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Tests and diagnosis
By Mayo Clinic staffPinpointing the reason for knee pain can be challenging because of the wide range of possible causes. Often, a comprehensive medical history and thorough physical exam play a larger role in knee pain diagnosis than does any single test.
In addition to asking about your pain — its location, what it feels like, when it started, what makes it seem better or worse — your doctor may inquire about your exercise program, sports you play or used to play, and any previous injuries to your knee joint. During the physical exam, your doctor is likely to inspect your knee for swelling, pain, tenderness, warmth and visible bruising; check your range of motion; and perform a number of maneuvers to evaluate the integrity of the structures in your knee.
One of these maneuvers, the Lachman test, helps detect injuries to the ACL. In the Lachman test, your knee is bent at a 30-degree angle and your doctor gently moves your lower leg forward at the knee. If your lower leg moves freely without reaching a firm endpoint, you're likely to have a torn ACL. Other maneuvers assess the PCL, tendons and menisci.
These tests may not be accurate in some instances — when movement in your knee is restricted by swelling or by contracted muscles in the back of your leg, for example. In that case, your doctor may order a magnetic resonance imaging (MRI) test or another imaging test to aid in the diagnosis.
Unlike an X-ray, which isn't useful for viewing ligaments, tendons and muscles, an MRI can help identify injuries and damage to soft tissue. MRI uses a powerful magnet to create 3-D images of the inside of your knee. Generally, no special preparation is needed for this test; however, if you're bothered by confined spaces, be sure to let your doctor know. He or she may be able to send you to a facility with an open MRI machine, which allows you to see outside of the machine, or you may be prescribed a mild sedative for the test.
Depending on the type of injury, your doctor may order other imaging tests, including:
- X-ray. Your doctor may first recommend having an X-ray, which can help detect bone fractures and degenerative joint disease.
- Computerized tomography (CT) scan. This specialized X-ray, which creates cross-sectional images of the inside of your body, may help diagnose bone problems and detect loose bodies.
If your doctor suspects an infection, gout or pseudogout, you're likely to have blood tests and sometimes arthrocentesis, a procedure in which a small amount of fluid is removed from your injured joint with a needle and sent to a laboratory for analysis.
