Equine - Timely Topics

Synovial infections in adult horses

Elizabeth Taylor, DVM

Septic arthritis and tenosynovitis are common orthopedic conditions in horses that carry serious complications. Sequela to septic arthritis and tenosynovitis include arthritis, irreversible cartilage damage, fibrosis and intrathecal adhesions, and severe lameness sometimes requiring humane euthanasia. It is important that these conditions be recognized promptly in order to instill immediate and accurate diagnosis and treatment aimed at eliminating the infection, reducing pain and inflammation and ultimately returning the horse to function.

In adult horses, joint or tendon sheath infection usually results from contamination via wounds. Because the distal limb of horses is poorly covered with soft tissue, synovial structures are located very superficially and are prone to contamination following many lacerations, including heel bulb lacerations, palmar/plantar lacerations to the pastern, dorsal lacerations to the fetlock, etc.

It is very important to contact your veterinarian if your horse has a laceration of the distal limb. Typically, horses are severely lame (grade 4/5), however if the affected synovial structure is open and draining, lameness can be less severe. Frequently there is marked effusion, heat and sensitivity to the touch of the synovial structure and the horse may not be responsive to nonsteroidal anti-inflammatories if severe infection is present. It is vital that your veterinarian obtain a sample of synovial fluid for analysis if a synovial infection is suspected. Grossly, normal fluid should be pale yellow, clear and viscous.

The mainstay of treatment is to remove bacteria, devitalized tissue and other debris and reduce pain and inflammation. This is accomplished by administration of systemic and local antimicrobials, systemic nonsteroidal anti-inflammatories and physical removal of bacteria via through-and-through needle lavage, open drainage or arthroscopy. Commonly, our choice of therapy includes penicillin or an aminoglycoside (gentamicin). Phenylbutazone once daily is given to reduce pain and inflammation. In addition, following physical removal of bacteria via lavage, intra-synovial administration of amikacin (250 mg) is instituted to achieve very high antimicrobial levels in the synovial fluid.

Synovial infections can be life threatening in adult horses if they are not promptly recognized. However, with early recognition, accurate diagnosis and aggressive therapy prognosis can carry a very good outcome and result in a return to athletic function.