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What Movable Joint Allows Side-to-Side Movement?

Joints are formed when two or more bones are in alignment. Joint surfaces are covered by cartilage, which acts as padding to keep bones from rubbing on each other. Joints are held together by ligaments that connect bone to bone. Tendons connect muscles to bones and provide movement of the joint. The skeleton is made up of several different types of joints. Ball-and-socket joints not only allow side-to-side movement, they allow movement in all directions.

  1. Ball-and-Socket Joints

    • Ball-and-socket joints are formed when the rounded end of one bone articulates with the hollowed-out end of another bone. The shoulder and hip joints are the only ball-and-socket joints in the human body. These joints allow motion in all directions: forward and back, side to side, and clockwise and counterclockwise rotation. Ball-and-socket joints are the only type of joint that allows side-to-side motion. This movement is referred to as abduction, or moving away from the body, and adduction, or moving toward the body. These motions are important for activities that require reaching and stepping to the side.

    Fixed Joints

    • Fixed or fibrous joints are immovable. They consist of bones held together with cartilage and don't have tendon attachments. The skull is made up of fixed joints that are held together by sutures, a fibrous material, at birth. These sutures allow the skull to move during childbirth and allow the skull to expand as the brain grows. Over time, the sutures close to form the skull. Fixed joints also exist in the mouth, where teeth connect to the jaw bone.

    Hinge Joints

    • Hinge joints allow movement forward and back but prevent motion from side to side. The elbow and knee are examples of hinge joints in the human body. They're made up of the concave end -- curved inward -- of one bone and the convex end -- the rounded edge that fits into the curved area of the other bone -- of another bone. Strong ligaments attach on each side of these joints to prevent side-to-side motion from occurring.

    Other Joints

    • Saddle joints are named after their shape, which resembles a horses' saddle. The joint at the base of the thumb is a saddle joint. A pivot joint limits joint movement to rotation only. This occurs in the forearm close to the elbow where the ulna and radius bones come together. Movement of this joint causes the forearm to rotate from the palm-up to palm-down position. A pivot joint is also present at the top of the spine to allow rotation of the head from side to side. Joints that are made up of more than two bones are called compound joints.

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