Doctors may use imaging to diagnose and monitor the progression of osteoarthritis (OA), a degenerative joint disease.

Medical professionals use several imaging tests to diagnose and monitor people with OA, including X-rays, MRI scans, and CT scans.

OA is a condition that occurs when the cartilage between a person’s joints wears down over time, causing pain and stiffness. It usually occurs in people who are middle-aged and older and those who have experienced joint injuries.

This article provides an overview of the tests doctors use for OA, what a person can expect during each one, and what doctors look for in test results. It also discusses grading systems for OA and when it is best for a person who suspects they may have the condition to contact a doctor.

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Doctors typically use X-rays to look for changes in a person’s bones and soft tissues, such as:

  • bone growth, including sclerosis and bone spurs
  • cysts
  • decreased space between the bones, where the cartilage has worn away
  • fractures

Before an X-ray, a medical professional may ask a person to remove any clothing covering the affected area and any metal objects they may be wearing. They will also give the person a lead apron to protect them from radiation.

It is important to stay still during the scan to produce clear images. The procedure is painless and should only take a few minutes.

An X-ray of the knees may include:

  • a weight-bearing view
  • a side view with a slightly bent knee
  • a view of the kneecaps, usually with the person lying on a table with their knees bent

Healthcare professionals place the X-ray beam to maximize visualization of the space between the patella and femur or tibia. This is called a sunrise view or mountain view.

Doctors use MRI scans to get highly detailed images of the inside of a person’s body.

MRIs are more sensitive to soft tissues and short-term changes in OA than X-ray scans. Doctors use them to look for the narrowing of space between a person’s joints and lesions in the bone marrow.

During the scan, the person lies down inside the MRI scanner. Before the procedure, the doctor may provide the person with headphones to block out the sounds of the scanner. People will need to tell the doctor about any metal inserts in the body that may cause problems with the MRI machine.

Open MRIs are available for those with claustrophobia.

Long-standing OA, a degenerative joint disease, can lead to tearing, most commonly of the medial meniscus. This can occur without a specific precipitating injury. MRI scans can also help diagnose injuries such as these.

CT scans combine multiple X-rays to build an image of the inside of a person’s body.

In people with OA, doctors use CT scans to look for the formation of cysts, bone spurs, and bone growth in areas where cartilage used to be, also known as sclerosis.

Before the scan, the person may need to remove clothing and jewelry and change into a gown.

In some cases, a medical professional may inject the person with or ask them to ingest a substance known as contrast before the scan begins. Contrast helps illuminate certain areas in greater detail. The use of contrast may require fasting before the procedure.

During this type of scan, a person lies on a table that moves them through the ring-shaped CT scanner.

Ultrasound scans use sound waves to create a picture of the inside of a person’s body.

In people with OA, doctors use ultrasound scans to look for bone spurs and examine ligaments and synovium around the joints.

A bone scan, also known as bone scintigraphy, involves injecting a radioactive material known as a radiotracer into a person’s bloodstream.

These can detect bone growths, cysts, and bone marrow lesions. However, doctors rarely use bone scans for OA evaluation.

A specialized camera picks up the radiation from the radiotracer and turns this information into internal images of the person’s body.

Before the scan, the person may need to remove clothing and jewelry and put on a gown. After they receive the radiotracer injection, they must drink at least a liter of water and may need to wait up to 4 hours for the scan to begin.

Optical coherence tomography (OCT) is an imaging technique that uses infrared light to produce images of tissue at an extremely fine level of detail.

OCT may help show cartilage degeneration and roughness on the surface of the cartilage, which can be early signs of OA.

However, doctors do not yet use OCT to diagnose or monitor OA outside of clinical research.

When a doctor diagnoses OA, they will assign a grade with the diagnosis. This grade represents the severity of a person’s OA.

The grading system doctors use will depend on the joint they are assessing and the imaging procedure in question.

Most grading systems have between three and five grades. The most common grading system for OA is the Kellgren-Lawrence system. It uses five grades, with zero meaning no OA and five meaning severe OA.

Most OA grading systems are for assessing X-ray images. There are separate grading systems for MRI, CT, ultrasound, bone, and OCT scans.

It is best for people to contact a doctor if they regularly experience potential OA symptoms in their joints, such as:

These symptoms may be more severe in the morning and worsen with intense physical activity.

People may also want to consider contacting a doctor if they have multiple risk factors for OA, including:

  • previous joint injury
  • being middle-aged or older
  • having family members with OA
  • being assigned female at birth
  • having obesity

Doctors may use several imaging tests to diagnose and monitor the progression of OA. These imaging tests may include X-rays, MRIs, and CT scans.

Not every imaging test is suitable for every situation, and each diagnostic or monitoring tool has its advantages and disadvantages. A doctor will select the most appropriate one for each case.