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Joint and Tendon Sheath Infections

Although a large wound across your horse’s chest can be rather impressive with exposed muscle and obvious bleeding, one of the most dangerous wounds your horse can sustain is a small wound on the lower limb that enters a joint or tendon sheath.  This type of wound may not be immediately recognized or considered important, but can be career and life threatening for your horse.

Joints and tendon sheaths are both synovial structures, which are cavities lined with cells that produce synovial fluid.  This fluid lubricates and provides nutrition for the structures within the joint or tendon sheath.  Joints and tendon sheaths have a variety of functions, but the most important is to help movement.  Joints occur between two bone ends and minimize friction and concussion as two bones glide or rotate in relation to each other.  Tendon sheaths wrap around tendons and lubricate and protect them as they travel over joints.

A wound that enters a joint or tendon sheath introduces bacteria.  Synovial structures are great environments for bacterial growth and are challenging locations for the body to fight infection.  Once bacteria have been introduced and start to replicate the synovial structure is septic or infected.  A wound that enters a synovial structure may also introduce foreign material such as dirt, hair, or wood.  This foreign material is irritating and is a wonderful place for bacterial to collect and multiply.  One scientific study found that 33.8% of infected joints or tendon sheaths have foreign material present (1).  Joint or tendon sheath infection results in severe inflammation, pain, and lameness.  Infection within a joint can destroy the articular (joint) cartilage causing arthritis.   This can result in permanent and often severe lameness.  Joint infections that are not treated can also spread into the surrounding bone, which worsens the prognosis(1).  Infection within a tendon sheath results in inflammation and the development of adhesions or fibrous connections between the tendon and the sheath wall.  Adhesions prevent proper movement and cause pain.  Uncontrolled tendon sheath infections can also result in spread of infection into the tendons themselves(2).  Infected synovial structures are extremely painful.  If an infection within a joint or tendon sheath cannot be controlled it may even result in euthanasia.

Septic joints and tendon sheaths can be successfully treated, but the key is to start treatment early and to be aggressive. The first step is to determine if a wound enters a synovial structure.  With a fresh wound your veterinarian will prepare a location away from the wound to place a needle in the joint, or tendon sheath.  Thus if there is a wound over the outside of the fetlock joint, your veterinarian may clean and prepare a location on the inside of the fetlock joint.  The joint is tapped at this separate location and sterile saline is injected.  If saline exits through the wound, then the wound communicates with the joint.

If the wound is older and has sealed over, your veterinarian will evaluate your horse for lameness or extra fluid (effusion) within the joint or tendon sheath.  A sample of synovial fluid from the suspected structure is removed, analyzed, and cultured.  This procedure can also be used to determine how a synovial structure is responding to treatment.

If a wound enters a joint or tendon sheath, extensive flushing of the affected area, antibiotic therapy, and pain medication are the most important parts of treatment.  The best way to treat an infected joint or tendon sheath is by making small incisions to insert a small camera and separate flush cannula or tube into the joint (arthroscopy) or tendon sheath (tenoscopy).  With this procedure, the horse is anesthetized in an operating room and liters of fluid are flushed through the synovial structure while it is evaluated with the camera.  If foreign material or large clumps of fibrin (inflammatory material) are present, they can be removed.  Rainland Farm Equine Clinic is one of the few hospitals in the Western Washington area with the facilities and expertise to offer arthroscopic surgery.

If this minor surgery is not an option for an individual horse, the joint can also be lavaged by flushing saline through multiple large needles placed in different locations in the joint.  This type of treatment is more likely to be effective when performed soon after the injury.  Systemic (oral or intravenous) and local antibiotic therapy is also started.  Systemic (oral or IV) antibiotics are important, but are often not enough. There are several choices of local antibiotic therapy and your veterinarian will decide which options are best for your horse.  Antibiotics can be directly injected into the joint or tendon sheath.  Antibiotics can be repeatedly injected through a drain left in the affected joint or tendon sheath.

Regional limb perfusions with antibiotics are another option.  With a regional limb perfusion a tourniquet is placed above the affected joint.  Antibiotics are injected into a superficial vein in the limb below the tourniquet and the tourniquet is left in place for 30 minutes.  This procedure concentrates antibiotics in all of the tissue below the tourniquet.

All of this information sounds very scary, but many septic joints and tendon sheaths that are appropriately treated respond well.  Recent scientific studies looking at the outcomes of horses with infected joints and tendon sheaths report a survival rate of 73% – 90% and a return to athletic performance of 54%-81% (1,2,3,4).  Thus if you get prompt veterinary care, your horse has a good chance of recovery.  Wounds near a joint or tendon sheath are always an emergency.  At Rainland Farm Equine Clinic we recommend that you contact your veterinarian right away about any wound on your horse’s lower leg that goes all the way through the skin.

References

  1. Wright IM, Smith MR, Humphrey DJ, Eaton-Evans TC, Hillyer MH. Endoscopic surgery in the treatment of contaminated and infected synovial cavities. Equine Vet J 2003;35:613-9.
  2. Wereszka MM, White NA, Furr MO. Factors associated with outcome following treatment of horses with septic tenosynovitis: 51 cases (1986-2003). J Am Vet Med Assoc 2007;23:1195-200
  3. Walmsley EA, Anderson GA, Muurlink MA, Whitton RC. Retroscpective investigation of prognostic indicators for adult horses with infection of a synovial structure. Aust Vet J 2011;89:226-31.
  4. Taylor AH, Mair TS, Smith LJ, Perkins JD. Bacterial culture of septic synovial structures of horses: does a positive bacterial culture influence prognosis? Equine Vet J 2010;42:213-8.
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