The feet and hands have similar skeletal structures. However, the bones of the foot are understandably stronger and capable of carrying more weight, a feature that comes at the cost of mobility. Anatomists and physicians divide the foot into three regions: the hindfoot, the midfoot, and the forefoot.
The tarsal group of foot bones contains the bones of the midfoot and hindfoot. The talus is the second largest bone in the group. It works with two other tarsal bones -- the navicular and calcaneus -- to articulate the foot at the talocalcaneonavicular joint. These articulations shift the weight of the body to the foot. The head of the talus bone forms the lower portion of the ankle joint and connects to the tibia and fibula bones of the leg. Articular cartilage covers a significant portion of the surface area of the talus.
Within the hindfoot is the largest bone in the foot: the calcaneus or heel, which is also one of the most important bones in the foot. The portion of the calcaneus closest to the heel is the calcaneal tuberosity. A roughened area on the upper portion of the calcaneal tuberosity acts as the insertion location for the Achilles tendon. This area also possesses three sections for articulation with the talus bone. On the anterior side of the calcaneus are articulation areas for the cuboid bone. The calcaneus also possesses many grooves through which the tendons pass.
Another tarsal bone, the cuboid, is slightly cubical, as its name suggests. A rough upper or dorsal surface allows for ligament attachments. The plantar area on the underside of the bone has a deep groove to accommodate the tendon of the peroneus longus. The posterior surface of the cuboid is smooth and connects to the calcaneus at the calcaneocuboid joint. A small projection from this region supports the anterior portion of the calcaneus. The anterior surface of the cuboid forms the fourth and fifth tarsometatarsal joints. The medial area is broad and meets the navicular bone and the third cuneiform.
Between the talus and cuneiforms sits the navicular bone, named for its curved, boat-like shape. It lies on the medial side of the foot and forms a joint with the talus, cuneiform bones, and cuboid. The only muscle that connects to the navicular bone is the tibialis posterior, the primary stabilizing muscle of the lower leg. Some individuals develop an accessory navicular bone, a growth that is typically asymptomatic, though large or fused accessory bones may require surgical removal.
There are three cuneiform bones in the foot: the medial, intermediate, and lateral. Some individuals refer to these bones as the first, second, and third cuneiforms, respectively. The medial cuneiform is the largest and forms a joint with the intermediate cuneiform and the first two metatarsals. The intermediate cuneiform has a wedge-like shape and articulates with both of the other cuneiforms and the second metatarsal. Like the intermediate cuneiform, the lateral cuneiform is also wedge-shaped. It meets the cuboid, intermediate cuneiform, and the third metatarsal. All three cuneiforms form joints with the navicular.
The metatarsal bones, or metatarsus, are a group of five bones that sit between the phalanges of the toes and the cuneiforms. Unlike other bones, the metatarsals do not possess individual names. Instead, each bone has a number from one to five, beginning at the inside of the foot. Each metatarsal bone tapers gradually from the extremity.
Each toe, with the exception of the big toe, possesses three bones: the distal, middle, and proximal phalanges. The big toe has only distal and proximal phalanges. Like the metatarsus, the phalanges use numbers rather than individual names. The phalanges of the fourth and fifth toes often fuse together. Each phalanx consists of a base, shaft, and head. Between each phalanx is an interphalangeal joint. The distal phalanges connect to the metatarsus at the metatarsophalangeal joints. The phalanges provide balance and assist in the motions of running, walking, and jumping.
In a few places, the body develops a bone within a tendon or muscle. These are sesamoid bones, and they act as pulleys for tendons, providing a smooth surface for the tendons to slide across to increase muscular force. The first metatarsal bone typically develops two sesamoid bones near the distal phalanx of the big toe. Some individuals develop only one sesamoid on the first metatarsal bone.
The many points of articulation in the foot allow it to carry a significant amount of weight, adjust for different levels of force, and provide unique movements such as pronation and supination. These are anatomical terms that describe the motions of walking and running. Pronation describes landing on the exterior side of the heel, as well as the rolling and flattening of the foot. Supination describes the opposite of pronation, such as when we push off during a step.
The feet constantly experience force and impact. Despite their strength, this makes them particularly prone to injury, especially in athletes. Many physicians refer to foot bone fractures as tarsal fractures. Despite the name, fractures in the tarsal bones are rare. Instead, most fractures in the foot occur in the metatarsal bones. It is also possible for the calcaneus and the navicular bones to develop stress fractures. Usually, this is the result of a high trauma impact such as a car accident or landing from a great height.
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