2009 In-Depth Equine Podiatry Symposium Notes
Written and presented January 2009 by R.F. (Ric) Redden, DVM
Puncture wounds are a direct or indirect introduction of bacteria into the sensitive zones of the foot. They can be career or even life threatening and range from subtle and difficult to locate to quite severe and devastating to soft tissue and bones. Regardless of their form, they should never be taken lightly. Treat all puncture wounds with the respect they deserve, as what initially seems like a routine problem can quickly get out of control and threaten the career or even life of the horse.
The most commonly occurring puncture wound is an indirect introduction of bacteria into the foot via small fissures that open along the terminal laminae. Once the laminae reach the inner sole surface they cornify and become non-sensitive. The cornified cells resemble the anatomy of the sensitive laminae but have a totally different function. The zone of laminae that lies between the wall and sole is called the terminal laminae, and it acts as a buffer union between the wall and sole, as they grow at the same rate.
The terminal laminae were formerly referred to as the white line, a term that has been the subject of much debate simply due to its non-descriptive meaning. The only white zone of the hoof is the stratum medium, the inner, non-pigmented horn wall that lies between the outer horn and the laminae. This white zone runs the length of the horn wall, is clearly seen at the ground surface and is often referred to as the white line.
The fissures that allow bacteria to enter the sensitive laminae and sole corium occur in the terminal laminae and innermost area of the non-pigmented horn layer. They are the product of poor quality protection, which occurs as a result of insufficient hoof mass . The wall fails to be protective due to less than optimum density, toughness and mass. Ground friction carries bacteria motes into the sensitive, blood rich laminae and sole corium, breaching the last zone of defense.
Clinical signs: Clinical signs of an abscess include acute, Obel grade 5/5 lameness, a hot foot and a thumping pulse.
Diagnosis: Suspect areas will have little black lines in the terminal laminae and inner horn wall. Very light hoof tester pressure can quickly locate the area of concern. Be cautious. Use the tester lightly over areas of the foot where you do not suspect sensitivity and work towards the likely sensitive area from both sides. Avoid putting pressure directly over the hot area. The horse has enough pain without us causing any more. Note that an abscess can be quite easy to confuse with laminitis, especially when it is found bilaterally. Radiographs can help make this distinction.
Treatment: If the horse is wearing a shoe, pull it one nail at a time using a crease puller or side cutter to easily crack each nail out. Yanking the shoe off with a shoe puller, a very common way to remove shoes, will cause the horse extreme pain and can result in injury to those who are holding the horse. Lightly rasp the foot, looking for any small, dark fissures that run perpendicular to the terminal laminae. Quite often there will be several such lines, especially in the bare foot. Identify the ones closest to the seat of sensitivity with the tester. Using a small curette or the end of a farrier knife, make a small hole along the wall side of the fissure. Stay away from the sole side; this will prevent the unwarranted problem of solar prolapse that frequently occurs when the sole is opened. After opening a small area, insert a horseshoe nail with a small bend at the tip into the fissure, which you can now see penetrate well above the sole margin. Tip it in towards the sensitive sole until you get a drop or two of exudate. At this point you have vented the abscess.
I often make a notch in the outer wall at this location, put a piece of Betadine/DMSO soaked cotton in the hole and reapply the shoe, leaving out any nails that might be too close to the hot, sensitive area, clinching down very easily. When the foot is extremely painful, block the foot before nailing and be careful not to stick the foot while it is desensitized. The shoe protects the opening to the fissure. I frequently administer antibiotics for 5-7 days and Bute for a couple of days. Within 3-5 days the horse should be 100% sound without the benefit of Bute.
Bone Involvement: Bone involvement is rare in an indirect invasion of bacteria, but it is possible. If the horse remains sore (not lame - just sore) after 5 days, bone involvement is likely and radiographs are highly indicated.
Radiographs: Take a 65º DP in a Hickman or Redden style positioning block. This will greatly limit distortion and enhance your ability to see very subtle lucent zones along the palmar rim. The commonly used tunnel distorts the 65° DP image, reducing our ability to detect subtle changes. I also take a 65º 45º oblique view and occasionally a DP view with beam alignment at the level of the palmar rim. All exposures should be extremely soft, or you will miss the subtle changes that occur long before there is significant bone loss.
When using digital units it is imperative to develop a technique chart includes a range of contrast below a standard "one shot" technique. While the contrast on the digital image can be manipulated with software, there is a limit to its range. I frequently review digital film that does not reveal palmar rim alterations as the range of contrast has been exceeded.
Complications from a hot nail: If the foot becomes hot 3-5 days post-shoeing, pull the shoe, locate the sensitive areas with a hoof tester, then open the sole wall junction just enough to let a few drops of exudate to escape. With other direct nail or foreign body punctures, note the color of the exudate. If the exudate is yellow and thick or green and has air bubbles, suspect a pseudonoma or proteus invasion. As a rule there is bone involvement in these cases as both types of exudate are caused by very virulent organisms. Culture sensitivity is indicated, along with baseline radiographs.
Chronic indirect punctures: When an abscess has persisted for several days to weeks and the horse has alternated between lameness and soundness, the problem must be sorted out quickly for several reasons. Bone sequestrum can form, large areas of bone can be eroded and contra limb laminitis becomes a concern for the opposite foot. At this stage the abscess is career threatening and can easily become life threatening. Immediately apply a Modified Ultimate with Advance Cushion Support (ACS) and sole support to the good foot and continue using it until the problem has been corrected.
As an adjunct to therapy for any abscess that hasn't been opened at the bottom and is going to pop at the top or back of the heel, I cut a piece of animalintex 2º to 6º long, soak it in hot water and wrap it around the coronary band and cover with a bandage. Animalintex expands the foot with moisture, making it much easier to break at the coronary band. However, most of the time opening the abscess at the ground surface early will bypass this complication. In very cold weather if I feel I need to keep the poultice warm, which many times eases the pain, I will put a four hour hand warmer under the bandage. Once the abscess breaks at the coronary band it will clearly define the areas of the foot involved in case you haven't already found them. Just follow the tubules from the top to the ground surface. Those that break out the bulb of the heel have migrated from the toe area along the sole and sensitive frog. This is often the route of least resistance. Note the color, texture and odor of the exudate. This can tip you off as to how aggressive you may need to be with additional treatment. When pseudonoma , proteus or staph is cultured, be very aggressive with broad spectrum antibiotics for at least 10-15 days.
An abscess should never be taken lightly. Always treat it as a red alert and work closely with the farrier, who may be able to see the horse more often and provide good information concerning the healing response. I can't stress enough the essence of time. I have been an expert witness on several occasions for suits against veterinarians, farms and farriers concerning cases that began with a single abscess that was not properly diagnosed.
Surgery: When antibiotics fail to eliminate the drainage and soreness or exposed sensitive tissue will not cornify, surgery is indicated. Radiographs will also reveal progressive increases in the size and darkness of the lucent palmar lesion. I prefer to perform the surgery in the standing horse, as I find orientation is enhanced when viewing the foot from this position. The procedure is very easy to perform.
Make and apply a hospital plate shoe prior to surgery. For all my hospital plate shoes I use a 1/4" aluminum plate and a steel shoe tapped for 1/4" number 20 thread 1/2" bolts. Cutting the inner web close to the edge of the crease often exposes all the sole wall junction that is needed to surgically curette the lytic bone. Trim the foot, clean it up quite well and apply the shoe once the foot is blocked. Prep the area with a surgical scrub. Apply a tourniquet at the fetlock and curette the soft bone. Pack the defect off with Betadine and gauze. Place ACS in the sole and heel area, leaving a window only around the surgery site. This prevents debris from entering the sole area and greatly reduces the amount of gauze that is needed to pack the foot. When applied over the frog it can offer sufficient frog pressure as well.
Hospital plates are great protective bandages and most any horseman, even with limited experience, can manage them. I apply a cotton wrap over the hospital plate using Vetrap, then cover it with a layer of Duct tape. Change the bandage every time the plate is removed until the defect is well granulated. This helps prevent unwarranted bacteria invasion via moisture contaminants from the stall. Note the hole needs to be packed in a firm fashion to avoid exuberant granulation tissue from forming. If there is no room for granulation there will be none, and the hole will heal from the bottom to the top. This is one area that I find many struggle with. Failing to pack the defect firmly enough will invariably result in complications. The hole will fill up with granulation within a few hours to days. Though it appears to do quite well, bacteria will be trapped beneath the tissue and the bone margin will not heal.
Post Op Care: I change my packs daily using firm, blunt debridement with dry gauze. Between days three and five the bone proper should be covered with a thin layer of pink, firm granulation. If not, most likely a small area of necrosis or sequestrum remains at the site, which should be examined closely with a sterile curette at this time.
When I have a very painful case I rocker the belly of the hospital plate, using Equilox to build the surface up to the desired height. I usually like to establish at least a 15-18º palmar angle (PA) once the shoe and plate are on. This will adequately reduce download of the palmar rim into the sensitive sole, which seems to give most cases immediate relief.