Definition, Classification and Importance of Joints

Joints – Definition and Classification

One of the crucial attributes that distinguish living organisms from non-living is the capability to locomote and move. This is feature is vital for survival as living organisms require to adjust to their environment and accommodate their own biological requirements such as food, self-preservation, and mating. Most living organisms have their own special systems for mobility and movement.

These might consist of basic structures such as cilia, flagella, or a lot more intricate structures like wings or feet. The significant key elements that assist in locomotion are bones and muscles. In humans and other vertebrates, the bones form a framework called the skeletal system that provides structure and shape. Additionally, these bones allow motion through different kinds of joints.


A joint, likewise referred to as an articulation or articular surface, is a connection that is present between bones in the skeletal system. Joints provide the means for movement. The type and characteristics of a joint determine its degree and type of movement. Joints can be categorized based upon structure and function.

Babies start with about 270 bones. Some of these bones fuse together during growth. Adults have about 206 bones. So, the estimated number of joints in the body is between 250 and 350.

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The inclusion of sesamoids

Sesamoids are bones embedded in tendons, but not connected to other bones. The patella (kneecap) is the largest sesamoid. These bones differ in number from person to person.

Classification of Joints

The body has 3 primary kinds of joints. They’re categorized by the movement they enable:


Synarthroses (immovable)

These are fixed or fibrous joints. They’re specified as two or more bones in close contact that have no motion. The bones of the skull are an example.

Types of Fibrous Joints

There are three kinds of fibrous joints:

  • (1)Sutures are immovable joints that link bones of the skull. These joints have actually serrated edges that lock together with fibers of connective tissue.
  • (2) The fibrous expressions between the teeth and the mandible or maxilla are called gomphoses and are also immovable.
  • (3) A syndesmosis is a joint in which a ligament connects two bones, permitting a little motion (amphiarthroses). The distal joint in between the tibia and fibula is an example of a syndesmosis.
Amphiarthroses (slightly movable)

Also called cartilaginous joints, these joints are defined as two or more bones held so securely together that just restricted movement can occur. The vertebrae of the spine are good examples.

Types of Cartilaginous Joints

There are two types of cartilaginous joints:

  • (1) A synchondrosis is an immovable cartilaginous joint. One example is the joint between the first pair of ribs and the sternum.
  • (2) A symphysis includes a compressible fibrocartilaginous pad that connects two bones. This type of joint allows for some motion. The hip bones, linked by the pubic symphysis, and the vertebrae, connected by intervertebral discs, are examples of symphyses.
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Diarthroses (freely movable)

Likewise known as synovial joints, these joints have synovial fluid enabling all parts of the joint to efficiently move against each other. These are the most common joints in the human body. Examples include joints like the knee and shoulder.

Types of Synovial Joints

There are six kinds of synovial joints:

(1) Gliding joints move against each other on a single plane. Significant gliding joints include the intervertebral joints and the bones of the wrists and ankles.

(2) Hinge joints move on simply one axis. These joints enable flexion and extension. Significant hinge joints consist of the elbow and finger joints.

(3) A pivot joint provides rotation. At the top of the spine, the atlas and axis form a pivot joint that enables rotation of the head.

(4) A condyloid joint enables circular movement, flexion, and extension. The wrist joint between the radius and the carpal bones is an example of a condyloid joint.

(5) A saddle joint enables flexion, extension, and other movements, but no rotation. In the hand, the thumb’s saddle joint (in between the very first metacarpal and the trapezium) lets the thumb changeover the palm, making it opposable.

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(6) The ball-and-socket joint is a freely moving joint that can rotate on any axis. The hip and shoulder joints are examples of ball and socket joints.

Importance of Joints

The joints help us to rotate our shoulder, bend our knees and elbows, rotate our neck, and more. A joint is a point where two bones meet to supply a framework that permits movement.


Joints are formed where bones meet. Joints link the skeletal system to the whole body and make it functional. These are designed so to allow movements where the specific movement is required.

On the basis of the amount of movement, joints are classified into three classes. Joints that allow no movement are immoveable. Those which allow a slight degree of movement are slightly moveable and those which allow a greater degree of movement are freely moveable joints.

On the basis of structure joints can be fibrous joints; held together by fibers embedded in connective tissues. The cartilaginous are those which allow little or no movement.

Synovial joints are those having cavity filled with fluid and is surrounded by fibrous capsule. And these are further classified as hinge and ball and socket joints.