Joints in the Body, 3 classification and their functions

Joints in the Body and their functions

Joints, also known as articular surfaces are connections that exist between bones in the human body. Through these joints we have a complete functional skeletal system. Joints are built in such a way that they permit certain types and degree of movements.

The joints in the elbow, knee and shoulder are almost without friction as they are self-lubricating in nature, capable of withstanding heavy loads and compression while still carrying out Smooth and exact movements.
Joints such as Sutures which are found in the skull allow for little movement so as to protect the sense organs and the brain as well.

Classification of Joints

Joints are classified based on their structures and functions.

Based on Structures

Classification of Joints based on structure is determined by how bones link to each other.
Examples of these joints are:

Cartilaginous Joints

These are joints that link bones with cartilage. cartilaginous joints are of two types namely:
(1)A symphysis: this consists of a compressible fibrocartilaginous pad that links two bones. This type of joint allows for some movement. The vertebrae which are connected by intervertebral discs, and hip bones which are connected by the pubic symphysis are two examples of symphyses.

(2)A synchrondosis is an immovable cartilaginous joint. One example is the joint between the first pair of ribs and the sternum.

Synovial Joints

The existence of the articular capsule between two connected bones is what characterizes synovial joints. The facets of bones at synovial joints are shielded by a coating or articular cartilage. The reinforcements and supports usually received by synovial joint are always provided by surrounding ligaments which limits movements in order to avoid injury.

(1)Hinge joints move on one axis. These joints allow for extension and flexure. Major hinge joints include the elbow and finger joints.

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

(3) A pivot joint provides rotation. The atlas and axis form a pivot joint that allows for the rotation of the head, at the top of the spine,

(4) 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.

(5) A saddle joint allows for flexion, extension, and other movements, but no rotation. In the hand, the thumb’s saddle joint (between the first metacarpal and the trapezium) lets the thumb cross over the palm, making it opposable.

(6) A condyloid joint allows for circular, flexure, extension, motion. The wrist joint between the radius and the carpal bones is an example of a condyloid joint.

Fibrous Joint

Between the connections of fibrous joints is a thick connective tissue, which explains why most fibrous joints are synarthroses (immovable). Fibrous joints are of three types, they include:
(1) Sutures: These are immovable joints that articulate with the bones of the skull. These joints have saw-toothed edges that lock together with fibers of connective tissue.

(2) A syndesmosis: this is a joint in which a ligament connects two bones, allowing for a little movement (amphiarthroses). The distal joint between the tibia and fibula is an example of a syndesmosis.
(3)The fibrous articulations between mandible or maxilla and the teeth are called gomphoses and are also immovable.

Based on Function

The Classification of Joints based on their functions is determined by the degree of movements between connecting bones.
Synarthrosis – allows for little or no movement. Most synarthrosis joints are fibrous joints (e.g., skull sutures).
Amphiarthrosis – allows for slight movement. Amphiarthrosis joints are mostly cartilaginous joints (e.g., intervertebral discs).

Based on Anatomy

Joints can also be classified based on their anatomy. Joints are subdivided into compound and simple according to Classification based on their anatomy, depending on the number of bones involved, and also into complex and combination joints.

Compound joint: three or more articulation surfaces (e.g. radiocarpal joint)
Simple joint: two articulation surfaces (e.g. shoulder joint, hip joint).
Complex joint: two or more articulation surfaces and an articular disc or meniscus (e.g. knee joint).

Clinical Importance

In clinical science, Arthropathy is known as a joint disorder, but when it there is inflammation of more than one joint, it is termed Arthritis.

Arthropathies are called polyarticular (multiarticular) when involving many joints and monoarticular when involving only a single joint. Many disabilities experienced by people who are over 55 years of age are caused by Arthritis. Arthritis is of various forms but the most common form of Arthritis is Osteoarthritis, which results from aging or deterioration of articular cartilage.

It is always advisable to exercise regularly and swimming is a very good way of exercising the joint with less damage.

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