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Bacterial (septic) arthritis occurs most commonly in children younger than 3 years. Staphylococcus aureus is the most common cause of bacterial arthritis in all age groups.
Prepatellar bursitis (septic) is seen in children with local cellulitis and often local trauma. Children will present with local signs of infection and preservation of joint function. Treatment is focused on local aspiration and drainage and antibiotics targeted at S. aureus.
Discitis presents in children most commonly with abnormal gait or lower back pain. Clinical improvement comes with early anti-inflammatory medications and antibiotics targeted at S. aureus and Kingella kingae.
Clinical manifestation of infectious tenosynovitis ranges from pain with passive extension to tenderness along the tendon sheath. Management includes surgical intervention and antibiotic therapy
Osteomyelitis typically develops after a period of bacteremia and presents with fever, and progressively increasing bone pain or limp. S. aureus is the most common cause of acute hematogenous osteomyelitis in children; however, K. kingae is increasingly identified in preschool aged children with osteoarticular infections.
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Infections of the joint are most commonly bacterial but may be caused by an array of organisms (i.e., fungal or viral). The term septic arthritis encompasses bacterial arthritis, pyogenic arthritis, suppurative arthritis, purulent arthritis, and pyarthrosis. It occurs most commonly in childhood; children younger than 3 years are affected most frequently. Boys are affected more often than girls (male-to-female ratio of 1.2–2:1). Infections of the knee, hip, and ankle account for at least 80% of cases, with the hip and knee most commonly affected. Early diagnosis and treatment of a septic hip is essential in preserving function. Delay in treatment increases the risk of complications, including osteonecrosis of the capital femoral epiphysis, osteomyelitis, chondrolysis, systemic sepsis, and secondary osteoarthritis.1
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Normal joints contain a small amount of synovial fluid, which is viscous, clear, and mostly acellular. Microorganisms can enter the joint space by hematogenous spread (which accounts for most cases), direct inoculation, or extension of a contiguous focus of infection, that is osteomyelitis. The high, effective blood flow and lack of basement membrane in the synovium facilitate the entry of bacteria into the joint space during episodes of bacteremia. Host cells responding to bacterial endotoxin release cytokines, which stimulate the release of proteolytic enzymes and increase leukocyte migration, thus destroying the synovium and collagen matrix and inhibiting cartilage synthesis. Gram-positive organisms, specifically S. aureus, are the most common causative organisms (see Table 61-1 for other organisms to consider).
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