Microbiology

Stages of disease

An osteomyelitis staging system is present in the literature for adult treatment and diagnosis of osteomyelitis. The Cierny-Mader classification is the newest system to account for host factors to aid with treatment. It categorizes the first part by anatomical involvement of infection, such as type 1 as medullary osteomyelitis and host type A as a normal host.

Generally the suppurative disease process involves 5 stages:

Inflammation: This stage represents initial inflammation with vascular congestion and increased intraosseous pressure. Obstruction to blood flow occurs with intravascular thrombosis.

Suppuration: Pus within the bones forces its way through the haversian system and forms a subperiosteal abscess in 2-3 days.

Sequestrum: Increased pressure, vascular obstruction, and infective thrombus compromise the periosteal and endosteal blood supply, causing bone necrosis and sequestrum formation in approximately 7 days.

Involucrum: This is new bone formation from the stripped surface of periosteum.

Resolution or progression to complications: With antibiotics and surgical treatment early in the course of disease, osteomyelitis resolves without any complications.

Complications include the following: (1) chronic osteomyelitis resulting from the persistence of the infective organisms (5-25%), (2) metastatic infection, (3) septic arthritis in children younger than 2 years as a result of the transphyseal spread of the infection (in adults, it occurs in the joints where the epiphysis is enclosed in the joint capsule [eg, hip and elbow joints]), (4) angular deformity of bones as a result of arrest of bone growth, (5) pathologic fractures, (6) bacteremia and septicemia, (7) soft tissue infection and persistent sinuses, and (8) premature epiphyseal fusion.

Staphylococcus aureus is the organism most commonly isolated from all forms of osteomyelitis (70-90%). Mycobacterium species, Gram-negative bacteria, syphilis, and fungal and viral agents are less common causes of osteomyelitis. Salmonella osteomyelitis may occur, particularly in children with sickle cell disease.

Osteomyelitis is a secondary complication in 1–3% of patients with pulmonary tuberculosis. In this case, the bacteria, in general, spread to the bone through the circulatory system, first infecting the synovium (due to its higher oxygen concentration) before spreading to the adjacent bone. In tubercular osteomyelitis, the long bones and vertebrae are the ones that tend to be affected.

A Brodie abscess is a localized form of osteomyelitis that appears in a subacute stage without preceding acute symptoms. Histologic evaluation shows an intraosseous abscess cavity lined by granulation tissue. The infecting organism is usually S. aureus. Patients typically present with relatively mild pain, which recurs over several months or sometimes years. The most common sites are the tibial or femoral metaphysis or diaphysis. The infection may cross the growth plate. Local soft tissue swelling is minimal, and no soft tissue mass is present.

Mortality/Morbidity

In the preantibiotic era, the mortality rate was as high as 25-40%. Antibiotics have reduced the rate to almost 0%; the complication rate is about 5%.

Дата добавления: 2014-10-15