A joint is the point at which two bones are connected. Many joints provide support and stability and allow movement, although some, such as those of the pelvis, are not movable.
Joints contain bones, cartilage, and a lining called synovium, which produces a lubricating fluid. Most joints are held together by muscles, tendons, and ligaments and are often cushioned by fluid-filled sacs called bursae.
There are several types of joints, including:
- Hinge joints, such as the elbows and knees.
- Ball-and-socket joints, such as the hips and shoulders.
- Pivot joints, which allow rotation. For example, the joints in the neck allow the head to turn from side to side.
- Condyloid joints, such as the wrist, which allow movement in many different directions.