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Flexibility: Joints enable your body to move
Ball and socket joints: Are the most mobile type of joint in your body
Saddle joints: Enable you to grasp things
Where bones meet
Joints are the place where two bones meet. All of your bones, except for one (the hyoid bone in your neck), form a joint with another bone. Joints hold your bones together and allow your rigid skeleton to move.
Some of your joints, like those in your skull, are fixed and don't allow any movement. The bones in your skull are held together with fibrous connective tissue.
Slightly movable joints
Other joints, such as those between the vertebrae in your spine, which are connected to each other by pads of cartilage, can only move a small amount.
Most of your joints are 'synovial joints'. They are movable joints containing a lubricating liquid called synovial fluid. Synovial joints are predominant in your limbs where mobility is important. Ligaments help provide their stability and muscles contract to produce movement. The most common synovial joints are listed below:
- Ball and socket joints, like your hip and shoulder joints, are the most mobile type of joint in the human body. They allow you to swing your arms and legs in many different directions.
- Ellipsoidal joints, such as the joint at the base of your index finger, allow bending and extending, rocking from side to side, but rotation is limited.
- Gliding joints occur between the surfaces of two flat bones that are held together by ligaments. Some of the bones in your wrists and ankles move by gliding against each other.
- Hinge joints, like in your knee and elbow, enable movement similar to the opening and closing of a hinged door.
- The pivot joint in your neck allows you to turn your head from side to side.
- The only saddle joints in your body are in your thumbs. The bones in a saddle joint can rock back and forth and from side to side, but they have limited rotation.
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