Joint infections, also known as septic arthritis, are serious and potentially life-threatening conditions in horses. These infections can lead to severe lameness, joint damage, and, if not treated promptly, long-term disability or even the need for euthanasia. Understanding the causes, symptoms, diagnosis, and treatment options for joint infections is crucial for horse owners, vets, and equine caretakers.
Causes of joint infections
Joint infections in horses are usually caused by the invasion of bacteria into the joint space, leading to inflammation and destruction of joint structures. The most common causes include:
- Trauma: Penetrating wounds, such as punctures or lacerations near a joint, can introduce bacteria directly into the joint space. This is generally the most common way joint infections occur.
- Iatrogenic causes: Medical procedures, including joint injections or surgery, can sometimes inadvertently introduce bacteria into the joint. It is worth noting that some medications can also change the normal joint defences making them more susceptible to infection.
- Haematogenous spread: In foals, bacteria can enter the bloodstream (often due to septicaemia) and localise in the joints. This route is less common in adult horses but can occur in cases of severe systemic (body-wide) infections.
A note on joint injections
Rarely synovial infections can occur following the administration of joint injections, where a vet injects therapeutic substances into the joint capsule.
Although the vet may clean the skin surface and use sterile needles, there is still a risk of introducing bacteria into the joint capsule with injectable medications.
Studies show that around 1 out of 1000 joint injections administered to horses result in a synovial infection. There is no difference in the risk of joint infection for injections performed in a hospital setting versus a yard setting.
Known factors that increase the risk of synovial infections after joint injections include:
- Clipping the hair over the joint
- Using non-sterile needles or gloves
- Limited practitioner experience
- Using multi-dose vials of medications
- Larger needle sizes
Symptoms
The signs of joint infections in horses can vary but often include:
- Severe lameness: Horses with joint infections typically exhibit acute, severe lameness, often non-weight-bearing on the affected limb. The range of motion will be significantly reduced.
- Swelling: The joint may appear swollen, warm to the touch, and painful when palpated.
- Fever: Some horses may develop a fever, particularly if the infection is also affecting the rest of the body (i.e. it is a systemic infection).
- General malaise: Horses may exhibit signs of general discomfort, depression, and loss of appetite.
Did you know?
In adult horses, fever occurs after the infection becomes established. In foals, the fever often begins before there are signs of lameness or swelling in the joint.
Diagnosis
Early and accurate diagnosis of joint infections is essential for a positive outcome. Diagnostic methods include:
- Clinical examination: Vets begin with a thorough physical examination, assessing the horse’s gait, joint swelling, and overall condition.
- Synovial fluid analysis: Collecting and analysing synovial fluid from the affected joint is a critical diagnostic step. In cases of infection, the fluid often appears cloudy, with an elevated white blood cell count and increased protein levels. Bacterial cultures can identify the causative agent.
- Imaging: X-Rays and ultrasound may be used to assess joint damage, the presence of gas pockets, or foreign bodies. In some cases, advanced imaging techniques like MRI or CT scans are needed.
- Blood tests: Bloodwork can help assess the overall health status of the horse and the presence of systemic infection.
A note on joint infections in foals
As noted, with foals, bacteria entering the bloodstream can infect the joint. Often, the bacteria come from the umbilicus, but they can also originate in the gut, with the main symptom being diarrhoea or the lungs due to pneumonia. Fascinatingly, in studies of foals with septic joints, 50-88% had a total or partial failure of passive transfer (e.g. failure to drink enough high-quality colostrum from their dam).
Treatment
Prompt and aggressive treatment is crucial to prevent permanent joint damage. The primary goals are to eliminate the infection, reduce inflammation, and restore normal joint function. Treatment options include:
- Antibiotics: Broad-spectrum antibiotics are often administered initially, followed by targeted therapy based on the results of the joint fluid culture. These antibiotics can be given intravenously, intramuscularly, or directly into the joint. A popular technique for antibiotic treatment of lower limb infections in horses is regional limb perfusion (RLP), and antibiotic-impregnated materials are also gaining popularity as options for joint infections.
- Joint lavage: Flushing the joint with sterile fluids helps remove bacteria, inflammatory debris, and toxins, making antibiotic treatment more effective. This procedure may need to be repeated multiple times.
- Surgery: In severe cases, surgical intervention may be necessary in the form of arthroscopic lavage to remove infected tissue, debride the joint, or insert drains.
- Pain management: Non-steroidal anti-inflammatory drugs (NSAIDs) are commonly used to control pain and inflammation.
- Supportive care: Horses may require additional supportive care, including rest, fluid therapy, and nutritional support.
Regional limb perfusion (RLP)
This procedure involves administering antibiotics directly into the blood vessels of a specific limb to achieve high local concentrations of the drug in the target area.
The primary aim of RLP is to achieve a higher concentration of antibiotics in the infected area while minimising systemic exposure and potential side effects.
To perform an RLP, the vet places a tourniquet higher up on the limb than the affected joint to prevent blood flow back to the body. Following this, antibiotics are injected into a blood vessel, resulting in an elevated concentration of antibiotics in the area below the tourniquet. The horse stands with the tourniquet in place for 15-30 minutes after antibiotic administration to allow the medication time to work.
Use of antibiotic-impregnated materials
Antibiotic-impregnated materials are a novel and increasingly popular approach in the treatment of joint infections in horses. These materials include small discs or beads that deliver high concentrations of antibiotics directly to the site of infection. The medication releases slowly after the material is placed in an infected synovial space. The most common material is polymethylmethacrylate (PMMA) beads, but some vets may have access to gentamicin-collagen sponges, which are also effective in treating synovial infections.
Did you know?
Arthroscopic lavage involves inserting a small camera as well as surgical forceps into the joint cavity to remove inflammatory debris.
Prognosis
The prognosis for horses with joint infections depends on several factors, including the promptness of treatment, the severity of the infection, and the horse’s overall health. Early intervention typically leads to a better outcome, but some horses may suffer from chronic lameness or arthritis even after successful treatment.
Researchers evaluated racehorses in America (Thoroughbreds and Standardbreds) with joint infections. They found that 85 percent of aggressively treated horses survived and 56 percent returned to racing.
The outcome for foals with septic joints, however, is poor. Studies report that only 42 to 84 percent of foals with infected joints survive. Early and aggressive treatment is key to success. A study showed that 71 percent of foals treated within two days of clinical signs survived. Only 4 percent survived when treatment started after 2 days.
Prevention
Preventing joint infections involves:
- Proper wound management: Wounds near a joint or synovial structure (e.g., a tendon sheath) require prompt veterinary evaluation. Small wounds are often ignored, but they can penetrate into the joint, so do not underestimate their severity. All wounds, regardless of location, should be cleaned as soon as possible and kept clean.
- Aseptic techniques: Ensuring strict aseptic techniques during medical procedures involving joints can reduce the risk of infections occurring due to joint injections or other procedures.
- Monitoring foals: Early recognition and treatment of systemic infections in foals can prevent the spread to joints.
Final thoughts
Joint infections in horses are medical emergencies that require swift action to prevent long-term consequences. With appropriate and timely treatment, many horses can recover and return to their previous level of activity. However, prevention through careful wound management, vigilant monitoring of at-risk horses, and adherence to proper medical procedures remains the best strategy to protect horses from this serious condition.