The tarsal bones, collectively known as the tarsus, are a complex group of seven bones situated in the rear and mid-section of the human foot, directly below the ankle joint. They bridge the lower leg with the rest of the foot. These bones establish the foundation of the foot’s structure, providing the necessary stability and flexibility for standing, walking, and running.
Classification by Shape
Tarsal bones are anatomically categorized as “short bones,” a classification based on their general morphology. A short bone is typically cube-shaped, meaning its length, width, and thickness are roughly equal in dimension. This contrasts with long bones, like the tibia or femur, which are much longer than they are wide.
Short bones are primarily composed of spongy bone tissue, also known as cancellous bone, which is encased in a thin outer layer of dense compact bone. This structure provides stability and support with limited movement, a function necessary for the complex joint system of the ankle and foot. This design allows them to absorb and distribute mechanical stress effectively in the weight-bearing foot.
The Seven Individual Tarsal Bones
The tarsus is comprised of seven distinct bones organized into proximal, intermediate, and distal rows. The proximal row consists of the two largest bones: the talus and the calcaneus, which form the hindfoot. The calcaneus, or heel bone, is the largest of the seven and forms the prominence at the back of the foot, serving as an anchor point for the Achilles tendon.
The talus sits superiorly on the calcaneus and is the only tarsal bone that directly articulates with the tibia and fibula of the lower leg to form the ankle joint. The navicular bone constitutes the intermediate row, positioned medially between the talus and the three cuneiforms. The navicular is boat-shaped and connects the ankle to the midfoot.
The distal row includes the cuboid and the three cuneiform bones. The cuboid is situated on the lateral side of the foot, articulating with the calcaneus posteriorly and the fourth and fifth metatarsals anteriorly. The three cuneiform bones—medial, intermediate, and lateral—are wedge-shaped and located in front of the navicular. They connect the navicular to the first three metatarsals, completing the midfoot framework.
Primary Role in Foot Structure
The arrangement of the tarsal bones is instrumental in creating the foot’s structure, allowing it to function as both a rigid lever for pushing off and a flexible platform for shock absorption. The talus forms the talocrural joint with the tibia and fibula, which is the primary hinge joint responsible for up-and-down foot movement. The calcaneus bears the initial impact of the body’s weight during heel strike when walking or running.
The collective shape and articulation of the tarsal bones form the foot’s three arches: the medial longitudinal, lateral longitudinal, and transverse arches. These arches distribute body weight evenly across the foot, preventing excessive pressure on any single point and acting as natural springs to absorb ground forces. The relatively small movements between the numerous tarsal joints allow the foot to adapt to uneven terrain while maintaining a supportive structure.
The tarsals transmit forces from the lower leg to the five metatarsals of the forefoot. The stability provided by these short, tightly interlocked bones is necessary for converting the downward force of the body into forward momentum. This arrangement provides the necessary combination of rigidity and slight flexibility for efficient bipedal locomotion.