Annie is a 15-year-old Quarter Horse x TB mare who presented with a four-week history of lameness after having stepped on a stone.
Annie’s problem first came to the attention of her owner when Annie was noticed limping in the field. Out of nowhere, she was “dead lame,” recalls her owner. Presuming this sudden-onset lameness to be a foot abscess, Annie’s owner took steps to encourage drainage, including poulticing and soaking the foot in Epsom salt baths. After a week of this treatment, and no results, Annie’s owner decided to call the farrier to dig out the abscess.
The farrier was surprised to find a small stone lodged in the sole of Annie’s foot. With some skilled knife work, he managed to coax the nasty stone from the foot, albeit with a little bleeding. Presuming the ordeal to be dealt with, he very reasonably encouraged Annie’s owner to continue bandaging and soaking the foot for a few days until the bruising resolved.
Indeed, Annie initially improved dramatically. She bore full weight on the foot and, although lame at the trot, she walked comfortably enough in the field to get to her feeder.
As the days went on, however, the initial optimism Annie’s owner felt began to dissipate. Annie started getting sore again. And now her foot was really hot. She would stand in the stall with the sore foot pointing forward, as if to take pressure off it. After a time, Annie’s owner noticed that a warm swelling moving up the leg, past the fetlock, even up to the cannon bone.
Enough was enough! Annie’s owner called us to have a look.
Physical Exam And Diagnosis
On physical examination, Annie was bright and alert. Her temperature was in the normal range (37.0-38.0 degrees Celsius), as was her pulse (28-40 beats/min) and her respiratory rate (8-16 breaths/min).
Palpation of the left front limb revealed mild swelling extending from the coronet of the foot to just above the fetlock (ankle). The foot itself felt like a furnace, and the palmar digital pulses felt at the back of the foot were bounding, producing a very strong “digital pulse.”
Hoof tester examination of the sole produced an exquisitely painful response, particularly around the area of stone bruising and hoof-knife excavation. This was to be expected. What was unexpected, however, was the black, foul-smelling, sludgy discharge coming from the hole in the sole.
At this point in the examination, I’m concerned we’re dealing with a deep foot infection, possibly even as deep as the coffin bone. I recommend radiographing the foot to learn more – just how bad is this?
The following images are the radiographs taken of the left front foot:
What the radiographs are showing us is pretty straightforward: Infection, introduced into the foot initially by the stone, has weaselled its way up through the foot and taken a cookie-monster bite out of the coffin bone. In technical terms, we would call this pedal osteomyelitis, with radiographic finding of demineralization of the solar margin of the distal phalanx.
NOM NOM NOM.
This focal infection was causing resorption of the bone and chronic inflammation, not to mention constant pain.
Surgery would be ideal in this case, to dig out the infected bone and clean everything up, but this was not an option for Annie.
The next best treatment option we had for her on farm is what is called a “regional limb perfusion.” Obviously, this foot infection is going to need antibiotics, but giving muscle injections or administering oral antibiotics would not necessarily produce the required concentration of antibiotic at the foot to kill a sufficient number of the bacteria. So we aim to achieve the required concentration of antibiotic in the foot by doing a regional limb perfusion.
In the procedure, a tourniquet is placed above the foot, effectively trapping a pool of blood in the foot. Next, we find a vessel, now bulging under the pressure of the tourniquet, and inject a relatively large quantity of antibiotic DIRECTLY INTO THE FOOT! We are essentially going nuclear on it.
To achieve the same concentration in the foot with systemically administered antibiotics would require so much antibiotic pumped into the horse that the side effects would be disastrous. With a regional limb perfusion, we’re targeting a specific area of the body, so we can use a much smaller, safer amount of antibiotic, but achieve a massive concentration in a small area.
And so we did this, as illustrated in the photo below:
Annie’s treatment plan consisted of the following:
- Regional limb perfusion with antibiotic right into the foot every 48 hours for 3 treatments
- Intramuscular penicillin 2x daily for 10 days
- Intravenous gentamicin (another antibiotic) 1x daily for 5 days
- Continued soaking of the foot in Epsom salts and poulticing of the foot with poultice pads
- Bute powder to control the pain/inflammation – minding how much and how long we give this so as not to promote gastric ulceration
- Stall rest
After 2 weeks of aggressive treatment, Annie slowly began showing signs of improvement. The heat in the foot began to decrease day by day, and Annie gradually began putting more weight on the foot.
For the first few days following the regional limb perfusion, Annie’s owner reported a large amount of discharge being drawn out by the poultice pads. By the third treatment, however, little if no discharge would be seen on the poultice the next day.
Bar shoes were put on Annie’s feet to protect the tender sole from further bruising, and she was restricted to her stall for 4 weeks to protect the inflamed and painful coffin bone.
One Year Later
We’re happy to report that it’s been a year since we initially diagnosed Annie with coffin bone osteomyelitis, and Annie is doing very well. The cookie-monster bite in her foot may never fully fill in with bone, instead filling in with scar tissue. However, with proper farriery and shoeing, she shouldn’t experience any major issue with the foot in the future.