Causes. The more common causes of necrosis as it affects horses are blows and bruises directly applied to the bone; hence it occurs that those bones or parts of bones most superficially placed, and consequently most exposed to injury, are especially liable to the disease. Bones deeper seated and enveloped in thick layers of muscle are comparatively seldom affected. For the above reasons necrosis is found to implicate the front of the shin or canon bones both in the fore and hind limbs, and also the lower jaw-bone and the ribs. The shin-bones in the act of jumping are not unfrequently brought into forcible contact with posts and rails, gates and stone walls, or they are injured by kicks from other horses, etc. The most common seat of the disease is the lower jaw at the resting-point of the bit, where the resistance to runaways, pullers, and hard-mouthed horses is specially applied. In addition to external violence necrosis may be induced by acute inflammation of bone in any part of the skeleton.

Symptoms

Where an injury is inflicted on bone sufficiently severe to destroy its vitality the immediate effects are more or less swelling, heat, and tenderness of the part, and when involving the bones of the extremities more or less lameness. In superficial bones the swelling-is not generally considerable and may soon altogether subside, leaving behind, however, an abiding tenderness of the part. Sooner or later the swelling reappears, or if still present becomes considerably increased, while the heat and soreness return with greater severity than before. As the inflammation becomes more and more severe an abscess is formed, which may break, and heal, and break again and again, and finally resolve itself into a chronic running sore. During this time the dead piece of bone is being separated from the living. If a probe be passed into the wound the harsh grating of its point on the dead bone will be felt. These cases are always of a protracted nature, and when neglected extend over months.

When the lower jaw is the seat of injury the animal jibs when ridden or driven, or turns the head towards the side on which the disease exists. The saliva is raised into foam by champing of the jaws, and may be stained with blood. Feeding is rendered painful, and swelling appears on the outer part of the injured bone and extends for some distance around it. If the finger be applied to the spot a wound in the gum will be found corresponding to the injured part, through which the dead fragment is readily felt, and if completely detached may be brought away. The odour emitted in these cases is usually very offensive. Although sloughing may have completely taken place, and the dead bone have been quite detached from the living, it may still be retained unless means are adopted for its removal.

Treatment

Here the aim and object of treatment should be to remove the dead bone as speedily as possible, but no attempt should be made in this direction until nature has defined its limits and well-nigh completed its separation from the living. If after this it is allowed to remain it becomes a source of irritation, and the wound continues to discharge and refuses to heal. It becomes necessary, therefore, that a periodical examination of the diseased part should be made, in order that the earliest opportunity may be seized to extract the offending matter. For this purpose it may be necessary to lay the wound open. This done the finger should be introduced, and the necrosed mass will be found probably grown over by granulations or "proud flesh", or at least united by them to the body of the bone. If detachment has not been completely effected a little force, by means of a small lever placed under the dead fragment, may be sufficient to disconnect it.

The dead bone having been removed the wound may be freely dressed with a strong solution of chloride of zinc, and afterwards treated with antiseptic applications until reparation is complete.