Fibula

Jai Ganesh · Yesterday 16:48:52

Fibula

Gist

The fibula (calf bone) is the slender, long bone located on the lateral (outer) side of the tibia in the lower leg. While it does not bear significant weight, it is crucial for stabilizing the ankle joint, supporting lower-leg muscles, and forming the lateral malleolus. It connects to the tibia via an interosseous membrane.

The fibula, or calf bone, is the slender, outer bone in the lower leg, running parallel to the larger shin bone (tibia) from just below the knee to the ankle, forming the bony bump (lateral malleolus) on the outside of your ankle and providing vital stability and muscle attachment for movement, though it's not a primary weight-bearing bone.

Summary

Fibula is the outer of two bones of the lower leg or hind limb, presumably so named (fibula is Latin for “brooch”) because the inner bone, the tibia, and the fibula together resemble an ancient brooch, or pin. In humans the head of the fibula is joined to the head of the tibia by ligaments and does not form part of the knee. The base of the fibula forms the outer projection (malleolus) of the ankle and is joined to the tibia and to one of the ankle bones, the talus. The tibia and fibula are further joined throughout their length by an interosseous membrane between the bones. The fibula is slim and roughly four-sided, and its shape varies with the strength of the attached muscles. In many mammals, such as the horse and the rabbit, the fibula is fused for part of its length with the tibia.

Fractures of the fibula usually are associated with an ankle injury, though they can occur in isolation (without ankle involvement) or in combination with fractures of the tibia (e.g., in severe injuries). Though less common that tibial stress fractures, fibular stress fractures can occur, most typically in long-distance runners.

Details

The fibula (pl.: fibulae or fibulas) or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity is small, placed toward the back of the head of the tibia, below the knee joint and excluded from the formation of this joint. Its lower extremity inclines a little forward, so as to be on a plane anterior to that of the upper end; it projects below the tibia and forms the lateral part of the ankle joint.

Structure

The bone has the following components:

* Lateral malleolus
* Interosseous membrane connecting the fibula to the tibia, forming a syndesmosis 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.

Blood supply

The blood supply 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)

Development

The fibula is ossified from three centers, one for the shaft, and one for either end. 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 about the fourth year. The lower epiphysis, the first to ossify, unites with the body about the twentieth year; the upper epiphysis joins about the twenty-fifth year.

Head

The upper extremity or head of the fibula is of an irregular quadrate form, presenting above a flattened articular surface, directed upward, forward, and medialward, for articulation with a corresponding surface on the lateral condyle of the tibia. On the lateral side is a thick and rough prominence continued behind into a pointed eminence, the apex (styloid process), which projects upward from the posterior part of the head.

The prominence, at its upper and lateral part, gives attachment to the tendon of the biceps femoris and to the fibular collateral ligament of the knee-joint, the ligament dividing the tendon into two parts.

The remaining part of the circumference of the head is rough, for the attachment of muscles and ligaments. It presents in front a tubercle for the origin of the upper and anterior fibers of the peroneus longus, and a surface for the attachment of the anterior ligament of the head; and behind, another tubercle, for the attachment of the posterior ligament of the head and the origin of the upper fibers of the soleus.

Body

The body of the fibula presents four borders - the antero-lateral, the antero-medial, the postero-lateral, and the postero-medial; and four surfaces - anterior, posterior, medial, and lateral.

Borders

The antero-lateral border begins above in front of the head, runs vertically downward to a little below the middle of the bone, and then curving somewhat lateralward, bifurcates so as to embrace a triangular subcutaneous surface immediately above the lateral malleolus. This border gives attachment to an intermuscular septum, which separates the extensor muscles on the anterior surface of the leg from the peronaei longus and brevis on the lateral surface.

The antero-medial border, or interosseous crest, is situated close to the medial side of the preceding, and runs nearly parallel with it in the upper third of its extent, but diverges from it in the lower two-thirds. It begins above just beneath the head of the bone (sometimes it is quite indistinct for about 2.5 cm. below the head), and ends at the apex of a rough triangular surface immediately above the articular facet of the lateral malleolus. It serves for the attachment of the interosseous membrane, which separates the extensor muscles in front from the flexor muscles behind.

The postero-lateral border is prominent; it begins above at the apex, and ends below in the posterior border of the lateral malleolus. It is directed lateralward above, backward in the middle of its course, backward, and a little medialward below, and gives attachment to an aponeurosis which separates the peronaei on the lateral surface from the flexor muscles on the posterior surface.

The postero-medial border, sometimes called the oblique line, begins above at the medial side of the head, and ends by becoming continuous with the interosseous crest at the lower fourth of the bone. It is well-marked and prominent at the upper and middle parts of the bone. It gives attachment to an aponeurosis which separates the tibialis posterior from the soleus and flexor hallucis longus.

Surfaces

The anterior surface is the interval between the antero-lateral and antero-medial borders. It is extremely narrow and flat in the upper third of its extent; broader and grooved longitudinally in its lower third; it serves for the origin of three muscles: the extensor digitorum longus, extensor hallucis longus, and peroneus tertius.

The posterior surface is the space included between the postero-lateral and the postero-medial borders; it is continuous below with the triangular area above the articular surface of the lateral malleolus; it is directed backward above, backward and medialward at its middle, directly medialward below. Its upper third is rough, for the origin of the soleus; its lower part presents a triangular surface, connected to the tibia by a strong interosseous ligament; the intervening part of the surface is covered by the fibers of origin of the flexor hallucis longus. Near the middle of this surface is the nutrient foramen, which is directed downward.

The medial surface is the interval included between the antero-medial and the postero-medial borders. It is grooved for the origin of the tibialis posterior.

The lateral surface is the space between the antero-lateral and postero-lateral borders. It is broad, and often deeply grooved; it is directed lateralward in the upper two-thirds of its course, backward in the lower third, where it is continuous with the posterior border of the lateral malleolus. This surface gives origin to the peronaei longus and brevis.

Clinical significance

As much of the fibula can be removed without it impacting an individual's ability to walk, the fibula is utilised as a source of bone material in fibular free flap surgeries.

Fractures

The most common type of fibula fracture is located at the distal end of the bone, and is classified as ankle fracture. In the Danis–Weber classification it has three categories:

* Type A: Fracture of the lateral malleolus, distal to the syndesmosis (the connection between the distal ends of the tibia and fibula).
* Type B: Fracture of the fibula at the level of the syndesmosis
* Type C: Fracture of the fibula proximal to the syndesmosis.

A Maisonneuve fracture is a spiral fracture of the proximal third of the fibula associated with a tear of the distal tibiofibular syndesmosis and the interosseous membrane. There is an associated fracture of the medial malleolus or rupture of the deep deltoid ligament.

An avulsion fracture of the head of the fibula refers to the fracture of the fibular head because of a sudden contraction of the biceps femoris muscle that pulls its site of attachment on the bone. The attachment of the biceps femoris tendon on the fibular head is closely related to the lateral collateral ligament of the knee. Therefore, this ligament is prone to injury in this type of avulsion fracture.

Additional Information

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.

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.

Development

The 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 body 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 body 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).

Proximal end

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.

Body

The majority of the fibula is made up by its body (or 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).

Distal end

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.

Joints

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.

Muscle attachments

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.

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.

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Fibula

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