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Anatomy and function of the fibula.

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Hello everyone! This is Matt from Kenhub, and in this tutorial, we will be looking at one of the long bones of the lower leg – the fibula.

The fibula shown here in green in both an anterior and posterior view is a long bone of the lower leg located posterolaterally to the tibia. The tibia and fibula are a similar length but the fibula is significantly more slender which helps to explain their differing functions. The tibia or shin bone indicated here is primarily a weightbearing bone while the fibula plays more of a supportive role helping to stabilize the ankle and providing numerous sites for muscle attachments.

The enlarged proximal head of the fibula shown from an anterior view and highlighted in green has an irregular shape and is directed upward, forwards and medially. Its proximal medial aspect articulates with the fibular articular facet of tibia on the inferolateral surface of the lateral condyle of the tibia labeled on the image. The head of the fibula also possesses a palpable upward pointing bony prominence known as the styloid process now indicated by an arrow located about 2 centimeters distal to the knee joint. The narrow neck of the fibula – highlighted – connects the head to the body of the fibula.

Shown here in green on the posterior surface of the right lower leg, the common fibular nerve, also known as the common peroneal nerve, passes over the head and neck of the fibula where it is sensitive to palpation. The body or shaft of the fibula is long and narrow which is again an indicator of its nonweightbearing functionality. It has a lateral, anterior, medial and posterior surface with four borders – anterolateral, anteromedial, posterolateral and posteromedial which will be discussed a bit later. The shafts of the tibia and fibula are connected by an interosseus membrane for much of their lengths which helps to give the two bones together and provides extra stability.

The distal end of the fibula – called the lateral malleolus highlighted in green – extends 1 centimeter further distally than the tibia's distal end – the medial malleolus – here indicated by the arrow. The lateral malleolus forms the outer lateral prominence of the ankle. The medial aspect of the lateral malleolus gives rise to the posterior talofibular ligament which it's anterior aspect gives rise to the anterior talofibular ligament. From its tip arises the calcaneofibular ligament. Together, these three ligaments form the lateral collateral ligament complex of the ankle which work to prevent inversion of the ankle joint.

The fibula articulates with the tibia proximally via two joints. The superior tibiofibular joint, a synovial plane joint whose transverse joint lines spans the lateral tibial condyle and the medial fibular head, and the inferior tibiofibular joint, a syndesmosis joint found just above the ankle region between the medial distal end of the fibula and the fibular notch region of the tibia.

The anterior surface of the fibula is extremely narrow. It runs between the anterolateral and anteromedial borders of the fibula. Muscles that originate from the anterior surface of the fibula are the extensor digitorum longus, the extensor hallucis longus.

The medial surface of the fibula faces the tibia and is situated between the anteromedial and posteromedial borders of the fibula. The tibialis posterior muscle originates from a groove located on the medial surface of the fibula and forms the posterior surface of the tibia as shown in the image.

The lateral surface of the fibula faces slightly upward. This deeply grooved surface of the fibula is found between the anterolateral and posterolateral borders. It is also the site of origin for the fibularis longus or peroneus longus muscle and the fibularis brevis or peroneus brevis muscle.

The posterior surface of the fibula lies between the posterolateral and posteromedial borders. The upper third of the posterior surface of the fibula is rough and is the origin of the soleus muscle. Inferiorly, it is connected to the tibia via a strong interosseus ligament. The origin of the flexor hallucis longus muscle is also located posteriorly.

We have already seen most of the muscles that have attachments on the fibula in relation to the fibular surfaces but let us now review for clarity all of the muscles with fibular attachment.

Biceps femoris attaches to the head of the fibula. Extensor hallucis longus originates from the medial surface of the fibula. Extensor digitorum longus originates from proximal part of the medial surface of the fibula. Peroneus longus or fibularis longus originates anterolaterally from the head and lateral surface of the fibula. Peroneus brevis or fibularis brevis originates from the distal two thirds of the lateral surface of the fibula. The soleus originates from the proximal one third of the posterior surface of the fibula. Tibialis posterior originates from the posterior surface of the fibula between the medial crest and the interosseus border. And, finally, flexor hallucis longus originates on the posterior surface of the fibula distal to the soleus muscle.

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