Symptomatology.—­Lameness is the primary indicator and a constant symptom which attends navicular disease wherever much structural change affects the infirm parts.  As the degree of intensity or extent varies, so is there a dissimilarity in the character of the impediment.  Incipient cases of bilateral involvement are more difficult to diagnose than are unilateral affections, particularly when lameness is not marked.  There is manifested a supporting-leg-lameness which varies as to degree in the same subject at different times.  This may be noticed during the same trip in an animal that is being driven.  There is a tendency for the subject to stumble and, of course, where the affection is bilateral, there is a stilted gait owing to shortened strides.

At rest the lame animal usually points with the affected member.  Because of the fact that the distance is lessened between the origin and insertion of the deep flexor tendon (perforans) by this attitude, one may readily understand the reason for the position assumed by the subject.  Pressure on the navicular bone is diminished and tension on the flexor tendon is relieved by even slight volar flexion.

In acute inflammatory affections abnormal heat may be detected in the region of the heel.  By exerting tension on the flexor tendon, by means of passive dorsal flexion of the member, evidence of hyperesthesia may be detected.  With the hoof testers one may determine supersensitivenss in most instances.  There occurs more or less contraction of the hoof in navicular disease, but this is not to be taken as a cause of the affection, but rather a sequence.

[Illustration:  Fig. 32—­“Pointing”—­the position assumed by horse having unilateral navicular disease.]

In some cases of unilateral navicular disease there is a marked contrast in size between the sound and unsound foot.  However, one must not be misguided in this particular, for in some pairs of sound feet there exists considerable difference in size.  Finally, by a change from the normal position of the foot to one in which the heel is somewhat elevated (as may be obtained by shoeing with high heel calks), relief is evident, and in the opposite position, the condition is aggravated.  This experiment may be used for diagnostic purposes.

Treatment.—­When the anatomy of the diseased parts is taken into consideration, and an analysis of the lesions which occur in cases where considerable structural change is occasioned by this affection, it is obvious that recovery is impossible.  Only in cases where the inflammation is promptly checked before damage has been done the navicular bone or the flexor tendon, is permanent recovery possible.  The disease is not frequently treated during this stage, however, and in the majority of instances the condition becomes chronic.