Each leg is supported by two bones, the tibia on the inner side (medial) of the leg and the fibula on the outer side (lateral) of the leg.

The medial malleolus is the prominence on the inner side of the ankle, formed by the lower end of the tibia.

The lateral malleolus is the prominence on the outer side of the ankle, formed by the lower end of the fibula.

Medial malleolus

The medial surface of the lower extremity of tibia

Lower extremity of tibia

The lower extremity of the tibia, much smaller than the upper extremity of tibia, presents five surfaces; it is prolonged downward on its medial side as a strong process, the medial malleolus.- Surfaces :...

 is prolonged downward to form a strong pyramidal process

Process (anatomy)

In anatomy, a process is a projection or outgrowth of tissue from a larger body. The vertebra has several kinds of processes,such as: transverse process, prezygapophysis, postzygapophysis.-Examples:Examples of processes include:...

, flattened from without inward - the medial malleolus.

• The medial surface of this process is convex and subcutaneous.
• The lateral or articular surface is smooth and slightly concave
  Concave
  The word concave means curving in or hollowed inward, as opposed to convex. The former may be used in reference to:* Concave lens, a lens with inward-curving surfaces.* Concave polygon, a polygon which is not convex....
  
  , and articulates with the talus
  Talus bone
  -External links:* *...
  
  .
• The anterior border is rough, for the attachment of the anterior fibers of the deltoid ligament of the ankle-joint.
• The posterior border presents a broad groove, the malleolar sulcus
  Malleolar sulcus
  There are two malleolar sulci, medial and lateral.The medial malleolar sulcus is the posto-inferior groove just lateral to the medial malleolus on the distal part of the tibia...
  
  , directed obliquely downward and medially, and occasionally double; this sulcus lodges the tendons of the Tibialis posterior and Flexor digitorum longus.

The summit of the medial malleolus is marked by a rough depression behind, for the attachment of the deltoid ligament.

Lateral malleolus

The lower extremity of the fibula, also called the distal extremity or external malleolus, is of a pyramidal form and somewhat flattened from side to side; it descends to a lower level than the medial malleolus.

• The medial surface presents in front a smooth triangular surface, convex from above downward, which articulates with a corresponding surface on the lateral side of the talus. Behind and beneath the articular surface is a rough depression, which gives attachment to the posterior talofibular ligament
  Posterior talofibular ligament
  The posterior talofibular ligament, runs almost horizontally from the depression at the medial and back part of the fibular malleolus to a prominent tubercle on the posterior surface of the talus immediately lateral to the groove for the tendon of the flexor hallucis longus....
  
  .
• The lateral surface is convex, subcutaneous, and continuous with the triangular, subcutaneous surface on the lateral side of the body.
• The anterior border is thick and rough, and marked below by a depression for the attachment of the anterior talofibular ligament
  Anterior talofibular ligament
  The anterior talofibular ligament passes from the anterior margin of the fibular malleolus, forward and medially, to the talus bone, in front of its lateral articular facet. It is one of the lateral ligaments of the ankle and prevents the foot from sliding forward in relation to the shin...
  
  .
• The posterior border is broad and presents the shallow malleolar sulcus, for the passage of the tendons of the Peronæi longus and brevis.

The summit is rounded, and gives attachment to the calcaneofibular ligament

Calcaneofibular ligament

The calcaneofibular ligament is a narrow, rounded cord, running from the apex of the fibular malleolus downward and slightly backward to a tubercle on the lateral surface of the calcaneus.It is covered by the tendons of the Peronæi longus and brevis....

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Often, when a patient fractures his or her ankle, this is the area of bone that suffers a chip or other significant damage.

External links

• Diagnostic imaging