Joints, also known as articulations, are the points where two or more bones come together. They enable movement and provide structural support to the skeletal system. Joints can be classified based on their structure and function.
Classification of Joints by Structure:
1. Fibrous Joints: These joints are connected by dense connective tissue and allow minimal to no movement. Examples include sutures in the skull and syndesmoses in the tibia and fibula.
2. Cartilaginous Joints: These joints are connected by cartilage and allow limited movement. Examples include the intervertebral discs between vertebrae and the pubic symphysis.
3. Synovial Joints: These joints have a synovial cavity containing synovial fluid, which reduces friction and allows significant movement. They are further categorized into different types based on their shapes and movements.
Classification of Synovial Joints by Function:
1. Ball-and-Socket Joints: These joints allow the widest range of motion in all directions. The rounded end of one bone fits into the cup-like depression of another bone. Examples include the hip and shoulder joints.
2. Hinge Joints: These joints allow movement in only one plane, like a door hinge. They facilitate flexion and extension. Examples include the elbow and knee joints.
3. Pivot Joints: These joints allow rotation around a central axis. One bone pivots or rotates around another bone. An example is the joint between the radius and ulna in the forearm.
4. Gliding Joints: These joints allow sliding or gliding movements between flat or slightly curved surfaces of adjacent bones. Examples include the joints between the carpal (wrist) and tarsal (ankle) bones.
5. Saddle Joints: These joints allow movement in two planes, resembling a saddle. The surfaces of the bones are shaped like a rider sitting in a saddle. An example is the joint between the carpal bone (trapezium) and the thumb's metacarpal bone.
6. Condyloid (Ellipsoidal) Joints: These joints allow movement in two planes, with one bone's oval-shaped end fitting into the elliptical cavity of another bone. Examples include the joints between the wrist bones and the metacarpals.
Joints play a crucial role in enabling movement and maintaining skeletal stability. The type of joint determines the range of motion possible and the specific movements that can occur.