External signs of fatal sinker syndrome
Externally, horses with fatal sinker syndrome will show several signs. The hoof capsule may appear dry and friable. The entire sole will appear flat and collapsed. The hair above the coronary band will stick straight out or up, depending on how far the articular column has sunk into the hoof capsule.
Figure 5: A typical coronary band shear.
A sunken area or ledge above the coronary band will be noted all the way around the foot except in the bulbar area. The ledge will correlate with the change in the hair pattern. The coronary band will swell (Figure 4). A dry crack or shear lesion will follow as a sequela to the sunken ledge (Figure 5). The soft tissue of the bulbs will appear weak visually and palpably and may exude blood, serum or pus.
Figure 6: The coronary band and bulbs that have separated and deformed.
In the final stages, the coronary band will start to separate all the way around the hoof capsule and will, like the bulbs, leak serum, blood or pus (Figure 6). The hoof capsule will shrink as it loses its blood supply, acting like a tourniquet around the internal structures (Figure 7), further worsening the condition and resulting in complete hoof capsule avulsion.
Figure 7: A hoof capsule prior to avulsion that has shrunken around the soft tissue structures, compressing circulation.
Treatment: Plan A vs. Plan B
In the early stages of fatal sinker syndrome, if blood flow—albeit diminished—is still observed in the dorsal, circumflex and bulbar regions of the foot (as observed through your venography study) (Figure 8), then a casting procedure of the foot may be tried—this is your Plan A. The cast is a simple foot cast from the mid-pastern region, incorporating the entire hoof capsule. The cast is applied to a standing, sedated horse.
Figure 8: A lateral venogram of a horse with fatal sinker syndrome that has diminished blood flow and may benefit from a hoof casting procedure. Note the flattened appearance of the bulbar circulation and the complete absence of the circumflex circulation often seen with severe sinkers. Also visible is the dorsal circumflex junction that is contorted from the sinking P3.
Here are the steps for treatment Plan A:
- Create a groove into the hoof wall just distal to the coronary band in the area below the ledge.
- Tape a 0.5-inch-thick-by-1-inch-wide strip of felt to the mid-pastern where your cast will end.
- Apply a second strip of felt to the coronary band.
- Cut a third piece of felt to the size of the solar surface and apply it to the sole. (The coronary band and sole felt may be impregnated with povidone-iodine if you think they will become compromised while in the cast.)
- Apply cast padding to the entire area to be casted. Apply a thin cotton material over the cast padding to make the casting tape easier to remove later.
- Apply fiberglass casting tape. The width of the casting tape depends on the size of the foot to be cast.
- Once the cast has dried, apply a hoof acrylic to the bottom or solar region of the cast to give a slightly domed shape to aid in the mobility of the foot.
Leave the cast on for four weeks and obtain radiographs weekly. Multiple casts will be required. Strict stall rest is required, as in all acute laminitis cases. Should any deterioration in your parameters occur, or should increased swelling, pain or heart rate occur during that time, then the cast needs to be removed and the situation reassessed.
If improvement is not progressive with the simple foot cast, then it may be time for Plan B, which will be discussed in Part 5 of this series.
Andrea E. Floyd, DVM, has specialized in equine podiatry for more than 25 years. She is the owner of Serenity Equine in Evington, Va., and the author of Equine Podiatry. Dr. Floyd is a member of the American Veterinary Medical Association, American Association of Equine Practitioners and the American Farriers Association.