Cracks in the hoof wall are thought to occur primarily because of excessive forces placed on the hoof wall and the germinal tissue of the coronary band. It is proposed that shoeing does not allow the hoof wall to expand normally with weight bearing and that quarter cracks commonly form at the placement of the caudal nail, because the hoof wall will deform caudal to the nail but not cranial to it. This would place abnormal forces on the laminar tissue and the germinal tissue of the coronary band at that point, resulting in a defect in horn growth that appears as a crack. The same excessive force on a quarter can occur with a shoe in which the branch is too short (either due to placement of a shoe that is too small or to an inappropriate interval between resetting the shoe), resulting in excessive pressure and wall stress at the point where the shoe ends on the quarter. Toe cracks are also thought to occur in shod horses due to the fact that the toe expands abnormally between the cranial-most medial and lateral nails, leading to disruption of tubule formation at the coronary band.
A crack in the horn emanating distally from the coronary band is the most obvious sign. Lameness may be present, depending on the degree of wall instability or the presence of submural sepsis. If infection is established, there may be a purulent discharge and signs of inflammation and lameness.
Therapy first involves proper trimming of the foot to remove abnormal forces on the coronary band and wall. Once the farrier and veterinarian are satisfied that the foot is responding to the corrective trimming and shoeing (including the application of a bar shoe), the crack should be debrided (usually with a rotary tool), and any moisture or sepsis treated with appropriate antiseptic and/or astringent agents (eg, 2% iodine) until the crack is dry. Multiple wires are then applied across the crack to stabilize it. The wires can be placed either around sheet metal screws placed in the hoof wall on either side of the crack or through small holes drilled through the horn of the hoof wall on each side and exiting through the crack. The crack can be filled with either a resilient acrylic or putty, but it is critical that there be no moisture or sepsis present. Fenestrated tubing can be placed between the deepest aspect of the crack and the acrylic to allow for drainage. The hoof is then bandaged until new horn formation is evident.