Treating Puncture Wounds

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.

Indirect Puncture

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.