The knee joint, the structure of which should be well known to every person involved in sports, is the largest in the human body. It is formed by three bones. The structure of the human knee joint is determined by its location. The ends of the bones that form its structure are covered with very dense cartilage tissue up to 6 mm thick. This provides one of the main functions of the articulation - shock absorption when walking.
Knee joint, structure
The photo shows us the main structures of this joint: muscles, bones, menisci, ligaments (cruciate), nerves and blood vessels. Let's begin to consider its structure from the bones. The joint is formed by three bones. Two long ones - tubular tibial and femoral. The third is the patella. It is round and very small. Located in front. The femur below forms condyles - protrusions covered with cartilage. These protrusions are in contact with the so-called tibial plateau, which, in turn, consists of two halves. The patella moves in a groove-like depression formed by the condyles. This recess is also called patellofemoral. The fibula is located on the side of the tibia. It does not participate in the formation of the knee joint.
Structure and meaning of cartilage
The function of this fabric is to absorb shock loads, reduce the friction force during movements. It is needed where two bony surfaces rub against each other. Articular cartilage is very dense. At the knee joint, it covers not only the ends of the femur and tibia, but also the surface of the patella. Cartilage is of several types. In the knee joint - hyaline. A feature of this tissue is the high water content in the intercellular substance. This provides elasticity and helps protect the knee joint from injury.
The structure of ligaments and menisci
Dense connective tissue formations that fix the ends of bones are called ligaments. In the case of the knee joint, its capsule is strengthened by two such structures from the outside - medial and lateral. And two from the inside - front and rear cruciform. They limit excessive movements in the anteroposterior direction, preventing it from slipping relative to the femur. All ligaments of the knee are extremely important for its stable operation. Between the femur and tibia are two more structures called menisci. They can also be called cartilage, although their structure differs from the structure of hyaluronic that covers the articular surfaces. The menisci fill the space between the tibial plateau and the articular end of the femur.
They seem to serve as an elastic pad, redistributing weight. Without them, all his weight would be concentrated at one point on the tibial plateau. Two types of menisci (medial and lateral) are connected by a transverse ligament. Lateral (external) is less often damaged due to its greater mobility. The internal (medial) meniscus is located near the internal lateral ligament and has less lability. This is due to his frequent traumatization. In the center of the meniscus is thicker than at the edges - this forms a small depression on the tibial plateau and makes the joint more stable. If there were no ligaments, we would have a much greater imbalance in the lower limb and would more often injure the knee joint. The structure of the supporting elements of the knee provides stability to the knee
Bags
They lie along the course of the muscles and tendons. The largest is the patella (under the tendon of the quadriceps muscle), it almost does not communicate with the joint cavity. Behind there is a deep sub-patellar bag, in the thickness of the joint there are several more smaller ones. When some of them are filled with intra-articular fluid, cysts can form.
Muscles involved in joint flexion and extension
The quadriceps muscle is located on the front of the thigh. When it is reduced, the leg is extended at the knee joint. The patella lies in the thickness of the tendon, serving as a fulcrum and changing the direction of movement if necessary. It increases the strength of said muscle. Calf flexors (posterior)hips and near the knee) bend the leg at the knee joint.
Innervation
Consider the popliteal nerve. It is the largest of those located on the back of the joint. This nerve is a branch of the sciatic nerve. It provides sensory and motor innervation to the joint capsule. Above the joint, it divides into the tibial and peroneal nerves. They are worth mentioning because they are often damaged when a knee is injured. The obturator nerve also innervates the capsule from behind. Some branches of the tibial nerve provide sensitivity to its posterior part. The fibula innervates the posterior and anterolateral surfaces. This is due to the fact that in the body there are few such mobile formations as the knee joint - the structure and innervation with a large number of overlap zones provide high sensitivity.
Blood supply
The extensive vascular network surrounding the knee consists of four large arteries that are interconnected and form the choroid plexuses (there are about 13 such networks on the surface of the joint) and inside it. The first and largest artery is the femoral. Popliteal, deep and anterior tibial are slightly smaller. All of them develop collateral circulation if one of the vessels is ligated. The anatomical structure of the popliteal artery can be easily represented by dividing it into three sections. The first one is the top one. Bandaging is best done at the second level. Superficial veins in the knee joint are located intwo layers. The deeper one is represented by the great saphenous vein. Superficial - venous network from the accessory. The latter is not found in every person. The small saphenous vein arises from the posterior surface of the knee joint. Sometimes it goes with one barrel, and sometimes with two. The place of its confluence also varies, but more often flows into the popliteal.
