Growth plates (epiphyseal plates) are specialized areas of developing cartilage near the ends of long bones, such as those in the arms and legs. Their primary function is to drive longitudinal bone growth throughout childhood and adolescence. These flexible cartilage zones allow bones to increase in length, determining a person’s final adult height. This process continues until the cartilage is completely replaced by solid bone tissue, an event known as growth plate closure.
The Biological Role of Growth Plates
Increasing bone length occurs through a precise, coordinated process called endochondral ossification. This process is driven by specialized cells called chondrocytes, which are organized into distinct zones within the growth plate. Progenitor cells in the resting zone continuously supply new chondrocytes to the adjacent proliferative zone.
Chondrocytes in the proliferative zone multiply rapidly, arranging themselves in columns parallel to the bone’s long axis and pushing the ends of the bone apart. Moving away from this zone, the cells enter the hypertrophic zone, where they increase in size. These enlarged cells then secrete a calcified matrix before undergoing programmed cell death.
Blood vessels and bone-forming cells (osteoblasts) invade the calcified cartilage scaffold left behind by the dying chondrocytes. Osteoblasts deposit new lamellar bone tissue, permanently replacing the original cartilage structure. This continuous cycle of cell division, maturation, and replacement is regulated by systemic hormones, including growth hormone and sex hormones, which dictate the speed and completion of the growth process.
Clinical Assessment: The Definitive Way to Know
The only definitive way to determine the status of growth plates—whether open, partially fused, or closed—is through medical imaging. Radiographic imaging (X-rays) provides a clear visual of the bone structure, as cartilage appears darker than dense bone tissue. Assessment commonly focuses on the hand and wrist, which offer many growth plates that close sequentially.
Specialized staging systems estimate skeletal age by interpreting these images, as skeletal age may not align with chronological age. The Greulich and Pyle (GP) atlas and the Tanner-Whitehouse (TW) method are primary tools that compare the patient’s X-ray to standardized images of skeletal maturity. These systems allow clinicians to assess the degree of ossification (bone formation) across various growth centers.
Assessment may also involve X-rays of the knee, which has large, easily visualized growth plates. The Risser staging system evaluates ossification across the iliac crest in the pelvis, serving as a reliable marker for overall skeletal maturity. While X-rays are standard, modalities like magnetic resonance imaging (MRI) are also used for detailed assessment, as they better visualize the cartilage structure.
Non-Clinical Signs of Approaching Closure
While imaging provides definitive proof, the most recognizable non-clinical sign of approaching growth plate closure is the deceleration and eventual cessation of height gain. This slowdown follows the intense growth spurt that occurs during puberty. Hormones released during puberty, particularly estrogen, stimulate the final phase of growth followed by the fusion of the plates.
For most individuals, the majority of height growth concludes approximately two years after the peak of their pubertal growth spurt. Growth plates in females typically complete fusion between the ages of 14 and 16 years. For males, closure usually occurs later, often between 16 and 19 years of age. A noticeable absence of measurable height increase over a six-month period indicates that growth plate fusion is complete.
Skeletal Maturity: The Implications of Closed Plates
Fully closed growth plates signify the achievement of skeletal maturity. At this point, the entire cartilaginous growth plate has been replaced by solid, mineralized bone tissue, forming a continuous structure known as the epiphyseal line. The direct implication of this fusion is the definitive end of any further increase in vertical height.
An immature skeleton with open growth plates is more vulnerable to certain types of injuries. The cartilage of an open growth plate is inherently weaker than the surrounding mature bone, tendons, or ligaments. A child or adolescent is susceptible to a physeal fracture, where the break occurs directly through the vulnerable growth plate area. Once the plates have closed, the bone structure is consolidated, possessing the full strength of mature bone and altering the type and location of fractures that may occur.