Study: Joint Injections have Low Risk of Synovial Sepsis

Injecting medication directly into a horse's joint might make some owners wary of complications. But British researchers have recently shown that, when careful aseptic techniques are used, the risks are actually very low.

Synovial sepsis—infection of the intra-joint (synovial) area—following therapeutic injection is “extremely low” when the veterinarian uses aseptic techniques, said Lewis C.R. Smith, BVetMed, CertES(Orth), DipECVS, MRCVS, of Rossdales Equine Hospital in Newmarket, Suffolk, England.

Smith and colleagues reviewed all 9,456 intra-synovial medications (ISMs) administered by nine different veterinarians in the practice over a five-year period (2006-2011). They administered these injections to 1,732 horses—mostly Thoroughbred racehorses—in 4,332 sessions. The most commonly medicated joints were the knee, the front fetlock, and the hind fetlock.

After reviewing the records, the team noted only 12 complications from nearly 9,500 injections—and only four of those actually developed into synovial sepsis. All four synovial sepsis cases were successfully treated with joint lavage, and the horses returned to their regular training and performance routine in two to six months, Smith said.

One specific injection appeared to carry an increased risk of synovial sepsis compared to the others, he said. While only 15 polysulfated glycosaminoglycan (PSGAG) injections were given (0.0016% of the ISMs administered), this drug was associated with two of the four (50%) synovial sepsis cases.

The other two sepsis cases resulted from corticosteroid injections, he said. Of the 12 complications, two resulted from PSGAG injections (both leading to synovial sepsis), and 10 resulted from corticosteroid injections (20% leading to synovial sepsis).

Additionally, Smith said, administering the antiobiotic amikacin with the injection appeared to have a protective effect, he said, as three of the four synovial sepsis cases stemmed from injections in which amikacin was not used. Smith said he recommends including an antimicrobial in ISM protocol, especially when using PSGAGs.

Smith also outlined the proper aseptic technique to follow during joint injections, including the use of sterile materials and thoroughly scrubbing the skin covering the joint prior to injection. For the ISMs included in the study, veterinarians scrubbed the horse's skin for five minutes using a chlorhexidine-based scrub, applied in concentric circles. Then, they cleaned the scrub off the area with surgical spirit (alcohol). Veterinarians drew injections from single-use bottles while wearing sterile surgical latex gloves, with care taken to ensure that the gloves were not contaminated prior to injection.

Ensuring an aseptic environment during injections did not require hospitalization—in fact, all of the horses included in the study were treated in the field, Smith said. Clipping (because some individuals believe hair at the injection site contributes to increased bacteria flora) was also unnecessary, as none of the horses were clipped for the procedure.

“As veterinarians we do worry about causing a complication, especially one a serious as synovial sepsis,” said Smith. “So while I will continue to warn clients over the risk, at least now I can give them an accurate figure.”

The study, "Risks of Synovial Sepsis Following Intrasynovial Medication in Ambulatory Practice, 2006–2011: 9456 Intrasynovial Injections," was published in the Equine Veterinary Journal

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

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