Horse Wounds: How to Know if a Joint is Involved

Wounds are one of the more common injuries veterinarians assess in the field. And, when wounds occur near a joint or tendon sheath, there is always a risk the synovial structure is involved. If so, that becomes an even more serious problem.

Synovial structures include joints, tendon sheaths, and bursas (cushioning, fluid-filled sacs) contain synovial fluid that protects and lubricates the surrounding anatomy. When a wound involves a synovial structure, synovial fluid and, therefore, lubrication is lost, and infection can occur. Because wounds involving synovial structures are serious and can be life-threatening, veterinarians need to quickly assess whether a wound does, in fact, involve one of these structures.

The challenge becomes how best to do this in the field. The gold standards—synovial fluid cultures and cytology (examining cells under a microscope)—are either challenging on the farm, take days to get results, or are only helpful about 50% of the time, said Jacqueline Hill, DVM, Dipl. ACVS-LA, of Littleton Equine Medical Center, in Colorado. This leaves field veterinarians needing other tools with which to conduct an accurate assessment when treating a horse in the field.

Hill presented her approach to these cases at the 65th Annual American Association of Equine Practitioners Convention, held Dec. 7-11.

Horse Wounds: How to Know if a Joint is Involved

Tools to Identify Potentially Affected Structures

Practitioners need a clear understanding of which structures the wound might involve, said Hill. These could include tendons, ligaments, tendon sheaths, and bursas. Smartphone apps exist that can help veterinarians identify specific anatomy, and taking photos of veterinary texts to use as resources in the field can be useful, as well, she said. Once the veterinarian has identified potential structures involved, it’s time to assess the damage. One way is using mobile ultrasound.

While not commonly used for this purpose, Hill said assessing a wound via ultrasound can provide useful information about the wound’s direction, depth, and proximity to important structures. The veterinarian can place the ultrasound probe directly over the wound, using it to image the amount of synovial fluid and thickness of the synovial membrane, for example.

Radiographs are useful for identifying bony trauma, as well as where the wound is located relative to a joint. Any built up gas in the wound, as well as the wound tract, might be visible. Hill recommended taking four images of a region to check the bones for potential fractures from all angles.

If these noninvasive diagnostic techniques don’t provide a definitive answer, Hill recommended practitioners conduct a synoviocentesis. During this procedure the veterinarian collects a sample of synovial fluid to assess its color and viscosity. She recommended inserting the needle away from the wound and any area where cellulitis might exist to reduce the risk of introducing bacteria into the joint. Strict aseptic technique during this procedure is vital, she said.

When collecting synovial fluid, Hill recommended first sending it for cytology; then only culture it if you’ve collected enough sample. After taking samples, the veterinarian should distend the synovial structure with saline or contrast solution. Contrast solution can be particularly helpful, she said, if you couldn’t previously see the wound tract. However, it requires taking additional radiographs after injecting the contrast material and, often, a second pair of hands.

Take-Home Message

Hill’s key points from her presentation include:

  • Wounds are common in the field.
  • Determining whether a synovial structure is involved is critical for determining appropriate treatment.
  • The first step is knowing what structures may be involved.
  • Veterinarians can use a combination of ultrasound, radiographs, and synoviocentesis in the field to assess synovial involvement.