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11.8: Joints

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    Why does his knee hurt?


    Joints and How They Move

    A joint is a point at which two or more bones meet. There are three main types of joints in the body:

    1. Fixed joints do not allow any bone movement. Many of the joints in your skull are fixed (Figure below). There are eight bones that fuse together to form the cranium. The joints between these bones do not allow movement, which helps protect the brain.
    The skull has fixed joints that do not allow any movement
    Figure \(\PageIndex{1}\): The skull has fixed joints. Fixed joints do not allow any movement of the bones, which protects the brain from injury.
    The joints between your vertebrae are only partially movable
    Figure \(\PageIndex{2}\): The joints between your vertebrae are partially movable.
    1. Movable joints allow the most movement.

    Movable joints are also the most common type of joint in your body. Your fingers, toes, hips, elbows, and knees all provide examples of movable joints. The surfaces of bones at movable joints are covered with a smooth layer of cartilage. The cartilage reduces friction between the bones. Ligaments often cross a joint, holding two nones together. For example, there are numerous ligaments connecting the leg bones across the knee joint.

    Types of Movable Joints

    Four types of movable joints are discussed here.

    Ball and socket joints allow for a wide range of flexibility
    Figure \(\PageIndex{3}\): Your hip joint is a ball-and-socket joint. The “ball” end of one bone fits into the “socket” of another bone. These joints can move in many different directions.
    Hinge joints like the knee allows forward and backward movement
    Figure \(\PageIndex{4}\): Hinge Joint. The knee joint is a hinge joint. Like a door hinge, a hinge joint allows backward and forward movement.
    Pivot joints only allow rotation
    Figure \(\PageIndex{5}\): Pivot Joint. The joint at which the radius and ulna meet is a pivot joint. Movement at this joint allows you to flip your palm over without moving your elbow joint.



    Explore More

    Use the resource below to answer the questions that follow.

    2. What are the best joints for movement?
    3. What is the function of synovial fluid? Where is it located?
    4. What is the function of the knee cap?


    1. What's the difference between a fixed joint and a movable joint? Give examples of each.
    2. Describe the four types of movable joints.
    3. What type of joint are each of the following?
      1. the shoulder
      2. the wrist
      3. the knee