Preparing Joint Injection Sites in Horses (AAEP 2012)

When administering equine joint injections, veterinarians must take steps to minimize the risk of septic arthritis developing in the treated joint. Particularly in equine athletes, septic arthritis can be a devastating and debilitating complication, though aggressive treatment returns a large range (27-92%) of affected horses back to work.

Stephen Adams, DVM, MS, Dipl. ACVS, of Purdue University’s School of Veterinary Medicine, described appropriate site preparation and needle selection for septic arthritis prevention at the 2012 American Association of Equine Practitioners’ (AAEP) Convention, held Dec. 1-5 in Anaheim, Calif.

“Up to 80% of septic arthritis cases subsequent to joint injections are due to Staph species that, in fact, live on the horse’s skin, as well as the veterinarian’s skin,” Adams remarked. “One can never completely disinfect all layers of all portions of the skin.”

Still, preparing the injection site helps minimize the risk of joint contamination. In previous studies veterinarians have demonstrated that the presence of hair at the injection site does not inhibit antiseptics’ ability to effectively reduce the skin surface bacterial flora to an acceptable level. In other recent studies investigators proved that scrubbing with chlorhexidine was superior to using tamed iodine (Betadine solution).

Adams recommended that veterinarians perform a two-stage prep using sterile gauze sponges, chlorhexidine/saline, and isopropyl alcohol applied with gloves. He discouraged using prefabricated solutions, such as jars of gauze presoaked in Betadine or chlorhexidine solution, as they are susceptible to airborne contamination.

Needle size and direction of insertion can also impact the veterinarian’s chances of introducing tissue fragments and hair into a joint. Adams reported that using 18-gauge spinal needles in humans during arthroscopy produced identifiable tissue fragments in the joint 100% of the time. In two studies in which he sought to find methods to minimize the joint contamination risk, Adams came to the following conclusions:

  • Clipped or razored hair increases the risk of hair contamination into the joint by 2.4 times and 1.69 times, respectively.
  • Reusing a needle increases contamination risk by 1.7 times.
  • It is best to use the smallest needle possible; 22 gauge is better than 20- or 18-gauge.
  • After placing a needle in the joint, allow the needle to clear with dripping joint fluid when possible.
  • It is preferable to insert a needle at an angle to the joint surface rather than straight in.
  • It is preferable to use 22-gauge spinal needles (rather than larger needles) to decrease the risk of introducing hair fragments.
  • Removing the stylet (the fine wire that runs through the needle) from a spinal needle increases contamination risk fivefold.
  • Deep layers of the skin cannot be disinfected.
  • There is no need to remove hair prior to joint injection unless using 20-gauge or larger spinal needles.

In conclusion Adams stressed that veterinarians should take considerable care when preparing a site for joint injection, along with selecting optimal needle size and placement to minimize joint contamination and risk of developing infection.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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