The lateral malleolus is the thickened end of the fibula involved in the upper ankle joint. This so-called lateral malleolus creates the conditions for dorsal and plantar flexion and extension of the foot. Fractures of the upper ankle are the most common bone fractures of all and often correspond to a malleolus fracture.
What is the lateral malleolus?
The fibula is one of two lower leg bones and attaches to the tibia. It is a typical long bone that undergoes thickening at the lower end. The thickening at the lower end of the fibula is called the lateral malleolus. More specifically, the malleolus lateralis is the laterally located bony prominence at the distal end of the fibula. Together with the malleolus medialis, this anatomical structure is involved in the formation of the so-called malleolar fork, which surrounds the ankle bone in a bifurcated manner and extends into the ankle joint. The ankle joint is the name given to the two main joints of the human foot and can move the foot at three different levels. The human lateral malleolus is even more concretely involved in the lateral malleolus. The structure is different from the fibula structures of most animals. Ruminants bear the remnant of an independent bone called the os malleolare at the lower end of the fibula. Horses have fibulae that are fully fused to the tibia. Their fibula is thus formed as a separate bone only in the upper half of the lower leg. The lateral malleolus is also known as the fibula tip or fibular bone.
Anatomy and structure
As a long bone, the fibula is a long bone made of two bone ends called epiphyses. In addition, there is a bone shaft: called the diaphysis. The junction of the epiphysis and diaphysis is called the metaphysis. The epiphyses are made up of a meshwork of bone bellows that align themselves according to the directions of the forces acting on them. The bone bellows form a bone spongy substance and carry cavities with red bone marrow between them. The substantia spongiosa is covered externally by compact bone substance and carries a layer of hyaline cartilage on the articular surfaces. An artery for bone supply is located at de diaphysis. Except for the cartilaginous articular surfaces, the entire area of long bones is covered by the periosteum, the so-called periosteum. The lateral malleolus forms the lower end of the long bone fibula and has a thickening. A groove runs across the outside of the bone: the sulcus malleolaris lateralis, which carries the tendons of the peroneus muscle. Inside lies an articular surface called the facies articularis malleoli, which connects to the talus. With these structures, the lateral malleolus participates in the ankle joint and also forms a pit. Ligaments attach to this pit-shaped fossa malleoli lateralis.
Function and tasks
The anatomical structure of the lateral malleolus or fibular process is instrumental in the formation of the ankle and lateral malleolus. Thus, the most important functions of the fibular process include, in particular, the individual forms of ankle motion in the upper ankle joint. Each joint has specific axes of motion. The human ankle joint has a total of three different axes of motion and can thus perform six different forms of foot motion. Inversion, eversion, supination and pronation take place in the lower ankle joint. The extent of each of these movements varies with the type of motion. The lateral malleolus does not play a role in the lower ankle joint, but rather in the upper ankle joint, where movements occur on an axis. The upper ankle joint is most likely a hinge joint. In this joint, the lateral malleolus creates the conditions for two different movements of the foot: extension and flexion to the dorsal or plantar. Without the lateral malleolus, for example, the foot would not be able to bend toward the dorsum of the foot or the sole of the foot. Likewise, it would not be able to extend from these positions. The individual types of flexion have different degrees. Flexion of the foot toward the dorsum of the foot has a range of motion of 30 degrees from the zero position. Flexion toward the sole of the foot encompasses only 20 degrees. The movement types of the ankle joint play a major role in everyday movement processes.Without the ability to move in the ankle joint, humans would not be able to walk, run or jump well. Because the lateral malleolus is involved in the upper ankle joint, its structure is also irreplaceable for the aforementioned everyday movements.
Diseases
In relation to the lateral malleolus, ankle fractures and deformities play the most important role in clinical practice. The ankle joint is exposed and subjected to heavy loads day after day. Traumas of the ankle joint are therefore not uncommon. Injuries of the ligamentous apparatus in the malleolus lateralis are among the most frequent traumas of the upper ankle joint and in most cases result from a twisted ankle. Such phenomena can cause the ligaments in the pit of the lateral malleolus, for example, to overstretch or, in the worst cases, tear. All ligament injuries in this area are grouped together as distortions of the upper ankle. In addition to pain and pain on movement, restricted flexion and extension of the foot characterize a distortion in this area. In addition to ligament injuries, fractures of the upper ankle joint also occur frequently. In adults, such fractures are even the bone fracture with the highest prevalence. A fracture of the upper ankle joint is usually preceded by a dislocation in the joint. The bone loosens from its articulated connection and the outer ankle breaks. The dislocation fracture is noticeable by pain and limited range of motion in the upper ankle joint. If the fracture is not treated in time, permanent deformities of the ankle joint may result. Such deformities can permanently limit range of motion and also promote osteoarthritis in the upper ankle.
