The American Association of Equine Practitioners Performance Horse Committee put on a webinar for veterinarians this year about the differences between post-injection joint flares and infections in horses. The four-person panel included Steve Adair, DVM, DACVS, DACVSMR, of the University of Tennessee College of Veterinary Medicine; Michael Fugaro, VMD, DACVS, of Mountain Pointe Equine Veterinary Services in Long Valley, New Jersey; Cheryl Malin, DVM, of Align Equine Veterinary Services in Stettler, Aberta; and Meghan McCarthy, DVM, of Kansas State University College of Veterinary Medicine.
The panelists noted that joint flares rarely occur from trauma; most are subsequent to an injection of medication into a synovial structure. The clinical presentation tends to be a severe, acute lameness with effusion of the joint or tendon sheath and/or surrounding soft tissues. There might be heat in the area and an amplified digital pulse. The horse is usually reactive to palpation or manipulation with static flexion or when asked to stand on the painful limb with the opposite limb off the ground.
Diagnostic tools are important for distinguishing a flare from sepsis. All the panelists agreed it’s difficult to discern the difference between a flare and sepsis, at least initially. Adair said timing of the problem might yield some information. For example, flares develop a bit faster than sepsis and tend to respond quickly to NSAIDs. It might take three to five days post-steroid-injection for a horse to show signs of infection but only 24-48 hours for signs of a flare. Fugaro said he has experienced flares develop at 6-8 hours.
A thorough physical and lameness exam (when possible) helps identify any injury or wound, confirm the presence of cellulitis, and localize the painful area. It is useful to pursue imaging with radiographs, with or without contrast agents, and/or ultrasound to look for swirling fluid with debris or fibrin strings. Findings can be compared to the opposite, normal limb. Synoviocentesis provides invaluable information about cell counts and total protein of the affected joint or tendon sheath.
Joint Fluid Analysis Survey Results
Fugaro shared the results of a survey about joint fluid interpretations answered by nine surgeons in private referral surgery centers and one at a university. Most reported that a total nucleated cell count < 1,000 is normal. Most of the participants reported flare cases having cell counts less than 20,000-30,000 with the presence of nondegenerate neutrophils. In contrast, the majority interpreted cell counts greater than 20,000-30,000 with the presence of degenerate white blood cells (> 90%) to be their cutoff for a septic synovial structure. They also reported that chronic septic synovial structures can have significantly lower cell counts (> 5,000).
Total protein < 2 g/dl is normal for synovial structures. While a total protein value with a flare may be 2-4 g/dl and sepsis > 4 g/dl, many of the survey respondents stated that protein measurements were a less reliable parameter for diagnosis.
All the respondents said they perform aerobic culture and antimicrobial sensitivity (C/S) testing, while half also do anaerobic C/S. Fungal culture is usually only evaluated in chronic, intractable cases.
All respondents said systemic bloodwork is not helpful except in the case of foals, especially to check BUN and creatinine if a foal is to be treated with an aminoglycoside.
Half the respondents considered serum amyloid A (SAA) useful in this scenario. That said, they reported that it is not useful as a standalone test but can help corroborate other diagnostic procedures. Initial SAA levels could provide a baseline for later comparison in the following days.
Advice for Managing Flares and Sepsis
Here are some key takeaways from the presentation to help equine practitioners mitigate both flares and sepsis:
- If a veterinarian often sees flares following synovial injections, he or she should check scrub containers and supplies, and autoclave appropriate equipment.
- If a low-motion joint is affected and only a small volume of fluid is obtainable, it helps to irrigate the joint with saline, then aspirate the joint and submit for culture.
- Joint fluid can also be assessed for cell count, cytology, and total protein to help differentiate between a flare or sepsis.
- If referral is an option, don’t start the horse on antimicrobial drugs (AMDs) so the referral practitioner can obtain samples for a culture.
- If using AMDs, a broad-spectrum combination of gentamycin and potassium penicillin is most efficacious. Adair said it’s important to be aggressive with antimicrobial therapy as soon as possible. Besides systemic AMDs, regional limb profusion every 2-3 days is beneficial. Adair advised trying interosseous perfusion if veins are so blown that regional limb perfusion is not an option.
- For treating sepsis, synovial lavage of the joint with sterile Lactated Ringer’s or physiological saline solution (PSS) is very effective even on a standing horse. Local anesthesia, regional or intrasynovial, allows the practitioner to insert multiple needles—at least 14 gauge—to irrigate with at least 1 liter of flush and allow egress through many ports.
- Arthroscopy is best if synovial fluid is full of fibrin and floaters, as these won’t pass through a needle. Arthroscopy allows the veterinarian to visualize the joint surfaces and thoroughly clean and lavage synovial structures and joint surfaces.
- If the horse is extremely painful and not wanting to bear weight, Adair urged practitioners to guard against contralateral limb laminitis with Soft-Ride boots or dental impression material. Use NSAIDs to get the horse as comfortable as possible.
The Importance of Communicating With Clients
Communication with the client is key to managing adverse problems related to joints. Before injecting a synovial structure, Adair recommended being up front and clear with the client about potential risks and complications.
Obtain informed consent, preferably in writing, especially if using an extra-label product. Adair said informed consent puts some of the responsibility back on the owner for the decision to proceed. Document in the medical record that you communicated to the client about potential risks. The panelists stressed the importance of filling out the horse’s medical record immediately rather than waiting a few days, especially if there is a possibility of litigation.
If infection is a concern, it is important to communicate and be transparent about it with the client, maintain clear and thorough medical records, and contact your liability insurance carrier. Insurance carriers often provide an advocate to help walk veterinarians through unfortunate complications.
If a referral center is handling an infected joint, the referral veterinarians should remember that “bad things happen to good people” and avoid making any comments that would “throw a referring veterinarian under the bus.”
McCarthy recommended having every new client sign a form stating that “they are aware of the inherent risks of equine practice, that they authorize the veterinarian to perform medical treatment, and that sometimes things go wrong but everything possible is attempted to prevent poor outcomes.” This covers all manner of veterinary care, diagnosis, and treatment, not just joint injections.
Take-Home Message
The panelists urged practitioners to consider why they are putting a needle into a horse’s joint in the first place. Is the horse, according to the owner, “due for injections” or going to a big event soon? Has their trainer insisted this is normal protocol and needs to be done? Veterinarians should remember to advocate for the best interests of the horse rather than succumb to client and trainer pressures. Take all precautions for sterile technique, and communicate thoroughly with the client about potential risks and complications.
Related Reading
- Chlorhexidine Flush: Potential Treatment for Septic Arthritis in Horses?
- Daily Vet Life: Diagnosing and Treating Septic Tenosynovitis
- Administration Method Does Not Affect Antibiotic Levels After IVRLP
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