Diagnosing Knee Problems

Last Updated: Nov. 1, 2003

What causes knee problems?
There are two general kinds of knee problems: mechanical and inflammatory.

Mechanical knee problems: Some knee problems result from injury, such as a direct blow or sudden movements that strain the knee beyond its normal range of movement. Other problems, such as osteoarthritis in the knee, result from wear and tear on its parts.

Inflammatory knee problems: Inflammation that occurs in certain rheumatic diseases, such as rheumatoid arthritis and systemic lupus erythematosus, can damage the knee.


Diagnostic Tests
Following a physical examination, the doctor may use one or more tests to determine the nature of a knee problem.

X-ray (radiography): An X-ray beam is passed through the knee to produce a two-dimensional picture of the bones.

Computerized axial tomography (CAT) scan: X-rays lasting a fraction of a second are passed through the knee at different angles, detected by a scanner, and analyzed by a computer. This produces a series of clear cross-sectional images (“slices”) of the knee tissues on a computer screen. CAT scan images show soft tissues such as ligaments or muscles more clearly than conventional X-rays. The computer can combine individual images to give a three-dimensional view of the knee.

Bone scan (radionuclide scanning): A very small amount of radioactive material is injected into the patient’s bloodstream and detected by a scanner. This test detects blood flow to the bone and cell activity within the bone and can show abnormalities in these processes that may aid diagnosis.

Magnetic resonance imaging (MRI): Energy from a powerful magnet (rather than X-rays) stimulates knee tissue to produce signals that are detected by a scanner and analyzed by a computer. This creates a series of cross-sectional images of a specific part of the knee. An MRI is particularly useful for detecting soft tissue damage or disease. Like a CAT scan, a computer is used to produce three-dimensional views of the knee during MRI.

Arthroscopy: The doctor manipulates a small, lighted optic tube (arthroscope) that has been inserted into the joint through a small incision in the knee. Images of the inside of the knee joint are projected onto a television screen. While the arthroscope is inside the knee joint, removal of loose pieces of bone or cartilage or the repair of torn ligaments is also possible.

Biopsy: The doctor removes tissue to examine under a microscope.


Source: National Institute of Arthritis and Musculoskeletal and Skin Diseases

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