Definition. - A condition of periostitis and ostitis in the region of the pyramidal process of the os pedis, usually preceded, but sometimes followed, by fracture of the process, and characterized by deformity of the hoof and an alteration in the normal angle of the joint.
Causes. - In the majority of cases buttress foot is brought about by fracture of the pyramidal process. Thus, although distinct evidence of such is nearly always wanting, we may assume that the original cause is violent injury to the part in question. Properly, therefore, one would say that this condition should be described under Fractures of the Os Pedis. It appears, however, that other cases of the kind arise in which fracture is altogether absent, or in which it is plainly seen to be subsequent to the diseased processes in the bone. For that reason, and also for the reason that the condition has come to be known by the name we have given, we give it special mention.
Symptoms and Diagnosis. - Even when the condition arises as the result of fracture, the ordinary manifestations of such a lesion are absent. By reason of the situation of the parts within the hoof we are unable to detect crepitation, and the resulting lameness is perhaps - in fact, nearly always is - neglected until such time as any heat or swelling caused by the injury has disappeared, in which case we are denied what evidence we might have obtained from that. All that is presented is lameness, and lameness that is at times excessive. But with the lameness there is nothing distinctive. The foot is tender on percussion, and the gait suggestive of foot lameness, that is all. We are unable, therefore, to make an exact diagnosis, and the condition goes for some time undetected.
Later, however, changes in the form of the hoof and the coronet begin to appear. The skin of the coronet, especially in the region of the toe, becomes more or less thickened and indurated, and the same remark applies to the subcutaneous tissues. The most marked change, however, is the alteration in the shape of the hoof. The wall protrudes at the toe in a manner that has been termed 'buttress-like,' and has given to the condition one of its names. This, of course, entirely alters the contour of the horny box. From being more or less U-shaped, it approaches nearer the formation of the letter V, the point of the V being at the toe.
In the later stages the coronary enlargement is plainly seen to be due to an extensive formation of bone. It is, in fact, a reparative callus, and the reason it reaches so large a size is probably to be accounted for by the pull of the extensor pedis upon the detached pyramidal process. As might be expected, this displacement of the fractured portion, with its effect of giving greater length to the extensor pedis, leads to a backward displacement of the os coronae upon the pedal bone. As a result there is a marked depression at the coronet, the depression being heightened in effect by the exostosis in front. Pyramidal disease is, as a rule, met with in the hind-feet, but occurs also in the fore.
Pathological Anatomy. - When occurring without fracture, the first observable change is a thinning of the articular cartilage of the pyramidal process, through which the bone beneath appears abnormally white. Later the thinning of the cartilage progresses until at last it becomes entirely obliterated. This destruction of the cartilage commences first at the highest point of the articular surface of the pyramid, and gradually reaches further backward into the joint. While this is taking place the new bone is being formed on the front of the os pedis, below and around the process, until, as we have already seen, an exostosis is formed, large enough to be noticeable at the coronet. This, of course, partly implicates the joint and the points of the insertion of the extensor tendon.
Finally, fracture may, or may not, take place. When it does, the exostosis is larger, and the general deformity of the hoof greater.
Treatment. - Ordinary treatment, such as point or line firing, repeated blisters, or hoof section, each of which we have tried, appears to be utterly useless. So far as we have been able to gather from the writings of other practitioners, however, neurectomy returns the animal for a time to usefulness. If the fore-limb is the seat of trouble, either plantar or median neurectomy may be practised; if the hind, then the best results are obtained by section of the posterior tibial.
Reported Cases. - 1. This animal, a mare, had been rested for lameness behind for two or three weeks, and then sent out to work, going sound. This was repeated several times, and each time the coachman reported, "Goes very lame behind after she has been at work about fifteen to twenty minutes." She always pulled out sound when I saw her in a halter on the following day, so I had her ridden, and after about seven or eight minutes she began to go lame in a hind-limb. Her lameness got rapidly worse as she was being ridden, and within a quarter of mile of her first showing lameness, she dropped and carried the lame foot in a way that suggested a badly fractured pastern. There was no recognisable disease in the limb to account for this lameness.
'I divided the posterior tibial nerve, and she went back to work moving sound, and continued to work sound up to her death from one of the regularly fatal bowel lesions twist or rupture.
'She worked nearly two years after unnerving, and developed the usual thickening at the coronet.'[A]
[Footnote A: W. Willis, M.K.C.V.S., Journal of Comparative Pathology and Therapeutics, vol. xv., p. 366.]
2. 'The subject of this note was a chestnut mare, nine years old, and used for omnibus work.
'History. - For about two months the mare was lame on the off fore-leg, and in spite of treatment the condition became steadily worse. The off fore-foot was rather long and narrow, and the fetlock-joint was inclined to be bowed outwards, but the degree of lameness was out of proportion to these defects, and the diagnosis was obscure.
'Median neurectomy was performed on May 10, 1902, and reduced the lameness to about half of what it was before. On June 5 ulnar neurectomy was performed, with the result that the mare became sound, and went to work three weeks later. She continued to work soundly and well, being inspected from time to time.
'During February of 1903 the coronet began to enlarge in front and slightly to the outer side, and gradually a ridge of bone grew down from the coronet to the toe. The case, in fact, became a typical one of so-called "buttress foot," which my friend Mr. Willis has described as diagnostic of disease of the pyramidal process of the pedal bone. Meanwhile the swelling of the coronet, which appeared to be mainly composed of fibrous tissue, increased in size, until the whole of the front and sides became involved, assuming the appearance shown in Fig. 156.
'In spite of the coronary enlargement the mare worked well, and remained free from lameness till June 8, 1903, on which day the limb became swollen up to the site of the median operation. The appearance of the limb closely simulated an attack of lymphangitis. The mare was kept under observation till the 13th of the same month, during which time the swelling increased, as did also the lameness to a slight degree. During progression she brought the heel to the ground and "rocked the toe," as in a case of rupture of the perforans tendon. The mare was killed on June 13.
Fig. 156. - A Case Of Buttress Foot.
Fig. 157. - Fracture Of The Pyramidal Process In Buttress Foot.
'Post-mortem. - In trying to pull away the hoof from the sensitive structures with a pair of farrier's pincers, the tendons and ligaments of the corono-pedal articulation gave way, leaving the pedal bone in situ. The flexor perforans tendon showed inflammatory softening, and was very nearly ruptured through at the level of the navicular bone. There was slight evidence of navicular disease. The articular cartilage of the corono-pedal joint had been almost completely removed, and there was sclerosis of the opposed bony surfaces, which by unequal wear had brought about deformity of the os coronae and os pedis.
There was very old-standing fracture of the pyramidal process (see Fig. 157), with the formation of a false joint between the process and the pedal bone. There was also a recent fracture of the part of the pedal bone which carries the articulation for the navicular bone, and this and the tendon lesions probably accounted for the final symptoms of 'break-down.'
Neurectomy enabled us to get a year's useful work out of what would otherwise have been a hopeless cripple.[A]
[Footnote A: A.R. Routledge, M.R.C.V.S., Journal of Comparative Pathology and Therapeutics, vol. xvi., p. 371.]