Growth plates, formally known as epiphyseal plates, are specialized areas of cartilage located near the ends of long bones in children and adolescents. Their primary function is to facilitate longitudinal bone growth, which increases a person’s height during development. The plates represent the only site where a bone can lengthen. Determining the closure status of these plates is the only reliable way medical professionals can confirm whether an individual’s vertical growth has concluded.
Anatomy and Role in Skeletal Development
The growth plate is a layer of hyaline cartilage positioned between the epiphysis (the end of the long bone) and the metaphysis (the wider part of the shaft). This structure, also called the physis, is where bone lengthening occurs through endochondral ossification. This process involves the systematic replacement of cartilage tissue with solid bone tissue.
Within the physis, cartilage cells called chondrocytes are organized into distinct zones. Chondrocytes in the proliferative zone actively divide, pushing the epiphysis away from the diaphysis (the central shaft of the bone). This cellular division creates new cartilage, forming the template for future bone.
The cells then enter the hypertrophic zone, where they enlarge and die, leaving behind a calcified cartilage matrix. Blood vessels and bone-forming cells (osteoblasts) invade this matrix from the metaphysis side. The osteoblasts deposit new bone material onto the remnants, permanently replacing the cartilage and extending the length of the bone.
As a child matures, the rate of new cartilage formation slows down while the rate of replacement by bone remains constant or accelerates. Eventually, the entire cartilaginous plate is replaced by bone, and the epiphysis and metaphysis fuse completely. This final fusion leaves behind a bony line, known as the epiphyseal line, which marks the permanent closure of the growth plate and the end of further increase in height.
Medical Procedures for Assessing Growth Plate Status
The definitive way to check the status of growth plates is through a plain X-ray (radiograph), a quick and non-invasive diagnostic procedure. X-rays are the standard tool because they clearly differentiate between dense bone and less dense cartilage. On the radiograph, the growth plate appears as a distinct, dark line or gap because the soft cartilage absorbs less radiation than the hard bone segments.
To assess skeletal maturity, physicians typically request a single X-ray of the non-dominant hand and wrist. This area is chosen because it contains numerous small bones, including the carpal bones and the growth plates of the radius, ulna, metacarpals, and phalanges. These bones provide a detailed chronological record of skeletal development.
A physician or radiologist examines the X-ray image for the visible gap between the two main sections of the bone. If the gap is wide and distinct, the plates are considered “open,” indicating active growth potential remains. As the individual approaches skeletal maturity, the gap narrows until the bone on either side crosses the space, a process called epiphyseal fusion. Once fusion is complete, the growth plate is “closed,” and the dark line disappears, confirming the bone has reached its final length.
Interpreting Results and Predicting Future Growth
The interpretation of a growth plate X-ray uses Skeletal Age Assessment, which determines a person’s biological maturity rather than their chronological age. A common method involves comparing the patient’s X-ray image to standardized images compiled in an atlas, such as the Greulich and Pyle Atlas. This comparison assigns a “bone age” based on the image that most closely matches the patient’s current stage of ossification and fusion.
If the plates are still open, the skeletal age assessment helps predict the remaining growth potential. A bone age that is behind the chronological age suggests delayed maturation and a longer period of future growth. Conversely, an advanced bone age indicates that growth will conclude sooner. For a more precise height forecast, physicians may use calculation methods like the Bayley-Pinneau tables, which combine current height, chronological age, and skeletal age to project the final adult height.
A fully “closed” growth plate signifies complete fusion, meaning the cartilage has been entirely replaced by bone. This is the definitive indicator that vertical growth is finished. The timing of this closure varies between genders, occurring earlier in females than in males due to hormonal influences.
On average, growth plates close between the ages of 13 and 15 for females. For males, this process happens later, with most plates closing between the ages of 15 and 17. The final closure of all plates, particularly in the longer bones of the legs, confirms the end of the adolescent growth spurt and the attainment of final adult stature.