Horse Side Vet Guide ®

Equine Health Resource

Arthrocentesis, Synoviocentesis, Joint or Tendon Sheath Tap



This diagnostic involves the collection of synovial fluid (a clear pale yellow, viscous fluid normally found in the joint cavity or within a tendon sheath) to assess the health and status of a joint or tendon sheath.

In equine practice, this procedure is commonly used when a bacterial infection of the joint or tendon sheath is suspected.

The skin surface overlying a joint or tendon sheath is clipped and disinfected using a surgical scrub. The horse is restrained appropriately prior to needle insertion. Using sterile and meticulous technique, the vet inserts a needle into the joint and fluid is retrieved with a syringe. The fluid is evaluated visually. Then laboratory tests are run on it: a total protein is typically determined, and a cell count is performed.


The appearance of the joint fluid, and laboratory findings are helpful in determining the nature of a disease process within a joint or tendon sheath. The findings are especially valuable in confirming or ruling out bacterial infection.


Depending on the joint and particular case, fluid may be difficult to retrieve. In the process of harvesting, the fluid may become contaminated with blood, which reduces the diagnostic value. Any time a needle is introduced into a joint, there is a chance of infecting the joint, which can be very serious.


  • Can this procedure help make or refine a diagnosis?
  • Will this procedure provide additional information regarding treatment and prognosis?
  • Author: Doug Thal DVM Dipl. ABVP


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