Causes of changes in synovial fluid from joints

Changes in synovial fluid in arthritis and arthrosis

Sign	Arthritis	Arthrosis
Number of cells	>10,000 in 1 µl	<400 in 1 µl
Dominant type	Polynuclear cells,	Lymphocytes, monocytes,
Cells	Plasma cells	Plasma cells
Phagocytes	6-80% and above	Less than 5%
Protein concentration	Significantly increased	Moderately elevated
	(>6 g%)	(<4 g%)

In clinical practice, joint damage is most often detected in the following diseases.

Infectious arthritis is divided into gonococcal (arises as a result of dissemination of gonococcal infection) and non-gonococcal - most often caused by Staphylococcus aureus (70% of cases) and Streptococcus, as well as in many viral infections (especially rubella, infectious mumps, infectious mononucleosis, hepatitis) and Lyme disease, caused by the spirochete Borrelia burgdorferi, transmitted by tick bites. Septic arthritis can be caused by fungi and mycobacteria.

Synovitis caused by crystals. Crystal deposition in joints or periarticular tissues underlies gout, pseudogout, and apatite disease. Polarization microscopy of the sediment obtained by centrifuging synovial fluid is used to diagnose gout and pseudogout. A polarization microscope with a red filter is used. Needle-shaped urate crystals, characteristic of gout, glow yellow (if their long axis is parallel to the compensator axis) and have strong negative birefringence. They are found both in synovial fluid and in neutrophils. Crystals of calcium pyrophosphate dihydrate, detected in pseudogout, have a variety of shapes (usually rhomboid), glow blue, and are characterized by weak positive birefringence. Complexes containing hydroxyapatite (specific for apatite disease), as well as complexes containing basic calcium and phosphorus salts, can be detected only by electron microscopy. It should be emphasized that hyperuricemia should not be considered a specific sign of gout, and calcification of joints - pseudogout, in any case, to confirm the diagnosis, a study by polarization microscopy is necessary.

Rheumatoid arthritis. If inflammation clearly predominates in one joint, synovial fluid should be examined to rule out infectious genesis of its origin, since rheumatoid arthritis predisposes to infectious arthritis.

Spondyloarthropathies. This group includes a number of diseases characterized by asymmetric oligoarthritis. Synovial fluid is examined to rule out septic arthritis. The following spondyloarthropathies are distinguished.

• Ankylosing spondylitis. Of the peripheral joints, the hip and shoulder are most often affected.
• Arthritis in inflammatory bowel disease: 10-20% of patients with Crohn's disease and ulcerative colitis develop joint damage, especially in the knees and ankles.
• Reiter's syndrome and reactive arthritis developing after urogenital or intestinal infections.
• Psoriatic arthritis develops in 7% of patients with psoriasis.

Systemic lupus erythematosus. Changes in the synovial fluid can be of both non-inflammatory (arthrosis) and inflammatory (arthritis) nature.

Osteoarthritis is a degenerative joint disease characterized by the “wear and tear” of articular cartilage followed by bone growths along the edges of the articular surfaces.

The most pronounced changes in the synovial fluid are found in bacterial arthritis. Externally, the synovial fluid may look like pus; the cell content reaches 50,000-100,000 in 1 μl, of which neutrophils make up more than 80%. Sometimes, in the first 24-48 hours of acute arthritis, the number of cellular elements may be less than 25,000 in 1 μl.

In patients with rheumatoid arthritis, synovial fluid examination is important to confirm the diagnosis and determine the local activity of the inflammatory process. In rheumatoid arthritis, the number of leukocytes in the synovial fluid increases to 25,000 in 1 μl due to neutrophils (25-90%), the protein content reaches 40-60 g / l. Inclusions, vacuoles similar to a bunch of grapes (ragocytes) are found in the cytoplasm of leukocytes. These cells contain phagocytized material - lipid or protein substances, rheumatoid factor, immune complexes, complement. Rhagocytes are also found in other diseases - rheumatic, psoriatic arthritis, systemic lupus erythematosus, bacterial arthritis, gout, but not in such quantities as in rheumatoid arthritis.

Changes in synovial fluid in various pathological processes

Sign	Type of changes
	Non-inflammatory	Inflammatory	Septic
Color	Straw yellow	Yellow	Varies
Transparency	Transparent	Translucent	Cloudy
Leukocytes, in 1 µl	200-2000	2000-75 000	>75,000
Neutrophils,%	<25	40-75	>75
Crystals	No	Sometimes	No
Bacteriological examination	Negative	Negative	Sometimes positive
Diseases	Osteoarthritis, traumatic arthrosis, aseptic necrosis, systemic lupus erythematosus	Rheumatoid arthritis, gout, pseudogout, systemic lupus erythematosus, seronegative spondyloarthropathies	Gonococcal arthritis, tuberculous arthritis, infectious arthritis (staphylococcal and streptococcal)

Monitoring the effectiveness of the treatment based on the results of synovial fluid testing is indicated for infectious arthritis.

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