The growth plate, or physis, is a specialized layer of cartilage located near the ends of long bones in children and adolescents. Its primary function is to facilitate the longitudinal growth of the bone, determining a person’s final adult height. This region constantly produces new cartilage cells that are then converted into hardened bone tissue. Once bone lengthening is complete, this cartilage layer is entirely replaced by solid bone, a process known as epiphyseal fusion or growth plate closure. The closure of the physis signifies the end of a bone’s ability to grow in length.
The Role and Location of Growth Plates
Growth plates are found in the metaphysis, the wider portion of a long bone shaft adjacent to the joint ends, or epiphyses. Most long bones contain two growth plates, one at each end, allowing the bone to expand symmetrically. The process responsible for this elongation is called endochondral ossification, where cartilage is systematically replaced by bone tissue.
The structure of the physis is highly organized into distinct zones. Cartilage cells, called chondrocytes, begin in the resting zone before entering the proliferative zone, where they rapidly multiply. They then move into the hypertrophic zone, where they enlarge significantly before dying.
This cell death leaves behind a calcified cartilage matrix, which is then invaded by blood vessels and bone-forming cells called osteoblasts. Osteoblasts deposit new bone tissue onto the calcified remnants, effectively lengthening the bone shaft. This process continues until hormonal signals trigger the final replacement of the cartilage with a solid bone line, known as the epiphyseal line.
General Timeline of Skeletal Maturity
The timing of growth plate closure is not uniform across all individuals, but it generally correlates with the end of puberty. Females typically experience skeletal maturity earlier than males, accounting for a shorter average growth period. For girls, growth plates usually close between the ages of 13 and 15, marking the end of their adolescent growth spurt.
Boys typically continue growing longer, with most growth plates fusing between the ages of 15 and 17. The timing of this fusion is heavily influenced by sex hormones, particularly estrogen, which accelerates the maturation and eventual closure of the cartilage. While the majority of growth concludes in the mid-to-late teens, some final fusion events can extend into the early twenties, determining the cessation of height increase.
The Specific Sequence of Growth Plate Closure
Growth plate fusion follows a predictable sequence throughout the skeleton, generally moving from the extremities toward the center of the body. The earliest growth plates to close are typically those in the small bones of the hands and feet, such as the phalanges and some carpals. This early closure means the hands and feet reach their adult size well before the long bones of the arms and legs.
The sequence then progresses into the larger joints of the limbs, favoring the elbows and ankles before the shoulders and knees. For example, plates around the elbow joint often fuse before those around the knee. In the lower body, the calcaneus, a small bone in the foot, is often one of the first sites to completely close.
For the long bones that contribute most significantly to overall height, the plates around the knee are among the last to fuse, specifically the distal femur and proximal tibia. The closure of the proximal tibia plate is often considered the final event that stops vertical height growth.
The very last growth plate in the entire body to complete its fusion is the medial end of the clavicle, or collarbone, which connects to the sternum. This plate may not fully fuse until a person is between 23 and 25 years old, serving as a late marker for complete skeletal maturity long after height has stabilized.