Definition. - An abnormal condition of the lateral cartilages, in which the substance of the cartilage becomes gradually removed and bone formed in its place.
Fig. 143. - Ossified Lateral Cartilages (Side-Bones).
Symptoms and Diagnosis. - Side-bones are nearly always met with in heavy draught animals, and are rarely seen in the feet of nags. They are, moreover, nearly always confined to the fore-feet. In the ordinary way little need be said concerning their characteristics, and the way in which they may be detected. Neither need any concern be ordinarily manifested with regard to the effect they may have on the animal's gait and future usefulness. Seeing, however, that side-bone constitutes one of the recognised hereditary diseases, and that at the various agricultural and horse shows its existence or otherwise in a certain animal is a matter of great importance, some little attention must be given to these two points.
With a side-bone anywhere approaching full development, diagnosis is easy. The thumb is pressed into the coronet over the seat of the cartilage, when, in place of the elasticity we should normally meet with, we have the solid resistance offered by bone. In some instances diagnosis is even easier still. We refer to those cases in which the side-bone stands above the level of the coronet with such prominence as to be readily seen and recognised without manipulation, and where its growth has caused distinct enlargement and bulging of the wall of the affected quarter. It seems that in such cases the bone-forming process does not end with simply depositing bone in place of the removed cartilage, but that, after that is accomplished, the bone still continues to be produced, as in the case of an exostosis elsewhere.
Although diagnosis in cases such as these is easy, it becomes a very different matter when we are called upon to give an opinion in cases where ossification of the cartilage is only just commencing. Whether the result of our examination is to decide the sale or purchase of an animal, to determine his fitness or otherwise to enter the show-ring, or to merely advise a client as to whether or no a side-bone is in course of formation, our position is equally difficult, and in either case our examination must be searching.
Perhaps the best advice we can give is to say that the whole of the cartilage must be manipulated both with the foot on and off the ground. What the reason may be we do not pretend to say, but it is a well-known fact that in many instances the cartilage, with the foot bearing weight, is so rigid as to at once convey the impression that ossification has commenced or is even far advanced. And yet that same cartilage, with the foot removed from the ground, is as pleasantly yielding to pressure of the thumb as the most exacting of us could wish for. In any case, then, where doubt exists, the foot should be lifted to the knee, and the cartilage carefully examined with the foot in that position. If, then, at any spot above the normal contour of the os pedis we meet with hardness or rigidity, we are to look upon that foot with suspicion. Nevertheless, providing our conscience is sufficiently elastic, the animal may be passed sound so far as the existence of a side-bone is concerned. We know, however, that with commencing rigidity we may ere long expect one, and if our opinion is asked with regard to that particular, it must be admitted that with rigidity of the cartilage once commenced it is usually not long afterwards before a fully-developed side-bone makes its appearance.
As is only to be expected, the first noticeable hardening of the cartilage is to be found near the normal bone. We may thus look for it more particularly in the lower portions of the cartilage. We think we may say, too, that in the vast majority of cases the ossification of the cartilage commences in its anterior half. It is thus brought about that often we are called upon to examine and report on the condition when we have anteriorly a side-bone in course of formation, and posteriorly a perfectly normal cartilage. It is to the latter half of the cartilage that dealers and others mainly, if not wholly, devote their attention. A horse with the cartilage in this transition state will therefore pass muster, and a nice little point of ethics has again to be decided by the veterinary surgeon before giving his signature to a certificate of examination of an animal in this condition.
With regard to alteration in gait, we may say at once that side-bones in heavy animals are not often the cause of lameness. In fact, where the foot is well developed, when neither the foot as a whole nor the phalangeal bones give evidence of disease, and where the pasterns are fairly oblique and well formed, this alteration of the cartilages may be looked upon as of no serious import at all. Neither is the side-bone due to blows or other injuries likely to be productive of lameness - that is, always supposing, of course, that the foot in other respects is of good shape. If lameness is met with at all, then it is where we have a foot that is in other respects unsound, with badly contracted heels and upright 'stumpy' hoof, or where side-bones have occurred in a young animal, and have already reached a large size before the horse is put to labour. In this latter case, the added effects of concussion and the evil influences of shoeing are sufficient to turn the scale. Directly the animal, previously sound, is asked to work, lameness is the result.
It follows, therefore, that side-bone in the feet of young animals is of far more serious import than when occurring in older horses. In a nag animal they constitute a positive unsoundness, and lameness in this case is more often than not an accompanying symptom.