Causes / typical injury mechanism: Proximal tibia metaphyseal fractures, also known as Cozen fractures, in pediatric patients can occur as a result of direct or indirect force applied to the area. This injury as a result of direct force can occur when a child has impact of the proximal tibia against an object. Onset of Cozen fracture results more commonly from indirect force, when the lower leg is forced into hyperextension with lateral pressure applied. Jumping on a trampoline was found to be one of the leading causes of proximal tibia metaphyseal fractures in pediatric patients.

Classic history and presentation: Typically, a proximal tibia metaphyseal fracture results in a medial cortex fracture, proceeding to a valgus deformity as a result of failed tension in the cortex of the medial metaphysis.

Prevalence:

• Age – This injury is most commonly seen in pediatric patients between the ages of 2 and 8 years. The same mechanism of injury in older patients would result in fractures more proximally through the physis.
• The overall incidence rate of metaphyseal tibial fractures in children is 5.6 per 100 000.

Pathophysiology: This injury most commonly occurs through indirect pressure applied laterally to a hyperextended leg. A major tendency for this fracture to result in valgus deformity, known as Cozen's phenomenon, is emphasized for its late onset after the occurrence and remediation of the injury.

Proposed hypotheses for valgus deformity include the iliotibial band or fibular tethering effect, unbalanced blood supply between the medial and lateral cortices, and entrapment of periosteum to the fracture gap.