Joints are connections between neighbouring bones in the body skeleton. There are three types of joints in humans. These are: fibrous joints and cartilaginous joints in addition to synovial joints. In the first two types of joints there is direct connection between the bones with a connection that can be either fibrous or cartilaginous. In the third type of joints there is synovial cavity between the bones that make up the joint.
In fibrous joints there is no existence of a synovial cavity. The same is true for the cartilaginous joints with the difference being the connection between the bones is cartilaginous and not fibrous. The first two types of joints usually do not permit movement of bones that form the joint. In synovial joints there is freedom of movement for the bones that make up the joint as occurs in the knee joint.
The degree of movement of the joint bones is divided in to three categories. These are, first, a joint which does not permit movement at all. This type of joint is called synarthrosis. The second type of joints permit certain movement of the bones that make up the joint. This type of joints is called amphyarthrosis. The third type of joints permit free movement of the joint bones. This type of joints is called diarthrosis.
Examples of fibrous joints occur between the bones of the skull. These are called sutures. Other type of fibrous joints is called syndesmoses. This type of fibrous joints has larger distance between the articulating bones and has more fibrous tissue between the bones that make up the joint. A third type of fibrous joint occurs in the teeth and is called gomphoses.
The second type of joints, the cartilaginous joint has two main subtypes. These are: synchondroses and symphysis. In synchondrosis the joint has a connecting material between the articulating bones that is made of hyaline cartilage. An example of this type of joints occurs in the epiphysial plate of growing bones which connect the epiphysis with the diaphysis.
In cartilagious joints there is no possible movement in this type of joints or the movement is very restricted. In this type of joints the bones that make up the joint are connected by either hyaline cartilage or by fibrocartilage connection. The second subtype of cartilaginous joints is the symphysis.
Symphysis is a joint that is made of cartilage in which the ends of the bones that make up the joint have hyaline cartilage covering them. An example of such a joint occurs in the symphysis pubis. This type of joints occurs also in the connection between the manubrium and the sternum bones.
The third type of joints that is discussed here is the synovial joint. This type of joints differ than the other two types by the ability of the articulating bones to move freely. In addition, there is a space between the bones which is called the synovial cavity. All synovial joints are of the diarthrosis type.
The connecting bones in this type of joints are covered by a hyaline cartilage that is known as the articular cartilage. The synovial joint is surrounded by an articular capsule which also connects the articulating bones. This articular capsule is composed of two layers. These are: a fibrous capsule and a synovial membrane.
Clinically speaking, most disorders of bone joints that are clinically important are caused due to disorders of synovial joints. One clinical condition that involves this type of joints is the presence of fluids in the synovial cavity due to an inflammation of the joint. This condition is treated by withdrawing the fluid from the synovial cavity using a syringe that is injected into the synovial cavity. Another important condition that can affect synovial joints is called osteoarthritis. It involves damage to the cartilage of the synovial joint.