Introduction to Joints and Connective Tissue

Gross Anatomy of Bone

• Long bones have epiphyses with articular cartilage at both ends.

• Articular cartilage reduces friction and smooths connections between bones.

Joints

• Joints are where bones articulate.

• Types of joints include:

  • Synarthroses: Immovable joints (e.g. sutures).

  • Amphiarthroses: Limited movement joints (e.g. intervertebral discs).

  • Diarthroses: Freely movable joints (e.g. synovial joints).

Types of Diarthroses

• Classified based on movement:

  • Uniaxial: One axis of movement (e.g. elbow).

  • Biaxial: Two axes of movement (e.g. metacarpal knuckles).

  • Multiaxial: Multiple axes of movement (e.g. ball and socket joints like hip and shoulder).

Structural Classifications of Joints

• Fibrous Joints:

  • Sutures: Dense regular connective tissue fusion (skull bones).

  • Syndesmoses: Joined by fibrous tissue allowing some movement (e.g. radius and ulna).

  • Gomphoses: Specialized joints that connect teeth to mandible.

• Cartilaginous Joints:

  • Synchondroses: Joints connected by hyaline cartilage (e.g. epiphyseal plate).

  • Symphyses: Joints connected by fibrocartilage (e.g. pubic symphysis).

Synovial Joints

• Composed of articular capsule and synovial membrane for lubrication.

• Features include:

  • Synovial fluid for cushioning and reducing wear.

  • Ligaments (holding bones) and bursae (reducing friction).

• Types include:

  • Hinge, pivot, saddle, ball-and-socket joints.

Aging and Joints

• Aging can lead to arthritis, often due to loss of articular cartilage and changes in connective tissue.

  • Osteoarthritis: Caused by cartilage wear leading to bone-on-bone friction.

  • Gout: Accumulation of uric acid in joints.

  • Rheumatoid Arthritis: Autoimmune inflammation of synovial membranes.

Joint Development

• Joints form during embryonic development alongside bones from mesenchyme (stem cells).

• Fibrous joints develop as surrounding mesenchyme differentiates into dense connective tissue.

• Synovial joints arise as mesenchyme at bone ends differentiates during endochondral ossification.