The growth plate (physis or epiphyseal plate) is specialized tissue that determines the final length and height of a person’s skeleton. These temporary structures are found near the ends of the long bones in children and adolescents. Linear growth occurs as long as these plates remain open, allowing the bone to lengthen. Growth plate closure marks the end of this skeletal lengthening, occurring when the soft, active cartilage is completely replaced by solid bone.
Understanding the Growth Plate Structure
Growth plates are layers of hyaline cartilage positioned between the wider end of a long bone (the epiphysis) and the shaft (the metaphysis). These cartilaginous zones produce new bone material through endochondral ossification. The plate is organized into distinct layers, including the resting zone, the proliferative zone, and the hypertrophic zone.
In the proliferative zone, cartilage cells (chondrocytes) rapidly divide, stacking in columns parallel to the bone’s long axis. As these cells are pushed toward the shaft, they enter the hypertrophic zone, where they swell and prepare the surrounding matrix for calcification. This calcified matrix serves as a scaffold for bone-forming cells to invade and lay down new bone tissue. This continuous cycle of cartilage creation and bone replacement drives the longitudinal growth of the skeleton.
Typical Age Ranges for Closure
The timing of growth plate closure is not instantaneous across the entire skeleton but follows a general sequence that is distinct between sexes. Closure is a gradual process, beginning at different times in various bones. Generally, the plates in the hands and feet are among the first to fuse, while those in the major long bones, like the femur and tibia, tend to close later.
For girls, the majority of growth plates typically complete fusion between the ages of 14 and 16 years. This timing often correlates with a period one to two years after the onset of the first menstrual period, signaling the end of the pubertal growth spurt. Boys generally experience a later and more prolonged period of growth, with plate closure commonly occurring between the ages of 16 and 18 years.
The exact age can vary based on genetics, nutrition, and overall health, resulting in a wide range of normal development. Once the growth plate has fused, the active cartilage is replaced by a solid line of bone, known as the epiphyseal line, and no further increase in bone length is possible.
The Biological Mechanism of Closure
Growth plate closure is primarily signaled by a change in the body’s hormonal environment during puberty. The main hormonal driver is estrogen, which is produced in higher amounts in females and converted from testosterone in males. Estrogen binds to receptors on the chondrocytes within the growth plate, initiating the end of growth.
This hormonal signal accelerates the programmed aging (senescence) of the cartilage cells. The rapid multiplication of chondrocytes in the proliferative zone slows down, and the remaining cartilage is quickly replaced by bone. Individuals with certain hormonal deficiencies can continue to grow well into adulthood until their plates are exposed to a sufficient level of the hormone.
Medical Assessment and Injury Implications
Medical professionals assess the status of growth plates, known as determining a person’s “bone age,” using a simple X-ray, typically of the non-dominant hand and wrist. The degree of ossification and fusion shown on the image is compared to age-based standards to estimate remaining growth potential. An open growth plate appears as a dark line (representing cartilage), while a closed plate appears as a continuous white line of solid bone.
Injury to an open growth plate is a significant concern, classified by the Salter-Harris system based on the fracture’s involvement of the physis. Since the cartilaginous plate is often the weakest point in a child’s bone structure, a severe injury can damage the cells responsible for growth. If the fracture extends into the germinal layer, it can lead to a growth disturbance, resulting in a bone that is shorter or develops an angular deformity. Type V crush injuries, which compress the growth plate, often carry the worst prognosis for future growth.