Synovial joint

Synovial joint

A synovial joint, also known as diarthrosis, is the most common and most movable type of joint in the body of a mammal. As with most other joints in the body, synovial joints achieve movement at the point of contact of the articulating bones.

Structure

Synovial joints contain a variety of structures which are not seen in fibrous or cartilaginous joints:

• Articular cartilage: This covers the part of the bone in the joint. It absorbs shocks and reduces friction.
• Joint capsule: This seals the joint space and provides stability by limiting movements.
• Synovial membrane: This lines the joint capsule and secretes synovial fluid.
• Synovial fluid: This lubricates the joint, reducing friction and wear.
• Ligaments: These are fibrous tissues that connect bones to other bones.
• Tendons: These connect muscle to bone and provide additional stability.
• Bursae: These are sacs filled with synovial fluid that cushion the joint.
• Meniscus: This is a curve of cartilage that provides additional stability to the joint.

Types of synovial joints

There are six types of synovial joints. Some are relatively immobile, but most allow considerable movement:

• Plane joints, such as the acromioclavicular joint, allow gliding movements.
• Hinge joints, such as the elbow, allow flexion and extension.
• Pivot joints, such as the atlantoaxial joint, allow rotation.
• Condyloid joints, such as the wrist, allow all movements except axial rotation.
• Saddle joints, such as the thumb, allow all movements except axial rotation.
• Ball and socket joints, such as the hip, allow all movements.

Clinical significance

Diseases of the synovial joints include osteoarthritis, rheumatoid arthritis, gout, and lupus. Injuries to synovial joints can also occur, such as sprains, strains, and dislocations.

See also

• Cartilaginous joint
• Fibrous joint
• Joint
• Synovial fluid
• Synovial membrane

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