Osteitis And Osteomyelitis have to be considered together, as the two conditions do not exist separately. This condition results from infection, either by micro-organisms from the blood, from local infections, or from a pre-existing periostitis. The inflammation generally starts in the medullary cavity of the long bones, the marrow of which is much congested at first and dark red in color. Later there is a cellular infiltration, and finally suppuration occurs, the pus being localized or in streaks. The surrounding bone becomes involved, and more or less extensive necrosis follows. The periosteum becomes inflamed, and the suppuration may extend to and involve the epiphyses. The necrotic portion may remain as a sequestrum, being surrounded by a layer of normal bone. As long as the sequestrum remains, healing will not take place, but when it is removed, either entire or by absorption, new bone is formed and there is a return to nearly the normal. When the condition terminates fatally, it is generally due to pyemia.

Chronic osteomyelitis generally is a condition following the acute form as a result of a retained sequestrum. The changes in this disease are more marked in the bone than in the marrow. There are two varieties of the chronic form: osteoporosis, in which absorption takes place with an increase in the size of the Haversian spaces. The bone becomes more spongy, and the enlarged spaces become filled with marrow; osteosclerosis, in which there is an increased formation of bone, particularly beneath the periosteum, but also within the marrow cavity. ' The subperiosteal deposit may be very dense and possess an ivory-like eburnation.

Rarefying osteitis consists of the formation within the marrow spaces, Haversian canals, or beneath the periosteum of a new, very cellular and vascular tissue, resembling granulation of young marrow tissue. This causes an absorption of the basement substance of the bone.