Epiphyseal cartilage, also known as growth plates, plays a fundamental role in human development. These temporary structures are located at the ends of long bones in children and adolescents. They are responsible for the lengthening of bones, directly contributing to a person’s height. This specialized cartilage guides the growth process throughout childhood.
What is Epiphyseal Cartilage?
Epiphyseal cartilage is a plate of hyaline cartilage found in the metaphysis, the wider part of a long bone between the shaft (diaphysis) and the end (epiphysis). It is also known as the physis. This cartilage has a gelatinous texture and is composed of chondrocytes, cells suspended within a collagen matrix.
The epiphyseal plate’s structure allows for rapid cell division and organized growth. It is divided into several distinct zones, each with a specific function in the bone lengthening process. These zones, from the epiphysis towards the diaphysis, include the reserve zone, proliferative zone, hypertrophic zone, calcification zone, and ossification zone. This layered organization facilitates bone growth.
How Epiphyseal Cartilage Drives Bone Growth
Longitudinal bone growth occurs through endochondral ossification, where cartilage is replaced by bone. The growth plate acts as a scaffold for this process, with chondrocytes at the epiphyseal side continuously forming new cartilage. These chondrocytes then undergo rapid cell division, stacking into columns and pushing older cells towards the diaphysis.
As these older cells move away from the epiphysis, they enter the hypertrophic zone, where they enlarge. These hypertrophic chondrocytes produce a cartilaginous matrix rich in type X collagen, which eventually calcifies. Following calcification, these chondrocytes undergo programmed cell death. Osteoblasts then move into the area and replace the degenerated cartilage with new bone tissue, lengthening the bone. This continuous cycle of cartilage formation, maturation, and replacement by bone allows long bones to grow in length.
When Growth Plates Close
Epiphyseal cartilage eventually undergoes complete ossification, a process often referred to as growth plate closure or fusion. This closure marks the end of longitudinal bone growth. The timing of growth plate closure varies among individuals, but it generally correlates with the end of puberty.
Girls typically experience growth plate closure earlier than boys, usually between ages 13 and 15, while boys tend to continue growing until ages 15 to 17. Hormonal influences, particularly sex hormones during puberty, accelerate this ossification process. Once the epiphyseal plate has completely ossified and fused, only a thin epiphyseal line remains, and further lengthening of that bone is no longer possible.
Injuries and Conditions Affecting Epiphyseal Cartilage
Epiphyseal cartilage is a vulnerable area, making it susceptible to injuries, particularly in children and adolescents. Growth plate fractures are common in pediatric populations, accounting for up to one-third of all childhood fractures. These injuries can occur from falls, competitive sports, or recreational activities.
The concern with growth plate fractures is their potential to disrupt normal bone growth, leading to complications like limb length discrepancies or skeletal deformities. If a growth plate is damaged, it can close prematurely, causing the affected limb to be shorter or crooked. Beyond fractures, other conditions can impact growth plate function. For instance, rickets, a condition caused by a deficiency in calcium or vitamin D, can soften and weaken bones, potentially leading to bowed legs. Genetic disorders like achondroplasia, a common cause of dwarfism, involve defects in cartilage formation and abnormal growth plate function.