The tarsus is a complex system of bones in the human foot, playing a significant role in mobility and support. This arrangement of bones is fundamental to how we stand, walk, and absorb impacts. Understanding the tarsus provides insight into the human body’s ability to manage diverse forces and movements. It performs functions central to upright posture and locomotion.
What the Tarsus Is and Does
The tarsus is a cluster of seven bones located in the posterior and mid-regions of the foot. It sits between the lower leg bones (tibia and fibula) and the metatarsals, which lead to the toes. It connects the leg to the rest of the foot and forms the ankle joint. This configuration allows the tarsus to distribute the body’s weight to the sole of the foot, acting as an effective shock absorber during movement.
The design of the tarsal bones enables both stability and flexibility, adapting to various terrains and activities. They facilitate complex foot movements like dorsiflexion (lifting the foot), plantarflexion (pointing the foot), inversion (turning the sole inward), and eversion (turning the sole outward). This interplay of bones and joints helps maintain balance and contributes to the arches of the foot, important for efficient gait and weight bearing. The tarsus supports the body’s mass and propels it forward.
Bones Forming the Tarsus
The tarsus comprises seven bones, each contributing to the foot’s structural integrity and function. The talus, also known as the ankle bone, sits superiorly and articulates directly with the tibia and fibula to form the ankle joint. It transmits the body’s weight from the lower leg into the foot and has no direct muscle attachments. The calcaneus, or heel bone, is the largest tarsal bone, located beneath the talus and forming the prominent heel. It is a weight-bearing bone that provides a foundation for the other tarsals and metatarsals.
The navicular bone is boat-shaped and positioned on the medial side, supporting the medial arch of the foot. It transfers forces from the talus to the cuneiform bones and to the metatarsals. The cuboid bone is found on the lateral side of the foot, cube-shaped, and provides stability while aiding in weight distribution and toe movement. It articulates with the calcaneus posteriorly and the fourth and fifth metatarsals anteriorly.
The final three tarsal bones are the cuneiforms: medial, intermediate, and lateral. These wedge-shaped bones are located anterior to the navicular bone and articulate with the first, second, and third metatarsals respectively. The cuneiforms are important in forming and maintaining the transverse arch of the foot, which aids in balance and weight distribution.
Common Issues of the Tarsus
Due to its role in weight-bearing and complex structure, the tarsus is susceptible to various injuries and conditions. Sprains are common, occurring when the ligaments connecting the tarsal bones are stretched or torn, often from twisting or rolling the foot. Symptoms typically include pain, swelling, and difficulty bearing weight.
Fractures of the tarsal bones can result from trauma, such as direct blows, twisting injuries, or falls from a height. The calcaneus is the most frequently fractured tarsal bone and can cause severe pain and mobility issues. Repetitive stress from activities like running can also lead to stress fractures, which are small cracks in the bones.
Arthritis also affects the tarsus, involving degeneration or inflammation of the joints. Osteoarthritis, a degenerative joint disease, affects the tarsus with increasing age. Rheumatoid arthritis, an autoimmune condition, can also occur. These conditions can lead to pain, stiffness, and reduced mobility, impacting daily activities and overall foot function.