Osteomyelitis

Descriptive text is not available for this imageBASICS

DESCRIPTION

  • Infection of any bone
  • Most commonly occurs in the metaphysis of a long bone (especially the distal femur or proximal tibia)

EPIDEMIOLOGY

  • One of the most common invasive bacterial infections in children, accounting for 1% of all pediatric hospitalizations
  • One third occurs in children <2 years of age, and ~50% of cases occur in children ≤5 years of age.
  • A history of minor trauma to the affected site is common but of unclear significance.
  • Boys are more commonly affected than girls (2:1 ratio).

ETIOLOGY

  • Staphylococcus aureus is responsible for 70–90% of osteomyelitis in all age groups, with community-acquired methicillin-resistant S. aureus (CA-MRSA) an increasingly common problem.
  • Streptococcus pyogenes accounts for ~10% of osteomyelitis and is more common in preschool and early school–aged children.
  • Streptococcus pneumoniae causes ~10% of osteomyelitis in children <3 years old, although a decline in pneumococcal infections has been seen with widespread vaccination. Conversely, S. pneumoniae remains an important cause of osteomyelitis in children who are at increased risk for invasive pneumococcal disease (e.g., chronic heart disease, chronic lung disease, diabetes mellitus, sickle cell disease, asplenia, splenic dysfunction, immunodeficiency).
  • Kingella kingae, a gram-negative organism found in the respiratory tract, is an important pathogen in children 6 to 36 months of age, especially in those who attend day care centers.
  • Group B Streptococcus, gram-negative enterics, and Candida spp. are important causative organisms in neonates.
  • Salmonella spp. can be the cause in children with sickle cell disease and in patients from or traveling to tropical countries.
  • Pseudomonas aeruginosa is a common cause following puncture wounds to the foot.
  • There has been a significant decline in the incidence of Haemophilus influenzae type b (Hib) osteomyelitis since immunization with the Hib conjugate vaccine became widespread.
    • Prior to widespread vaccination, this organism was an important cause of bone and joint infection in children and infants <2 years of age.
  • Other more unusual pathogens may be seen in patients with specific risk factors (e.g., coagulase-negative staphylococci in the presence of prosthetic material, anaerobes after animal or human bites; Aeromonas after injuries sustained in fresh water settings).
  • In a significant percentage of cases, a definitive causative microorganism is not identified. The use of antibiotic prior to collection of samples, presence of fastidious organisms, low inoculum, or inappropriately collected samples, may be a factor in culture-negative osteomyelitis.
  • Infections after open fractures or puncture wounds may be polymicrobial.

PATHOPHYSIOLOGY

  • Hematogenous spread is most common in children (inoculation of bone during an episode of bacteremia). The infecting organism enters the bone via a nutrient artery and then is deposited in the metaphysis due to its rich vascular supply. The organism replicates in metaphyseal capillary loops, causes local inflammation, spreads through vascular tunnels, and adheres to the bone matrix. Increased pressure in the metaphysis allows pus to perforate through the cortex and lift the periosteum.
  • In newborns and young infants, rupture of pus into the adjacent joint space is more common because blood vessels connect the metaphysis and epiphysis.
  • Local spread from a contiguous focus of infection and direct inoculation (e.g., penetrating injury) are less common mechanisms of infection.

RISK FACTORS

  • Sickle hemoglobinopathy
  • Primary or acquired immunodeficiency, especially chronic granulomatous disease (CGD) and HIV
  • Bone trauma (open fractures, puncture wounds, bites, surgical manipulation)
  • Implanted orthopedic devices or indwelling vascular catheters
  • Pressure ulcers

There's more to see -- the rest of this topic is available only to subscribers.