Management of Infected Joints and Tendon Sheaths in Horses

Synovial infections in horses include infectious arthritis, infectious tenosynovitis and infectious bursitis. Early diagnosis and treatment of those synovial infections is very important to guarantee a successful outcome.
Synovial infection produces the classical signs of inflammation around the joint or tendon sheath. These include heat, painful periarticular swelling and oedema, distension of the joint, erythema of the surrounding skin and pain on pressure and flexion. Lameness is often very severe/non-weight bearing. In some cases the lameness is less severe if the infection is seen early in the disease process, if analgesics have been administered (systemic NSAID or corticosteroids intra articular) or if a larger wound is present which allows easy drainage of synovial fluid (less pressure in the joint).
In some cases it is very difficult to differentiate an acute traumatic joint injury from an early septic joint. Because synovial infection often leads to permanent lameness early recognition of an infection and appropriate treatment with a sensitive antibiotic is paramount. Repeated synovial fluid analysis are very helpful in monitoring the response to treatment and isolation of microorganisms by culturing will help the clinician in deciding which antibiotic to use.

However, there are a few problems encountered in isolating micro-organism from a joint:

• Synovial fluid cultures in horses with suspected infectious synovitis may yield (false) negative results in up to 27% (Schneider et al, 1992) to 45% (Madison et al, 1991) of cases.
• The accuracy of a standard agar plate method to detect bacterial growth is not high.
• Synovial fluid cultures can be negative after a couple of days of antibiotic treatment (systemically and/or intra articular).
• Collecting synovial fluid is not always possible especially in cases where synovial fluid can drain out of the joint (e.g. through a wound).
• Care should be taken during the sampling to avoid iatrogenic contamination of the synovial fluid sample.
• Synovial fluid cultures may take up to 7-10 days before having a result. Meanwhile, a treatment should be ongoing.

Another important issue to deal with is the permanent thickening and fibrosis of the fibrous part of the joint capsule. This will often lead to permanent joint dysfunction also in absence of infection. Early treatment with steroidal drug is very tempting to reduce this capsulitis and reduced joint motion but one has to be sure that the infection is under control.

During the talk those problems will be discussed together with some research result of Pille F. et al, 2004 using PCR (polymerase chain reaction) techniques to detect bacterial DNA directly from clinical samples of synovial fluid of horse suspected of infectious synovitis.  [...]