Growth plates (physes) are temporary, highly active structures found within the skeletal system of children and adolescents. These specialized layers drive bone lengthening and are essential for normal skeletal development. Understanding the location and function of the growth plate is important when considering the developing ankle joint. They are only present during the years of growth and are replaced by solid bone once skeletal maturity is reached.
What is a Growth Plate and Its Purpose
A growth plate is a layer of hyaline cartilage positioned near the ends of long bones, separating the bone’s main shaft from its tip. This cartilaginous disk facilitates longitudinal growth, making the bone longer. Cells within the growth plate constantly divide, pushing older cells toward the main shaft where they are replaced by new bone tissue in a process called endochondral ossification.
The specialized cartilage is structurally distinct from the surrounding bone tissue, making it the weakest point in the growing bone structure. While ligaments and tendons are strong and resistant to pulling forces, the growth plate is inherently more fragile. This fragility has implications for how a young person’s body responds to physical stress or injury.
Precise Location of Ankle Growth Plates
The ankle joint is formed by the talus, the tibia, and the fibula. The growth plates are located at the distal ends of the two leg bones. One plate is situated at the bottom of the tibia, the larger, weight-bearing shin bone.
A second plate is located at the distal end of the fibula, the thinner bone running parallel to the tibia. These two plates form the bony prominences on either side of the ankle, known as the malleoli (medial and lateral).
The growth plate is positioned between the rounded end (epiphysis) and the wider shaft (metaphysis). The cartilaginous plate lies just above the joint surface. The distal tibial growth plate contributes approximately 40% of the tibia’s entire length.
The Process of Growth Plate Closure
Growth plates are temporary structures that disappear once skeletal maturity is reached. Closure, or fusion, involves the cartilage gradually being replaced by solid bone tissue through ossification. Once fully ossified, the former growth plate becomes a faint line on the bone, known as the epiphyseal line, and the bone can no longer lengthen.
The timing of closure varies between the two ankle growth plates and between sexes. The distal tibial physis generally begins to close first, typically between ages 11 and 13 for females and 12 and 14 for males. The distal fibula growth plate closes slightly later, often making it one of the last growth plates in the body to fuse. Complete fusion across both ankle plates usually concludes by the late teens.
Why Growth Plates are Susceptible to Injury
Growth plates are susceptible to injury because they are composed of softer cartilage rather than bone. During physical stress, a force transmitted across the ankle joint seeks the path of least resistance. In a child, this path is often through the weak growth plate instead of the adjacent ligaments or surrounding mature bone.
An ankle trauma that results in a sprain in an adult frequently causes a growth plate fracture in a child. These fractures are categorized using the Salter-Harris classification, which describes the fracture pattern based on how the break passes through the plate. Ankle injuries involving the growth plate are common, especially in sports, because rotational or twisting forces can easily shear the weaker cartilaginous layer.
A fracture that damages the growth plate’s cellular layers can disrupt the normal process of bone lengthening. Any significant ankle injury in a growing child requires prompt medical evaluation, even if symptoms resemble a simple sprain. The risk of a growth disturbance or angular deformity relates directly to the severity of damage to the growing cartilage cells.