A fracture is a break in the bone that occurs when a force applied to the skeletal structure exceeds the bone’s physical capacity to withstand it. While fractures can occur at any age, the types of breaks seen in children often differ from those in adults. This difference is a result of the unique composition and ongoing development of the pediatric skeleton, which is more flexible and porous, leading to distinct patterns of injury.
The Structural Differences in Child Bones
The unique fracture patterns in children stem from three primary characteristics of their developing bones. Pediatric bone tissue contains a lower mineral content and a higher proportion of collagen, making the bone more pliable and less brittle than mature adult bone. This increased elasticity allows the long bones to absorb more energy from an impact before breaking.
The periosteum, the dense, fibrous membrane covering the bone’s outer surface, is also thicker and stronger in children. This robust covering can act like a hinge, often keeping the fracture fragments partially connected and contributing to stability. Moreover, the periosteum supplies the bone with nutrients, which is why a child’s bones generally heal much faster than an adult’s.
A third difference is the presence of the physis, or growth plate. Located near the ends of long bones, this layer of cartilage is responsible for all future bone length and represents a biomechanical weak point vulnerable to injury.
Characteristic Incomplete Fractures
The flexibility of the young bone often results in incomplete fractures, where the bone does not break entirely into separate pieces. One of the most common incomplete injuries is the Greenstick fracture, named after how a young, flexible tree branch breaks when bent. In this injury, a bending force causes the cortex to fracture on the side under tension, while the opposite side remains intact.
Greenstick fractures are typically seen in children under the age of ten and most often affect the long bones of the forearm. Although the break is partial, the fracture is generally considered unstable and often requires a cast after gentle realignment.
A second common incomplete injury is the Torus fracture, also known as a buckle fracture. This injury occurs when a compressive force, such as falling onto an outstretched hand, causes the bone cortex to crumple or bulge outward at the metaphysis. Torus fractures are stable injuries, often treated with simple splinting or a short period of immobilization. The increased plasticity of the pediatric bone can also lead to plastic deformation, where the bone is permanently bent without any visible fracture line.
Injuries Affecting the Growth Plate
Fractures that involve the growth plate (physis) are unique to the pediatric population and are concerning due to their potential to disrupt normal bone development. These injuries are classified using the Salter-Harris system, which categorizes fractures based on the path of the break through the physis, epiphysis, and metaphysis. There are five basic types in this classification, each carrying a different prognosis for future bone growth.
The growth plate is the weakest component of the pediatric long bone, making it more susceptible to trauma than the surrounding ligaments. If an injury to the physis is not treated properly, it can result in a growth disturbance, leading to limb length discrepancies or angular deformities.
Salter-Harris Type I fractures involve a complete separation of the epiphysis from the metaphysis, with the fracture line passing entirely through the physis. Although the growth plate is separated, the fracture typically does not involve the bone itself, resulting in a good prognosis for continued growth. This type of injury can sometimes be difficult to see on an X-ray because the physis is made of cartilage.
The most frequently encountered growth plate injury is the Salter-Harris Type II fracture, accounting for approximately 75% of all physeal fractures. This pattern involves a fracture that runs along the physis but then extends upward into the metaphysis, leaving a characteristic triangular fragment of bone attached to the growth plate. Type II fractures generally have a favorable outcome, provided they are managed correctly.