Arcuate Sign
Other Names
- Arcuate Sign
Introduction
- Subtle finding on knee xrays
- Represents an avulsion fracture of proximal fibula at insertion of arcuate ligament complex
- Usually associated with a cruciate ligament injury and/or injury to posterolateral corner
- Fracture fragment attached to LCL, biceps femoris tendon or both
Mechanism of Injury
- Direct varus force with the tibia in external rotation[3]
- Sudden hyperextension of the knee with the tibia internally rotated
- Either one can result in posterolateral subluxation
Standard Views
Radiographs
- Avulsed fragment is usually small, <1 cm, involves styloid process of fibula
- Displaced superomedially
- Can be larger, include the lateral aspect of the proximal fibula
- Best view is on slightly rotated PA films[4]
MRI
- Useful to delineate soft tissue/associated injuries
Ultrasound
- Visible as a hypoechogenic gap in the cortex of the bone
- Place transducer in long axis of the fibula[5]
Pediatrics
- Unknown
Pathology
- Posterolateral Corner Injury
- Cruciate Ligaments
- Collateral Ligaments
- Bone bruise
- Anteromedial femoral condyle: 50%
- Anteromedial tibial plateau: 28%
- Meniscal Tear
- Medial: 28%
- Lateral: 22%
- Popliteus muscle injury
Evidence
- Unknown
See Also
References
- ↑ Case courtesy of Frank Gaillard, Radiopaedia.org, rID: 7986
- ↑ Kushare, Indranil, et al. "Arcuate sign—fibular head avulsion fracture and associated injuries in the pediatric and adolescent population." Emergency Radiology 28 (2021): 723-727.
- ↑ Lee J, Papakonstantinou O, Brookenthal KR, Trudell D, Resnick DL. Arcuate sign of posterolateral knee injuries: anatomic, radiographic, and MR imaging data related to patterns of injury. Skeletal Radiol 2003;32:619 – 627
- ↑ Huang GS, Yu JS, Munshi M et-al. Avulsion fracture of the head of the fibula (the "arcuate" sign): MR imaging findings predictive of injuries to the posterolateral ligaments and posterior cruciate ligament. AJR Am J Roentgenol. 2003;180 (2): 381-7.
- ↑ Pękala P, Mizia E, Mann M et al. The Popliteofibular Ligament: A Cadaveric Ultrasound Study. Skeletal Radiol. 2022;51(1):183-9