In this article, we'll discuss the anatomy of the fibula. The fibula is a slender, cylindrical leg bone that is located on the posterior portion of the limb. It is found next to another long bone known as the tibia. A long bone is defined as one whose body is longer than it is wide.
Like other long bones, the fibula has a proximal end (with a head and neck), a shaft, and a distal end. The fibula and tibia run parallel to each other in the leg and are similar in length but the fibula is much thinner than the tibia. This is indicative of the weight-bearing contributions of each bone. In other words, the thicker tibia has a much greater function in weight-bearing than the fibula.
|Proximal end||Apex – styloid process
Head of the fibula – with facet to articulate with the lateral tibial condyle
Short neck – with common fibular nerve behind it
|Shaft||Three borders – anterior, interosseous, posterior
Three surfaces – medial, lateral, posterior
|Distal end||Lateral malleolus
Point of ligamentous attachment
|Joints||Superior tibiofibular joint – plane synovial joint
Middle tibiofibular joint – attached by the interosseous membrane
Inferior tibiofibular joint – syndesmosis
Also participates in the ankle mortise joint
|Blood supply||Fibular artery|
|Innervation||Proximal end – genicular branch of the common fibular nerve
Distal end - deep fibular nerve
Periosteum - superficial and deep fibular nerves
|Clinical points||Fractures are most commonly traumatic
Isolated fibular fractures are less common than combined tibial and fibular fractures
Proximal fibular fractures are associated with common fibular nerve injury
Distal fibular fractures may be described using the Weber (Danis-Weber) system
|Mnemonic||FibuLA is LAteral|
There are several key facts about the fibula that most anatomy students should be familiar with. These and other important points about the anatomy, blood supply, innervation, and muscular and ligamentous attachments are addressed in this article. The article will also discuss important fractures of the fibula.
- Proximal end
- Distal end
- Muscle attachments
- Blood supply and innervation
- Clinical points
DevelopmentThe fibula is a part of the appendicular skeleton and develops via endochondral ossification. There are three points at which ossification begins in the fibula:
- the shaft around the 8th gestational week
- the distal end by the end of the first year of life
- the proximal end at around four-years-old in males and three-years-old in females
The ossification centers of the shaft and distal end of the bone eventually fuse during the mid-adolescent years (at 15 years old for females and 17 years old for males). The bony centers of the proximal part and shaft of the fibula are the last to unite during the late adolescent years (around 17 years for females and 19 years for males).
The proximal end of the fibula is characterized by an irregularly shaped head and a short neck. It has three segments which project in different directions: anteriorly, posteriorly, and laterally. An important question that pops up on a lot of anatomy tests is with what bony structure does the head of the fibula articulate? There is a round, flattened area on the medial part of the fibular head known as a facet. It articulates with a complementary facet on the inferolateral part of the lateral tibial condyle (proximal tibiofibular joint). The facet also acts as a point of attachment for the tibiofibular capsular ligament. Additionally, the tibiofibular capsular ligament surrounds the articular facet of the fibula.
There is a styloid process of the fibula that extends superiorly from the head; it is more commonly referred to as the apex of the head of the fibula. This apical projection protrudes from the posterolateral part of the fibular head. The neck of the fibula is a short bare region just below the fibular head. What important structures pass around the neck of the fibula? Importantly, the common fibular nerve (also called the common peroneal nerve) travels posterolaterally to the fibular neck. This has clinical significance as trauma to the neck of the fibula can present with neurological deficits.
The function of the proximal end of the fibula is to provide points of attachment for minor supporting ligaments of the knee joint. There is the fibular collateral ligament that arises from the fibular apex and is surrounded by the tendon of biceps femoris.
The majority of the fibula is made up by its shaft. This part of the bone is triangular in cross-section and consequently has three borders (anterior, interosseous, and posterior) and three surfaces (lateral, medial, and posterior) found along the shaft of the fibula. The borders are the sharp longitudinal edges that run along the bone’s long axis. On the other hand, the surfaces are the flattened areas that exist between the borders.
The anterior border starts at the fibular head and continues distally toward the lateral malleolus, where it diverges into two ridges that surround the triangular subcutaneous surface. On the medial aspect of the fibula is the interosseous or medial border. It is the point of attachment of the fibrous interosseous membrane of the leg that forms the middle tibiofibular joint. This fibrous septum acts as a barrier between the extensor and fibular muscles. There is a posterior border that runs along the back part of the fibula. The proximal part of the border appears slightly rounded. However, the border becomes more prominent distally, as it approaches the medial segment of the lateral malleolus.
The interosseous and anterior borders of the fibula act as medial and lateral boundaries of the medial surface. This surface provides a point of attachment for the muscles that extend the foot and cause the toes to point upward (dorsiflexion).
The lateral surface is found on the opposite side of the medial surface, between the posterior and anterior borders. The proximal part of the surface faces laterally; however, the surface spirals toward the distal end and as such part of the surface faces posterolaterally. By virtue of this shift, the distal part of the lateral surface is in continuity with the posterior groove of the lateral malleolus. The lateral surface provides a point of attachment for the fibular (peroneal) muscles.
The posterior surface is found between the posterior and interosseous borders. The surface is much more narrow at the proximal part (where the interosseous and posterior borders are closest) than it is distally (where the borders are farthest apart). This surface provides attachment for the flexor muscles of the foot which are responsible for pointing the toes downward (plantar flexion).
The distal end of the fibula forms the lateral malleolus of the lower limb. This is a bony projection noted on the lateral surface of the ankle, which is complementary to another bony projection on the medial aspect of the ankle called the medial malleolus (formed by the tibia). The lateral malleolus extends posteroinferiorly, is round and rough anteriorly, and has a broad groove posteriorly. The lateral surface is covered by skin (so there is no muscular layer at this area) and the medial surface has a triangular area that is convex along the vertical axis. The distal end of the fibula tapers off as an apical projection that articulates with the lateral aspect of the talus.
The distal end provides attachment for several ligaments that support the ankle joint. The posterior tibiofibular, posterior talofibular, calcaneofibular, and interosseous (middle) tibiofibular ligaments all have attachments to the end of the fibula and participate in the stability of this joint.
The tibia and fibula articulate through three joints–the superior, middle, and inferior tibiofibular joints. The superior tibiofibular joint is a plane synovial joint (allows only gliding movement) with the transverse joint line spanning the lateral tibial condyle and the medial fibular head. The capsule is thickened anteriorly and posteriorly and joins with the anterior ligament of the fibular head, relating closely to the tendon of biceps femoris.
The tibia and fibula also articulate via an interosseous membrane that is also called the middle tibiofibular ligament. It is made of an aponeurotic lamina which is thin and made of oblique fibers. This ligament has medial and lateral attachments to the tibial and fibular interosseous margins respectively. The membrane separates the muscles in the back of the leg from the muscles located in the front of the leg.
The inferior tibiofibular joint is a syndesmosis joint (slightly movable, fibrous joint), just above the ankle region which lies between the medial distal end of the fibula and the concave fibular notch region of the lateral tibia. There is no fibrous capsule surrounding this joint but there is the anterior tibiofibular ligament which descends laterally between the two leg bones.
More information about the fibula, tibia, knee and ankle joint is provided below:
What is the function of the fibula? The bone provides a point of origin for a number of muscles of the foot. However, only one muscle inserts on this long bone. So what structures are attached to the fibula? The table below summarizes the muscles that originate from, and insert on the fibula. Note that the muscles are listed from cranial to caudal, and those attached to the anterior surface are listed before those on the posterior surface.
|Biceps femoris||Inserts on the head of the fibula|
|Extensor digitorum longus||Proximal half of medial surface of fibula (and lateral tibial condyle)|
|Fibularis longus||Head of fibula, Superior two-thirds of lateral surface of fibula,
|Extensor hallucis longus||Medial surface of fibula, Interosseous membrane|
|Fibularis brevis||Inferior third of lateral surface of fibula|
|Fibularis tertius||Distal anteromedial surface of fibula|
|Soleus||Head of fibula, Posterior border of fibula (and the soleal line of the femur)|
|Tibialis posterior||Posterior surface of fibula, Interosseous membrane (and posterior surface of tibia)|
|Flexor hallucis longus||Posterior surface of fibula, Interosseous membrane|
Blood supply and innervation
A branch of the fibular artery brings oxygen-rich blood to supply the bone. It travels through a nutrient foramen on the posterior surface of the fibula that facilitates passage of a branch of the fibular artery into the bone. The foramen is a few centimeters proximal to the midpoint of the shaft.
The nerves that supply the knee (genicular branch of the common fibular nerve) and ankle (deep fibular nerve) joints also innervate the proximal and distal ends of the fibula, respectively. Similarly, superficial and deep fibular nerves, which innervate the muscles attached to the fibula, also innervate the fibular periosteum.
Fractures of the fibula are most likely related to traumatic injuries. They are almost always associated with fractures of the adjacent tibia or disruption of the ankle joint. However, although it seldom happens, there are cases of isolated fibular fractures. Logically, since the fibula is thinner than the tibia, it is easier to fracture than the tibia. However, the infrequency of isolated fibular fractures is related to the fact that the fibula is not the principal weight-bearing bone of the leg. As a result, it is more common for the tibia to be fractured than it is for the fibula to succumb to the same fate. The nature of the fracture is dependent on the mechanism of injury.
Combined tibia and fibula fractures may be the result of rotational or angular forces. Rotational forces generate spiral fractures, while angular forces generate transverse or oblique fractures. Isolated fibular shaft fractures are often the result of direct trauma to the area over the bone. Symptoms of bone fracture such as localized pain, swelling, and history of trauma over the site of injury are often present. Immobilization of the fracture is intended to prevent trauma to the overlying skin, adjacent muscles, or nearby neurovascular structures.
Proximal fibular fractures most often result in damage to the common fibular nerve. This will result in reduced sensation in the lateral aspect of the forefoot and weakness of ankle dorsiflexion. The attitude of the foot would be such that the toes are pointed downward at all times. This deformity is known as a foot drop. A Maisonneuve fracture occurs when transmitted forces fracture the proximal fibula following an ankle injury. This usually involves fracture of the medial malleolus, of the proximal fibula or fibular shaft, and damage to the distal tibiofibular syndesmosis.
Distal fibular fractures often result in disruption of the ankle mortise joint, owing to the fact that the lateral malleolus is important in the stability of the joint. In 1949, a Belgian general surgeon, Robert Danis, classified different types of lateral malleolar fractures. This classification was later rearranged and became more widely used in 1972 thanks to Bernhard Georg Weber (a Swiss orthopedic surgeon). The Weber (or Danis-Weber) classification looks at the level of lateral malleolar fractures in relation to the ankle joint.
|Type A||Transverse fracture below the top of the talus (talar dome)
Tibiofibular syndesmosis intact
Deltoid ligament intact
Medial malleolus may be fractured
|Type B||Spiral fracture extending to or a little above the talar dome
Widening of distal tibiofibular joint, but syndesmosis may be intact
The deltoid ligament may be torn
Medial malleolus may be fractured
May require surgical intervention (open reduction and internal fixation [ORIF])
|Type C||Fracture extends above the ankle joint
Widening of distal tibiofibular joint with disruption of the syndesmosis
May result from a Maisonneuve fracture; require full-length radiographs
Unstable and requires surgical intervention (ORIF)
Stress fractures of the fibula are relatively common, typically affecting the fibular neck of military recruits and athletes following vigorous training. Metastatic lesions can result in stress fractures of the bone. The distal third of the fibula is most commonly affected. Nevertheless, the other parts of the bone may also be affected.