Dr. Pomeranz's Ultimate Guide to :

MRI of the Knee

Arcuate Ligament

The arcuate ligament arises from the fibular styloid with lateral limb attachment to the femur and popliteus tendon, and medial limb attachment to the posterior horn of the lateral meniscus of the knee. 2
anatomy of the knee


Arcuate Ligament: Injury

The arcuate sign is an avulsion fracture of the proximal fibula at the site of insertion of the arcuate ligament complex and is usually associated with cruciate ligament injury. The avulsion fracture is usually small, less than one centimeter, and involves the styloid process of the fibula. 1



Arcuate Ligament: Differentials

Segond fracture or “lateral capsular sign” - an avulsion “flake” from the lateral tibia.



Arcuate Ligament: MRI

Under axial and sagittal imaging, arcuate ligaments appear as low-signal intensity along the posterolateral capsule, overlying the popliteus tendon. The ligament is more conspicuous on non-fat-saturated images.3 The vertical lateral limb is inverse in size to the fabellofibular ligament. The medial limb is more oblique in its orientation.



Arcuate Ligament: References

  1. Hapugoda S, Gaillard F, et al. Arcuate Sign: Radiopaedia (sourced 10Jan2018): https://radiopaedia.org/articles/arcuate-sign-knee
  2. Pomeranz SJ. Gamuts & Pearls in MRI & Orthopedics. Ohio, The Merten Company, 1997.
  3. Rosas HG., RadioGraphics, Unraveling the Posterolateral Corner of the Knee, Vol 36: 1776-1791, 2016.



Arcuate Ligament: Example

Click here to launch this case
This 17-year-old male reports with knee pain following a football injury.
What are the anatomical structures indicated by the arrows? Hint: While this patient’s anterior cruciate ligament (ACL) is intact, these structures are very important in the setting of acute ACL tear.
satitall t2 fse .                  sagittal t2 fse
Image 1 - Sagittal T2 FSE                       Image 2 - Sagittal T2 FSE
The green arrow on image 1 indicates the popliteus muscle (there is a mytotendinous strain in this case), and the red arrows on image 2 point to the arcuate ligament (there is an arcuate ligament tear with fluid leaking from the joint capsule).

Popliteus muscle injuries seldom occur in isolation and are an important ancillary finding of internal derangement of the knee joint. Associated injuries include cruciate and collateral ligament injuries as well as meniscal tears and bone bruises. It is important not to overlook posterolateral corner injuries in the presence of an anterior cruciate ligament tear because the reconstructed cruciate ligament will likely fail without repair of the posterolateral corner injuries. Posterolateral corner injuries with PCL tears are associated with posterolateral rotatory instability (PLRI). The lateral tibia sags posteriorly on external tibial rotation. 


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