The epiphyseal plate, commonly known as the growth plate, is a layer of specialized cartilage found near the ends of long bones in children and adolescents. These structures are the only mechanism by which long bones, such as those in the arms and legs, can increase in length. Assessing growth plate closure is a widely used medical procedure to help determine a child’s remaining growth potential and predict final adult height. Once the cartilage in these plates fully hardens into bone, linear growth stops, signifying the end of vertical growth.
The Function and Location of Growth Plates
Growth plates are situated between the wider end of a long bone (the epiphysis) and the long shaft (the diaphysis or metaphysis). These cartilaginous zones are responsible for endochondral ossification, which is the formation of bone from a cartilage template. The plate operates as a miniature production line where chondrocytes (cartilage cells) rapidly divide and proliferate on one side.
These newly formed cells then mature and swell (hypertrophy) before dying. The remaining calcified cartilage matrix is then invaded by blood vessels and replaced by osteoblasts, which deposit new bone tissue. This continuous cycle of cartilage creation and bone replacement pushes the epiphysis away from the diaphysis, causing the bone to lengthen. When growth concludes, this specialized cartilage is completely replaced by bone, and the epiphysis and diaphysis fuse together, leaving a faint line called the epiphyseal line.
Medical Imaging Techniques Used for Assessment
Determining the status of a growth plate requires medical imaging, with X-rays (radiographs) being the standard diagnostic tool for bone age assessment. An X-ray image visualizes the growth plate as a dark, radiolucent line or gap between the bone segments because cartilage does not absorb radiation as densely as mineralized bone. As the plate begins to close, this dark line gradually narrows and becomes indistinct.
The most common and standardized site used for this assessment is a single X-ray of the left hand and wrist. This site is favored because it contains numerous small bones that mature in a predictable sequence, providing a comprehensive snapshot of overall skeletal development. Although X-rays are the primary method, Magnetic Resonance Imaging (MRI) offers a radiation-free alternative that provides greater detail of the cartilage itself. However, MRI is not typically used for routine bone age estimation.
Interpreting Skeletal Maturity
Medical professionals interpret X-ray images to determine skeletal age, which may differ from the individual’s chronological age. This assessment relies on established reference systems that categorize the progression of bone maturation. The two most widely used methods are the Greulich and Pyle Atlas and the Tanner-Whitehouse (TW) scoring system.
The Greulich and Pyle method involves comparing the patient’s hand and wrist X-ray to standardized reference images in an atlas, where each image corresponds to a specific skeletal age. The Tanner-Whitehouse method is more complex, assigning numerical scores to the stages of maturation observed in specific bones (e.g., the radius, ulna, and short bones of the hand). Both systems track the fusion process: the progressive hardening of the growth plate from cartilage into bone. A plate is considered “closed” when the space between the epiphysis and metaphysis is completely bridged by solid bone, indicating that linear growth has ceased.
Factors That Influence Timing of Closure
The timing of growth plate closure is an individualized process dictated by a combination of internal and external factors. Genetic predisposition is a significant determinant, meaning a child’s growth timeline often mirrors that of their parents or siblings. Hormonal signaling is the direct mechanism that triggers the final fusion of the plates.
Sex hormones, particularly estrogen, play a role in regulating closure in both boys and girls. The surge in estrogen levels during puberty accelerates the maturation of the growth plate, leading to fusion. Growth hormone and thyroid hormones are also regulators; imbalances in these substances can either speed up or delay skeletal maturation. Environmental influences, such as adequate nutrition, chronic illnesses, or long-term use of certain medications like glucocorticoids, can also impact the timing of plate closure.