Joints
What do Joints do?
The human body contains about 360 joints, about a 100 of which are mobile. Basically, joints are connecting pieces between two or more rigid bones or cartilaginous structures that facilitate the mobility of the human body.
What do Joints look like?
Joints consist of a joint head and socket that fit together like two puzzle pieces. These two surfaces are covered with cartilage. In addition, there is a cavity between them that is filled with joint fluid or grease to prevent the surfaces from rubbing against each other. The joint is surrounded by a tight layer of connective tissue - the capsule - as well as muscles and tendons.
Additional buffers - the bursa filled with synovial fluid - can be found on joints that are exposed to heavy loads, such as the knee or the elbow. These buffers are urgently needed because the force exerted on a joint can be several times the bodyweight depending on the movement. To demonstrate, in a downward jump, the force on the knee joint can be 24 times the body weight. Clearly these buffers are important. They serve to relieve tendons, muscles and bones. They inhibit the pressure that a movement triggers because this force must be intercepted again and again. However, it should be noted that different forms of movement affect our joints differently. When walking, the force acting on our joints is, for example, only half of our body weight.
What types of Joints and directions of movement are there?
People often talk about real and fake joints. The term fake refers to a joint that is not very flexible. That is, although there are connections between bones or cartilage, they do not have a cavity or buffer but are directly connected to each other. Therefore, like our ribs which move only slightly up and down when we breathe, they are less mobile.
Five different directions of movement
In addition to being classified as real or fake, joints are also divided into five types, each of which allows a different combination of directions of movement:
- The ball joint, which is located at the connection between the femur and the hip, is the most flexible joint in our body. It allows movements in six directions.
- The egg joint can be found in the wrist. Its name refers to its shape. In addition to stretching, bending and turning sideways, it also allows rotational movement.
- With the saddle joint, the joint socket lies like a saddle on a horse's back on the joint head. Saddle joints can be moved in four directions. A thumb, for instance, can be rotated because the base joint allows flexion, extension and lateral movement.
- Hinge joints can be found in the elbows. Like a hinge on a door, it can move in only two directions; open or closed, stretched or bent.
- Last but not least, there are the wheel joints; aptly named because of how the joint head and socket are connected to each other like a wheel on an axle. For this reason, only rotational movements are possible, like the one between our forearm bones ulna and radius.
Walking, running and sitting
We would be unable to move without our joints. The way we walk, stand, sit, run, lift and much more is determined by various sophisticated, pre-defined directions of movement in different parts of our body. The shape of our skeleton is exactly adapted to the shape of the joints and we perform each of our movements unconsciously in co-ordination with this system.
