Pathogenesis. Neonatal osteomyelitis arises as a consequence of hematogenous spread of microorganisms, which is the most common route of infection. In preterm infants,

Microbiology

Neonatal osteomyelitis arises as a consequence of hematogenous spread of microorganisms, which is the most common route of infection. In preterm infants, neonatal osteomyelitis frequently results from directly inoculated bacteria (secondary to heel or venipuncture, umbilical catheterization, infected cephalhematoma, etc.). Premature rupture of membranes and transplacental infection have also been described as risk factors for neonatal osteomyelitis.

The most common bacterial pathogen causing osteomyelitis in children is Staphylococcus aureus in all age groups. Group B streptococcus (Streptococcus agalactiae) and gram-negative organisms (E. coli and Klebsiella pneumonia) are also important bacteria in the neonatal period. Community-acquired strains of methicillin-resistant Staphylococcus aureus have emerged as being relevant in recent years and cause serious infections in the neonate.

Hematogenous infection of the long bones, which are most frequently affected, begins in the capillary loops of the metaphysic, adjacent to the cartilaginous growth plate (physis). These areas are very susceptible to hematogenous infection, because of its high vascularity and because the blood flow within the vessels is slow. Bacteria can pass through gaps from the sinusoidal veins to the capillaries into the tissue, where they are provided an ideal environment to grow, resulting in abscess formation. These abscesses frequently rupture into the joint. In neonates acute hematogenous osteomyelitis and septic arthritis co-exist in up to 76% of all cases as a result of this unique vascular anatomy of the epiphysis; the bone marrow compartment is seldom involved. The epiphysis receives its blood supply directly from metaphyseal blood vessels (transphyseal vessels) and the adjacent cartilaginous growth plate is traversed by capillaries, allowing spread of the pathogenic bacteria to the physis, epiphysis and joint and resulting in slipped epiphyses, fractures, premature physeal closure and chronic infection.

Characteristics of the neonatal bone prevent many of the features of chronic osteomyelitis: cortical sequestra are often completely absorbed due to extensive bone blood supply in the newborn and, in addition, efficient vasculature of the inner layer of the periosteum encourages early development of new bone formation. Complete destruction of joints is rare, but serious growth disturbances may occur.

Дата добавления: 2014-10-15