The arcuate ligament is a Y-shaped ligamentous complex on the posterolateral knee forming an inverted Y arch over the popliteus tendon, one limb of which is the fibular collateral ligament. It is part of the posterolateral corner complex and contributes to resistance against varus and external tibial rotation forces. The arcuate sign on plain radiographs — a small avulsion fracture of the fibular styloid — indicates arcuate ligament avulsion and suggests posterolateral corner injury.
| Origin | Head of the fibula and lateral femoral condyle |
|---|---|
| Insertion | Posterior capsule of the knee forming an arch over the popliteus tendon |
| Actions | Part of the posterolateral corner complex — resists varus stress and external tibial rotation; forms the roof of the popliteal fossa laterally |
|---|
The arcuate sign (fibular styloid tip avulsion fracture) on plain radiographs is a highly specific indicator of posterolateral corner injury, triggering further assessment of the LCL, popliteus tendon, and popliteofibular ligament. Its identification at the time of multiligament knee injury ensures the posterolateral corner is not missed and left unrepaired.
Fibular styloid avulsion of the arcuate ligament in posterolateral corner injuries, the radiographic arcuate sign indicating high probability of complete posterolateral corner disruption.
