If, in spite of these treatments, the disease persists, then nothing remains but neurectomy.
D. DISLOCATIONS.
The firm and rigid manner in which the bones of the pedal articulation are held together renders dislocation of this joint an exceedingly rare occurrence, and then it is only liable to happen under the operation of great force. In the literature to our hand we have only been successful in discovering one reported instance, and, strange to say, in this, a well-marked case, the cause was altogether obscure. We quote the case at the end of this section.
FIG. 165.—DIAGRAM SHOWING THE COURSE TAKEN BY THE NEEDLE WHEN SETONING THE FROG. This is shown by the dotted curved line a, b. 1, The navicular bone; 2, the plantar cushion; 3, the os pedis; 4, the perforans tendon.
A partial dislocation of this articulation is the condition met with in 'Buttress Foot.' In this case the fracture of the pyramidal process, and the consequent lengthening of the tendon of the extensor pedis, allows the os coronæ to occupy upon the articulatory surface of the os pedis a more backward position than normally it should.
It is quite probable, too, that slight lesions of the other restraining ligaments and tendons of the articulation may bring about a similar though less marked condition. We may be quite sure of this—that whenever such lesions (as, for example, sprain and partial rupture of the lateral ligaments) do occur, and the normal position of the opposing bones is changed, if only slightly, that great pain and excessive lameness must be the result, and this with but little to show in the foot. Many of our cases of obscure foot lameness might, if capable of demonstration, turn out to be cases of sprain and partial dislocation of the pedal articulation.
Recorded Case.—'The animal, a trooper of the 8th Hussars, was found on the morning of April 17 unable to bear any weight on the limb (the near hind). Cause not known—the heel-rope I thought at first; but on investigation I found the heel-rope had been on the other leg.
Diagnosis.—Dislocation of the left os coronæ from the articulating surface of the os pedis in a backward direction.