The question of how many bones are in the ankle has two distinct answers because the term is used differently in common language and anatomy. The narrow, specific anatomical answer refers to the true ankle joint, which is formed by only three bones. The broader, regional answer includes the seven tarsal bones, totaling ten bones in the rear and mid-foot structure. Understanding the difference between the talocrural joint and the wider ankle region is key to accurately describing this structure.
The Three Bones of the True Ankle Joint
The true ankle joint, known scientifically as the talocrural joint, is a synovial hinge joint formed by three bones: the tibia, the fibula, and the talus. This joint is primarily responsible for the foot’s up-and-down movement. The tibia, or shin bone, is the larger of the two lower leg bones and forms the ceiling of the joint’s socket.
The fibula is the thinner lower leg bone; its lower end forms the lateral malleolus, the bony bump on the outside of the ankle. The tibia contributes the medial malleolus, and together, the lower ends of the tibia and fibula form a bracket-shaped socket called the ankle mortise. This mortise holds the talus securely in place.
The talus is a tarsal bone that sits directly beneath the tibia and fibula, acting as a connector between the leg and the rest of the foot. The talus is wider at the front than at the back, which provides stability. When the foot is pulled upward (dorsiflexion), the wider anterior part of the talus wedges into the mortise, making the joint more stable.
The articulation between these three bones allows for the primary movements of plantarflexion (pointing the foot down) and dorsiflexion (pulling the foot up). Although the fibula bears less weight than the tibia, its lateral malleolus is important for stabilizing the talus. Strong ligaments surround the joint, binding these three bones together and resisting excessive movement.
The Seven Tarsal Bones That Provide Structure
The broader definition of the ankle includes the seven tarsal bones, which form the rear and mid-foot structure. These bones provide the foundation for the entire foot and act as a bridge between the leg bones and the metatarsals. The talus, already mentioned as part of the true ankle joint, is the first of these seven tarsals.
The largest tarsal bone is the calcaneus, or heel bone, which forms the foundation of the rear foot and is the main attachment point for the Achilles tendon. The other five tarsals are the navicular, the cuboid, and the three cuneiform bones.
The navicular is positioned in front of the talus and helps form the inner arch of the foot. The cuboid bone is located on the outer side of the foot, providing lateral stability. The three cuneiforms—medial, intermediate, and lateral—are wedge-shaped bones situated between the navicular and the metatarsals. These bones contribute to the foot’s transverse arch and help distribute forces. All seven tarsal bones are tightly bound by ligaments, creating a strong, weight-bearing platform.
Ankle Bone Function: Movement and Stability
The collective purpose of the three true ankle bones and the seven tarsal bones is to facilitate movement and manage the high forces of weight-bearing. The true ankle joint focuses on the straightforward hinge motion of dorsiflexion and plantarflexion. This up-and-down movement is essential for walking and running, allowing the body to push off the ground and clear the foot during the swing phase.
The seven tarsal bones play a greater role in shock absorption and adapting the foot to uneven surfaces. Movement between the talus and the calcaneus forms the subtalar joint, which is the primary site for side-to-side motion. This joint allows for inversion, where the sole of the foot turns inward, and eversion, where the sole turns outward.
When the foot contacts the ground, the joints unlock to absorb impact, and then they lock again to create a rigid lever for push-off. This complex interplay of the three main ankle bones and the seven tarsals ensures stability and adaptability during all forms of locomotion.