Causes / typical injury mechanism: The growth plate, or physis, can be injured in long bone fractures in pediatric patients. Distal femoral physeal fractures generally occur as a result of hyperextension or varus and valgus stresses on the knee due to trauma or sports-related injuries. The physis is more susceptible to injury than adjacent bone, articular cartilage, and ligaments. In skeletally immature patients (pediatric / adolescent), the physis acts as a plane across which the fracture propagates.

Classic history and presentation: Look for a painful, swollen knee at the distal femur and the inability to bear weight secondary to pain.

Prevalence: Physeal fractures account for an estimated 15%-18% of all pediatric fractures, and the distal femoral physis is fractured in approximately 2%-5% of all physeal injuries.

• Age – Distal femoral physeal fractures typically occur in older children and adolescents.
• Sex / gender – There is a 2:1 male to female incidence ratio.

Risk factors: There is an increased incidence of fracture in patients with underlying bone diseases / pathologies, such as osteogenesis imperfecta.

Pathophysiology: A physeal fracture occurs when force is placed through the growth plate. Typically, this occurs through the hypertrophic zone of the physis, specifically at the zone of provisional calcification, as this is the weakest portion of the growth plate. This can occur as the result of an acute trauma (or sudden stop during athletic activities) or it can result from chronic overuse injury.

Leg-length discrepancies and angular deformities are the most frequent forms of growth disturbance. The frequency of physeal arrest increases with the severity of the physeal fracture due to surrounding damage and the need for more invasive management. Due to the proximity of the popliteal vessels, there is a risk of vascular damage during the initial injury and during surgical repair. Vascular damage can lead to subsequent limb loss, compartment syndrome, and loss of function. There is also a risk of long-term pain, extremity malalignment, and posttraumatic osteoarthritis if the joint is not returned to anatomic position. Therefore, early identification and management are essential to reducing the risk of long-term morbidity.

Grade / classification system: The Salter-Harris (SH) system is the primary classification tool to describe physeal fractures and their relationship to the surrounding metaphysis and epiphysis.

• Type 1 fractures – Extend across the physis; more common in younger patients due to a relatively thicker physis.
• Type 2 fractures – Occur most frequently (almost 75% of physeal fractures); they extend along the physis and exit through the metaphysis, generating a metaphyseal fragment known as a Thurston-Holland fragment.
• Type 3 fractures – Extend along the physis and exit through the epiphysis.
• Type 4 fractures – Extend across both the epiphysis and metaphysis.

Type 1 and 2 fractures typically preserve blood supply to the proliferative cells in the epiphysis, but type 3 and 4 fractures have a higher risk of damaging the proliferative cell layer. Higher-grade fractures therefore have an increased risk of long-term complications such as growth disturbance.