Causes / typical injury mechanism: The fracture arises from an injury commonly experienced during a jumping sport such as basketball or volleyball. Injury mechanism is typically a large eccentric load placed upon the extensor mechanism of the knee, which results in a fracture at the tibial tubercle. (This can occur through the physis, or growth plate.)
Classic history and presentation: This condition presents as a sudden onset of pain over the anterior knee, sometimes felt after a popping sensation. There is often tenderness over the tibial tubercle upon examination. It is also common to see a large hemarthrosis around the knee. Patients often experience difficulty and inability to extend the knee as well as pain with ambulation.
- Age – This fracture usually occurs between the ages of 12 and 15 years, toward the end of skeletal maturity.
- Sex / gender – This disproportionately affects males.
Pathophysiology: Pushing off or landing from a jump while the quadriceps are in eccentric contraction places a large force on the attachment site of the patellar tendon, which is the tibial tubercle. This can lead to an avulsion fracture of the tibial tubercle. The pathophysiology of the maturation process of the tibial tubercle makes younger patients more vulnerable to this fracture. Tibial tubercle develops from a secondary ossification center that matures into bone from posterior to anterior. This creates a weak spot anteriorly, allowing for avulsion fractures to occur when the quadriceps muscle contracts forcefully. The delayed age of skeletal maturity and athletic involvement explains why this fracture disproportionately occurs in males.
Grade / classification system:
Type 1: Avulsion of a small part of the apophysis without complete separation
Type 2: Epiphysis is lifted anteriorly without separating at the base
Type 3: Fracture of the entire epiphysis with the fracture line extending into the joint
Modifiers: A – nondisplaced; B - displaced
Type I: Fracture of the secondary ossification center
Type II: Fracture that extends between the primary and secondary ossification centers
Type III: Fracture that extends across the primary and secondary ossification centers
Type IV: Fracture through the whole epiphysis
Type V: Fracture through the epiphysis with intraarticular involvement