How Our Joints Work
Joints are the place where two or more 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 you 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 you vertebrae in your spine, which are connected to each other by pads of cartilage, can only move a small amount.
Synovial movable joints
Most of your joints are “synovial joints”. They are moveable 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 produced the desired movement. The most common synovial joints are listed here:
Ball and socket joints, like your hip and shoulder joints, are the most mobile of joints in the human body. They allow you to swing your arms and legs in many different directions.
Hinge joints like in your knee and elbow , enable movement similar to opening and closing a hinged door.
The pivot joints in your neck allow you to turn you head from side to side.
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 work by gliding against each other.
Conyloid joints. These joints are similar to ball-and-socket joints, just without the socket (the “ball” simply rests against another bone end).
Saddle joints are found in your thumbs, the bones in a saddle joint can rock back and forth and from side to side, but they have limited rotation.