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Clinical Summary

Synovial fluid normally appears colorless or straw colored (see Fig. 25.55), viscous, and stringy. Arthrocentesis is performed in patients with a joint effusion or suspicion for joint inflammation or infection. Fluid can appear transparent (normal), translucent (mild inflammation), opaque (purulent inflammation), or bloody (traumatic tap, trauma, or bleeding disorders). Synovial fluid is normally viscous due to high levels of hyaluronic acid. These characteristics make a long “string” when a drop of normal fluid is expressed from a syringe.

FIGURE 25.55

Synovial Fluid—Normal. Normal synovial fluid should be straw-colored fluid that is easy to see through. (Photo contributor: Amy C. Ramsay, MD.)

Management and Disposition

Patients with a septic joint (see Fig. 25.56) require orthopedic consultation and hospitalization. Joint washout is frequently necessary. Fat globules in bloody synovial fluid suggest an intra-articular fracture requiring orthopedics consult. Gout (see Fig. 25.57) should be treated with steroids and pain medications. Osteoarthritis should be treated with nonsteroidal anti-inflammatory drugs.

FIGURE 25.56

Synovial Fluid—Gout. Crystals were identified supporting the diagnosis of gout. Note the turbid, dark appearance suggesting inflammatory cells. (Photo contributor: Lawrence B. Stack, MD.)

FIGURE 25.57

Synovial Fluid—Septic Joint. Purulent aspirate from the right hip is obtained. Cell count suggests and culture confirms a septic joint. (Photo contributor: Lawrence B. Stack, MD.)


  1. Do not aspirate through an area of cellulitis or psoriasis to avoid seeding a joint with bacteria.

  2. Do not perform arthrocentesis if the international normalized ratio (INR) is greater than 3 due to risk of precipitating a hemarthrosis.

  3. The normal “string sign” of synovial fluid is lost with inflammatory conditions.

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