Caries ('rottenness') is a disease of bone analogous to the ulceration of soft tissues. It is characterised by a gradual loss of substance, from the particles of bone being absorbed, or being cast off and washed away in a purulent discharge. It begins as an unhealthy inflammation, followed by exudation of new materials, and softening of the part affected. On examination, the bone-cells are found filled with a reddish glairy fluid, and in scrofulous patients, deposits of tubercle. After caries has existed for some time, an abscess forms, and bursts; its aperture remains open, discharging a thin fluid, which contains particles of the bone. If a probe be passed through this opening, it will be felt to sink into some soft gritty substance; this is the carious bone, which, if removed and well washed, will be found to resemble in whiteness and fragility loaf-sugar softening in hot water.
Caries may attack any bone, but it usually selects the skull and face, the vertebrae, the bones of the foot, and the soft ends of long bones forming joints, especially in the lower limbs. To this terrible disease most deformities not congenital are owing. The carious vertebrae yield under the weight of the trunk, and the spine curves forwards, or to one side. In the joint-ends of bones the part enlarges, the cartilages become affected, matter forms, and amputation of the limb, or excision of the joint, is frequently necessary to save the patient's life. Too often the disease recurs with night-sweats, hectic symptoms, and death.
The causes of caries are usually constitutional, though it may be accidentally determined to some particular part of the body by any irritation, such as a blow, or exposure to atmospheric changes. Scrofulous persons, and those who have had syphilis or mercury in excess at any period of their lives, are more subject to it than others. If it affect a small bone, that bone may be entirely removed; and if the disease is strictly limited to the ends of bones forming a joint, these may be excised. Since 1860 great advances have been made in this department of surgery, and caries of the joints is comparatively seldom counted a sufficient reason for amputation; the knee, hip, shoulder, elbow, ankle, and wrist joints have all been repeatedly excised successfully. In situations where the part cannot be reached by instruments, lotions of dilute acid may be injected, with the view of stimulating the carious surface to assume a healing action.
The treatment of caries consists in supporting the patient's strength by judicious change of air and tonics, with the administration of medicines, such as cod-liver oil in scrofula, which appear to combat the constitutional predisposition to the disease. Under such treatment, with careful attention to free exit of the discharge and cleanliness of the wound, recovery often takes place without operation; but when the natural processes are not able to effect this in those parts where the diseased bone can be reached, it should be gouged or scraped away, or removed by caustics, so as to leave a healthy surface of bone, which may granulate up, and heal. See BONE. Caries of the Teeth is dealt with at TEETH.