Joints or articulations (connections between bones) can be classified in a number of ways. The primary classifications are structural and functional. Functional classification is based on the type and degree of movement permitted.
Three Categories of Functional Joints
Synarthrosis – These types of joints are immobile or allow limited mobility. This category includes fibrous joints such as suture joints (found in the cranium) and gomphosis joints (found between teeth and sockets of the maxilla and mandible).
Amphiarthrosis – These joints allow a small amount of mobility. Most joints in this category include cartilaginous joints such as those found between vertebrae and the pubic symphysis.
Diarthrosis – These are the freely-movable synovial joints. Synovial joints are further classified based on the different types of movement they provide, including:
- Plane joint
- Ball and socket joint
- Hinge joint
- Pivot joint
- Condyloid joint
- Saddle joint
Types of Synovial Joints.jpg
Image of a skeleton and skematics of the different classes of synovial joints.
Movement of Synovial Joints
Joints can also be classified by the number of axes of movement they permit:
Nonaxial (gliding) – Found between the proximal ends of the ulna and radius.
Monoaxial (uniaxial) – Movement occurs in one plane. An example is the elbow joint.
Biaxial – Movement can occur in two planes. An example is the wrist.
Multiaxial – Includes the ball and socket joints. An example is the hip joint.
The movements possible with synovial joints are:
- Abduction: movement away from the body’s midline
- Adduction: movement toward the body’s midline
- Extension: straightening limbs at a joint
- Flexion: bending the limbs at a joint
- Rotation: a circular movement around a fixed point