What Are the Characteristics of a Normal Knee MRI?

C.B. Fox

A normal knee magnetic resonance image (MRI) is characterized by the absence of any injuries or disease. Though the exact anatomy of every person's knees differs slightly, a normal knee MRI will show strong, undamaged bones that are held together by ligaments that have not been torn. An MRI can also show how much fluid there is in the knee joint and the condition of the knee cartilage.

A diagram of the knee.
A diagram of the knee.

One of the main things that doctors look at when viewing an MRI of the knee are the ligaments and tendons. These structures do not show up well on x-rays, but they can easily become damaged, especially if a person is athletic and plays a sport in which the knees can be twisted or overextended. In a normal knee MRI, the ligaments and tendons will not have any partial or complete tears, which are conditions that indicate previous damage to the knee.

An MRI machine.
An MRI machine.

Though the bones of the knee can be seen on an x-ray, in some cases doctors may order an MRI of the knee to look more closely at the condition of the bones. In some cases, bone bruises and small fractures can be seen in an MRI of the knee joint. These problems indicate injuries and the possibility of damage to the tendons and ligaments. Patients with a normal knee MRI will not have cracks or bruises present on the femur, fibula, or tibia.

An MRI machine uses a magnetic field and radio waves to create pictures of internal organs and bone structures.
An MRI machine uses a magnetic field and radio waves to create pictures of internal organs and bone structures.

In a normal knee MRI, the wedge of cartilage known as the meniscus will look like a small triangle and will be properly positioned within the knee joint. This piece of cartilage is an important part of the knee because it acts as a shock absorber, protecting the bones from the stress created when a person walks, runs, or jumps. Tears in this structure indicate a problem that may require surgery. A normal knee MRI should also show that the meniscus is uniform in color, indicating that the cartilage has a uniform density.

It is also possible for doctors to observe the level of fluid present in the knee joint on an MRI. In a normal knee MRI, there will be enough fluid to properly lubricate the joint and cushion it, though not so much that there is swelling in the knee. Certain types of cancer can also be seen on an MRI image of the knee. A normal knee MRI will not show cancerous growths on the bones.

Radiologists can often spot knee abnormalities in MRI scans as the scan taking place.
Radiologists can often spot knee abnormalities in MRI scans as the scan taking place.

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