Cartilages

Cartilages are a family of resilient connective tissues that provide flexible support and cushioning in the body. They are avascular and aneural, with chondrocytes housed in lacunae within an extracellular matrix rich in collagen, proteoglycans, and water. The matrix gives cartilage its elastic quality and ability to withstand compressive forces. Growth occurs by both appositional growth from the surrounding perichondrium and interstitial growth within the cartilage itself.

There are three main types of cartilage: hyaline, elastic, and fibrocartilage. Hyaline cartilage is the most common and has a glassy matrix with type II collagen. It covers articular surfaces, lines the ends of ribs, and forms structures such as the tracheal rings, larynx, and nasal septum. Elastic cartilage contains elastic fibers in addition to type II collagen, providing greater flexibility; it is found in the external ear and the epiglottis. Fibrocartilage has thick bundles of collagen type I, giving high tensile strength; it is resistant to compression and is found in intervertebral discs, the pubic symphysis, menisci, and the TMJ disc.

Most cartilage is surrounded by a perichondrium, a vascularized layer that supplies nutrients by diffusion. Articular cartilage on joint surfaces typically lacks a true perichondrium. Because cartilage is largely avascular, its capacity for repair is limited, and injuries often heal slowly with fibrocartilaginous tissue rather than true hyaline cartilage.

Developmentally, cartilage serves as a model for endochondral ossification in long bones and as a structural template in the growth of many skeletal elements. With aging, cartilage may calcify and lose elasticity, contributing to degenerative joint conditions.