Anatomy Joints Overview

Joints

• Joints are where two or more skeletal elements meet, whether or not movement is allowed.
• Joints are classified functionally based on the amount of movement allowed, and structurally based on the material binding the bones together and the presence of a joint cavity.

Functional Classification of Joints

• Immovable joints: No movement allowed.
• Slightly movable joints: Limited movement.
• Freely movable joints: Allow significant movement.

Structural Classification of Joints

• Fibrous joints: Joined by fibrous tissue, allowing fixed or limited movement.
  • Sutures: Between the bones of the skull.
  • Syndesmosis: Bones connected by ligaments or fibrous membranes, like the inferior tibiofibular joint.
  • Gomphosis: Teeth in sockets, connected by the periodontal ligament.
• Cartilaginous joints: Joined by cartilage, allowing fixed or limited movement.
  • Primary cartilaginous joints: Connected by hyaline cartilage, like the epiphyseal plate.
  • Secondary cartilaginous joints: Connected by fibrocartilage, like the intervertebral joints.
• Synovial joints: Characterized by articular cartilage covering the ends of bones, a joint cavity filled with synovial fluid, and a fibrous capsule.
  • The fibrous capsule is strengthened by ligaments.
  • Intracapsular structures, like discs and fat pads, may be present.

Axes of Movements

• Transverse axis: Flexion and extension movements.
• Anteroposterior axis: Adduction and abduction movements.
• Longitudinal axis: Rotation movements.

Classification of Synovial Joints by Movement

• Uniaxial: Movement around one axis:
  • Hinge joints: Flexion and extension (elbow, ankle, interphalangeal joints).
  • Pivot joints: Rotation around a longitudinal axis (atlanto-axial joint, radioulnar joints).
• Biaxial: Movement around two axes:
  • Condyloid joints: Flexion-extension and abduction-adduction (wrist, metacarpophalangeal joints).
  • Saddle joint: Flexion-extension and abduction-adduction (carpometacarpal joint of the thumb).
• Multiaxial: Movement around multiple axes:
  • Ball-and-socket joints: Flexion-extension, abduction-adduction, and rotation (shoulder and hip joints).
• Non-axial (Plane): Gliding movement (intercarpal, intertarsal joints).

Stability of Joints

Factors that contribute to joint stability:

• Shape of the articular surfaces
• Ligaments connecting the joint
• Muscles surrounding the joint