Epiphyseal cartilage is a type of cartilage found at each end of a long bone related to bone elongation, or growth. Cartilage is a connective tissue that provides flexible support attaching the bones of the skeleton. Made from a matrix of elastic protein fibers in a gelatinous protein base called chondroitin, this tissue lacks blood vessels and regenerative abilities. In time, cartilage turns into bone through a hardening process known as ossification. Epiphyseal plates, or growth plates that bookend bones, are found in children and adolescents; after reaching adult maturation, the epiphyseal plates reach their growth limit and become epiphyseal lines.
There are three types of cartilage: hyaline, elastic, and fibrocartilage. These differ by the protein fibers within the cartilage matrix. Epiphyseal cartilage is a hyaline cartilage. Composed primarily of collagen, it is the type of tissue found in the nose and voicebox as well as the epiphyseal cartilage of long bones. When it occupies the synovial, or membranous, joints between bones, this articular cartilage helps to provide support, shock absorption, and reduce friction between these skeletal structures.
Located between the diaphysis, or long shaft, and epiphysis, or end of the bone, the epiphysis starts out in young people separated from the main bone by a layer of epiphyseal cartilage. Eventually it melds with the main part of the bone. Cartilage grows in the epiphyseal plate by pushing the epiphysis away from the diaphysis and hardening into bone. Ossification actually takes place in two separate centers, the primary and secondary, from the primary central shaft of the bone and continuing all the way to its end portion, which is the secondary center of ossification at the epiphysis.
When growth has reached its maximum potential and stops, epiphyseal cartilage disappears. Growth is then eliminated by epiphyseal closure. Developmental defects may lead to growth disorders. A common defect in cartilage formation is known as achondroplasia, one cause of dwarfism.
Bone growth indicates not only developmental progress, but provides more accurate reflection of physiologic maturity than height or even chronological age. Injuries to these growth plates only occur in the pediatric population. Ossification appears in the embryo and continues over a growth period of about two decades.
Skeletal maturation can be indicated by the mineralization of these primary and secondary ossification centers. This process consists of the creation of new cells and tissues, and their formation into a mature, permanent form. Essentially, skeletal maturation occurs in three stages: ossification of the diaphysis, the epiphysis, and ultimately, their fusion.