In the case of crack extending the whole space of the wall some provision should always be made to keep it from opening, because every step of the horse, especially when drawing a load, causes an outward pressure at the coronet. This pressure forces the hoof apart and the injury caused does not cease with the pain and lameness which follow, and which may be temporary. Doubtless the original cause of a sandcrack is some morbid condition of the coronary band—the band from which the wall grows. The sensitive laminæ are at first not affected further than by the inflammation consequent upon the direct tearing which occurs when the crack takes place. The continued irritation, kept up by a persistent fissure in the horn covering the laminæ, soon causes other serious changes which tend to make the sandcrack a permanent disease. Thus even the smallest crack should be attended to and measures adopted to prevent its enlargement or, when extensive, to limit all opening and shutting movement of the hoof.
Fig. 83.—French Clips in Position.
This is sometimes attempted by a simple leather strap tightly applied, or by binding the foot with string or tape. Tape is less liable to slip than string. When the hoof is sufficiently thick two nails may be driven in opposite directions transversely through the crack and clinched; or French sandcrack-clips ([Fig. 83]) may be used which are easily applied. The instruments necessary are shown below ([Fig. 84]). The iron (b) is made red-hot and pressed on the hoof over the crack so as to burn a groove each side of it. Into these grooves the clip (a) is put and the pincers (c) are then used to compress the clip firmly into its place. There is a strain upon the clips, and sometimes one breaks. It is therefore necessary always to use two, and for an extensive crack three may be employed.
Fig. 84.
All these appliances tend to keep the lips of the crack from separating, but they do not prevent the edges of a deep wide crack from being forced together and thus pinching the sensitive parts. To provide against this injury a slip of hard wood may be fitted into the crack, and then the nails or clips may be more safely drawn tight without fear of injury, and with a better chance of preventing any movement in the edges of the crack. To insert the wood, the crack is converted into a groove nearly as deep as the wall, about three-eights of an inch wide, with straight sides, or better still, with a little greater width at the bottom than at the surface. Into such a groove a piece of wood formed to fit it is gently driven from below and rasped off to fit exactly. Or, softened gutta-percha may be pressed firmly into the space and levelled off when cold.
To "cut out" a sandcrack except for the purpose of refilling it is bad practice as it favours movement and helps to make the defect permanent. To rasp away the horn so that only a thin layer is left is also injurious. No horn should be removed except for the fitting of a plug as above described or, under veterinary direction, for the purpose of giving vent to matter which has formed within the hoof.