1-Anterior cruciate ligament is attached to posterior surface of the lower femur running to insert into anterior part of the articular surface of tibia.
3-If you do not see the anterior cruciate ligament in the sagital view, go directly to the coronal view, if you see it, this means that the technique taken for examination is taken wrong, if it is not seen this means that it is teared(empty notch sign).
4-How to adjusts the angle of the examination:
-First, draws a line parallel to the condyles.
-Then, draws a line perpendicular to the condylar line toward medial condyle.
-Finally, takes an oblige line with angle 10 degree toward medial condyle from perpendicular line.
-Now you are cutting horizontal to the anterior cruciate ligament including all of its substance in the MRI sections.
5-Sometimes, you see the part of ACL attached to the femur is enlarged, this is considered normal(sagital plane).
6-Normally you should find the ligament stand stretched, so any abnormality seen in a stretched ACL should be considered normal, but if the ligament is redundant, this means a tear.
7-If the ligament is torn at its attachment with femur, it will lies down toward articular surface of the tibia with a lake of fluid around.
8-ACL can be also torned from the middle with a lake of fluid around.
9-ACL can be also non visualized due to its torn resulting in formation of what is known as a cloud or a pseudo mass of edema and hemorrhage, in this case we needs to knows if this ligament is torned or not, here we can depend upon two signs to answer this question
-The first sign is the kissing bone contusion due to bone marrow edema in the femur and tibia(most important sign).
-The second sign is forward displacement of the tibia relative to the femur.
Here, we take a vertical line at the lateral meniscus touching both posterior surfaces of the femur and tibia, this line should be adherent to the posterior surface of the tibia, if the tibia is translocated (moving forward) anteriorly by more than 5 mm,this is a supportive sign of ACL torn.
10-So if you look in the sagital film and you find a cloud mass, go to the intercondylar notch, if you find the same appearance a cloud mass this means an empty notch sign which means that the notch is empty from ACL.
11-Partial ACL tear(Laxity and angulation):
-The only sign of partial tear of ACL is loss of stretching of the ligament, or by other means laxity of the ligament, again laxity of the ligament means it becomes near tibial plateau with angulation of its substance with convexity toward tibia.
Presence of white lines horizontal to the axis of the substance of the ligament does not means torn ACL(due to synovial recesses present inside parenchyma of ligament appears as white lines in T1 due to fat and white in T2 due to presence of water.
12-Chronic tear(Fragmentation):
-The only sign of chronic tear is fragmentation of ACL, with no kissing bone marrow edema and persistance of anterior translocation of the tibia.
13-Cruciate ligament cyst(inter condylar cyst):
-Could arises from both cruciate ligaments.
-More common in ACL.
-D.D. from tear.
In T2 image, it appears as a hyper intense cystic lesion containing fluid.
Summary of ACL lesions:
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| Click diagram to enlarge |
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