The treatment recommended is surgical. This consists in cutting the tendon of the peroneus muscle. The seat of the operation is a little below the hock and on the external face of the cannon.
[Illustration: FIG. 45.—String-halt.]
SPAVIN.—A spavin is a chronic inflammation of the articular faces of the hock bones, ligaments and synovial membranes. The inflammation may result in the formation of a bony enlargement on the inner surface of the region, and a union between the small bones forming the lower portion of the hock, and the upper extremities of cannon and lower hock bones (Figs. 46 and 47).
[Illustration: FIG. 46.—A large bone spavin.]
The predisposing causes are of the greatest importance. A spavin is one of the unsoundnesses of horses that may be transmitted to the offspring. Young colts that have heavy bodies and are fed a fattening ration are predisposed to it. Crooked hind limbs, small hocks and quarters that are heavily muscled are predisposing factors. The external causes are strains caused by slipping, turning quickly, rearing, pulling heavy loads and kicks. Horses three or four years of age if given work that favors hock strain, such as excavating cellars, may develop a spavin.
[Illustration: FIG. 47.—Normal cannon bone and cannon bone showing bony enlargement and lower hock bones united to superior extremity; this occurs in bone spavin.]
The symptoms or lameness are more characteristic than in most diseases of the limb. At the very beginning of the inflammation, and sometimes for several months afterward, the lameness is intermittent and disappears with exercise. After a time it is permanent. It is characterized by a stiffness of the hock. The extension of the hock is incomplete, the step is short and quick, the animal "goes on its toe" and the wall or shoe at the toe shows considerable wear. Because of the stiffness in the hock the animal raises the quarter when the limb is carried forward. Turning toward the well side may increase the lameness. The spavin test may be of value in diagnosing lameness. This consists in picking up the foot and holding the hock in a flexed position for a few minutes. The foot is then dropped to the ground and the animal moved off at a brisk trot. If the lameness is more marked, it indicates that the seat is in the region of the hock. This test is of greatest value in young animals. The bony enlargement can usually be seen best if the examiner stands in front and to one side of the animal. The hock should be observed from directly behind as well. The hocks of both limbs should be compared, and the general conformations of the other joints as well. This may prevent the examiner from mistaking rough hocks for spavin enlargements or "a pair" of spavins for rough hocks. A bony enlargement does not always accompany the lameness, and a spavin may be present without the horse going noticeably lame.
[Illustration: FIG. 48.—Bog spavins.]
The prognosis is always uncertain and should be guided somewhat by the conformation of the limb, character of the work required of the animal, position of the bony enlargement and the degree of lameness. The size of the enlargement is changed very little by the treatment. Veterinarians report recoveries in from fifty to sixty per cent of the cases treated.
The object of the treatment is to destroy the inflammation and bring about a union between the bones. The treatment recommended is counterirritation and rest. The most satisfactory method of counterirritation is firing followed by blistering. Following this treatment, the horse should be placed in a stall and given no exercise for a period of five or six weeks. It is sometimes advisable to repeat the counterirritation if the results of the first firing are unsatisfactory.