament (ITCL)
  • Cervical Ligament
• Anterior/Posterior Subtalar Dislocation (Rarest): These involve displacement primarily along the sagittal plane and are highly unstable. They involve extensive tearing of all surrounding talocalcaneal ligaments, including the ITCL, cervical, and anterior/posterior talocalcaneal ligaments.

Regardless of the direction, the Interosseous Talocalcaneal Ligament (ITCL) and the Cervical Ligament are almost always involved and often completely ruptured due to their critical role in maintaining talocalcaneal alignment and resisting the shearing forces that lead to dislocation. Their integrity is paramount for subtalar joint stability.

Clinical Significance and Recovery

The extensive ligamentous damage associated with a subtalar dislocation highlights the severity of this injury. Accurate diagnosis and prompt reduction are crucial to minimize complications such as avascular necrosis of the talus (due to disruption of blood supply) and persistent instability. Following reduction, a period of immobilization is necessary to allow for initial ligamentous healing. Long-term rehabilitation focuses on restoring range of motion, strength, proprioception, and dynamic stability, often addressing the significant residual laxity that can result from the severe ligamentous compromise.

Conclusion

Subtalar dislocation is a testament to the incredible forces required to disrupt the highly stable architecture of the foot. The injury invariably involves severe damage to the primary intrinsic stabilizers of the subtalar joint: the interosseous talocalcaneal ligament and the cervical ligament, along with other crucial talocalcaneal ligaments (medial, lateral, and posterior). Understanding the specific ligaments involved is fundamental for clinicians in diagnosing, treating, and rehabilitating this complex and debilitating injury, emphasizing the critical role these structures play in maintaining foot function and stability.