Dr. Patricia Provost
Foot abscesses are usually the result of a deep bruise or an injury that penetrates the sole of the foot. For example, a misdirected nail can cause enough injury to start an abscess. Foot abscesses generally result in a sudden onset of a moderate to severe lameness, initially seen at the trot and then even at the walk. Horses lift their foot off the ground or stand on one part of the foot. Alternatively, foot abscesses can cause more long-standing and/or more low-grade lameness. The affected foot is often warmer to touch
Drainage of the abscess and short-term rest can provide immediate relief of the pain and may be all that is necessary to effect resolution of the problem. Other patients may require antimicrobial therapy and on rare occasions, surgery.
What to Watch For
Digital pulses are increased
Swelling of the coronary band and pastern region
Not standing with all of the weight on the foot
Wound or a penetrating foreign body
Terminology for Foot Problems
Corn – a bruise that occurs between the outer hoof wall and the bar of the foot.
Gravel – the term given to abscesses that develop at the white line, but drain at the coronary band.
Seedy toe – the degeneration of the white line located at the toe and on the dorsal surface of the foot. Infection may occur secondary to this degeneration.
A diagnosis of a foot abscess or bruise should be suspected when a horse becomes acutely lame on a limb that has had no previous problems. Often the horse has a history of being normal one day, just a bit "off" the next day and showing obvious signs of lameness on the third day. At this point, it is considered an emergency.
Other historical scenarios may include recent exercise over hard or rocky surfaces, recent shoeing, or the presence of a previous penetrating wound.
There are several clinical tests that will help to differentiate a foot abscess from an unrelated lameness:
The use of the hoof-testers is critical. Application of pressure over the foot's sole can help to identify the location of a subsolar abscess. When pressure is applied directly over the site of the abscess the horse becomes resentful and will pull the foot away.
Nerve blocks may be required to localize the lameness to the foot and to facilitate therapeutic intervention. The nerves to the foot can be anesthetized in four steps, each step desensitizing a different region of the foot, which can provide further help in pinpointing the location of the infection.
Radiographs may be required to rule out injury to the coffin bone (fracture and infection) and should be taken before the removal of any foreign object that has penetrated the foot. A gas lucency will sometimes be present at the site of the abscess.
Treatment for simple forms of abscesses, those that are not complicated by bone injury or injury to the navicular bursa, coffin joint, or flexor tendon sheath, requires drainage of the abscess. If the abscess is located beneath the sole of the foot drainage will be established through the sole. If the infection is not beneath the sole, creating drainage will not be possible. Other treatment options include:
The horse, dependent on his comfort level, may also benefit from the use of phenylbutazone to reduce pain until healing occurs.
Depending on the location of the infection and its severity, antibiotics may also be required.
Surgery will be required if the infection involves the bone, the navicular bursa, the coffin joint, or the flexor tendon sheath.
A tetanus toxoid vaccine will also be required if the horse had not had a recent one.
The prognosis is excellent for recovery of uncomplicated foot abscesses.
Home Care and Prevention
To promote the abscess to drain and resolve, warm water foot soaks and the use of drawing salves, such as ichthamol or poultice can be used. The foot can be soaked for 15-20 minutes once to twice daily in warm water, Epsom salts, and betadine solution. Soaking should continue until the lameness and the drainage resolve and the wound closes.
In between foot soaks, the foot with a sole wound should be kept bandaged or placed into a protective boot to protect the sole and to keep the wound from becoming further contaminated.
Pastures should be kept clean of objects that can puncture the foot. Stones should be picked up routinely. In rocky environments or sports that require exercise over rough terrain, full shoe pads may prevent injury to horses with thin soles.
Horses feet should be cleaned frequently and shoes replaced on a timely basis.
All horses should be kept current on their tetanus vaccination.