The tarsal bones are a collection of seven bones collectively known as the tarsus. They form the foundational structure of the foot and ankle complex. The tarsals act as a bridge, connecting the bones of the lower leg to the smaller bones in the front of the foot. Their arrangement supports the body’s ability to stand upright, absorb impact, and move across varied surfaces.
Anatomy and Identification of the Tarsal Bones
The tarsus is made up of seven bones, which are organized into the hindfoot and the midfoot. The largest is the calcaneus, commonly known as the heel bone, which supports the body’s weight. Resting above the calcaneus is the talus. The talus is unique among the tarsals because it forms the lower part of the ankle joint by articulating directly with the tibia and fibula of the lower leg.
The midfoot region contains the remaining five bones, which begin with the navicular, a boat-shaped bone located on the inner side of the foot. The cuboid bone is positioned on the outer side of the foot, connecting the calcaneus to the outer metatarsals. The final three bones are the cuneiforms—medial, intermediate, and lateral—which are wedge-shaped and arranged side-by-side in front of the navicular.
The tarsals interface directly with other parts of the foot skeleton. The talus is the most proximal, articulating with the lower leg bones, while the calcaneus forms the base of the hindfoot. Distally, the navicular, cuboid, and cuneiforms articulate with the five metatarsal bones, which form the forefoot. The structure is characterized by numerous small joints and strong ligaments, which create a stable yet flexible platform.
Role in Movement and Stability
The tarsal bones function for weight distribution and shock absorption during locomotion. During walking or running, these bones absorb forces that can be several times the body’s weight, particularly through the calcaneus and talus. The calcaneus, being the largest, is structured to withstand the impact of heel strike and provides a strong lever for the calf muscles to propel the body forward.
The tarsals are also the foundational components of the foot’s arches—the medial longitudinal, lateral longitudinal, and transverse arches. This arched configuration provides elasticity, allowing the foot to flatten slightly upon impact to dissipate energy and then spring back to provide a rigid lever for push-off. The precise articulations between the seven tarsal bones permit limited but deliberate movements, particularly at the subtalar joint between the talus and calcaneus.
This subtalar movement facilitates inversion and eversion, which are necessary for navigating uneven terrain. The ability of the tarsals to lock together for stability and unlock for flexibility allows the foot to adapt to varied surfaces while maintaining balance. The talus transmits the entire body weight to the foot, acting as the central pivot for these movements.
Common Injuries and Ailments
The tarsal bones are susceptible to injuries, often stemming from high-impact trauma. Fractures of the calcaneus and talus are common in accidents, such as falls from significant heights or motor vehicle collisions, due to the high axial load placed on these bones. Talus fractures are concerning because the bone has a relatively poor blood supply. Trauma can disrupt this flow, leading to avascular necrosis, or bone death.
Another common condition affecting the region is Tarsal Tunnel Syndrome, which involves the compression of the posterior tibial nerve as it passes through a narrow channel in the ankle, similar to carpal tunnel syndrome in the wrist. The nerve compression causes pain, numbness, and tingling along the sole of the foot. Arthritis is also a frequent ailment, particularly osteoarthritis, which results from the wear and tear on the many small joints between the tarsal bones.
Tarsal Coalition is an abnormal connection between two or more tarsal bones. This coalition restricts the normal movement between the bones, leading to stiffness and pain, especially during activities that require inversion and eversion.