Osteomyelitis - Paediatric
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Summary
o Osteomyelitis in the pediatric population is most often the result of hematogenous
seeding of bacteria to the metaphyseal region of bone.
o Diagnosis is generally made with MRI studies to evaluate for bone marrow edema
or subperiosteal abscess.
o Treatment is nonoperative with antibiotics in the absence of an abscess. Surgical
debridement is indicated in the presence of an abscess.
Epidemiology
Incidence
 1 in 5000 children younger than 13 years old
o Demographics
 mean age 6.6 years
 2.5 times more common in boys
 more common in the first decade of life due to the rich metaphyseal blood supply
and immature immune system
 not uncommon in healthy children
o Anatomic location
 typically metaphyseal via hematogenous seeding
o Risk factors
 diabetes mellitus
 hemoglobinopathy
 juvenile rheumatoid arthritis
 chronic renal disease
 immune compromise
 varicella infection
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Etiology
o Pathophysiology
 mechanism
 local trauma and bacteremia lead to increased susceptibility to
bacterial seeding of the metaphysis
 history of trauma is reported in 30% of patients
 microbiology
 Staph aureus
 is the most common organism in all children
 strains of community-acquired (CA) MRSA have genes encoding for
Panton-Valentine leukocidin (PVL) cytotoxin
 PVL-positive strains are more associated with complex infections,
multifocal infections, prolonged fever, abscess, DVT, and sepsis
 MRSA is associated with increased risk of DVT and septic emboli
 Group B Strep
 is most common organism in neonates
 Kingella kingae
 becoming more common in younger age groups
 Pseudomonas
 is associated with direct puncture wounds to the foot
 H. influenza
 has become much less common with the advent of the Haemophilus
influenza vaccine
 Mycobacteria tuberculosis
 children are more likely to have extrapulmonary involvement
 biopsy with stains and culture for acid-fast bacilli is diagnostic
 Salmonella
 more common in sickle cell patients
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Pathoanatomy
 acute osteomyelitis
 most cases are hematogenous
 initial bacteremia may occur from a skin lesion, infection, or even
trauma from tooth brushing
 microscopic activity
 sluggish blood flow in metaphyseal capillaries due to sharp turns
results in venous sinusoids which give bacteria time to lodge in this
region
 the low pH and low oxygen tension around the growth plate assist in
the bacterial growth
 infection occurs after the local bone defenses have been
overwhelmed by bacteria
 spread through bone occurs via Haversian and Volkmann canal
systems
 purulence develops in conjunction with osteoblast necrosis,
osteoclast activation, the release of inflammatory mediators, and
blood vessel thrombosis
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macroscopic activity
 a subperiosteal abscess develops when the purulence breaks
through the metaphyseal cortex
 septic arthritis develops when the purulence breaks through an
intra-articular metaphyseal cortex (hip, shoulder, elbow, and ankle)
(NOT KNEE)
 Infants <1 year of age can have infection spread across the growth
plate via capillaries causing osteomyelitis in the epiphysis and septic
arthritis
 chronic osteomyelitis
 periosteal elevation deprives the underlying cortical bone of blood
supply leading to necrotic bone (sequestrum)
 sequestrum
 the necrotic bone which has become walled off from its blood
supply and can present as a nidus for chronic osteomyelitis
 an outer layer of new bone is formed by the periosteum (involucrum)
 involucrum
 a layer of new bone growth outside existing bone seen in
osteomyelitis
 chronic abscesses may become surrounded by sclerotic bone and
fibrous tissue leading to a Brodie's abscess
Anatomy
o Blood supply
 the metaphyseal blood capillaries undergo sharp turns prior to
entering venous sinusoids leading to turbulent flow and
predisposition of bacterial deposition
Classification
o Acute osteomyelitis
 see pathoanatomy above
o Subacute osteomyelitis
 uncommon infection with bone pain and radiographic changes
without systemic symptoms
 increased host resistance, decreased organism virulence,
and/or prior antibiotic exposure
 radiographic classification
 types IA and IB show lucency
 type II is a metaphyseal lesion with cortical bone loss
 type III is a diaphyseal lesion
 type IV shows onion skinning
 type V is an epiphyseal lesion
 type VI is a spinal lesion
o Chronic osteomyelitis
 see pathoanatomy above