The human bone is so hard that it can withstand about 10 thousand kilograms, but if the skeleton consisted of only one solid bone, our movement would be impossible. Nature solved this problem by simply dividing the skeleton into many bones and creating joints - places where bones intersect.
Human joints perform a rather important function. Thanks to them, the bones, teeth and cartilage of the body join each other.
Types of human joints
They can be classified by functionality:
A joint that does not allow movement is known as synarthrosis. Skull sutures and homphos (joining the teeth with the skull) are examples of synarthrosis. The joints between the bones are called syndesmoses, between the cartilages - synchordrosis, bone tissue - syntostoses. Synarthrosis is formed using connective tissue.
Amphiarthrosis allows a slight movement of the connected bones. Examples of amphiarthrosis are intervertebral discs and pubic symphysis.
The third functional class is free-moving diarthrosis. They have the highest range of motion. Examples: elbows, knees, shoulders and wrists. Almost always, these are synovial joints.
Joints of the human skeleton can also be classified by their structure (by the material from which they consist):
Fibrous joints are made up of hard collagen fibers. These include the sutures of the skull and the joint that connects the ulnar and radial bones of the forearm together.
The cartilaginous joints of a person consist of a group of cartilage that connect the bones to each other. Examples of such joints are joints between the ribs and costal cartilage, as well as between the intervertebral discs.
The most common type - the synovial joint - is a fluid-filled space between the ends of the connected bones. It is surrounded by a capsule of rigid dense connective tissue covered with a synovial membrane. The synovial membrane, which the capsule consists of, produces an oily synovial fluid whose function is to lubricate the joint, reducing friction and wear.
There are several classes of synovial joints, for example, ellipsoidal, block-shaped, saddle-shaped and spherical.
Ellipsoid joints connect smooth bones and allow them to slide past each other in any direction.
Block joints, such as the elbow and knee joint of a person, restrict movement in only one direction so that the angle between the bones can be increased or decreased. Limited movement in the blocky joints provides more strength and strength to bones, muscles and ligaments.
Saddle joints, such as between the first metacarpal and trapezium, allow the bones to rotate 360 degrees.
The human shoulder and hip joints are the only spherical joints in the body. They have the freest range of motion, they are the only ones that can rotate around their axis. However, the drawback of the spherical joints is that the free range of motion makes them more susceptible to dislocation than the less mobile joints of a person. In these places, fractures are more likely.
Some synovial types of human joints need to be considered separately.
Block joint
Block joints are a class of synovial. These are the ankles, knee and elbow joint of a person. Typically, a blocky joint is a ligament of two or more bones, where they can only move along one axis to bend or straighten.
The simplest blocky joints in the body are interphalangeal, they are located between the phalanges of the fingers and toes.
Since they have little body weight and mechanical strength, they consist of a simple synovial material with tiny extra ligaments to strengthen. Each bone is covered with a thin layer of smooth hyaline cartilage, designed to reduce friction in the joints. The bones are also surrounded by a capsule of rigid fibrous connective tissue coated with a synovial membrane.
The structure of the human joint is always different. For example, the elbow joint is more complex, is formed between the humerus, radius and ulna of the forearm. The elbow is subjected to more intense loads than the joints of the fingers and toes, therefore it contains several strong additional ligaments and unique bone structures that strengthen its structure.
The elbow and radial accompanying ligaments help to keep the ulnar and radius bones and strengthen the joints. The human legs also consist of several large blocky joints.
A similar elbow joint is located between the tibia and tibia in the lower leg and the talus in the leg. Branches of the tibia of the tibia form a bony nest around the talus in order to limit the movement of the leg along one axis. Four additional ligaments, including the deltoid, hold the bones together and strengthen the joint to support body weight.
Located between the thigh of the leg and the tibia and tibia of the lower leg, the knee joint is the largest and most complex blocky joint in the human body.
The elbow joint and ankle joint, the anatomy of which is similar, are most often prone to osteoarthritis.
Ellipsoid joint
An ellipsoid joint, also known as flat, is the most common form of synovial joints. They are formed near bones that have a smooth or almost smooth surface. These joints allow the bones to slide in any direction - up and down, left and right, diagonally.
Due to its structure, ellipsoidal joints are flexible, and their movement is limited (to prevent injuries). Ellipsoidal joints are covered with a synovial membrane, which produces fluid that serves as a lubricant for the joint.
Most ellipsoid joints are located in the appendicular skeleton between the carpal bones of the wrist, between the carpal joints and metacarpal bones of the hand, between the bones of the ankle.
Another group of ellipsoid joints is located between the faces of twenty-six vertebrae in the intervertebral joints. These compounds allow us to bend, unbend and rotate the body, while maintaining the strength of the spine, which supports body weight and protects the spinal cord.
Condylar joints
There is a separate type of ellipsoid joints - the condylar joint. It can be considered a transitional form from a blocky type of joint to an ellipsoidal one. Condylar differs from a blocky joint by a large difference in the shape and size of the articulating surfaces, as a result of which movement around two axes is possible. Condylar differs from an ellipsoid joint only in the number of articular heads.
Saddle joint
The saddle joint is a type of synovial joint, where one of the bones is shaped like a saddle, and the other bone rests on it, like a rider on a horse.
Saddle joints are more flexible than spherical or ellipsoidal.
The best example of a saddle joint in the body is the carpal-metacarpal joint of the thumb, which is formed between the trapezium bone and the first metacarpal bone. In this example, the trapezoid forms a rounded saddle on which the first metacarpal bone sits . The carpal-metacarpal joint allows the thumb of a person to easily cooperate with the other four fingers. The thumb, of course, is extremely important for us, since it is precisely this that allows our hand to firmly grab objects and use many tools.
Spherical joint
Spherical joints are a special class of synovial joints that have the highest freedom of movement in the body due to their unique structure. The human hip and shoulder joints are the only spherical joints in the human body.
The two main components of the spherical joint: bone with a spherical head and bone with a cup-shaped recess. Consider the shoulder joint. The human anatomy is so structured that the spherical head of the humerus (upper arm bone) fits into the articular cavity of the scapula. The joint cavity is a small and shallow recess, due to which the shoulder joint has the largest range of motion in the human body. It is surrounded by a ring of hyaline cartilage, which is a flexible bone reinforcement, while the muscles - cuffs of the rotator — hold the humerus inside the cavity.
The hip joint is somewhat less mobile than the shoulder, but is a stronger and more stable joint. Additional stability of the hip joint is necessary to support the weight of a person’s body on his legs, performing actions such as walking, running, etc.
In the hip joint, a rounded, almost spherical femoral head (femur) fits snugly on the acetabulum, a deep notch in the pelvic bone. A sufficiently large number of stiff ligaments and strong muscles hold the femoral head in place and resist the strongest tensions in the body. The acetabulum also prevents hip dislocation by restricting bone movement within its limits.
Based on the foregoing, you can make a small table. The structure of the human joint will not be included in it. So, in the first column of the table the type of joint is indicated, in the second and third - examples and their location, respectively.
Human joints: table
Type of joint | Joint Examples | Where are |
Blocky | Knee, elbow, ankle joint. The anatomy of some of them is given below. | Knee - between the femur, tibia and patella; ulnar - between the humerus, ulna and radius; ankle - between the lower leg and foot. |
Ellipsoid | Intervertebral joints; joints between the phalanges of the fingers. | Between the faces of the vertebrae; between the phalanges of the toes and hands. |
Globular | Hip and shoulder joint. Human anatomy pays special attention to this type of joint. | Between the femur and pelvic bone; between the humerus and the shoulder blade. |
Saddle | Metacarpal. | Between the trapezium bone and the first metacarpal bone. |
To make it clearer what the joints of a person are, we will describe some of them in more detail.
Elbow joint
Human elbow joints, the anatomy of which has already been mentioned, require special attention.
The elbow joint is one of the most complex joints of the human body. It is formed between the distal end of the humerus (more precisely, its articular surfaces - the block and condyle), the radius and block notches of the ulna, as well as the head of the radius and its articular circumference. It consists immediately of their three joints: brachioradial, brachiocephalic and proximal radiolactic.
The shoulder-elbow joint is located between the block notch of the ulna and the block (articular surface) of the humerus. This joint belongs to the block and is uniaxial.
The brachioradial joint is formed between the condyle of the humerus and the head of the humerus. Movements in the joint occur around two axes.
The proximal radiolactic connects the radial notch of the ulna and the articular circumference of the radial head. It is also uniaxial.
There are no lateral movements in the elbow joint. In general, it is considered a blocky joint with a helical form of sliding.
The largest of the upper body are the elbow joints. The legs of a person also consist of joints, which simply cannot but be told.
Hip joint
This joint is located between the acetabulum on the pelvic bone and the femur (its head).
This head is covered with hyaline cartilage almost throughout, except the fossa. The acetabulum is also covered with cartilage, but only near the lunar surface, the rest of it is covered with a synovial membrane.
The ligaments include the sciatica: the sciatic-femoral, iliac-femoral, pubic-femoral, circular zone, as well as the ligament of the femoral head.
The ileo-femoral ligament originates at the lower anterior iliac bone and ends at the intertrochanteric line. This ligament is involved in maintaining the body in an upright position.
The next ligament, the sciatic-femoral, begins at the sciatic bone and is woven into the capsule of the hip joint itself.
A little higher, at the top of the pubic bone, the pubic-femoral ligament begins, which goes down to the capsule of the hip joint.
Inside the joint itself is a ligament of the femoral head. It originates from the transverse ligament of the acetabulum and ends at the fossa of the femoral head.
The circular zone is made in the form of a loop: it is attached to the lower anterior ilium and surrounds the neck of the femur.
The hip and shoulder joints are the only spherical joints in the human body.
Knee-joint
This joint is formed by three bones: the patella, the distal end of the femur and the proximal end of the tibia.
The capsule of the knee joint is attached to the edges of the tibia, femur and patella. It is attached to the femur under the epicondyle. On the tibia it is fixed along the edge of the articular surface, and the capsule is attached to the patella in such a way that its entire front surface is outside the joint.
Ligaments of this joint can be divided into two groups: extracapsular and intracapsular. There are also two lateral joints in the joint - the tibial and peroneal collateral ligaments.
Ankle joint
It is formed with the help of the articular surface of the talus and the articular surfaces of the distal ends of the fibula and tibia.
The joint capsule is almost completely attached to the edge of the articular cartilage and retreats from it only on the anterior surface of the talus. On the lateral surfaces of the joint are its ligaments.
The deltoid, or medial ligament, consists of several parts:
- the posterior tibial-talus, located between the posterior edge of the medial ankle and the posterior medial sections of the talus;
- the front tibial-talus, located between the front edge of the medial ankle and the posteromedial surface of the talus;
- tibial-calcaneal part, extends from the medial ankle to the support of the talus;
- the tibial-scaphoid, originates from the medial ankle and ends at the dorsum of the scaphoid.
The next ligament, calcaneofibular, extends from the outer surface of the lateral ankle to the lateral surface of the neck of the talus.
Not far from the previous one is the anterior talon-fibular ligament - between the anterior edge of the lateral ankle and the lateral surface of the neck of the talus.
And the last, posterior talone-fibular ligament originates at the posterior edge of the lateral ankle and ends at the lateral tubercle of the process of the talus.
In general, the ankle joint is an example of a helical joint with a helical motion.
So, now we definitely have an idea of what human joints are. Joint anatomy is harder than it sounds, and you can see for yourself.