Ankle bone is the name given to a tarsal bone. It connects the foot to the lower leg.
What is the ankle bone?
The talus is one of a total of seven tarsal bones. It is also known as the talus or the navicular bone. The talus provides a connection between the human foot and the lower leg. In addition, it has a share in the upper as well as the lower ankle joint. The upper ankle joint (articulatio talocruralis) encompasses the talocalcaneal roll (trochlea tali) from the malleolar fork. This allows the foot to be lowered approximately 20 to 30 degrees. Within the lower ankle joint (articulatio talotarsalis), there is an interplay between numerous tarsal bones, in which the talus is also involved. This allows the foot to rotate 30 to 50 degrees both inward and outward.
Anatomy and structure
Anatomically, the talus is located between the calcaneus (heel bone) and the malleolus (ankle fork). Together with the bones, the talus forms joints. These are the upper as well as the lower ankle joint. The ankle bone is composed of a body, the corpus tali, as well as an ankle bone head (caput tali) and a neck (collum tali). On the top of the ankle bone is the talus. When the talus is viewed convexly, the anterior curvature proves to be greater than the posterior curvature. However, when viewed from the front, concavity occurs. Thus, the trochlea tali becomes indented in the middle. As a result, it adapts to the protrusion of the end of the tibia. In this way, further securing of the tibial roll within the ankle fork is created. On the posterior side, the trochlea tali is a little narrower. It is also less indented. This allows for more tilting motion in the upper ankle when the foot is flexed. On the anterior side, the ankle roll turns out to be slightly wider than the ankle fork. As a result, it is securely fitted, resulting in high stability of the upper ankle joint in normal stance. In the center of the ankle bone roll is a comma-shaped articular surface. This is called the facies malleolaris. The articular surface forms the starting point of the processus malleolaris lateralis. The articular surface for the lateral malleolus is also located in the region of the anklebone roll. This is known as the facies malleolaris lateralis and is triangular in shape. On the outside of this surface, the processus lateralis tali emerges. Another articular surface is formed by the facies articularis navicularis, which is located on the head of the talus. It represents the articular surface of the navicular bone (Os naviculare). The spherical head is also located there within the concave scaphoid articular surface. In this way, the talonavicular joint is formed. The articular surface is part of the anterior region of the lower ankle joint. On the back of the talus is the processus posterior tali, which is a distinct process. Its division is made by a groove. Through this runs the tendons of the long big toe flexor. The ankle bone’s underside has three articular surfaces. These are in contact with the calcaneus. The three surfaces are called the facies articularis posterior, facies articularis calcanea media and facies articularis calcanea anterior. Between 3 and 15 percent of all people have an additional small bone at the posterior end of the talus. This is the Os trigonum, which has an oval or roundish shape. It is located at the posterior edge of the ankle bone. However, in most people, this bone is not even discovered.
Function and tasks
The ankle bone has the function of connecting the foot to the lower leg. It is also involved in the interaction of the various tarsal bones with each other, allowing the foot to move on the inside and the outside.
Diseases and complaints
Various impairments can occur at the ankle bone. These are primarily deformities and injuries. Typical malformations of the talus include fusions (synostoses) with the calcaneus or tarsal coalitions. A talus cleft occurs rather rarely. This is a congenital cleft within the ankle bone. Deformities include a talus obliquus and a talus verticalis. Talus luxation (dislocation) is a possible injury to the ankle bone. This results in a displacement of the ankle joint surfaces.The cause of dislocation is usually a significant impact of force. The injury, which often occurs as a result of falls from a great height, can be seen in the upper as well as the lower ankle joint. Dislocation of the ankle bone is noticeable by restricted movement and swelling. It is not uncommon for changes in the shape of the ankle joint to occur. Effective therapy of talus dislocation requires dislocation of the ankle. Furthermore, relief of the ankle joint for 4 to 6 months is recommended. Besides dislocation of the ankle bone, its fracture is also possible. However, fractures of the ankle bone occur rather rarely. They account for only 0.3 percent of all bone fractures. The share of foot fractures is about 3.4 percent. A fracture of the ankle bone is caused by considerable compression. Typical of an injury of this type is, in addition to restricted movement and swelling, the development of a hematoma above the ankle joint. Surgical intervention is often required to treat the fracture. Provided there is no direct involvement of the joint in the injury, there may also be three months of immobilization.
