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Radiology/Recurring False Negative MRI


QUESTION: I have PVNS and a ruptured ACL that has been visualized via arthroscopy. It appears to have popped lose from the femoral wall since there are no frayed fibers seen. Its scarred down to the pcl and both are covered in PVNS affected synovium.  I had a MRI before surgery to remove the PVNS and it showed the ACL being intact. 3 months post surgery I had another MRI which showed the acl intact, I had another MRI at 6 months which showed the acl intact. My problem is, my ortho is hesitant to reconstruct because the mri'a all show it intact. He wasnt the surgeon who removed the pvns so he didnt see the tear first hand. So my question is, is there a technical reason as to why the scans are all negative when visually we know that there is a tear? I have a history of false negatives....and had a badly torn labrum which also came up negative on two mri's before being confirmed at arthoscopy.....are there physiologic anomalies that can cause the false negatives?

ANSWER: Hello, Nat.

So sorry you've hurt your knee. I'm a little confused about the above timeline. Was your ACL rupture discovered during the surgery to remove the PVNS? Was there an injury to your knee to cause the tear, or did it seem to happen out of nowhere? Do you have instability in that knee?

In my experience, if the ACL looks to be intact on an MRI, then it is intact. There is an easy, non-surgical test for ACL rupture, the Lachman test:

If you have metal screws in your knee from previous surgery, that would distort an MRI image.

Your ACL is like a rubber band. When it tears, the ends pull apart and there is a definite absence of ligament. In other words, when the ACL is torn, the torn ends do not stay together to look like a whole ligament. So, it's very obvious on MRI when the ACL is torn.

Unless your knee is unstable, I agree with your ortho. If you're still convinced your ACL is torn, get a second opinion and have another MRI.

Hope this helps,

---------- FOLLOW-UP ----------

QUESTION: Thanks for your reply Delia,

I dont think I described it quite right...or at least I missed some details.  This is what happened.  I knelt down to the ground to pick something up, felt a pop, had major pain for a few minutes, then it swelled to the size of a cantelope after about 20 min. Could bear weight at all. I saw the doc that day, had a MRI the next day assuming that the ACL was torn. The MRI reflected the acl intact, but showed a large tumor with a bunch of other crap in there which was the pvns. So I went to surgery to remove the pvns.  When they got in there, he has shocked to see the acl completely detached from the femoral wall and scarred to the pcl. He said it looked like it was a old injury. I had that same knee scope 1 year earlier for hoffa's syndrome and the acl was intact..clearly. He didnt fix the acl cause he didnt have consent for that. So while rehabing I kept having episodes of giving way and shifting I like to call it. So I had a 90 day mri for follow up, the mri showed the acl intact....which it very obviosly isnt as seen during surgery, I had a 6 month mri which showed it intact. My problem is that my doctor now isnt the doc that did the surgery (he has seen the operative pics and the operative report which both show the acl stump) he is hesitant to reconstruct because the clinical tests (lachmans, anterior drawer, and pivot shift) are all negative, but in real world situations it gives out under heavy stress. He is conflicted because the mri's are negative, the clinical tests are negtive, there are operative pics and report showing the rupture and pcl scarring, and my reports if it giving way. I am just really confused as to why the acl shows up intact on mri when it is clearly ruptured as seen during surgery. One doctor told me that sometimes when the acl is scarred heavily to the pcl, it can produce a firm end point which will give a false negative result. Its just frustrating that he is so stuck on the mri results and ignoring my symptoms and surgical results......I just am hoping to gather any information that will help support my problems

Hello, Nat.

Yes, this clarification helps. I tend to agree with the doctor that told you that the PVNS scar tissue could bind the ACL to the PCL. If the ACL is anchored on both ends, it WOULD look intact. And if the ACL is not attached to the appropriate points, you would probably experience some instability.

If you've had a PVNS tumor removed, that could also create instability because the ligaments joining bones at the knee would have stretched a little to accommodate the tumor tissue.

If you are able to modify your activities to minimize "heavy stress", you may be able to live without your ACL for a long time. Especially since it appears to be anchored at both ends. I've heard of football players that have continued to play without their ACL. I lived with ruptured ACL & had a trick knee for 14 years. (finally got it fixed)

On the other hand, if you've got your heart set on having your ACL repaired and your current ortho won't do it, then get a second opinion. I'd recommend you see a knee specialist, and bring all your evidence; reports, images, etc.

If you get another MRI, bring your previous MRIs with you to show the tech and explain your problem. S/He will be able to angle the images specifically to see the ACL, which may help to better visualize its origin & insertion points.

You may not find an orthopedic surgeon that will perform this surgery, especially since the ACL does appear to be intact. It may do more harm than good to try separating your ACL from your PCL.

Good Luck to you,


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Delia White


I am not qualified to interpret diagnostic imaging or to diagnose disease. Please consult a physician for that information. I am the photographer. I can tell you what to expect during most MRI, CT and X-ray procedures.


I now have more than 30 years experience in diagnostic imaging. My specialty is MRI. I am also very familiar with CT and the way we used to take x-rays (everything's digital now)!

I received my Bachelor of Science degree in Radiologic Technology.

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