2009 In-Depth Equine Podiatry Symposium Notes
Written and presented January 2009 by R.F. (Ric) Redden, DVM
Full thickness toe cracks are frequently found in brood stock and a few sport horses. The cracks are the result of mechanical failure. Normally the anterior/posterior balance is off the scale, and the horse has a long toe, underrun heel and dropped soles. A club foot can develop an abscess in worn areas of the toe that have been invaded by bacteria, which invariably breaks at the coronary band, resulting in a permanent scar. The wall fractures due to internal bending stress and the lack of anterior hoof capsule integrity. As the deep digital flexor (DDF) transfers load to the bone, the bone pulls on the laminae that were once secured to a very strong but now weakened wall, and the system fails. The laminae pull causes closing of the crack when the foot is loaded. The sole sags as the bone travels away from the normal arch of the wall, to seek ground support as the wall can no longer maintain the natural internal balance.
Many people are surprised that center toe cracks do not open when loaded, as the cow's foot would. It closes and closes very tightly, folding the sensitive laminae in on itself, perpetrating a permanent scar that becomes thicker and more invasive every time an abscess breaks at the coronary band. The sensitive tissue at the top of the crack becomes a painful area. A thin sole and traumatized apex also contribute to the painful condition.
The best option is an example of physics 101: Stop the movement of the two wall sections on each side of the crack and it will heal. There are two basic ways to stabilize the wall with rigid implantation. Pull the crack together and lace or band, or hold it apart and lace and band. I prefer the latter as this is the more natural anatomical position of each side of the crack, and it prevents the inevitable scar that forms when the crack is pulled together.
The DDF influence is the major force influencing movement in the wall, laminae and bone. Therefore the major goal regardless of bands, stitches and so forth is to significantly reduce DDF tension, as it continues to be a key player even when the wall is made less flexible with the band. This can be accomplished by creating a 20 degree palmar angle (PA). Using only wedges to produce the 20 degree PA will reduce DDF tension, but also crush the heel very quickly. Wedges and high breakover mechanics will accomplish the same with less heel crush. Add contact sole support (no positive pressure) and sole sag is significantly diminished. Add positive frog and buttress support to help open the contracted heels and you have a highly functional shoe. Once shod in this fashion, the breakover will be directly beneath the center of articulation. The toe is only backed up at the ground surface. The dish will grow off as new horn grows in line with the face of PIII and the new horn wall will remain intact as long as the DDF tension is adequately reduced. As a rule, I no longer band toe cracks unless the described rocker action shoe that provides a 15-18 degree PA fails to promote strong horn growth without evidence of the crack.
Very extensive toe cracks that occur in thin wall, poor quality feet may require a metal band to hold the crack apart. The goal for the shoeing concept is to prevent the crack from being pulled inward, closing the gap. If a band is required, I use a 10 gauge strip cut in the shape of the curvature of the wall. Drill three to four 3/16 inch holes in the plate on either side of the crack. Pick the foot up (unload the DDF) and hot seat the band onto the foot. Burn it in good, then place the screws in while the foot is totally unloaded. Four 1/2 inch number 8 pan head screws on either side of the crack work well.
Dr. Redden's Toe Crack Treatment
Loading the foot or closing the crack can also aid healing, but invariably creates a thicker scar as the laminae is folded tightly on itself. Quarter clips look great on paper but do nothing to stabilize the crack, as it does not open when loaded. They do, however, help hold the shoe on. The high score rocker rail shoe accelerates sole growth and subsequently toe growth. This shoe is often all that is needed to prevent new horn from being torn along the old scar. Chronic cracks that have caused several abscesses at the heels and coronary band will show signs of each blow out. Normally I will band these as well, to assure optimum mechanics. Radiographs used as an initial planning tool and for subsequent resets are an invaluable resource for the vet/farrier team. Prognosis is good for all toe cracks regardless of chronicity or severity.