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Can MRIs misdiagnose or miss a severe injury?

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I was doing hand-to-hand combat training in one of my classes, and my partner did a move completely wrong and I heard an awful popping noise and felt a painful "ZIP" running the entirety of my knee. It swelled up in three places almost immediately. Almost 3 weeks has now gone by and I am still constricted to crutches and can barely put any weight on it (Not for lack of trying.) When I do put what little weight I can on it, my knee is very unstable, pops all of the time, grinds, and blazing pain just comes up from all parts of my knee. It also has a tendency to give out on me. I had one X-ray within a week, that showed incredible amounts of fluid and some other sort of defect. I have now also had a regular, non-contrast MRI, which showed absolutely nothing. My doctor is confident it is just a sprain and that I don't need to see an orthopedic surgeon, however I am doubting that (I've had sprains before. The pain has NEVER been this bad.) Can MRIs misdiagnose or miss an injury, even a severe one?

I am a 22 year old female that has also had some issues with this knee in the past.
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replied May 25th, 2011
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You say the MRI did not show anything, but what did the MRI report actually say? I mean, was it actually a one line report that stated the anatomy was normal and there was no evidence of pathology? Usually radiologists will go out of their way to describe a study in great detail.

You state that the x-ray showed a lot of swelling (it's actually a referred finding in that only radiodense objects will show up on an x-ray). If that swelling was still present when the MRI was done, it would have been picked up. Effusion and soft tissue edema show up as bright white areas, that can be seen across the room.

The MRI is an incredibly sensitive study. However, if done too early, sometimes an effusion (fluid within the joint cavity) will mask a subtle injury. However, it will almost always pick up any major injuries.

There are certain structures within the knee that will cause an effusion. A torn ACL will usually give you an effusion over night, as it is usually a slow bleed. A meniscus torn from its peripheral attachments can set up an effusion within a few hours. An intraarticular fracture will also cause an effusion. Another cause would be a nondescript capsular tear. A patellar subluxation can give you an effusion from either a tear of the capsule, ligament, or an osteochondral fracture, or a combination of these.

A large effusion will show up as swelling (like a water balloon) across the top of the knee, above the patella (sometimes referred to as a horseshoe swelling), and in the dimples on either side of the patella (the dimples will actually puff out). The patella can actually float on a large effusion and one of the exam maneuvers is to actually push the patella down till it clicks, release it, and watch it rebound. If this sign is present, then there is a large effusion.

A tear of the collateral ligaments, will give you soft tissue edema, but not an effusion, as they are exterior to the joint capsule.

It takes a very good exam to differentiate an effusion from soft tissue edema. Also in the face of an acute injury, in a patient who is tender and apprehensive, an exam for instability and possible torn meniscus becomes very difficult. If a physician is not well trained in the orthopedic knee exam, injuries are sometimes overlooked.

Though the MRI is a very good tool, it is just that, a tool. The history and exam are the most important components of a diagnosis. Anytime the knee has a significant effusion, it should probably be seen by an orthopedic surgeon. Also, all orthopedic surgeon will do their own reading of the MRI. Any study has to be correlated with the patient's symptoms. No study should ever be used by itself. And most radiologists will end their report with the phrase: "...clinical correlation is needed.", as they rarely have a chance to see or examine the patient.

This sounds like your first major knee injury. The first one is always the worst, because of the unknown and apprehension, about what the future holds. So, you should probably see an orthopedic surgeon, since you are an active athlete and want to get back to activity as soon as possible. Be sure to take your x-rays and MRI with you (not the report, the actually studies).

Good luck.
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