MR evaluation of the "arcuate" sign of posterolateral knee instability.
OBJECTIVE
The purpose of this study was to evaluate associated knee injuries using MR imaging in patients with the "arcuate" sign, a term referring to avulsion fracture of the proximal fibula on conventional radiographs.


METHODS
MR imaging of 18 cases (17 patients, both knees in one patient) with the arcuate sign on conventional radiographs was retrospectively interpreted to evaluate the associated meniscal, ligamentous, and bony injuries. In 12 cases, MR findings were correlated with surgical results.


RESULTS
In all cases, avulsed bony fragments from the proximal pole of the fibula were attached to the fibular collateral ligament, the biceps femoris tendon, or both. Tear of the posterolateral capsule was seen in 12 cases (67%). Injury of the cruciate ligaments was noted in 16 cases (89%): injury to both the anterior cruciate ligament and posterior cruciate ligament was seen in nine cases (50%), injury to only the anterior cruciate ligament was seen in four, and injury to the posterior cruciate ligament only was noted in three. Bone bruises or gross fractures were seen in all cases: bone bruises on the anteromedial femoral condyle were noted in nine cases (50%) and were seen on the anteromedial tibial condyle in five cases (28%). Tear of the medial meniscus was seen in five cases (28%) and tear of the lateral meniscus in four cases (22%). Injury to the popliteus was seen in six cases (33%). Joint effusion was associated in all cases.


CONCLUSIONS
MR imaging is useful for evaluation of associated soft-tissue injuries in patients with the arcuate sign on conventional radiographs. Avulsion injury to the proximal fibula is an important indicator of the internal derangement of the knee and for predicting the mechanism of an injury with varus stress. Cruciate ligament tear and bone bruises on the anteromedial condyle of the femur and tibia are common associated findings.
Juhng
Seon-Kwan
SK
Department of Diagnostic Radiology, Wonkwang University School of Medicine and Institute of Wonkwang Medical Science, 344-2 Shinyong-dong, Iksan, Jeonbuk, 570-711, South Korea.
Lee
Joong K
JK
Choi
See-Sung
SS
Yoon
Kwon-Ha
KH
Roh
Byung-Suk
BS
Won
Jong-Jin
JJ
D000328:Adult; D005260:Female; D050723:Fractures, Bone / Q000175:diagnosis / Q000000981:diagnostic imaging; D006801:Humans; D007593:Joint Instability / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000209:etiology; D007718:Knee Injuries / Q000150:complications / Q000175:diagnosis* / Q000000981:diagnostic imaging; D008023:Ligaments, Articular / Q000000981:diagnostic imaging / Q000293:injuries / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011859:Radiography; D012189:Retrospective Studies