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Fibula

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The fibula, often called the calf bone, is a long bone located in the lower leg.

3D Medical Animation Fibula Structure
3D Medical Animation Fibula Structure

It sits on the lateral side of the tibia, which is the larger shin bone. While the tibia carries most of the body's weight, the fibula is much thinner. In fact, it is the most slender of all the long bones in the human body. The fibula is essential for providing stability to the ankle joint. It also serves as a critical attachment point for many muscles and ligaments.

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The structure of the fibula involves several specific components and joints. At the top, the head of the fibula connects to the tibia at the superior tibiofibular articulation. This is an arthrodial joint, meaning it is a joint that allows for small movements. The bottom of the bone forms the lateral malleolus, which is the outer part of the ankle joint. A strong connection called the interosseous membrane links the fibula to the tibia. This membrane creates a syndesmosis joint, which is a type of joint held together by dense connective tissue. This connection helps separate different muscle groups within the leg.

The bone is divided into distinct anatomical parts: the head, the body, and the ends. The head is an irregular, quadrate shape located at the top. It has a pointed part called the styloid process, which is an upward projection. The body, or shaft, has four borders and four surfaces. These borders include the antero-lateral, antero-medial, postero-lateral, and postero-medial edges. The surfaces allow muscles like the soleus and the peronei to attach firmly. The lower end of the bone inclines slightly forward to help form the ankle structure.

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Development of the fibula follows a specific timeline of ossification, which is the process of turning into bone. This process begins in the middle of the bone during the eighth week of fetal life. At birth, the ends of the bone are still made of soft cartilage. The lower end begins to ossify during the second year of life. The upper end follows later, starting around the fourth year. These parts eventually fuse with the main shaft. The lower end unites around age 20, while the upper end joins around age 25.

Understanding the blood supply is vital for medical procedures. The shaft receives blood through a large nutrient vessel from the fibular artery. This vessel supplies the middle third of the bone. The periosteum, which is the thin outer layer of the bone, also receives many small branches from the fibular artery. The proximal head and the epiphysis, or the end of the bone, are supplied by a branch of the anterior tibial artery. This rich blood supply is why surgeons often use the fibula in free tissue transfer. They can move parts of the bone to reconstruct other areas, such as the mandible, or jawbone.

Medical professionals study various types of fibula fractures. The most common fractures occur at the distal end, near the ankle. Doctors use the Danis–Weber classification to categorize these injuries. Type A fractures occur below the syndesmosis. Type B fractures happen at the level of the syndesmosis. Type C fractures occur above it. There is also a specific injury called a Maisonneuve fracture. This is a spiral fracture of the upper third of the bone. It is often linked to a tear in the interosseous membrane or the ankle ligaments.

The history of the word fibula is quite interesting. The term dates back to approximately 1670 and comes from the Latin word for a clasp or brooch. It was used in English to describe this specific leg bone around 1706. The name was chosen because the bone's shape resembles a small pin or clasp. This connection to a fastener is also seen in the Greek word peronē. In the animal kingdom, the fibula varies greatly. While humans use it for stability, some animals have a much smaller version. In horses, the fibula is even partially fused to the tibia.

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3D Medical Animation Fibula Structure.jpg
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