Structural Classification and Types of Joints in the Human Body

Structural Class, Types of Joints & Mobility

Functional Classifications of Joints

Joints in the human body are classified functionally based on the amount of movement they allow. This classification helps in understanding the range of motion and the role of each joint in the skeletal system.

• Synarthroses: Immovable joints; restricted mainly to the axial skeleton.

• Amphiarthroses: Slightly movable joints; also primarily found in the axial skeleton.

• Diarthroses: Freely movable joints; these are the predominant type in the appendicular skeleton.

Structural Classifications of Joints

Structurally, joints are classified based on the material binding the bones together and whether or not a joint cavity is present.

• Fibrous joints

• Cartilaginous joints

• Synovial joints

A combination of both functional and structural classifications is used to describe a joint in detail.

Fibrous Joints

Fibrous joints are connected by dense connective tissue consisting mainly of collagen fibers. These joints are typically immovable or allow very limited movement.

• At bone ends/parts

• Bones are united by collagen fibers

• Examples:

  • Suture (short fibers): Immobile (also called synarthrosis); found only in the skull.

Cartilaginous Joints

Cartilaginous joints are connected entirely by cartilage (either hyaline or fibrocartilage). They allow more movement than fibrous joints but less than synovial joints.

• At bone ends/parts

• Bones are united by cartilage

• Examples:

  • Synchondroses: Bones united by hyaline cartilage; typically immobile.

    • Example: Joint between the first rib and the manubrium of the sternum; epiphyseal plate in growing bones.

  • Symphyses: Bones united by fibrocartilage; slightly movable.

    • Example: Intervertebral discs, pubic symphysis.

Synovial Joints

Synovial joints are the most common and most movable type of joint in the body. They are characterized by the presence of a fluid-filled joint cavity.

• Found at ends of bones

• Bones are covered with articular cartilage and enclosed within a capsule lined with synovial membrane

• These are freely movable (diarthrotic joints)

Types of Synovial Joints

Synovial joints are further classified based on the shapes of their articulating surfaces and the types of movement they allow.

1. Ball & Socket Joint: The spherical end of one bone fits into a socket of another bone; allows multiaxial movement (movement in all axes).

   • Examples: Shoulder joint, hip joint

2. Condylar Joint: The egg-shaped end of one bone fits in an oval shape of another bone; allows side-to-side and back-and-forth movement; biaxial (movement in two planes).

   • Examples: Metacarpophalangeal (knuckle) joints, wrist joints

3. Plane Joint: Movement is in a flat plane; allows for short, gliding (nonaxial) movements.

   • Examples: Intertarsal joints, intercarpal joints, joints between vertebral articular surfaces

4. Hinge Joint: The cylindrical end of one bone fits in the trough of another bone; uniaxial (movement in one plane).

   • Examples: Elbow joints, interphalangeal joints

5. Pivot Joint: The round end of one bone fits into a ring of another bone, with a ligament encircling the two bones; uniaxial.

   • Examples: Radioulnar joint, atlantoaxial joint (where the atlas meets the dens of the axis)

6. Saddle Joint: The convex end of one bone fits into the concave part of another bone; biaxial; very similar to condyloid joints.

   • Examples: First carpometacarpal joint of the thumb

Summary Table: Structural and Functional Classification of Joints

Structural Class	Functional Class	Binding Material	Mobility	Examples
Fibrous	Synarthrosis	Collagen fibers	Immovable	Sutures of the skull
Cartilaginous	Amphiarthrosis	Cartilage (hyaline or fibrocartilage)	Slightly movable	Intervertebral discs, pubic symphysis
Synovial	Diarthrosis	Articular cartilage, synovial fluid	Freely movable	Shoulder, hip, knee joints

Key Terms and Definitions

• Synarthrosis: An immovable joint.

• Amphiarthrosis: A slightly movable joint.

• Diarthrosis: A freely movable joint.

• Articular cartilage: Smooth, white tissue that covers the ends of bones where they come together to form joints.

• Synovial membrane: The soft tissue found between the articular capsule and the joint cavity of synovial joints; secretes synovial fluid.