The arcuate ligament is a thickening of the posterolateral capsule at the back of the knee, that contributes to stability of the joint in this region.
Page updated Janauary 2024 by Dr Sheila Strover (Clinical Editor)
Does everyone have an arcuate ligament?
The arcuate ligament is not present in every knee.
Fibular avulsion fractures and the arcuate sign
In posterolateral corner injuries of the knee, the top of the fibula on the outer aspect of the knee may avulse - being torn off together with the attached arcuate ligament. This is an important sign to recognise on an X-ray and may explain post-injury instability. Surgery to reattach the avulsed fragment can restore posterolateral corner stability.
"The arcuate sign is a well described finding of fibular head avulsion [fracture] at the insertion site of the arcuate complex....[it] indicates an injury to at least one of the posterolateral corner structures of the knee....[with] resulting instability."
Citation: Crimmins JT, Wissman RD. The Arcuate Sign: A Marker of Potential Knee Dislocation? A Report of Two Cases. Radiol Case Rep. 2015 Dec 7;3(2):160. doi: 10.2484/rcr.v3i2.160. PMID: 27303520; PMCID: PMC4896228.