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Diagnostic Tests Help Determine

the Root of Your Knee Pain

X-rays and MRIs are the two main tests your doctor may use to determine the root of your knee pain. Though similar in many ways, these two procedures give your doctor different ways of looking at joint health.  

Knee x-rays

An x-ray film is a simple, two-dimensional picture of the bones in the knee. The picture is generated on a piece of film by a radiation beam that passes through the knee from an x-ray machine.

Only bones show up on an x-ray image, so the picture can tell your doctor if you have a broken bone, bone fragments, or the later stages of osteoarthritis. An x-ray image doesn't show muscles, ligaments, tendons, and other soft tissues, so it can't diagnose things like a ligament tear or meniscal injury.

The machine is usually located in a room of its own, with the controls behind a window off to the side. The procedure is painless and quick; you only need to remain motionless for a short period of time. The procedure is also safe, since an x-ray uses only a small amount of radiation.

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MRI scans

In magnetic resonance imaging (MRI), magnetic waves (rather than x-rays) stimulate tissues of the knee to produce signals. These signals are picked up by a scanner and analyzed by a computer to create a series of cross-sectional views. An MRI is particularly helpful in detecting damage, disease, or inflammation of soft tissues, such as ligaments and muscles. The procedure is extremely safe, but requires you to remain motionless for a long time—usually 10 to 45 minutes.

People who feel uncomfortable in confined spaces sometimes find a standard tunnel-like MRI machine upsetting. Some newer models have a more open design—the scanner itself is overhead, but there are no walls on either side of the table to make you feel closed in.

An MRI is painless. It usually does not require an injection with special dyes. If you have anything magnetic in your body, such as a pacemaker, an MRI may not be appropriate. Make sure to tell your doctor about this.

Getting ready for your MRI scan

Some people do need to have a dye injected in order to improve the clarity of the images. If you’re one of these people, don’t eat or drink anything for 4 to 8 hours before the test. Even if you aren’t being injected with dye, cut back on caffeine before the exam. You won’t be able to get to the bathroom during the scan. Since you’re not allowed to wear any metal during the scan, leave your watch and other jewelry at home. If you are uncomfortable in cramped spaces, your doctor can prescribe medicine to help you relax during the scan. If you’re pregnant, tell your doctor. An MRI should not harm the baby, but the doctor still needs to be aware of your condition. Many MRI machines tend to be noisy. Ask about earplugs or headphones to block out the sound.

During the scan

After putting on a gown, you’ll lie down on the scanner’s table. The table will then slide into the machine. Typically, you’ll hear knocking sounds when the procedure is going on. Despite the loud noise, the technicians operating the machine in the other room can hear you if you need to talk to them.

After the scan

If you were given medicine to relax during the test, have someone drive you home afterwards. Otherwise you can drive home yourself. Your doctor will review the pictures and call you with the results, or review the results with you at your next office visit.

Learn about your options for reducing knee pain.

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