Synovial JointsA joint in the human body is where two or more bones meet. There are three main classifications of joints, fibrous joints, cartilaginous joints and synovial joints. Fibrous joints are where two bones are connected by ligaments and are classified by their lack of movement. Cartilaginous joints are connected by cartilage and are more movable the fibrous joints but less than the synovial joint and lack a joint cavity. The synovial joint is the most movable joint in the human body and is characterised by the presence of a joint cavity filled with the lubricant synovial fluid.
There are many different types synovial joints which allow articulation in different ways and can be seen in the diagram to the right and the video below. The point of contact in the joint is marked by the yellow arrow. This is the point that must have low friction movement,be able to damp vibrations and absorb shock.
To facilate all these requirements the bone is covered in articulated cartilage which is surrounded by a cavity of synovial fluid. The composition and role articular cartilage will be explained in detail in the articular cartilage section of this website. The composition of synovial fluid will also be explained further in the synovial fluid section. Further information on the operation and composition of the knee can be obtained from the video below. |
The hip and shoulder are examples of ball and socket joint and allow full rotational movement of the limb. The elbow is hinge joints and only allows movement in one plane. The knee although mistaken as a hinge joint can also pivot and is therefore a hinge pivotal joint. The neck is made up of many joints one of which is a pivot joint. The wrists are ellipsoidal joints and allow restricted rotational movement in all planes.
The knee is a great example of a synovial joint and is one of the most complicated in the human body. The picture below shows the knee at near full extension. The joint is held together by ligaments (not seen in this diagram) and tendons. The meniscus is a cartilage seat that provide structural integrity to the knee. |