Atlas of Knee MRI Anatomy

Magnetic resonance imaging (MRI) is a radiologic procedure that uses a magnetic field and radio waves to develop detailed image cross-sections of the body, including the knee⁽¹⁾. 

Medical images from an MRI allow medical professionals to distinguish body tissues, including the meniscus (shock absorbers in the knee), cartilage, tendons, and ligaments. The images may also help physicians to distinguish normal, healthy tissues from dead tissues⁽²⁾. 

Doctors may recommend a knee MRI if a patient experiences the following⁽³⁾:

• An abnormal result on a bone scan or knee X-ray
• Joint fluid buildup behind the knee (Baker cyst)
• Weakened knee
• Knee cap injury
• Knee instability
• Knee joint infection
• Fever and knee pain
• Knee locking upon movement
• Signs of damage to the knee muscle, ligaments, or cartilage
• Knee pain that does not respond to treatment

Although abnormal results of a knee MRI may be due to a sprain or ligament tear, they may also be due to⁽⁴⁾:

• Knee degeneration
• Cartilage injuries
• Arthritis 
• Broken bone
• Bone tumor or cancer
• Osteonecrosis (a disease caused by abnormal blood supply to the bone)
• Baker cyst
• Bone infection
• Inflammation
• Knee cap injury

What to Expect From a Knee MRI

Before the Procedure

Patients must notify their doctor if they are claustrophobic or experience pain when on their back for over 30 minutes.

Before the procedure, the patient must tell the radiologic technologist if they have any of the following⁽⁵⁾: 

• Artificial heart valves
• Brain aneurysm clips
• Pacemaker or heart defibrillator
• Cochlear or inner ear implants
• Kidney disease or if they are undergoing dialysis
• Artificial joints
• Vascular stents or scaffolds
• History of working with sheet metal 

Patients must disclose the information above to avoid any complications once they enter the room with the MRI machine. Other materials prohibited in the room with the MRI scanner include: 

• Pens, eyeglasses, and pocket knives
• Jewelry, watches, and credit cards 
• Pins, metal zippers, hairpins, and other metallic items
• Removable dental work

They must also tell the attending technologist about any allergies they may have or if they are pregnant. 

During the Procedure

If the patient undergoing knee MRI has claustrophobia, their doctor may administer sedatives before the procedure.

The radiologic technologist helps the patient lie down on the scanning table feet first with their arms at their side. Coils may be placed around the patient’s body for better image quality.

Coils are devices used by radiologic techs to improve the quality of the medical images produced by the MRI machine⁽⁶⁾.

The scanning table moves the patient’s lower body to the center of the machine.

During the procedure, the patient may not feel anything. However, they may hear the MRI machine’s intermittent humming and thumping sounds. The attending radiologic tech may provide the patient with earplugs to help mask the noise.

The patient must lie still during the procedure. Excessive movement may blur the images from the machine and trigger errors⁽⁷⁾.

The rad tech must always be able to hear and see the patient during the procedure. A knee MRI exam takes approximately 45 to 60 minutes to finish⁽⁸⁾.

The rooms are equipped with intercoms to allow patients to speak to someone at any time. Some hospitals also have televisions and headphones in the scanner rooms to help patients pass the time.

In some cases, the patient’s radiologist may decide on using a contrast agent, like dye, to improve the quality of the images. The physician may administer the dye through an intravenous injection.

After the Procedure

After the MRI, the patient may drink, eat, or drive as normal. However, if the patient took a sedative for the procedure, they need to have someone drive them home.

An imaging physician may examine and interpret the medical images from the patient’s knee MRI. The physician may send their report to the consulting doctor, who may review the patient’s exam results.

Risks of Knee MRI

An MRI exam carries no risk of radiation exposure. Patients reported no side effects after using magnetic fields and radio waves for the procedure⁽⁹⁾.

However, some patients may experience allergic reactions to the contrast dye, which contains the chemical gadolinium. Patients must disclose their allergies to their physicians before undergoing an MRI procedure to avoid severe allergic reactions.

Although considered safe, gadolinium may be harmful to people who require dialysis for their kidney problems. If a patient suffers from kidney disease, they must inform their doctor before the test⁽¹⁰⁾.

The MRI scanner’s strong magnetic fields may also cause pacemakers and other medical accessories not to function well. These magnetic fields may also cause small pieces of metal inside the body to shift or move from their place.

To minimize the risks, patients must not bring any metallic items inside the scanner room.