What Is the Definition of a Joint?

In anatomy, the term "joint" refers to the physical point of connection between two bones. For example, the knee joint refers to the point of connection between the femur, or thigh bone, and the tibia, or shin bone. Joints also contain a variety of fibrous connective tissue such as ligaments, which connect the bones together and tendons which connect muscle to bone and cartilage, which covers the ends of bones and provides some cushioning.

The most common joints, freely movable joints in the body are called synovial joints. Synovial joints are surrounded by a fibrous tissue or sac called the joint capsule. This capsule surrounds the joint and is filled with a fluid called synovial fluid that lubricates the tissues and spaces within this capsule.

Joint Types

There are several types of joints. They include:

  • ball and socket joints
  • hinge joints
  • condyloid joints
  • pivot joints
  • gliding joints
  • saddle joints

Joint Movements

Joints can move in a variety of ways. The main type of joint movement include:

  • Gliding
  • Angular
  • Circumduction
  • Rotation

Range of Motion of a Joint

A majority of the human body’s joints allow for movement. A few, like joints in the skull, do not. Those joints that do allow for motion, such as the knee or ankle, have a predetermined range of motion. This range of motion is basically how far is each direction that joint can move or bend comfortably.

The range of motion of a joint is usually measured in degrees. Each individual joint has a separate range of motion. Typically, extension of a joint is limited to 180 degrees or less. In other words, that joint can basically be opened until it is straight. Think of your arm or leg as an example, as these can be bent until they are virtually straight.

Extension

Extension is the bending of a joint so that the bones forming the joint are moved farther apart, or straightened. Extension is a physical position that decreases the angle between the bones of the limb at a joint. It occurs when muscles contract and bones move the joint into a bent position.

Flexion

Flexion is the bending of a particular joint so that the bones that form that joint are pulled closer together. During flexion, the angle between the bones of limb at a joint is decreased. Flexion typically occurs when muscles contract and the bones thus move the nearby joint into a curved position. Flexion is a physical position that decreases the angle between the bones of the limb at a joint. It occurs when muscles contract and bones move the joint into a bent position.

History

The word "joint" is from the Latin word that means a joining or a junction, as bones are joined at a joint.

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