What Is the Fibula? Structure, Functions, and Exam Tips
This article contains the anatomy of the fibula. Tibia and fibula bone constitutes the part of the leg. Fibula bone is slender and cylindrical in shape and is located on the limb's posterior portion. Both fibula and tibia bones lie next to each other. Tibia and fibula anatomy are essential to be well understood by all the students of biology.
Like the other long bones, the fibula has a proximal end consisting of the head and neck, a shaft, and a distal end. Tibia fibula bone runs parallel to one another in the leg and is of similar length. However, fibula bone is a bit thinner than the tibia. Thus, the thicker tibia has a more significant function for weight-bearing than the thinner fibula parts.
What is a Fibula?
The fibula is located in the lateral aspect of the leg, and its primary function is acting as the attachment for muscles and does not have a significant role in weight-bearing. This bone has three main articulations, which are as follows:
Proximal Tibiofibular Joint: This portion articulates with the tibia's lateral condyle.
Distal Tibiofibular Joint: This portion articulates with the tibia's fibular notch.
Ankle Joint: This portion articulates with the foot's talus bone.
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Fibula Anatomy: Bony Landmarks
Proximal: At the fibula's proximal end, it has an enlarged head containing a facet for articulation with the tibia's lateral condyle. However, the fibular neck's lateral and posterior surface, the common fibular nerve, cannot be found.
Shaft: There are three surfaces in the fibular shaft: anterior, lateral and posterior. The leg is divided into three compartments, and each of the surfaces faces the respective compartment, like, anterior surface faces the leg's anterior compartment.
Distal: At the distal end, the lateral surface moves inferiorly and is known as the lateral malleolus. It is more prominent than the medial malleolus and can be palpated at the leg's lateral side's ankle.
Joints Related to the Fibula Bone
Tibia and fibula bone articulates through 3 joints: the inferior, middle, and superior tibiofibular joints. A superior tibiofibular joint is a plane synovial joint that only allows the gliding movement with the transverse joint line spanning the medial fibular head and the tibia condyle. The capsule is anteriorly and posteriorly thicker, and it joins with the fibular head's anterior ligament that closely relates to the biceps femoris's tendon.
Tibia fibula bone also articulates through the interosseous membrane, also known as the middle tibiofibular ligament. It is composed of an aponeurotic lamina that is thinner and composed of oblique fibers. This ligament contains the lateral and medial attachments to fibular and tibial intraosseous margins, respectively. The membrane separates the muscle towards the leg's back from the muscle situated at the leg's front.
The inferior tibiofibular joint is a syndesmosis joint that has a fibrous structure and is slightly movable. It lies just above the ankle region, lying between the fibula's medial distal end and the lateral tibia's concave fibular notch region. This joint does not have any fibrous capsule surrounding it, but it has the anterior tibiofibular ligament that laterally descends between the leg's two bones.
Innervation and Blood Supply
There is a branch of the fibular artery that brings oxygenated blood for supplying to the bone. It travels through the fibula's nutrient foramen on a posterior surface, facilitating the passage of the fibular artery's branch into the bone. The foramen is some centimeters proximal to the shaft's midpoint.
The nerves supplying the ankle joints and the knee (the genicular branch of the common fibular nerve) also innervates the fibula's distal and proximal ends, respectively. Similarly, the deep and superficial fibular nerves innervating the fibula's muscles also innervate the fibular periosteum.
Fibula's Fractures
The lateral malleolus of the fibula, at the ankle, is prone to fractures. This might occur in the two main ways, which are as follows:
By forced external rotation of the ankle. This force of the talus against the bone leads to a spiral fracture of the lateral malleolus.
By foot getting twisted outwards, known as eversion. This is less common. Here, the talus gets pressed against the lateral malleolus and causes a transverse fracture.
FAQs on Fibula: Anatomy, Function, and Clinical Significance
1. What is the fibula and where is it located in the human body?
The fibula, commonly known as the calf bone, is a long, thin bone located on the lateral (outer) side of the lower leg. It runs parallel to the tibia (shin bone), which is the larger of the two lower leg bones. The fibula extends from just below the knee to form the outer part of the ankle joint.
2. What are the primary functions of the fibula?
Although the fibula is not a primary weight-bearing bone, it plays several crucial roles in the leg's function. Its main functions include:
- Ankle Stability: The lower end of the fibula forms the lateral malleolus, a bony prominence on the outside of the ankle that is essential for stabilising the ankle joint.
- Muscle Attachment: It serves as an attachment point for numerous muscles of the lower leg and foot, which are vital for movements like pointing the foot down and turning it outward.
- Support for the Tibia: It provides lateral support to the tibia and helps distribute forces across the lower leg.
3. What are the key anatomical parts of the fibula?
As a typical long bone, the fibula consists of three main parts:
- Proximal End (Head): The upper end, which articulates with the tibia just below the knee joint. It features a pointed apex for muscle attachment.
- Shaft (Body): The long, slender middle section of the bone, which has multiple surfaces and borders for the attachment of various leg muscles.
- Distal End (Lateral Malleolus): The lower end, which is larger than the proximal end and forms the bony bump on the outer side of the ankle. It articulates with the talus bone of the foot to form part of the ankle joint.
4. How is the fibula fundamentally different from the tibia?
The fibula and tibia are the two bones of the lower leg, but they have key differences. The primary distinction is their role in weight-bearing; the tibia bears most of the body's weight, while the fibula bears very little (less than 10%). Consequently, the tibia is much thicker and stronger. Anatomically, the tibia is located medially (on the inner side of the leg), while the fibula is positioned laterally (on the outer side).
5. If the fibula is not a weight-bearing bone, why is a fracture still a significant injury?
While it's true the fibula isn't a primary weight-bearing bone, its importance lies in ankle joint stability. The lower part of the fibula, the lateral malleolus, acts as a crucial buttress for the ankle. A fracture here can destabilise the entire joint, leading to pain, swelling, and difficulty in walking. Therefore, even though you might be able to put some weight on the leg, a fibula fracture is significant because it compromises the structural integrity and function of the ankle.
6. How does the development of the fibula illustrate the process of endochondral ossification?
The fibula's development is a classic example of endochondral ossification, where a cartilage model is replaced by bone. This process begins at a primary ossification centre in the shaft around the 8th week of gestation. Later, secondary ossification centres appear at the ends (epiphyses)—first at the distal end around age one and then at the proximal end around age three or four. The bone continues to grow until these centres fuse with the shaft during adolescence, a process that perfectly demonstrates how long bones mature in the human body.
7. What type of bone is the fibula, and how does this classification relate to its structure?
The fibula is classified as a long bone. This classification is based on its shape, not its size. Long bones are characterised by being longer than they are wide and having a shaft (diaphysis) with two distinct ends (epiphyses). This structure is typical for bones found in the limbs, like the fibula, femur, and humerus, and is adapted for providing leverage for muscle action and support.
