Imaging Case: Answer

Diagnosis: Avulsion fracture of the fibular styloid process, compatible with an arcuate sign.

Fibular Styloid Fracture/Arcuate Sign:

  • Mechanism: Direct trauma to the anteromedial knee while in extension or sudden hyperextension. Case reports of this pathology also seen in knee dislocations.
  • Avulsion fracture at the proximal fibula at the insertion site of the arcuate ligament
  • 90% of fractures have disruption of the lateral collateral ligament
  • Injury to other structures of the posterolateral ligamentous complex is also common. 
  • This injury is highly suspicious of an unstable knee joint and needs emergent orthopedic evaluation.
  • Due to anatomic location of fracture, can also involve injury to peroneal nerve.

1. Knipe, D. "Arcuate Sign." Radiopeda.
2. Huang et al. "Avulsion Fracute of the Head of the Fibula (The "Arcuate" Sign). American Journal of Radiology. February 2003.