A Salter-Harris fracture occurs exclusively in the developing skeletons of children and adolescents. It is defined as a fracture that involves the physis, or growth plate. This specialized cartilage is responsible for the longitudinal growth of long bones, such as those in the arms and legs.
The growth plate is generally weaker than nearby ligaments and tendons, making it a common site of injury during trauma in physically active young people. The classification system, named after orthopedic surgeons Robert Salter and William Harris, determines the severity of the injury. Understanding the specific pattern of the break is important because damage to the growth plate can interfere with the bone’s future development.
The Structure of the Growth Plate
The growth plate (physis) is a disc of cartilage positioned between the ends of a long bone (epiphysis) and the shaft (metaphysis). This structure is organized into four distinct cellular layers that transition from the epiphysis toward the metaphysis:
- The resting or reserve zone, which contains cells that serve as the foundation for growth and provide nutrients.
- The proliferative zone, where cartilage cells rapidly divide and flatten into columns.
- The hypertrophic zone, which features enlarged, maturing cartilage cells and is the area where the fracture line most commonly propagates.
- The zone of provisional calcification, which prepares the cartilage matrix to be replaced by bone tissue, adding new length to the metaphysis.
The hypertrophic zone is the weakest point in the bone-cartilage structure due to its low mineral content, making it vulnerable to fracture. The specific pathway a fracture takes through these zones determines its Salter-Harris classification.
Classification of Salter-Harris Fractures
The classification system categorizes physeal fractures into five primary types based on the path the fracture line takes through the bone structure.
Type I is the simplest pattern, where the fracture runs horizontally straight across the growth plate, separating the epiphysis from the metaphysis without involving either bone. This is often described as a “slipped” separation, and because the germinal cells remain with the epiphysis, the prognosis for normal growth is favorable.
Type II fractures are the most common, accounting for approximately 75% of all Salter-Harris injuries. In this pattern, the fracture line travels through the growth plate but then extends obliquely upward into the adjacent metaphysis, leaving a characteristic triangular bone fragment attached to the physis. This break spares the epiphysis, and it generally carries a good prognosis due to the preservation of the epiphyseal blood supply.
A Type III fracture is less frequent and involves a break that goes through the growth plate and then turns downward, exiting through the joint surface and the epiphysis. This fracture pattern is considered intra-articular, meaning it enters the joint space, which raises concerns for long-term arthritis. Because the fracture splits the epiphysis and affects the growth plate, careful alignment is needed to prevent uneven growth.
Type IV fractures are more complex, with the fracture line passing vertically through all three structures: the epiphysis, the growth plate, and the metaphysis. This creates a single fragment involving the joint surface and the entirety of the growth mechanism. Due to the high risk of disrupting the physis and the articular cartilage, this type frequently requires surgical intervention and has a guarded prognosis for future growth.
The rarest and most severe injury is the Type V fracture, which is a crushing or compression injury to the growth plate. This injury compresses the delicate cellular structure of the physis, especially the germinal layer, causing irreversible damage. Because there is no initial displacement, the injury can be difficult to see on X-rays and is often diagnosed retrospectively when growth arrest becomes apparent months later.
Diagnosis and Implications for Growth
The initial step in identifying a Salter-Harris fracture is typically an X-ray of the injured limb, which visualizes the separation or displacement of bone fragments. For Type I and Type V injuries, the fracture line may be difficult to see because the growth plate is made of cartilage, which does not show up well. Localized tenderness over the growth plate can prompt a presumptive diagnosis or require further imaging.
Advanced imaging, such as magnetic resonance imaging (MRI), is sometimes used to evaluate soft tissue and cartilage damage, especially when X-rays are inconclusive or a Type V injury is suspected. Treatment is determined by the fracture type and displacement. Stable Type I and non-displaced Type II fractures are treated with simple casting or splinting. Displaced fractures usually require closed reduction, where the bone is manually realigned under sedation, followed by immobilization.
Surgical intervention, often involving open reduction and internal fixation, is frequently necessary for Type III and Type IV fractures to ensure anatomical alignment of the joint surface and the growth plate. The primary concern is the risk of premature physeal closure or growth arrest. This occurs when the damaged growth plate forms a bony bridge across the physis, preventing the bone from lengthening normally.
The risk of growth disturbance is directly proportional to the severity of the classification. Types I and II generally have a lower risk of growth arrest, but the prognosis is poorer for Types III, IV, and V. Type V carries the highest likelihood of permanent growth impairment and angular deformity. Monitoring the child’s bone growth over the following months or years is a standard part of long-term management.