A correct diagnosis is essential when a patient suffering from arthritis presents to a doctor. The most important tools are a thorough history and a physical exam. Diagnostic procedures such as magnetic resonance imaging and laboratory tests can also be useful. Another important element is the examination and diagnosis of joint fluid. This fluid, also known as synovial fluid (SF), plays an important role in normal joints. It is a viscous liquid that synovial cells, which are the cells that make the lining of a joint, produce. Normal circumstances only a small amount is produced.
Cartilage
SF’s purpose is to nourish cartilage and provide lubrication to the joint. It is important to examine SF when evaluating a patient suffering from arthritis. The fluid should be examined for appearance, total white cell count, types of white cells, and cultured for bacteria. Normal SF is clear and slightly yellowish, clear enough to read newsprint. SF with a lot white blood cells will appear cloudy and turbid. An inflammatory form arthritis can cause cloudy synovial fluid. It is important to consider infection if it becomes very cloudy.
Normal conditions will see less than 200 white cells per cubic ml of SF specimen. Infection can cause a dramatic increase in the number of white cells and a change in the type of white cell. Infection is almost always a problem in joint fluids that contain more than 100,000 white blood cell per cubic milliliter. If the fluid is suspected of being infected, it should be cultured. It is possible to diagnose a condition by carefully examining the SF for crystals.
Gout and Pseudogout
Gout and pseudogout are the most common forms crystal-induced arthritis. A polarizing microscope is essential to diagnose crystal-induced arthritis. Monosodium urate crystals in gout are very different from calcium pyrophosphate crystals, which can be seen in pseudogout.
Monosodium-urate crystals have a needle-like shape, while calcium pyrophosphate crystals have a stubby rod shape. One caveat: Just because crystals exist doesn’t necessarily mean that there isn’t an infection. It is important to culture joint fluid. Rarely, fat drops can be seen in SF. This could indicate a fracture or a disorder in the pancreas.