Puncture wounds of the sole in horses can range from simple to complex—even life-threatening—depending on the area of penetration.
All foreign objects (e.g., nails, screws, glass, wooden objects) that manage to gain entrance to the internal structures through the sole of the foot have one thing in common—they carry debris and bacteria with them. Regardless of the injury's location, consider all sole punctures medical emergencies.
When encountering a patient with a puncture wound, I always ask the client, "Did you pull the object out?" Usually the answer is yes. But I prefer to hear, "No, I left it in and placed blocks around it, so you could see it and radiograph it first." Ah, but that's unlikely.
My second question is, "Did you save the object?" Usually the client has.
Another question of vast importance: "When did you pull the object out?" If it was removed several days ago, my job just got a lot harder, as we now have an anaerobic Petri dish brewing somewhere in the foot.
It's important to have the penetrating object in hand so you can judge its length and width. If it's a metal object, determine how corroded it is. In the case of many types of porous objects, the piece may appear broken (i.e., you'll be searching for fragments). Sometimes nails, screws or other metal objects are bent, which indicates forceful puncture of the foot. Or the object may have been bent before entry, which would indicate you need to look for a puncture that doesn't follow a straight route into the foot.
After you've gathered as many clues as possible about your penetrating object, sedate the horse and perform the following:
1. Proceed with an apical or posterior digital nerve block of the foot, depending on the location of the puncture.
2. Aseptically prepare the foot, find the entry hole and place a probe within the sole.
3. Obtain lateral, dorsopalmar and oblique radiographs of the foot.
4. Use curettes to open the wound all the way to its most distal extreme in an aseptic manner.
5. Take a sterile swab for culture and cytology.
Once opened and explored, puncture wounds should be packed with antibiotic-soaked gauze (amikacin is most commonly used) or diluted povidone-iodine and gauze. The greater the hole's diameter, the more pressure should be applied to the packing. Aseptically bandage the foot as soon as possible, and then affix a shoe with a water-tight hospital plate to the foot (Photo 1).
Photo 1: A typical hospital plate in place.
Review the anatomical location of the sensitive structures below the equine sole. This will help you with diagnosis and prognosis (Photo 2). The ungular tissue or bulbar mass below the heels (red dots in Photo 2) consists of collagenous tissue rich with circulation. An object penetrating the heel area can cause abscessation of the tissue and possible bacterial migration along the ungular cartilage, which may even gain entrance to either the distal interphalangeal or proximal interphalangeal joint.
Photo 2: A typical solar view of a hoof. The colored dots indicate the approximate puncture sites and the underlying structures.
Nails or other objects that enter the middle and medial sulcus of the frog (green dots in Photo 2) often go in at an angle, following the path of least resistance toward the deep flexor tendon (Photo 3).
Photo 3: A radiograph with a probe inserted to the depth of the navicular bone.