Diagnosing a Knee Injury With the McMurray Test

Knee injuries can happen for any number of reasons, causing pain and inflammation that can interfere with walking, exercising, or performing everyday tasks. Pinpointing the problem can be difficult. In many cases, it's easier to describe when the pain happened—for example, when walking up steps or running—than where in the knee it is occurring.

One of the more common knee injuries involved the tearing of internal cartilage surrounding the joint. For this type of condition, diagnosis can be made simple by performing what we call the McMurray test.

What the McMurray Test Tells Us

The McMurray test (also known as the McMurray circumduction test) is used to detect internal tears in the knee joint. It is a procedure by which the knee is systemically rotated to identify where tears in the cartilage (called the meniscus) may have occurred or developed.

A torn meniscus is a common injury caused by the forceful twisting of the knee during sport, when running, or during a fall or misstep.

While many people assume that an MRI (magnetic resonance imaging) scan would be the first step in diagnosing this type of injury, the McMurray test is often enough to provide a definitive diagnosis.

How the Test Is Performed

The McMurray test is performed in a doctor's office with the patient undressed to his or her underwear. Once undressed, the person will be asked to lie flat on the examining table.

The procedure itself involves two steps, as follows:

• The doctor holds the knee in one hand and the sole of the foot in the other.
• The knee is then fully bent and pulled toward outwards in a "knock-kneed" position.
• Meanwhile, the doctor will start rotating the foot internally while extending the knee.
• Any pain or "clicks" serves as a positive diagnosis of a lateral tear of the meniscus.

The second half of the test proceeds similarly: 

• The doctor holds the knee in one hand and the sole of the foot in the other.
• The knee is fully bent and pulled toward outwards in a "bow-legged" position.
• The doctor will then start rotating the foot externally while extending the knee.
• Any pain or "clicks" serves as a positive diagnosis of a medial tear of the meniscus.

A test is considered positive when a click is felt over the meniscus as the knee is brought from full flexion (completely bent) to 90 degrees. 

Advantages and Disadvantages

The McMurray test is especially useful for detecting tears in the posterior (back) aspect of the knee. Central tears are sometimes detected with this maneuver.

By contrast, anterior tears (to the front of the knee) are not easily diagnosed and may require an MRI or arthroscopic investigation to pinpoint the damage.

Overall, the McMurray test was shown to have a 78.5 percent specificity (the percentage of results correctly negative) and a 79.7 percent sensitivity (the percentage of results correctly positive) in diagnosing meniscal tears.An MRI, by contrast, had a reported specificity of 85.7 percent and sensitivity of 78.3 percent.