Articular Cartilage

Articular Cartilage

Prepared by Dr. Alper DUNKI

Articular cartilage is a specialised connective tissue covering joint surfaces, providing a low-friction, load-bearing interface essential for joint motion and integrity.

Structure and Composition:

• Composed of chondrocytes embedded in an extracellular matrix (ECM) of collagen (mainly type II), proteoglycans, and water (up to 80%).
• Organised into four histological zones:
  Superficial (Tangential) Zone – flat chondrocytes, high collagen, resist shear
  Middle (Transitional) Zone – rounder chondrocytes, high proteoglycans
  Deep Zone – vertical collagen fibres, resist compressive forces
  Calcified Zone – anchors cartilage to subchondral bone

Functions:

• Provides smooth articulation and shock absorption
• Distributes mechanical loads across the joint
• Lacks blood vessels, lymphatics, and nerves → limited intrinsic repair capacity

Biomechanical Properties:

• Viscoelastic behaviour due to proteoglycan-water interaction
• Maintains joint congruity and lubrication
• Damage leads to increased friction and joint degeneration

Injury and Degeneration:

• Can occur due to trauma, overuse, or inflammatory conditions
• Partial-thickness defects often do not heal
• Full-thickness defects may undergo limited fibrocartilage repair

Assessment Modalities:

• MRI with cartilage-sensitive sequences (e.g., dGEMRIC, T2 mapping)
• Arthroscopy provides direct visualisation
• Scoring systems: Outerbridge classification, ICRS grading

Repair Techniques:

• Microfracture: promotes fibrocartilage repair
• Osteochondral autograft/allograft transplantation
• Autologous chondrocyte implantation (ACI)
• Matrix-assisted ACI (MACI)
• Biologic adjuncts (e.g., PRP, stem cells) under research

Orthopaedic Relevance:

• Central to sports injuries, osteoarthritis, and joint preservation surgery
• Success of cartilage procedures depends on patient age, defect size, and mechanical alignment