Several tests are commonly used to determine or rule out the causes of knee pain. A physician will take a medical history to learn about any injuries or conditions that may be related to the knee pain. A physical examination will include movement of the knee to determine how much it can bend, straighten and rotate. The patient may be asked to walk or squat to further assess knee function.

The physician may conduct a pain assessment and may order tests such as:

• X-ray. Uses low-dose radiation to create images of bones.
  
  
• CAT scan (computed axial tomography). Uses multiple x-ray images combined to provide a three-dimensional image of the knee. CAT scans can show soft tissue, such as ligaments and muscles.

• MRI (magnetic resonance imaging). Uses powerful magnets to create cross-sectional images of tissues. MRIs are useful in diagnosing soft tissue damage or disease.
  
  
• Arthroscopy. Specialized tube with optic fibers (arthroscope) is inserted in an incision in the knee. It can provide images of the interior of the joint. Special instruments may also be inserted to remove loose bone or cartilage fragments or repair injuries.
  
  
• Bone scan. A small amount of radioactive material is injected into the bloodstream and is detected with a scanner. This type of radionuclide imaging may detect abnormalities in blood flow or other cell activity.
  
  
• Blood tests. May be used to identify or rule out the possibility of infection and certain kind of arthritis.
  
  
• Biopsy. A small amount of tissue can be removed from the knee and examined for abnormalities.