Causes of Osteomyelitis: some important points

This is the abstract prepared from the latest edition of Campbell Orthopaedics.

Acute hematogenous osteomyelitis is the most common type of bone infection and usually is seen in children. The incidence of acute hematogenous osteomyelitis has decreased dramatically over the last several decades. Blyth et al. reported a 70% decrease in the incidence of acute hematogenous osteomyelitis in the Greater Glasgow Health Board from 1970 to 1997. A higher standard of living and improved hygiene probably have contributed to this trend.
Acute hematogenous osteomyelitis is more common in males in all age groups affected. It is caused by a bacteremia, which is a common occurrence in childhood. The causes of bacteremia are many. Bacteriological seeding of bone generally is associated with other factors such as localized trauma, chronic illness, malnutrition, or an inadequate immune system. In many cases, the exact cause of the disease cannot be identified.

In children, the infection generally involves the metaphyses of rapidly growing long bones. The age distribution of acute hematogenous osteomyelitis in children is bimodal, generally affecting children younger than 2 years and children 8 to 12 years old. The effects of osteomyelitis in children vary with age based on differences in blood supply and the anatomical structure of the bone.
Hematogenous seeding of bone in adults usually is seen in a compromised host. Although it can occur anywhere and in any part of the bone, generally the vertebral bodies are affected.

Spread of infection to a contiguous joint also is affected by the patient's age. In children younger than 2 years, the common blood supply of the metaphysis and epiphysis crosses the physis and can allow spread of a metaphyseal abscess into the epiphysis and eventually into the joint. The hip joint is the most commonly affected in young patients; however, the physes of the proximal humerus, radial neck, and distal fibula also are intraarticular, and infection in these areas can lead to septic arthritis as well.

Staphylococcus aureus is the most common infecting organism found in older children and adults with osteomyelitis. Gram-negative bacteria have been found to cause an increasing number of vertebral body infections in adults.
Pseudomonas is the most common infecting organism found in intravenous drug abusers with osteomyelitis.
Fungal osteomyelitis is seen increasingly in chronically ill patients receiving long-term intravenous therapy or parenteral nutrition.
Salmonella osteomyelitis has long been associated with SS or SC hemoglobinopathies. This infection tends to be diaphyseal rather than metaphyseal
In infants with acute hematogenous osteomyelitis, S. aureus is still a frequent isolate, but group B streptococcus and gram-negative coliforms also are commonly found. S. aureus or gram-negative organisms are the usual cause of orthopaedic infections found in premature infants undergoing treatment in the neonatal intensive care unit; more than 40% have multifocal involvement.
Group B streptococcus is the most likely infecting organism found in otherwise healthy infants 2 to 4 weeks old.
Haemophilus influenzae infections occur primarily in children 6 months to 4 years old. The incidence of this infection has been reduced dramatically because of routine immunizations against the organism.