The lower legs of humans are not only important tools for human gait, but often also a visual feature: they can be tight or hairy, they are tanned or riddled with varicose veins. All this often has to do with health. Time, then, for a closer look at the lower leg.
What is the lower leg?
The lower leg is that section of the lower extremity that connects the knee to the foot. It is also commonly referred to as the “calf.” It consists of two bones and lots of muscles, and is strictly compartmentalized by internal skins (fascia).
Anatomy and structure
The anatomy of the lower leg is actually quite straightforward: two bones provide stability to this part of the leg, the tibia on the inside and fibula on the outside run side by side between the knee joint and the upper ankle joint. However, the tibia bears the majority of the load – the fibula is not involved at all in the knee joint itself and only has a small partial joint with the tibia a little below it, in which, however, hardly any movement takes place. At the ankle joint, the fibula is at least slightly involved, yet the weight of the body is largely transferred to the foot bones via the tibia. The function of the fibula is essentially to provide suspension for the upper ankle joint, and it also serves as a muscle origin. Four main muscle compartments surround the bony skeleton of the lower leg: the anterior foot-lifting muscles, the anterior-lateral “fibularis group” (also called the “peroneus group”), the posterior superficial as well as the posterior deep muscle group, which are responsible for flexion in the ankle joint and in the tarsal joints. The most prominent muscle here is probably the triceps surae muscle, which is a three-headed muscle that inserts over the Achilles tendon on the heel bone and contributes a lot of force to human gait here. Blood vessels pass completely through the popliteal fossa into the lower leg and then divide into smaller branches between the superficial and deep muscle groups. A large branch passes back anteriorly through the membrana interossea, a membrane between the two bones, and supplies the anterior muscle compartment down to the dorsum of the foot. The upper part of the anterior lower leg is also supplied by a nerve that passes externally around the head of the fibula just below the knee and is vulnerable to pressure damage at this point. The rest of the pathways, including the nerves, travel posteriorly under the medial malleolus to below the sole of the foot. Venous drainage is often of particular interest medically: Superficial cutaneous veins run along the entire lower leg and also drain continuously into a deeper drainage system. All leg veins eventually drain into the iliac vein in the groin.
Function and tasks
The function of the lower leg is, of course, first to provide stability for upright standing and to provide musculature for gait. Furthermore, it must allow enough blood to pass through it to safely supply oxygen and nutrients to the foot as well – this is not a difficult task at first when standing upright, since in addition to the blood pressure generated by the heart, there is also the force of gravity, which alone would move blood from the heart to the feet. On the other hand, however, it is a particularly difficult task to transport the blood that has flowed downhill back to the heart against the force of gravity. For this purpose, nature has invented a complex system of superficial and deep veins: Venous valves are located at regular intervals in the veins, which allow blood to flow only in the direction of the heart and prevent backflow. In order to generate any flow at all, the muscle pump is of decisive importance, in addition to the “suction effect” of the heart, which is still quite weak down here: the veins are all located between the various muscle groups of the lower leg or pull through them, so that they are literally “squeezed out” with every muscle contraction – thanks to venous valves, always only upwards.
Diseases and complaints
There are a number of complaints and diseases that can occur in the lower leg. First mentioned are the fairly common accidents in which bone fractures can happen, especially in the tibia.In this case, a so-called compartment syndrome easily forms, an absolute emergency in which hematomas in the very narrow muscle compartments of the lower leg “pinch off” the blood supply of the entire lower leg. Torn ankle ligaments are also a common sports injury. A great many people have to deal with spider veins and varicose veins, which form when the muscles and connective tissue in the lower leg weaken, the venous valves wear out and the blood column in the leg practically “stops”. This means enormous pressure on the lower leg, which can lead to pain. The arterial system is also the scene of serious disease: In pAVD, peripheral arterial occlusive disease, the arteries are narrowed by arteriosclerosis and the blood supply to muscles and other tissues in the leg and foot is put at risk.
