Cartilage: Types, Structure, Functions & Clinical Relevance

Cartilage is a specialized avascular connective tissue composed of chondrocytes embedded in a rich extracellular matrix (ECM) of collagen, proteoglycans (aggrecan), and glycoproteins.

Three Types

Type	Collagen	Key Locations	Properties
Hyaline	Type II (fine fibrils)	Articular surfaces, costal cartilages, nasal septum, tracheal rings, epiphyseal plates	Smooth, low-friction, semi-rigid; glassy appearance
Fibrocartilage	Type I (dense bundles)	Intervertebral discs (annulus fibrosus), menisci, pubic symphysis, tendon/ligament insertions	Tough, tensile strength, shock absorption
Elastic cartilage	Type II + elastin fibers	External ear, epiglottis, auditory tube	Flexible, resilient, shape-retaining

Key Functions

• Load-bearing & shock absorption: Articular hyaline + meniscal fibrocartilage distribute joint forces.
• Low-friction articulation: Superficial zone lubricin + hydration → coefficient of friction 0.001–0.01.
• Structural support: Tracheal rings (patency), nasal septum, ear pinna.
• Growth template: Endochondral ossification — hyaline cartilage model replaced by bone.

Clinical Significance

• Avascular → limited repair capacity: Chondrocytes rely on diffusion; no progenitor recruitment from blood.
• Osteoarthritis: Progressive loss of articular hyaline cartilage → pain, stiffness, disability.
• Meniscal tears: Fibrocartilage injury → mechanical symptoms, OA risk.
• Tracheomalacia / Laryngomalacia: Cartilage weakness → airway collapse.
• Relapsing Polychondritis: Autoimmune destruction of cartilage (ears, nose, trachea, joints).
• Regenerative strategies: Microfracture, MACI (autologous chondrocytes), MSC injections, tissue-engineered constructs — evolving.