Synovial fluid analysis

Q: A normal synovial fluid viscosity when expelled from the syringe to drop into a suitable receptacle will produce ______________ as it falls? - select one

A) a long string-like extension 

B) a circular formation 

Answer: A

The first step in the synovial fluid analysis is the gross inspection, which consists of three major components: 

• Clarity 
• Color
• Viscosity

The best way to test viscosity is to slowly expel the fluid from the syringe and allow it to drop into a suitable receptacle. A normal fluid usually starts forming a long, string-like extension as it falls. 

The inflamed joint releases proteolytic enzymes into the synovial fluid, leading to a loss of viscosity. This is an excellent way of quickly distinguishing a normal joint from an inflammatory joint. In contrast, in septic arthritis, the effusion may be relatively more viscous.

A clinician should be aware of some caveats. If the fluid sits for a long time, the test may become unreliable.

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References:

1. Pascual E, Jovaní V. Synovial fluid analysis. Best Pract Res Clin Rheumatol. 2005 Jun;19(3):371-86. doi: 10.1016/j.berh.2005.01.004. PMID: 15939364.

2. Martínez-Castillo A, Núñez C, Cabiedes J. Análisis de líquido sinovial [Synovial fluid analysis]. Reumatol Clin. 2010 Nov-Dec;6(6):316-21. Spanish. doi: 10.1016/j.reuma.2009.12.010. Epub 2010 Jun 26. PMID: 21794741.