Why Won’t My Horse’s Wound Heal?

Why won’t my horse’s wound heal?

Horses are fantastic creatures in many ways but one of the things at which they appear peculiarly adept is cutting themselves! Such wounds are often the result of a close encounter with the hoof of another equine taking exception to some imagined slight. The strength of the forces involved can have consequences even if the blow was not hard enough to cause either a fracture outright or a stress fracture, as we discussed in a previous newsletter article.

Sequestrum formation is something that we vets commonly warn owners about when their horses have received a kick particularly over a bony part, but what does the term mean? A sequestrum describes a bone fragment becoming dislodged from its associated bone during a traumatic episode and which causes the body to produce a marked, inflammatory reaction. This reaction involves swelling around the site and the production of pus. Frequently, this will break the surface of the skin some time after the injury had appeared to have healed. This may be weeks, months or sometimes years later. Sequestra are commonest in the long bones of the limbs but fragments of any bone from the jaw to the vertebrae of the spine can occasionally occur.

In most cases these bits of bone must be surgically removed to allow the wound to heal. Very occasionally, where the fragments are very small and localised well away from sensitive structures such as joints, long periods of convalescence may allow the condition to resolve. However, there is a risk that this may predispose the adlacent bone to undergo serious infection and even fracture. In most cases involving a limb, the horse is lame.

A recent case was “Sunny”, a 15 year old thoroughbred mare, which cut her hind leg below the hock by knocking it against a wall. The wound was sufficiently far below the bottom of the hock joint for a joint penetration not to be of concern. Initially, the mare was sound and the wound appeared to have healed with standard treatment including dressings and antibiotics. However, I did give the usual warning about sequestrum formation!

Unfortunately, in this case my warning proved to be warranted because, despite the mare never becoming lame, the injured area subsequently swelled up again and the wound broke open (Figure 1). Sunny was brought over to the equine clinic at Aston Munslow and X-rays showed four bone fragments that originated from her the top of her outside splint bone (Figure 2).

Radiographs are generally very good for looking at bony changes but even modern digital X-rays can struggle to identify very small fractures. Fortunately, the clinic has recently invested in a new, high-resolution ultrasound machine and on scanning Sunny’s injured leg 31 fragments could be seen (some of which are visible in Figure 3)!

Removing the fragments was indicated in this case and on discussion with her owner this was carried out under sedation and local anaesthesia. Removing all the tiny, numerous pieces was an extremely lengthy and painstaking task! An X-ray after surgery indicated that all fragments had been removed; it is not possible to use ultrasound on the area once the skin has been broken because the entry of air into the wound precludes the visualisation of a diagnostic ultrasound image.

As is so often the case with lower leg wounds, this one took some time to heal properly but now has done so. Although not every non-healing equine wound is the result of a Sequestrum, it is always worth checking with an X-ray and potentially an ultrasound scan to put one’s mind at rest. Sunny remains sound having been put back into full work and she is looking forward to hunting again next season.

by Dr Nicholas Graham MA VetMB MRCVS CertAVP

Further Advice