Articular System - Classification of Joints

Study Notes

Joints: Articulations where two or more bones meet, joined by soft tissue. They allow movement, provide shock absorption, and maintain stability. Balance between mobility and stability is crucial.
Joint Functions:
- Movement: Muscle action allows joint movement.
- Shock Absorption: Cartilage, menisci, and synovial fluid cushion the joint.
- Stability: Ligaments, joint capsules, and other structures stabilize the joint.

Fibrous Joints: Connected by dense fibrous connective tissue. They allow little to no movement.
- Types:
  - Sutures (skull): Allow for cranial bone movement during birth.
  - Gomphoses (teeth): Connect teeth to the jawbone.
  - Syndesmoses: Connect bones with ligaments (e.g., distal and proximal radioulnar joints).
Cartilaginous Joints: Connected by cartilage. They allow limited movement.
- Types:
  - Symphyses: Connected by a fibrocartilaginous disc (e.g., pubic symphysis, intervertebral discs).
  - Synchondroses: Connected by hyaline cartilage (e.g., sternocostal joints).
Synovial Joints: Contain a joint cavity. They allow significant movement.

Joint Capsule: Outer fibrous layer, inner synovial membrane, encloses the joint.
Synovial Membrane: Produces synovial fluid, a lubricant.
Synovial Fluid: Reduces friction between joint surfaces, provides nutrients.
Hyaline Cartilage: Covers articular surfaces of bones, smooths movement.
Ligaments: Fibrous structures that run between bones (extra-articular or intra-articular).

Uniaxial Joints: Movement in one plane around one axis.
- Hinge Joints: Elbow, knee, ankle (one surface is spool-like, the other concave).
- Pivot Joints: Atlantoaxial joint, superior radioulnar joint (one surface is ring-shaped).
Biaxial Joints: Movement in two planes around two axes.
- Condyloid/Ellipsoid Joints: Radiocarpal joint, MCPs of hand (one bone concave, the other convex).
- Saddle Joints: CMC of thumb, sternoclavicular joint (both bones have convex and concave parts).
Triaxial Joints: Movement in three planes around three axes.
- Ball and Socket Joints: Glenohumeral joint, hip (ball-shaped surface fitting into a socket).
Nonaxial/Plane Joints: Gliding motion occurs, no movement around an axis; e.g., intercarpal joints and facet joints.