Fig. 393. - Keratoma or Horn Tumour.
A tumour composed of horn sometimes forms on the internal face of the hoof, from which it projects inwards, and by continued pressure imbeds itself in the substance of the pedal or foot bone, some of which it causes to be absorbed. These growths may be elongated, ovoid, or cone-shaped. They mostly occur at the toe, but, rarely,also appear at the coronet, from which they extend downwards towards the lower border of the foot. Keratoma is produced by an abnormal growth of horn from the laminae or papillae of the vascular tissues by which the hoof is secreted.
These growths have their origin in some injury or irritation of the horn-secreting structures. A blow or tread on the coronet may be the exciting cause, but more commonly it would seem to have some connection with injury done to the toe, which is generally believed to be inflicted by too much force being used in hammering down the toe clip. Injury by a nail driven too near the quick may also be the starting-point, or it may follow a crack in the hoof. However produced, there is evidently a chronic state of congestion excited in the horn-forming structures at the seat of the morbid growth.
Fig. 394. - Keratoma or Horn Tumour Transverse section of foot, showing Keratoma (a) in situ.
The development of these tumours is slow and progressive, and there is reason to believe that but little or no inconvenience or suffering arises •during their early formation; but as they become larger they not only press directly upon the sensitive quick, but tend to cramp the whole of the internal parts of the foot, and cause absorption of the pedal-bone. The horse then becomes more or less lame. If the tumour is in front, he inclines the weight of the body towards the heel. There may be a bulging in the horn over the seat of the mischief, but it is just as likely that no outward change may be observed.
But little can be done in these cases short of removing the tumour, and this seldom succeeds in curing the lameness, and frequently aggravates the mishap.
Some relief may be afforded if the shoe be carefully seated out in such a way as to remove the pressure from the seat of the growth. Should the tumour be in front, a bar shoe gradually thinned off towards the heels may be applied to the foot, so as to incline the weight backwards and away from the diseased part.