In the human body there are 206 bones, most of which do not exceed the size of several cubic centimeters. The most diseased and massive bone in the body is the femur. Its structure allows us to walk straight and not fall. Through the knee joint, the femur connects to the tibia and fibula, forming a free lower limb.
Free lower limb anatomy
Anatomy of the lower extremities of a person includes bones, muscles, ligaments, joints and fascia. This is if you understand it seriously and thoroughly. But for this article, a small digression into the structure of the leg will be enough . So, the lower limb of a person is divided into the thigh, lower leg and foot.
The base of the thigh is the femur. It is overlapped in layers by muscles, thanks to which a person can walk, stand, run, swim and much more. Working on the principle of leverage, they act on the hip or knee joint. The anatomy of myofibrils allows them to stretch and contract, adapting to the needs of the body.
The core of the tibia is the tibia and fibula. Between themselves they are connected by a joint and a connective tissue membrane in which the vessels pass. From above this structure is covered with several layers of muscles that extend to the foot.
The ankle and foot are parts of the body that are under constant stress. A relatively small portion of the sole holds the weight of the whole body (and sometimes it can reach three hundred kilograms). The foot consists of the calcaneus, tarsus and metatarsus, which are covered with fascia and muscle. Also, this area is richly supplied with blood, so that the muscles always have a supply of oxygen.
The main structures of the knee joint
What, then, is the anatomy of the human knee joint? For a first-year medical student, this is one of the most difficult questions, because you need to remember all the structures that form this joint:
- bones (as a basis);
- muscles (contracting, they change the position of the lower leg);
- nerves and blood vessels (nourish tissues and transmit information from the brain to the periphery);
- menisci (form the surface of the joint);
- ligaments (hold bones together);
All of the above components in a healthy person work together as a single mechanism. But it’s worth “breaking down” at least one component, and a smooth gait will no longer work.
Bones
The large bones of the knee joint are the femoral and tibial. But besides them there is still a small rounded bone, located separately from the rest. It is called a patella or patella. On the diaphysis of the femur are spherical elevations - the condyles, covered with cartilage for better gliding. They are the upper part of the knee joint. The lower part is formed by a flat head of the tibia, also covered with cartilage.
The fibula is not long enough to form a knee joint. The anatomy of its head allows it to fit to the tibia so that the lower leg can be slightly rotated without receiving fractures. The thickness of the cartilage covering the articular surfaces reaches five millimeters. It is necessary to reduce friction, as well as cushioning.
Cruciate ligaments
As mentioned above, in addition to bones and muscles, there are also ligaments of the knee joint. Their anatomy is very entertaining, since it is these strips of tissue that hold all parts of the mechanism together. To strengthen the joint capsule, medial and lateral collateral (envelope) ligaments are located on the sides of the bones. Cruciate ligaments are located between the upper and lower articular surfaces. Topographically, the anterior and posterior ligaments can be distinguished, limiting excessive flexion and extension of the knee.
Ligaments are important elements of the joint. They stabilize it, make the gait harder and avoid dislocations.
Menisci and their function
If you look at the picture of the knee joint, then in addition to the bones, you will see two small formations. These are dense connective tissue formations - menisci. They are located between the femur and tibia.
Two main functions of menisci:
- increase the surface area of the joint for better distribution of human weight;
- Improving the stability of the knee joint along with ligaments.
In order to imagine what role menisci perform, you need to imagine a ball located on a smooth flat surface. If there is nothing between the ball and the “plateau”, it will roll away. Nature does not tolerate emptiness, which means that inside the joint also should not be empty. Connective tissue fills the space between the articular surfaces, increasing their area and protecting against excessive loads. Meniscus damage is fraught with joint inflammation and cartilage destruction
Muscle
Extensor muscles descend from the front surface of the thigh to the knee joint. One end is fixed to the femur or pelvis, and the other goes into the tendons and weaves into the joint capsule. The main one in this muscle group is the quadriceps. When it contracts, the leg extends in the joint.
On the back of the thigh are flexor muscles. They also begin on the belt of the lower extremities, and end in the capsule of the joint in the form of tendons. When this group contracts, the leg bends.
Nerves and vessels
Nerve fibers, arteries and veins like a network around the knee joint. The anatomy of the vessels in this area is not fundamentally different from the rest of the body. An artery, accompanied by two veins, passes along the posterior surface of the joint, supplying blood to the lower leg and foot.
Next to them is the popliteal nerve, which is a continuation of the sciatic nerve. A little higher than the knee joint, it is divided into two parts and already in this form descends to the lower leg and foot. Thanks to him, the free lower limb is a sensitive and motor innervation.
Functional tests of the knee
When a knee injury occurs , the traumatologist needs to find out what is damaged and how seriously everything is using physical and hardware methods. It’s not enough just to look at the knee joint.
1. Lachman test or drawer symptom. It is carried out to determine damage to the anterior cruciate ligament, if a picture of the knee joint could not be made. For this patient, they put it on their back and bend the damaged leg in the knee joint by thirty degrees. Then the doctor fixes the hip and at the same time advances the lower leg forward. If movement is possible, then the ligament is damaged.
2. Contactless test. If for some reason the doctor cannot touch the patient (for example, between them there is an obstacle in the form of blockage or water), and the examination should be carried out, then this technique allows you to determine the presence of a complex injury. For this, the patient, lying on his back, with two hands holds on to the hip of the injured leg near the knee joint. Then the victim tries to raise the lower leg without bending the knee. If he succeeds and the tibia does not move, then there is damage to the ligament.
3. Back sag test. In order to detect damage to the posterior cruciate ligament, you can also not do an x-ray of the knee joint. The technology of this study is simple, reliable and widely available. The patient should be asked to lie on his back and bend his knees at an angle of ninety degrees. If the tibia moves posteriorly, the ligament is damaged.
Instrumental studies of the joint
The most common method for examining bones is radiography. If the patient complains of joint pain after a fall, fever, swelling and hematoma, it is advisable to check if there is a fracture. An X-ray of the knee allows you to see bones, soft tissues and tendons. Looking at the picture, a traumatologist can diagnose a fracture, dislocation, sprain, damage to the patella, arthrosis, arthritis, a tumor or cyst, osteoporosis or osteomyelitis. These are the most common diseases affecting the knee joint. A photo, of course, can be of different quality, rigidity and size, but this will not be difficult for a specialist.
In order to exclude rheumatoid arthritis, degenerative pathology and joint trauma, an ultrasound scan can be performed. Another positive point is that the patient does not need to undergo preliminary training (hunger, heavy drinking, etc.) before examining the knee joint. Its anatomy allows you to look inside the articular bag, to see the menisci, the surface covered with cartilage, bone formations.
Ultrasound allows you to see the knee from all sides. For a clear picture, you need to properly lay the patient:
- on the back with straightened legs (the front and side walls of the joint are clearly visible);
- the legs are bent at the knee joints (menisci are visualized);
- in position on the abdomen (for examination of the posterior wall of the joint).
Such a procedure can be performed in almost any medical institution.