Tibia and Fibula (Leg)
The tibia, also known as the shin bone, is a long bone of the lower leg found between the patella and the ankle. It is the larger and stronger of the two bones in the leg below the knee in vertebrates (the other being the fibula), and connects the knee with the ankle bones. The tibia is named for the Greek aulos flute. It is commonly recognized as the strongest weight-bearing bone of the body. It forms the medial part of the ankle joint and is the second largest bone next to the femur. Like the femur, the tibia bears much of the body's weight and plays an essential role in movement and locomotion. In the male, its direction is vertical and parallel with the bone of the opposite side. In the female, it has a slightly oblique direction downward and laterally, to compensate for the greater obliqueness of the femur. The tibia is prismoid in form, which means it is polyhedron-like in shape with parallel planes containing an equal number of points. It is wider at the top, where it enters into the knee-joint, contracted in the lower third, and again enlarged but to a lesser extent towards the ankle joint.
The superior tibiofibular articulation is an arthrodial joint between the lateral condyle of the tibia and the head of the fibula. The inferior tibiofibular articulation (tibiofibular syndesmosis) is formed by the rough, convex surface of the medial side of the lower end of the fibula, and a rough concave surface on the lateral side of the tibia. The tibia is connected to the fibula by an interosseous membrane, forming a type of joint called a syndesmosis. The forward flat part of the tibia is called the fibia, often confused with the fibula.
The fibula, also known as the calf bone, is a long, thin bone running parallel to the tibia. Its upper extremity is small, placed toward the back of the head of the tibia, below the level of the knee-joint, and excluded from the formation of this joint. Its lower extremity inclines a little forward so that it is on a plane anterior to that of the upper end. It projects below the tibia forming the lateral part of the ankle joint.
The fibula has the following components:
- Body of fibula Lateral malleolus;
- Interosseous membrane connecting the fibula to the tibia, forming a syndesmoses joint;
- The superior tibiofibular articulation is an arthrodial joint between the lateral condyle of the tibia and the head of the fibula;
- The inferior tibiofibular articulation (tibiofibular syndesmosis) is formed by the rough, convex surface of the medial side of the lower end of the fibula, and a rough concave surface on the lateral side of the tibia.
The blood supply to the fibula is important for planning free tissue transfer because the fibula is commonly used to reconstruct the mandible. The shaft is supplied in its middle third by a large nutrient vessel from the fibular artery. It is also perfused from its periosteum which receives many small branches from the fibular artery. The proximal head and the epiphysis are supplied by a branch of the anterior tibial artery. In harvesting the bone, the middle third is always taken and the ends preserved (4 cm proximally and 6 cm distally).
In addition, in the tibia, ossification, which is the formation of the bone, starts from three centers; one in the shaft and one in each extremity, while the fibula is ossified from three centers, one for the shaft and another for either end. For the fibula, ossification begins in the body about the eighth week of fetal life, and extends toward the extremities. At birth the ends are cartilaginous. Ossification commences in the lower end in the second year, and in the upper end around 4 years old. The lower epiphysis, the first to ossify, unites with the body around 20 years old and the upper epiphysis joins around 25 years old.