Types Of Synovial Joints

Synovial joints are those in which the bony elements that contact each other are separated by a cavity. They are surrounded by a sleeve-shaped joint capsule that encloses the synovial cavity and joins the bones of the joint.

Synovial joint characteristics

First, they have a layer of cartilage that covers the articular surfaces of the skeletal elements. In this way, the bone surfaces do not contact each other directly. So when these joints are seen on x-rays, there appears to be a wide gap between adjacent bones.

A second characteristic of synovial joints is the presence of a joint capsule consisting of an inner synovial membrane and an outer fibrous membrane.

The synovial membrane

This membrane is attached to the margins of the articular surfaces at the interface between cartilage and bone and surrounds the articular cavity.

The synovium is highly vascularized and produces synovial fluid, which accumulates in the joint cavity and provides lubrication to the joint surfaces.

Closed synovial sacs also appear outside the joints, where they form synovial bags or tendon sheaths. Bursae are often interposed between structures such as tendons and bone, tendons and joints, or skin and bone, and reduce the friction of one structure as it moves over another. The tendon sheaths surround the tendons and also decrease friction.

The fibrous membrane

It is made up of dense connective tissue and surrounds and stabilizes the joint. Parts of the fibrous membrane may be thickened to form ligaments, which further stabilize the joint. Ligaments outside the capsule often provide additional reinforcement.

Other characteristic structures of the synovial joints

Another common feature of synovial joints is the presence of additional structures within the area encompassed by the capsule or synovial membrane, such as:

• Joint discs : usually composed of fi brocartilage. They absorb compressive forces, adjust changes in the contour of joint surfaces during movements, and increase the range of movements that can occur in the joints.
• Fat pads : Fat pads are usually found between the synovium and the capsule. In addition, they move in and out of these areas as the joint contour changes during movement.

Types of synovial joints

1. Flat joints : allow gliding movements when one bone moves over another. Among them is the acromioclavicular joint found in the shoulder.
2. Hinge joints: these are the joints that allow the joint to move around a transverse axis. In this way, they regulate flexion and extension movements. A hinge joint is the elbow joint.
3. Pivot joints : are those that allow movement around an axis that crosses the diaphysis of the bone in a longitudinal direction. Pivot synovial joints regulate rotation.
4. Bicondylar joints : they mainly allow movement around one axis, with limited rotation around a second axis. They are formed by two convex condyles. These articulate with concave or flat surfaces. In this type is the knee joint.
5. Condylar joints : are those that allow movement around two axes that are at right angles to each other. In this way, they regulate movements of flexion, extension, abduction and circumduction. This is the case with the wrist joint.
6. Saddle joints : allow movement around two axes that are at right angles to each other. Its name is due to the fact that the joint surfaces are saddle-shaped. They regulate movements of flexion, extension, abduction, adduction and circumduction.
7. Ball Joints : allow movement around multiple axes. These joints regulate movements of flexion, extension, abduction, adduction, circumduction, and rotation. This type of synovial joint includes the hip.

Conclution

If it weren’t for the joints, the bones in our body would not be able to move. Therefore, thanks to them, we can perform the different movements such as bending, rotating and flexing the different extremities of the body.