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ESSENTIALS OF DIAGNOSIS

  • The major components of synovial fluid analysis are assessing fluid clarity and color, determining the cell count, examining for crystals, and obtaining culture.

  • Joint aspiration should be performed promptly whenever septic arthritis is suspected because synovial fluid cell count, Gram stain, and culture are necessary to establish or exclude joint space infection.

  • Synovial fluid analysis can be diagnostic in cases of crystalline arthritis.

  • The synovial fluid white cell count is the most reliable means of distinguishing noninflammatory (<2000 cells/mm3) from inflammatory (>2000 cells/mm3) forms of arthritis.

  • Joint injections with corticosteroid are often the swiftest means of providing relief to patients with inflamed joints.

Joint aspiration (arthrocentesis) is a simple and important diagnostic and therapeutic procedure that can be performed in a rheumatologist’s office. Analysis of synovial fluid obtained from arthrocentesis is an integral component for the diagnosis of many rheumatologic conditions. Joint injections are safe and effective in the treatment of a variety of rheumatologic conditions. A fundamental knowledge of musculoskeletal anatomy, coupled with experienced supervision, are important in improving outcomes and minimizing complications.

INDICATIONS FOR JOINT ASPIRATION

The most important indication for joint aspiration is removal of fluid from a swollen, inflamed joint for synovial fluid analysis. Joint aspiration should be performed promptly when septic arthritis is suspected, such as the presence of an unexplained, acute monoarticular arthritis. Synovial fluid cell count, Gram stain, and culture are necessary to establish or exclude joint space infection, while the presence of crystals can be diagnostic of a crystalline arthropathy.

Removal of fluid from a tense, inflamed joint provides significant therapeutic benefit, often with immediate pain relief that allows weight bearing and movement of the affected joint. Aspiration of fluid from an infected joint decreases intra-articular pressure, the number of activated inflammatory cells, and the concentration of destructive enzymes and cytokines that can damage articular and periarticular structures. Although septic joints can be aspirated daily to prevent reaccumulation of inflammatory synovial fluid, current practice has moved to arthroscopic lavage, debridement, and drain insertion rather than repeated arthrocentesis. Removal of blood from a hemarthrosis may be beneficial by reducing intra-articular pressure and preventing the development of adhesions. Furthermore, untreated recurrent hemarthrosis may lead to joint damage.

SYNOVIAL FLUID ANALYSIS

Synovial fluid is normally present in a small volume in each joint. For example, even in a large joint such as the knee, the amount of synovial fluid is estimated to be less than 5 mL. Synovial fluid is an ultrafiltrate of plasma supplemented with protein and proteoglycans produced by fibroblast-like synoviocytes. The fluid forms a thin interface between surfaces of articular cartilage allowing for friction-free movement. The major proteoglycan found in synovial fluid is the high-molecular-weight molecule hyaluronan which gives the fluid its characteristic viscosity while the glycoprotein lubricin imparts the lubricating capacity of synovial fluid. ...

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