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.
Once the bone is well covered and the granulation bed is firm and non-sensitive I take the horse off antibiotics and continue to use the hospital plate for at least another 4-6 weeks. Removing the plate too early and using only a pad for protection can cause a serious relapse. Sand, dirt and other debris can get caught between the pad and sole and traumatize the very tender cornified layer of sole.
Needless to say, the sooner the soft area of bone is removed the less likely it is there will be complications and the better the prognosis is for a full recovery. I have treated several hundred cases in this fashion over the past three decades and do not remember one case that was not much improved clinically within 24 hours of surgery. Nor do I recall any complications following standing surgery with the shoe on at the time of surgery. However, I am very careful to only use fingertips on my instruments and touch only the tissue being removed with the instruments.
Things to avoid: What not to do with indirect puncture cases is just as important as knowing what is best. A very common practice shared by horsemen, farriers, vets is to apply caustic agents to solar abscesses in an effort to dry them up. This practice should be discontinued as it can cause very serious permanent damage to the growth centers, delaying or preventing the area from ever healing. Phenol, 7% iodine and iodine crystals with turpentine should never be used on sensitive tissue. They might have worked in the past on select cases and may seem like a cure all, but I have seen sales yearlings, race horses and extremely valuable brood stock suffer months of protracted, expensive care in an effort to deal with damaged bone that was the result of harsh, caustic agents. Some did not survive.
Direct puncture wounds
Any foreign object that penetrates the horn capsule is a direct puncture. Bacteria is introduced via the direct route. Direct puncture wounds should be considered an emergency and treated as such until proven otherwise, especially those that involve the sulci of the frog and part of the body of the frog.
Causes of deep punctures: The most common objects involved in deep punctures are sharp stones, metal objects, wire, nails, bits of farming equipment and nails or screws. Some of the worst punctures I see are caused by a steel fence post that has rotted off down to the ground, leaving a relatively sharp point that a horse steps on during wet weather. Often times the post will penetrate through the bottom and out through the top of the foot, carrying mud, debris, and grass with it. These cases look to be catastrophic in nature and often result in large bone fragments, but I have not had one case that didn't heal in a favorable fashion and none have resulted in contra limb laminitis.
Diagnosis: It is not always easy to find a puncture. Acute lameness is frequently assumed to be the result of an abscess, which means a deep puncture can elude the eyes of inexperienced professionals. As a rule the acutely lame foot will be the result of an abscess, but a direct puncture or fracture should also be suspected. Radiographs will quickly rule out a fracture, and as a rule most fractures are readily visible even when only hours old. If you possess farrier skills, clean the foot up by lightly paring all the sole, frog and sulci and look for small, dark entry holes or fissures. Farriers perform this task daily over and over and are the best person to clean up feet without over trimming.
Closely examine all suspected areas. Use hoof testers, but be very gentle. Deep puncture wounds often make the entire foot very sensitive. When a nail, wire or foreign object is still in the foot, tape a piece of wood along the side of the object to prevent it from penetrating any deeper and take radiographs as soon as possible with the foreign object still in the foot. Film taken with the object still in the foot can be invaluable as it will clearly reveal the areas of the foot that are involved with the object. This is very important as tendon, navicular bursa, navicular bone and joint spaces are all life threatening zones. You need to know which ones are involved on day one. When you feel for sure a puncture has occurred but cannot confirm it grossly, radiographs may help identify the affected area. Performing a venogram can also be helpful as the contrast will leak out through the area of sensitivity penetrated.
I feel all deep punctures need to be surgically examined at the time of injury. I have been presented with literally dozens of life threatening cases that started off with a very small area of bone or soft tissue involvement, but slowly escalated to life threatening circumstances because more aggressive options, such as surgery, were not pursued.
Solar punctures: It is almost impossible for a foreign body to penetrate the sole and not traumatize the bone to some degree. Therefore it is always wise to suspect bone damage with all punctures to the sole area. Note all non-complicated punctures are 100% sound with no drainage and no exposed sensitive tissue within 5-10 days of injury. Otherwise there is bone involvement.
When the bone damage is very mild, radiographs made at the time of injury are often non conclusive as small, thin bone fragments are often not demonstrable for a few days. However, a venogram will often reveal a doughnut-shaped lesion, as contrast is trapped under the bone, leaving a lucent center. Radiograph punctures to the sulci or frog with the object in place if possible. Scrub the foot, insert a sterile animal feeding tube (a 19 gauge needle with a bulb on the end) into the puncture track and take two views (remember the law of the circle). Take all the film needed to precisely locate the specific area involved. Note whether or not the bursa, DDF and navicular bones are damaged. If so, this is a life threatening case.
Heel area punctures: The goal with this type of puncture is to eliminate DDF action, as you will invade the tendon in order to clean up the navicular bone, and you must protect it while it heals. Make a therapeutic shoe that provides a 90° toe angle and has adequate heel extension bars in at least 3 decreasing sizes: for surgery, the first reset and the second reset. The base of the heel extension should be about the width of the foot. The shoe needs a toe extension plate to prevent the foot from rocking forward too much and a hospital plate to protect the puncture and surgical site.
Making the shoe:
Using lateral film, create an 80-90º hoof angle position with the ground surface and draw the shoe right on the film.
Take rough measurements on the film for the shoe length and heel height. Fabricate an egg bar shoe with extended square heels.
Drill 7/32 holes 2 inches on center in the heel of the square heeled egg bar. Use a consistent width between the holes. You can always make extra bars for any horse without taking measurements.
Tap the shoe for 1/4" 20 thread bolts.
Attach the extended bar, then make a hospital plate from 1/4" aluminum.
Drill and tap a shoe for the plate. Only two heel bolts will be needed.
Place a 3 - 4" piece of rasp under the toe and weld in place. This stops the foot from going too far forward.
The toe of the hospital plate will fit under the lip of the extended toe plate. Secure the plate with the two bolts at the heel. Use a grade A bolt (hard bolt) when attaching the shoe and double nut it. It must not come off.
Attach the shoe with bars on and you are ready for surgery.
Performing the surgery:
Block the foot at the fetlock. Prep the foot with surgical scrub and place a tourniquet on the fetlock.
Hold the foot between your knees (wear a farrier's apron) or have a farrier hold the foot. I prefer the former as it helps me stay oriented.
Insert a 19 gauge sterile metal animal feeding tube. Leave it in place as you make a clean cut around the needle down to the level of the navicular bone. The top of the hole must be much larger than the bottom. I prefer to remove the entire plug around the feeding tube in one piece. This will include a small section of DDF, exposing the navicular bone. Be careful not to penetrate the joint capsule.
Examine and test the surface of the bone with the curette. It may look ok, but many times there will be a loose piece of bone. This must be removed along with any necrotic bone.
Pack the hole firmly from bottom to top with gauze infused with 2% Betadine. Place a little extra at the surface so the hospital plate will fit snug, pushing the gauze tightly in the hole to control hemorrhage for the first 3-4 hours. At this time remove the plate and enough gauze to take slight pressure off. If you fail to do this, the extreme pressure you applied to control the hemorrhage will cause unwarranted pain.
I usually take a culture sensitivity of the bone fragment and start all cases on a Gentomicin/penicillin combination until the culture comes back. Always apply a Modified Ultimate on the opposite foot, making sure an 18-20º PA has been established. This will greatly aid the prevention of contra limb laminitis. Monitor this foot radiographically as well as with venograms to be assured that laminitis has not been triggered. You need to know this before the horse tells you.
Post surgical care: Change the gauze plug daily, being very careful not to disturb the healing, especially the layer that will be attached to the gauze. If there is necrotic bone I will place a small antibacteria impregnated methyl methacrylate bead in the bottom of the hole. It will be pushed to the surface as the lesion granulates from bottom to top. This time release antibiotic works great, especially when a virulent organism has been cultured.
It is vital that the hole be packed very tight in an effort to prevent granulation tissue from filling the hole before it has healed at the bottom. This is where most surgeons have a problem. Many of my referral cases over the years have been complicated by the simple failure to prevent exuberant granulation. Normally 5-10 days is required for the bone to be healed and solid granulation tissue cover the bone and tendon defect. It will take an additional 30-45 days for the hole to heal to the surface.
At the first reset take a lateral radiograph to determine sole depth and PA. Be prepared to remove the shoe, trim the foot and reapply the shoe with the second bar attached before setting it down. It is very important not to put the foot down with the shoe off, as you do not want to tear the adhesion that has healed at the bottom of the hole. The DDF remains very fragile at this time. The same applies for the second reset 30 days later. Once this shoe is removed, apply a flat shoe with hospital plate and rocker the bottom of the plate using Equilox. This is a nice letdown shoe that gradually increases pressure on the healing tissue, which must be stretched slowly to prevent unwarranted trauma to the newly healed tissue. The prognosis is quite good using this technique provided you do not have a staph resistant organism. When cases are referred from other hospitals you must always be alert to this possibility.
The prognosis for deep puncture wounds to the tendon, bursa and/or navicular bone is often considered grave, as many times they are non-responsive even to the most aggressive techniques. However, the tips discussed here compliment aggressive surgical and antibiotic therapy and can improve the prognosis when implemented quickly and efficiently. Heel puncture pain is due to tension on the traumatized and infected DDF and related structures. By creating a 90º hoof angle (40-45º PA) using the shoe described above we can greatly reduce post op pain even when the DDF is involved, as it eliminates all tension. This shoe has been a miracle shoe for me many times, and has saved the lives of several horses that might otherwise have been euthanized due to the cumulative damage incurred from the puncture wound.
Protecting the opposite foot from contra limb laminitis is another big part of my success. It is one thing to get the puncture wound out of the woods, but quite another to keep the opposite foot healthy throughout the healing period. By doing so we can greatly increase our chances of success.