The fibula is the long, thin and lateral bone of the leg. It runs parallel to the tibia and plays a notable role in stabilizing the ankle joint and supporting the muscles of the lower leg. The fibula is about the same length Compared to the tibia but is considerably thinner.
The difference in thickness corresponds to the varying roles of the two bones; the tibia bears the body’s weight from the knees to the ankles, while the fibula merely functions as a support for the tibia.
Structure of the Fibula
The fibula has an upper end, shaft, and a lower end.
Upper End of the Fibula
The upper end is slightly expanded in all directions making an irregular quadrate form. Its superior surface bears a circular articular facet 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 or styloid process, which projects upward from the posterior part of the head.
Immediately below the head, the fibula constricts and the part is referred to as neck of the fibula.
Shaft of Fibula
The shaft of the fibula is slim and its shape is moulded by attached muscles and therefore shows considerable variation in its form.
It has three borders and three surfaces
Anterior, Posterior, Interosseus borders & medial, lateral and posterior surfaces.
Borders of shaft of the Fibula
It begins just below the anterior aspect of the head. At the lower end, it divides to enclose an elongated triangular area which is continuous with the lateral surface of the lateral malleolus.
It is rounded and its top end is in line with the styloid process. Below, the border is continuous with the medial margin of the groove on the back of the lateral malleolus.
Interosseus or Medial Border
It lies just medial to the anterior border. In its upper two-thirds of the interosseous border lies very close to the anterior border. It ends below at the upper end of a roughened area above the talar facet of the lateral malleolus.
Surfaces of shaft of the Fibula
It lies within the anterior and interosseus borders. In its upper two-thirds, it is very narrow, measuring 1 mm or less.
It lies between the anterior and posterior borders. It is twisted backward in its lower part.
It is the largest of the three surfaces. It lies between the interosseous and posterior borders. In its upper two-thirds, it is divided into two parts by a vertical ridge called the medial crest.
Lower End of Fibula
It is also known as the lateral malleolus and along with the inferior surface of the tibia.The tip of the lateral malleolus is 0.5 cm lower than that of the medial malleolus, and its anterior surface is 1.5 cm posterior to that of the medial malleolus. It has the four surfaces-
The anterior surface is rough and rounded. The posterior surface is marked by a groove. The medial surface bears a triangular articular facet for the talus (anteriorly); and the malleolar fossa (posteriorly). The lateral surface is subcutaneous.
Attachments of the Fibula
Head of Fibula
- Insertion of the biceps femoris on the anterolateral slope of the apex.
- The fibular collateral ligament of the knee joint.
- Extensions of origins of-Extensor digitorum,Peroneus longus & Soleus muscles.
- The capsular ligament of the superior tibiofibular joint – Around the articular facet.
Medial Surface of Fibula
Origin of the
- Extensor hallucis longus muscle – From the posterior half of its middle two-fourths.
- Extensor digitorum longus muscle – from the whole of the upper one-fourth, and from the anterior half of the middle two-fourths.
- Peroneus Tertius muscle (from its lower one-fourth).
Lateral Surface of Fibula
- The peroneus brevis muscle (from the anterior half of its middle one-third, and the whole of the lower one-third).
- The peroneus longus muscle (from its upper one-third, and the posterior half of the middle one-third
Posterior Surface of Fibula
- Tibialis Posterior muscle – The part of the posterior surface between the medial crest and the interosseous border
- Flexor hallucis longus muscle – Lower three-fourths of the part of the posterior surface between the medial crest and the posterior border
- Soleus muscle – Upper one-fourth of the part of the posterior surface between the medial crest and the posterior border
The anterior border of the fibula gives attachment to:
- The anterior intermuscular septum
- The superior peroneal retinaculum ( lower part of the posterior margin of the triangular area)
- The superior extensor retinaculum ( lower part of the anterior margin of the triangular area)
- Posterior intermuscular septum.
- Anterior tibiofibular ligament (anteriorly)
- The triangular area above the medial surface of the lateral malleolus
- Interosseus tibiofibular ligament (in the middle)
- Posterior tibiofibular ligament (posteriorly).
- Interosseus membrane. The attachment leaves a gap at the upper end of the passage of the anterior tibial vessels.
- Deep transverse fascial septum at the medial crest.
- The capsule of the ankle joint along the edges of the malleolar articular surface.
- Anterior talofibular ligament to the anterior surface.
- Inferior transverse tibiofibular ligament (above) and posterior tibiofibular ligament (below) to the malleolar fossa.
- The groove on the posterior surface of the malleolus lodges the tendon of the peroneus brevis and peroneus longus muscle . The longus is superficial and brevis is in the deep.
Blood Supply of the Fibula
The peroneal artery is the nutrient artery for the fibula, which enters the bone on its posterior surface of the fibula.
Ossification of the Fibula</h2
One prima and two secondary centers.
Primary center – shaft of the fibula, appears during the 8th week of intrauterine life.
- The lower end of the fibula appears during the first year and fuses with the shaft by 15-17 years.
- The upper end of the fibula appears during the 4th year and fuses with the shaft by 17-19 years.
The fibula is different because it is an exception to the law of ossification. Its secondary center which performs first also fuses first. But the law of ossification, the center that appears first would fuse last.