A CT (computed tomography) scan is a type of X-ray that can show cross-sectional images of a specific area of the body. A CT scan of your knee helps doctors diagnose disease or inspect injuries to your knee.
A CT scanner circles the body and sends images to a computer that makes detailed pictures from the images. This allows doctors and trained technicians to see the muscles, tendons, ligaments, vessels, and bones that make up your knee.
A CT scan is also sometimes referred to as a CAT scan. It is done at a hospital or specialized outpatient testing facility.
A CT scan provides your doctor with more detailed images of the inside of your knee than traditional X-rays do. It gives your doctor an internal view of your knee without making an incision and performing exploratory surgery. This can help your doctor provide a more accurate diagnosis for knee problems including:
- collection of pus (abscess)
- fractured bone
- torn ligaments or tendons
While there are very few risks associated with a CT scan, occasionally the dye used in the procedure can cause temporary damage to your kidneys. This risk is greater if your kidneys have already been affected by disease or infection. However, there are newer dyes that carry much less risk to the kidneys.
As with any X-ray, there is some exposure to radiation. While typically harmless to adults, it is an important issue for women who are pregnant or could be pregnant as the radiation is not good for a developing fetus. Tell your doctor if you are pregnant or believe you could be pregnant.
Before your exam, your doctor will provide you with complete instructions on how to prepare for your knee CT scan.
In some cases, your doctor may use contrast dye that helps provide better images by reacting with the imaging equipment. If this is the case and you’ve had an allergic reaction to similar dyes in the past, tell your doctor before the test. The most common dye used contains iodine, so tell your doctor if you’re allergic to iodine (NIH).
If you are receiving dye, your doctor may instruct you to avoid foods and liquids four to six hours before the CT scan.
You’ll also have to remove all your jewelry and change into a hospital gown before the surgery. You will need to remove any braces or bandaging you are wearing over your affected knee.
If your doctor is using contrast dye for the scan, you’ll be given the dye intravenously. This means that a nurse will inject the contrast dye into one of your veins. You’ll typically need to wait an hour for the dye to work its way through your body before the scan can begin.
The CT machine looks like a large doughnut made of metal and plastic that is standing on its side. It has a sliding, moveable bench in its center. During the scan, you’ll lie on the bench, and the technician will move the bench in and out of the machine using a remote control.
The technician may require you to lie in a specific position during the test. He or she may use pillows or straps to ensure you stay in the correct position long enough to get a quality image. You may also have to hold your breath briefly during specific scans. Talk to your doctor beforehand if you think you’ll have trouble staying still.
After a round of scans, you may be required to wait for a short time while the technician reviews the images to ensure they are clear enough for your doctor to read them correctly.
A typical CT scan of the knee takes between 30 and 45 minutes to complete.
After the test, you will be able to go about your day normally.
If you’ve received contrast dye, you may want to drink extra fluids to help flush the dye out of your system. All traces of the dye are typically gone within 24 hours.
Results for a knee CT scan usually take a day to process. Your doctor will schedule a follow-up appointment to discuss the results and how to proceed based on the evaluation of your scans.