The joints are structures which contact two or more bones, joined by a fabric that allows rigid skeleton adopt different positions.
All joints are made up of the following elements:
- Articular surface: area where the bones are in contact.
- Articular cartilage: covers the joint surface and prevents them from rubbing against the bones.
- Articular ligaments: join bones that are involved in the joint.
According to their mobility, three types of joints are distinguished:
- Mobile or diarthrosis: they allow many types of movements, since the bones do not come into contact, since they are separated by a cartilaginous sheet. The synovial fluid contained in the synovial bag is responsible for lubricating the area and cushioning blows.
In some mobile joints, such as the knees, they also contain menisci, cartilaginous pads that increase the joint surface and cushion the weight of the body.
In addition, the joint is reinforced by ligaments. Examples of mobile joints are, in addition to the knee , wrist, ankle, elbow, shoulder or hip.
- Semi-mobile or amphiarthrosis: they allow some mobility. They are involved, along with the bones, a cartilage disc that separates the bones and ligaments that hold them.
An example would be the vertebrae, separated by intervertebral discs that provide some mobility and cushion shocks when pressure is placed on the spine .
The vertebrae are separated by intervertebral discs that provide some mobility, but the entire set of vertebrae, discs and ligaments allow flexion, twisting or extension of the spine.