The growth plates (epiphyseal plates or physes) are specialized sections of cartilage located near the ends of a child’s long bones. These areas are responsible for the bone’s longitudinal growth, determining a person’s final height. Active throughout childhood and adolescence, growth plates serve as the primary centers for lengthening the arms, legs, and other long skeletal structures. Knowing if these plates are still “open” or have “closed” provides a measure of skeletal maturity and remaining growth potential.
The Biological Role of Growth Plates
Growth plates are composed of soft, flexible cartilage cells, which makes them distinct from the surrounding hard, mineralized bone tissue. These cartilage cells, called chondrocytes, are constantly dividing and maturing in a highly organized process. The plate is situated between the epiphysis, the rounded end of the bone, and the metaphysis, the wider section of the bone shaft.
The process of bone lengthening is called endochondral ossification. New cartilage is created on one side of the growth plate, while older cartilage cells on the other side are transformed and replaced by solid bone tissue. This continuous cycle drives the outward extension of the long bones. The function of the growth plate is regulated by factors like genetics, nutrition, and systemic hormones, which control the rate and duration of growth.
The Natural Timeline for Plate Closure
The signal for growth plates to stop functioning and begin the closure process is primarily hormonal, specifically related to the surge in sex hormones during puberty. These hormones, particularly estrogen, trigger the eventual replacement of all the remaining cartilage with solid bone. Once this process, called epiphyseal fusion, is complete, the bone can no longer lengthen.
The timing of closure varies between individuals and sexes, but it follows a predictable skeletal pattern. Females generally complete growth and experience plate closure earlier than males, often between ages 13 and 16. Males typically continue growing longer, with most plates closing between ages 15 and 19. After closure, the growth plate is marked by a thin, faint line of bone called the epiphyseal line.
Diagnostic Methods for Assessing Plate Status
The most common and reliable method for determining whether a person’s growth plates are open or closed is a standard X-ray, also known as a bone age assessment. Since growth plates are made of cartilage, which is less dense than bone, they allow more X-ray energy to pass through. This makes an open growth plate appear as a distinct, dark gap or band near the end of the bone on the X-ray image.
Radiologists often X-ray the non-dominant hand and wrist because this area provides a comprehensive proxy for overall skeletal maturity. A physician compares the image to a standardized atlas of bone development to assign a “skeletal age.” If the plates are closed, the dark gap is replaced by a thin, bright white line, indicating the bone has fully fused and growth has ceased.
The Specific Risks of Growth Plate Injuries
The cartilaginous nature of the growth plate makes it the weakest point in a child’s developing skeletal structure, often more vulnerable to injury than surrounding ligaments or tendons. Injuries to this area are called physeal fractures, accounting for a significant percentage of all childhood fractures. An injury causing a sprain or ligament tear in an adult often results in a fracture through the growth plate in a child.
Because the growth plate is the site of bone lengthening, a severe fracture can disrupt the delicate process of cell division and ossification. This damage can potentially lead to complications like growth arrest, where the bone stops growing prematurely, or the development of an angular deformity. Prompt diagnosis and appropriate treatment are necessary to mitigate the risk of these long-term issues that could result in a limb-length discrepancy.