The chronic thickening of the periosteum, seen in many definite bone diseases, will be mentioned under those diseases.
Osteomyelitis. Infectious osteomyelitis is acute suppuration of the bone, always due to the infection of the bone marrow by pyogenic microorganisms. The process is essentially like the process seen in furuncle, and begins in the marrow of the alveolar spaces, which communicate freely with each other, but are enclosed by a dense shell of cortical bone. Hence the process may quickly at first involve the entire marrow of an infected bone, because the products of bacterial infection are retained in this dense shell, while the primary focus can only be reached by extensive bone operation.
Most cases are due to the staphylococcus pyogenes aureus and a few to the streptococcus. Typhoid bacilli may cause suppuration. The infecting organism is present in pure culture but sometimes a mixed infection occurs, and such cases are said to be severe.
In cases of chronic osteomyelitis with open sinuses and exposed bone, a great variety of organisms, pathologic and saprophytic, may be present. Hence infectious osteomyelitis is not a specific disease, but is acute inflammation of bone that may be produced by any one of a variety of pathogenic organisms, or by a mixed infection.
Any pyogenic organism which can be carried in the blood may be deposited in the bone and produce suppuration. Some of these organisms may settle by preference in the bone marrow, others beneath the periosteum, or in the joint.
Certain general causes favor the occurrence of osteomyelitis. Children are chiefly affected and it occurs in boys about three times as often as in girls. Acute osteomyelitis frequently occurs after injuries of moderate severity, because such injuries may lower resistance of the bones and make them unusually susceptible to pyogenic infection. One of the commonest causes is the infection of a compound fracture, and before the days of asepsis, such cases were very frequently fatal. Under modern methods the infection, when it does occur, is generally slight, although the destruction of bone may greatly delay healing and may lead to the formation of small sequestra and indurating sinuses. Infection of a similar sort may occur subsequent to amputation.
Osteomyelitis nearly always begins in the diaphysis of the long bones, usually near the epiphyseal line. This is an important point, clinically, because tuberculosis practically begins in the epiphysis. In rare cases, however, osteomyelitis begins in the epiphysis, and so may simulate tuberculosis. The femur and tibia are the bones most frequently attacked, but no bone is exempt. Usually only one bone is affected, but cases of multiple bone infections are not rare.
The primary area of infection is always in the bone marrow. The bony trabeculae and the cortex are destroyed only secondarily. The process nearly always begins in the diaphysis, but then may extend into the epiphysis and produce suppuration of the joint. Once the organisms have gained access to the marrow, they produce a toxin which causes necrosis of the adjacent marrow cells, and this necrosis may extend over a very considerable portion of the bone before marked infiltration with leucocytes occurs. The infection usually extends quite early through the dense cortex by way of the Haversian canals, and produces an inflammatory exudation and suppuration between the periosteum and the outer layer of the cortex, which is designated subperiosteal abscess.
Such an abscess may strip the periosteum from the bone over very extensive areas. The infection may then extend to the adjacent soft parts, muscles and subcutaneous tissue, and form an abscess outside the periosteum.