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How do MRI and x ray work
November 28, 2011 8:48 AM   Subscribe

MRI ...what it shows and x ray missed

Had inflamed right knee. Orthopedist took x ray and said nothing there to be cause (gave Cortizone shots etc) and sent me for physical therapy..did nothing, so went to new doctor. He sent me for MRI. Discovered I had fracture. Question: why doesn't x ray show fracture?
Doctor said I need brace on knee for some two months and if that did not fix things, knee replacement. Question: how, after two months, can he tell if it worked or not unless I get another MRI?
posted by Postroad to Health & Fitness (7 answers total)
 
Question: why doesn't x ray show fracture?

MRIs show a more detailed image. The fracture may have been missed on the x-ray.

Question: how, after two months, can he tell if it worked or not unless I get another MRI?

If you have less or no pain, then it worked.
posted by amro at 8:52 AM on November 28, 2011 [1 favorite]


X-rays will not show a fracture until they are several weeks old.
posted by roomthreeseventeen at 9:13 AM on November 28, 2011


I fractured a finger and believe me, x-ray showed it just fine one hour later. X-ray, which is a one-dimensional image, can miss a fracture due to various reasons, one being the angle at which the pictures are taken. MRI can make images of you in all three dimensions, making it much easier to see whatever they're looking for.
posted by Dolley at 9:22 AM on November 28, 2011 [1 favorite]


X-rays will not show a fracture until they are several weeks old.

That's a ridiculous blanket statement.
posted by amro at 9:26 AM on November 28, 2011 [9 favorites]


And flat out wrong. I can clearly see the fracture in my x-rays, taken the very next day, after I fractured my hand.
posted by spicynuts at 9:35 AM on November 28, 2011 [3 favorites]


X-Rays and MRIs use fundamentally different methods to image a body. A CT scan is a 3D X-Ray. Generally, X-Rays and CTs are better at showing detail in bone, while MRIs are better at showing soft tissue.
posted by demiurge at 9:43 AM on November 28, 2011


Some fractures show up better than others on X-rays. Scaphoid fractures are pretty notorious for not showing up on X-rays (they show up somewhat better on MRI/CT), so you tend not to bother with the X-ray and treat them on the basis of clinical findings. On the other hand, a fracture to the middle of a long bone is usually pretty bloody obvious on an X-ray.

Joint replacements are functional things. The decision on whether or not to replace basically boils down to: will the replacement be better than the function the patient has at the moment? There are some other bits about weighing up the risks and benefit of the operation, and factoring in how long the replacement will last. But the baseline decision is about the joint function, and talking to you and testing the movement will give your doctor that information. You will probably end up having extra scans, so they can see what's going on in the joint, but they are extra information for the clinical decision, not the most important bits.
posted by Coobeastie at 9:50 AM on November 28, 2011


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