Osteoarticular infections (OAI) are a set of infectious diseases located in the bones and joints, that can also affect adjacent soft tissues. Osteomyelitis (OM) refers to OAI limited to the bone; and septic arthritis (SA) to those located in the joints. It is important to keep in mind that both entities can coexist in up to 30% of pediatric patients with OAI.
OAIs are essentially caused by bacteria, although they can also be of viral or fungal etiology. In most cases, the bacteria reach the bone via hematogenous means, although in cases, such as open fractures or surgeries, it is also possible that the infection occurs through direct inoculation of the microorganisms.
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Epidemiology
It is estimated that the annual incidence of pediatric OAI in developed countries is 4 cases per 100,000 inhabitants for OM and 2-13 for SA. The incidence is higher in pediatric patients compared to the adult population, especially in younger patients. Thus, 50% of pediatric OAIs occur in patients under 5 years of age and 25% in those under two. This fact is explained by the greater vascularization of the growing bones and joints of children. Despite the above, it is rare for OAIs to affect neonates, and these often present risk factors, such as late neonatal sepsis or being carriers of central venous devices.
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Pathogenesis:
Hematogenous dissemination of microorganisms to the long bones begins from the metaphysis. Their blood vessels are abundant, with slow and tortuous blood flow and highly permeable endothelial cells. All of this makes it easier for circulating bacteria to locally invade the bone marrow. Consequently, there is an increase in intramedullary pressure that causes the release of purulent material towards the cortex through the Volkmann canals, potentially breaking the periosteum and potentially reaching adjacent tissues.
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Etiology:
The agent Staphylococcus aureus (S. aureus) is primarily responsible for OAIs in all age groups. In our environment, the rate of methicillin-resistant S. aureus (MRSA) is low in the community. Even so, hospitalized patients have a higher risk of suffering OAI due to MRSA, as do those patients from areas with higher rates of community MRSA, such as the USA, Latin America, North Africa or Eastern Europe. Table I shows the main agents causing OAIs by age groups.