The human foot is a complex structure designed for movement and support. A group of bones known as the tarsals are fundamental to this structure, forming the ankle and upper foot. Understanding these bones provides insight into the foot’s capabilities.
What Are Tarsal Bones?
Tarsal bones are seven irregularly shaped bones located in the hindfoot and midfoot regions. They are positioned between the lower leg bones (tibia and fibula) and the metatarsal bones, which lead to the toes. These bones collectively form the tarsus.
Unlike the long bones of the limbs, tarsals are short bones designed for stability and shock absorption. They are distinct from the metatarsals, the five long bones extending to the toes, and the phalanges, the bones of the toes themselves. The tarsals create a stable base for the foot, allowing for weight-bearing and movement.
Individual Tarsal Bones and Their Roles
The seven tarsal bones each possess a distinct shape, location, and function. The talus, often called the ankle bone, is positioned superiorly, articulating with the tibia and fibula to form the ankle joint. It is unique among tarsals as it has no direct muscular attachments, relying on ligaments for stability. The talus transmits body weight from the lower leg to the foot.
The calcaneus, known as the heel bone, is the largest tarsal bone and forms the prominence at the back of the foot. It articulates with the talus superiorly and the cuboid anteriorly, supporting significant body weight during standing and walking. The navicular bone is boat-shaped and located on the medial side of the foot, articulating with the talus posteriorly and the three cuneiform bones anteriorly. It is considered a keystone of the medial longitudinal arch, maintaining the arch’s integrity.
The cuboid bone is cube-shaped and situated on the lateral (outer) side of the foot, connecting with the calcaneus and the fourth and fifth metatarsals. It contributes to the stability of the foot, aids in toe movement, and helps with weight distribution. The three cuneiform bones—medial, intermediate, and lateral—are wedge-shaped and located in front of the navicular. These cuneiforms articulate with the navicular and the first, second, and third metatarsals, contributing to the formation of the transverse arch of the foot.
How Tarsals Support Movement and Stability
The tarsal bones work together to form the arches of the foot, which distribute pressure and absorb shock during movement. There are three main arches: two longitudinal (medial and lateral) and one anterior transverse arch. These arches, formed by the tarsal and metatarsal bones, are supported by ligaments and tendons, allowing the foot to act like a spring. This spring-like action helps dissipate impact forces and stores energy, contributing to economical walking and running.
The articulations between the tarsal bones, and between tarsals and leg bones (tibia and fibula) and metatarsals, enable various foot movements. The talus, articulating with the tibia and fibula, enables dorsiflexion (moving the foot upwards) and plantarflexion (moving the foot downwards) at the ankle joint. The subtalar joint, formed by the talus and calcaneus, allows for inversion (turning the sole inward) and eversion (turning the sole outward) of the foot. These movements, combined with the structural support of the arches, allow the foot to adapt to uneven terrain, bear the body’s weight, and propel movement.
Common Issues Affecting Tarsal Bones
Tarsal bones can be affected by various injuries and conditions, impacting foot function and mobility. Fractures of these bones can occur from sudden impacts, twisting injuries, or repetitive stress, leading to stress fractures. The calcaneus (heel bone) and talus are among the most frequently fractured tarsal bones, often due to high-impact events like falls or car accidents. Symptoms typically include sharp pain, swelling, and bruising, making weight-bearing difficult.
Sprains are another common issue, occurring when the ligaments connecting tarsal bones are stretched or torn. A midtarsal joint sprain, for instance, can result from excessive twisting or rolling of the foot, causing pain, swelling, and tenderness. Arthritis can also affect the joints between tarsal bones, leading to pain and inflammation. Additionally, conditions like tarsal tunnel syndrome involve the compression of the posterior tibial nerve as it passes through the tarsal tunnel in the ankle. This compression can cause pain, tingling, numbness, or a burning sensation in the foot and toes.