About the author of this section
Dr Karl Grindulis is a Consultant Rheumatologist within the Sandwell & West Birmingham Hospitals NHS Trust, one of the largest teaching Trusts in the UK.
Understanding the anatomy of joints
Joints are the areas of the body where two or more bones meet. Most joints are mobile, allowing the bones to move. Joints consist of the following elements:
- Cartilage - at the joint, the bones are covered with cartilage (a connective tissue), which helps reduce the friction of movement
- Synovial Membrane - a tissue called the synovial membrane lines the joint and seals it into a joint capsule. The synovial membrane secretes synovial fluid around the joint to lubricate it
- Synovial fluid - a clear, sticky fluid secreted by the synovial membrane
- Ligaments - strong ligaments (tough, elastic bands of connective tissue) surround the joint to give support and limit the joint's movement
- Tendons - tendons (another type of tough connective tissue) on each side of a joint attach to muscles that control movement of the joint.
- Bursas - fluid-filled sacs between bones, ligaments, or other adjacent structures help cushion the friction in a joint
- Meniscus - a curved part of cartilage in the knees and other joints
All bones in the body, except for the one (the hyoid bone in the neck), form a joint with another bone. There are many types of joints including those that do not move in adults, such as the suture joints in the skull, those that may move a little, such as the vertebrae, and mobile joints as those below:
- Ball-and-socket joints, such as the shoulder and hip joints, allow backward, forward, sideways, and rotating movements
- Hinge joints, such as in the fingers, knees, elbows, and toes, allow only bending and straightening movement
- Pivot joints, such as the neck joints, allow limited rotating movement
- Ellipsoidal joints, such as the wrist joint, allows all types of movement except pivotal movements