The human spine, composed of 33 vertebrae, intervertebral discs, ligaments, and muscles, serves as the central support for the body, protecting the spinal cord and enabling a wide range of movements. The process of growth is fundamental to human development, leading to natural questions about how different parts of the body, including the back, reach their full size and mature.
Understanding Growth Plates in General
Growth plates, also known as epiphyseal plates, are layers of hyaline cartilage found at the ends of long bones in children and adolescents. These cartilaginous structures are responsible for the longitudinal growth of bones, enabling them to increase in length. Within the growth plate, cartilage cells (chondrocytes) actively divide and proliferate. As new cartilage cells are produced, older cells are pushed towards the shaft of the bone, where they enlarge, degenerate, and eventually calcify.
Osteoblasts, bone-forming cells, replace this calcified cartilage with new bone tissue, a process called endochondral ossification. This continuous cycle of cartilage production and replacement by bone allows long bones to lengthen during childhood and adolescence. Once skeletal maturity is reached, these growth plates ossify and fuse, forming an epiphyseal line that marks the cessation of longitudinal bone growth.
How the Spine Grows
The spine does not contain traditional epiphyseal growth plates like those found in long bones. Instead, vertebral bodies, the main segments of the spine, grow in height through a similar endochondral ossification mechanism. This process primarily takes place at cartilaginous endplates on the top and bottom surfaces of each vertebra. These vertebral endplates, though distinct from epiphyseal plates, act as growth zones where cartilage is produced and replaced by bone, contributing to increased vertebral height.
In addition to the endplates, secondary ossification centers called ring apophyses play a role in spinal development. These ring-shaped structures encircle the edges of the vertebral endplates. While the ring apophyses do not directly contribute to the longitudinal lengthening of the spine, they are crucial for anchoring the intervertebral discs to the vertebral bodies, providing stability. The coordinated growth and eventual ossification of the vertebral endplates and the maturation of the ring apophyses allow the spine to lengthen and develop its adult form.
The End of Spinal Growth
Spinal growth concludes as cartilaginous structures within the vertebrae gradually ossify and fuse. The vertebral endplates undergo cartilage replacement by bone. Similarly, the ring apophyses, initially cartilaginous, ossify and eventually fuse with the main body of the vertebrae. This fusion signifies the end of significant height gain from spinal growth.
The timing of this closure varies among individuals, generally occurring during late adolescence to early adulthood. For girls, spinal growth typically ceases between 16 to 18 years, while boys may continue growing until 18 to 21 years. By around age 21, most ring apophyses are completely fused, providing structural stability to the adult spine.