The seven tarsal bones form a complex structure situated in the rear and mid-foot, acting as the foundation for the entire foot. These irregularly shaped bones connect the lower leg to the rest of the foot. The tarsals provide both stability and flexibility, allowing the foot to adapt to various surfaces and motions.
Anatomical Placement and Identification
The seven tarsal bones are collectively known as the tarsus and are grouped into the hindfoot and the midfoot regions. The hindfoot consists of the two largest bones, the talus and the calcaneus, which are positioned most proximally. The talus sits superiorly, articulating directly with the tibia and fibula to form the ankle joint. Directly beneath the talus is the calcaneus, which is the largest tarsal bone and forms the heel.
The remaining five tarsal bones constitute the midfoot, positioned more distally. Immediately in front of the talus is the navicular bone, which is boat-shaped and situated on the medial side of the foot. Lateral to the navicular is the cuboid bone, located anterior to the calcaneus on the outer side of the foot. The final three tarsal bones are the wedge-shaped cuneiforms, positioned in a row anterior to the navicular bone. These three are named according to their position: the medial (first), intermediate (second), and lateral (third) cuneiforms. These bones articulate distally with the bases of the five metatarsal bones.
Biomechanical Function
The primary role of the tarsal bones is to act as a robust yet flexible base for the body, managing weight distribution and absorbing forces during movement. The talus transmits the entire body weight from the lower leg down into the foot. This force is then distributed through the other tarsal bones, particularly the calcaneus, which acts as a lever for the calf muscles during push-off.
The tarsal bones are arranged to form three arches: the medial longitudinal, the lateral longitudinal, and the transverse arch. These arches act like a spring mechanism, flattening slightly upon impact to absorb shock and then recoiling to provide propulsion. The medial longitudinal arch is the highest and is formed by the calcaneus, talus, navicular, cuneiforms, and the first three metatarsals. The lateral longitudinal arch is flatter and is formed by the calcaneus, cuboid, and the fourth and fifth metatarsals. The arches are maintained by the shape of the tarsal bones, strong ligaments, and tendons. Subtle movements at the subtalar joint between the talus and calcaneus allow for inversion and eversion, enabling the foot to adapt to uneven terrain.
Common Health Issues Affecting Tarsals
The unique stresses placed on the tarsal bones make them susceptible to specific injuries and congenital conditions. Calcaneal fractures, or heel bone fractures, are common high-impact injuries, often resulting from falls from a height or motor vehicle accidents. The calcaneus is vulnerable due to its role in heel strike and shock absorption.
A congenital condition known as tarsal coalition involves the abnormal connection or fusion of two or more tarsal bones. This connection can be composed of bone, cartilage, or fibrous tissue and most often occurs between the calcaneus and the navicular, or the talus and the calcaneus. Tarsal coalition restricts normal motion, frequently leading to a painful, rigid flatfoot that becomes symptomatic as the bones mature, typically between ages nine and sixteen.
The alignment of the tarsal bones is fundamental to the overall shape of the foot, and their dysfunction contributes to conditions like flat feet (pes planus) or high arches (pes cavus). Misalignment or lack of structural support in the tarsals can compromise the integrity of the arches, affecting the foot’s ability to distribute weight effectively.