Equine joint infections
Septic arthritis, or joint infection, can be devastating to soundness, athletic careers, and even life for affected animals if treatment is delayed or inappropriate.
In foals, bacteria from a distant site invade the bloodstream and cause an infection of the joint. The umbilicus is commonly blamed, but the gut and lungs can be equally responsible. Foals may also have diarrhea, pneumonia, or failure of passive transfer (when foals have not consumed a sufficient amount of high quality colostrum). In studies of foals with septic joints, 50% to 88% were identified with partial or complete failure of passive transfer.
In older horses, joint infections are usually caused by trauma. Wounds over joints (areas that bend) are the most common cause of infected joints. Joint infections can also occur during diagnosis or treatment of joint problems (such as joint injections or surgeries). Some medications have been associated with a higher risk of joint infection due to changes in the normal joint defenses. Tendon sheath and bursa infections are very similar to joint infections in causes, treatment and prognosis.
Lameness from a joint infection takes approximately 8 to 24 hours to develop. It appears after sufficient bacteria have started growing in the joint. The joint reacts to the bacteria with swelling due to increased fluid (effusion) and pain. In some joints, swelling may not be easy to detect due to overlying tissues. Fever may be noticed after the infection is established in adults. Foals are more sensitive, and usually run a fever even before any signs of lameness or joint swelling.
Diagnosis of joint infections can be challenging, especially in foals and horses with open lacerations. When joint fluid drains out through an open laceration, the horse is rarely lame and may not have swollen joints. Foals can have multiple and deep joints infected. Due to the difference in their immune response, the development of clinical signs may be delayed in foals.
Joint infection is usually confirmed by obtaining joint fluid for analysis. A sample of joint fluid is taken and then submitted for culture. If the joint is open, fluid may not be obtainable. These joints have to be checked with other methods including fluid injection, ultrasound and radiographs (x-rays). Foals are also evaluated for signs of sepsis using blood work and a complete physical examination.
Radiographs are used to monitor for signs of deeper infection and arthritis. Radiographs may be taken initially to obtain a baseline view, and then repeated later to determine what changes are occurring due to the infection. It can take weeks to months for these changes to appear.
The goals of the joint infection treatment are to eliminate the infection, reduce the inflammation, and obtain a timely return to normal use of the limb. Early identification and aggressive treatment are essential to clear the infection and prevent problems due to overuse of other limbs. Treatment can be started at the farm, but an intensive approach can often be best accomplished at an equine hospital. Treatment ideally involves intravenous antibiotics, joint lavage (flushing), anti-inflammatory agents, and often surgical cleaning (arthroscopy).
A few years ago, the prognosis for adult horses with joint infections was guarded or poor, but with early intervention and more aggressive surgical treatment, the prognosis has recently been described as good or very good. In a paper published evaluating racehorses (Thoroughbreds and Standardbreds) with joint infections, 85% of the aggressively treated horses survived, and 56% actually returned to racing.
The prognosis for septic joints in the foal is still poor. Studies report that 42% to 84% of foals with infected joints survive. Early and aggressive treatment is paramount for success. One study showed that 71% of foals treated within 2 days of the onset of clinical signs survived, whereas only 4% survived when treatment was started after 2 days. Joint infection is a potentially lifethreatening condition. It can be devastating to soundness, athletic careers, and even life for affected animals. Any horse with a suspected infected or contaminated joint should be considered an emergency and warrants immediate attention. Wounds over joints (areas that bend) should be evaluated as soon as possible to ensure the joint is not involved.
Although the prognosis of joint wounds in horses is usually described as guarded to poor, with earlier intervention and more aggressive surgical treatment, the prognosis can be good or even very good.