I answered this question under the Orthopedics Forum, but I did not see the post there, so I will try to place a post here also:
Essentially, this part of the report is stating that the ACL (anterior cruciate ligament) does not appear to be attached to the femur (the thigh bone). Since the MRI could not confirm that the ACL was attached, the assumption is that it is torn.
The bone marrow edema is basically a bone bruise. It is very common to see a bone bruise in the lateral femoral condyle and the lateral tibial plateau (the outside half of the knee) in acute ACL ruptures. This is because, as the knee goes into the abnormal position to tear the ligament, the femur (thigh bone) and the tibia (shin bone) slam into each other. This hitting together, causes the bones to "bruise", producing the bone marrow edema.
Also, another reason for there to be edema just within the femoral condyle and not the associated tibia, is, if the ACL attachment was torn off the condyle (rather than tearing in its midsubstance) it could have injured the attachment, causing edema with in bone marrow around the attachment of the ACL.
One would have to actually look at the study itself, to determine the likely cause of the edema within the bone marrow.
You need to go over the results of the study with your surgeon, to correlate the findings with your history and examination. This should be done with all studies, as there can be many interpretation of a finding on a study, but with correlation the actual meaning of what was found on the study can usually be determined.
If you had an injury with a mechanism, which could cause an ACL tear (non-contact landing/twisting injury usually), felt a pop, and had massive swelling in the knee, then you probably tore the ACL.
But, if you have never had a significant injury, and the knee is stable, then the probability of an ACL tear goes way down.
The main symptom of an ACL tear is instability; where the knee feels wobbly or like it is sliding out of place, especially with stopping and cutting activities. The pain in these knees is usually secondary, from the instability.
However, everyone is different, and each person presents in his/her unique way. Some patients have very good proprioception and muscle control, and as such, can control the instability. In these patients, then pain may be a primary symptom.
In an MRI of the knee, it is sometimes difficult to see the cruciate ligaments. If the knee is not positioned exactly correctly in the machine, the "cuts" on the study may miss the important parts on the ACL. Because of the way the ACL lies in the knee, it is not directly anterior-posterior, but angles slightly; so the knee has to be angled slightly to get good pictures of the ACL during the MRI.
So, sometimes, the ACL is just not visualized very well. If the radiologist can't see the actual attachment, he/she will put down that it is not visualized and could be suspicious for a tear. Unfortunately, the radiologist usually does not have access to the patient's history, so he/she can only go by what is seen on the study. Sometimes, other clues can be used, such as the bone bruising or if there is a lot of swelling in the knee. If these are present, then the chances of an acute injury go up. But, these signs may not be present in a chronic tear.
This is why all study results have to be correlated with the patient's exam. Once the orthopedic surgeon has examined the knee thoroughly and looked at the MRI films, then a pretty firm diagnosis can be made. And actually, most knee surgeons can tell from their exams what is going on, and use the MRI just as a confirmatory study (and to make sure there is nothing else going on in the knee, like a cartilage tear.)
Be sure to ask as many questions as you need when you see your surgeon. Make sure you understand what he/she is saying, and if possible, have him/her show you on the MRI, what he/she is talking about.