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  • summary
    • Osteomyelitis in the pediatric population is most often the result of hematogenous seeding of bacteria to the metaphyseal region of bone.
    • Diagnosis is generally made with MRI studies to evaluate for bone marrow edema or subperiosteal abscess.
    • 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
    • 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
    • Anatomic location
      • typically metaphyseal via hematogenous seeding
    • Risk factors
      • diabetes mellitus
      • hemoglobinopathy
      • juvenile rheumatoid arthritis
      • chronic renal disease
      • immune compromise
      • varicella infection
  • Etiology
    • 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
      • 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
          • 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
    • Blood supply
      • the metaphyseal blood capillaries undergo sharp turns prior to entering venous sinusoids leading to turbulent flow and predisposition of bacterial deposition
  • Classification
    • Acute osteomyelitis
      • see pathoanatomy above
    • 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
    • Chronic osteomyelitis
      • see pathoanatomy above
  • Presentation
    • History
      • limb pain
      • recent local infection or trauma
      • obtain immunization history regarding H. influenza
      • ask about prior antibiotic use, as it may mask symptoms
    • Symptoms
      • limp or refusal to bear weight
      • generally not toxic appearing
      • +/- fever
    • Physical exam
      • inspection & palpation
        • edematous, warm, swollen, tender limb
        • evaluate for point tenderness in pelvis, spine, or limbs
      • range of motion
        • restricted motion due to pain
  • Imaging
    • Radiographs
      • recommended views
        • obtain AP and lateral of the suspected area
      • findings
        • early films may be normal or show loss of soft tissue planes and soft tissue edema
        • new periosteal bone formation (5-7 days)
        • osteolysis (10-14 days)
        • late films (1-2 weeks) show metaphyseal rarefaction (reduction in metaphyseal bone density) or possible abscess
    • CT
      • indication
        • more helpful later in the disease course to demonstrate bone changes or abscesses
    • MRI
      • detects abscesses and early marrow and soft tissue edema
      • indications
        • can assist with decision making when a poor clinical response to antibiotics or surgical drainage considered
      • views
        • T1 signal decreased
        • T1 with gadolinium signal increased
        • T2 signal increased
      • 88% to 100% sensitivity, sensitivity increased by Gadolinium contrast
    • Bone scan
      • indications
        • nondiagnostic x-ray
        • need to localize pathology in infant or toddler with non-focal exam
      • technetium-99m can localize the focus of infection and show a multifocal infection
      • 92% sensitivity
      • a cold bone scan may be associated with more aggressive infections
  • Studies
    • Serum labs
      • WBC count
        • elevated in 25% of patients and correlates poorly with treatment response
      • C-reactive protein
        • elevated in 98% of patients with acute hematogenous osteomyelitis
        • becomes elevated within 6 hours
        • most sensitive to monitor therapeutic response
        • declines rapidly as the clinical picture improves
        • CRP is the best indicator of early treatment success and normalizes within a week
          • failure of the C-reactive protein to decline after 48 to 72 hours of treatment should indicate that treatment may need to be altered
      • ESR
        • elevated in 90% of patients with osteomyelitis
        • rises rapidly and peaks in three to five days, but declines too slowly to guide treatment
        • less reliable in neonates and sickle cell patients
      • plasma procalcitonin
        • new serologic test that rises rapidly with a bacterial infection, but remains low in viral infections and other inflammatory situations
        • elevated in 58% of pediatric osteomyelitis cases
      • bone aspiration
        • helps establish a definitive diagnosis
        • 50% to 70% of affected patients have positive cultures
      • blood culture
        • is positive only 30% to 50% of the time and will likely be negative soon after antibiotics are administered, even if treatment is not progressing satisfactorily
    • Aspiration
      • assists in diagnosis and management
        • helps guide antibiotic selection when organism identified (50% of the time)
        • proceed with surgical drainage if pus is aspirated
      • technique
        • large bore needle utilized to aspirate the subperiosteal and intraosseous spaces under fluoroscopic or CT-guidance
        • start antibiotics after aspiration
    • Biopsy and culture
      • consider when diagnosis not clear (i.e. subacute osteomyelitis) and need to rule out malignancy
  • Treatment
    • Nonoperative treatment
      • antibiotic therapy alone
        • indications
          • early disease with no subperiosteal abscess or abscess within the bone
          • surgery is not indicated if clinical improvement obtained within 48 hours
        • modalities
          • antibiotics
            • begin with empiric therapy
              • generally, nafcillin or oxacillin, unless high local prevalence of MRSA (then use clindamycin or vancomycin)
              • mechanism of action for vancomycin involves binding to the D-Ala D-Ala moiety in bacterial cell walls
              • if gram stain shows gram-negative bacilli - add a third generation cephalosporin
            • convert to organism-specific antibiotics if organism identified
              • mycobacterium tuberculosis
              • treatment for initial 1 year is multiagent antibiotics and rarely surgical debridement due to risk of chronic sinus formation
            • duration
              • typically treat with IV antibiotics for four to six weeks
                • controversial duration
            • intravenous versus oral
              • often a case by case decision with input from infectious disease consultation
    • Operative treatment
      • surgical drainage, debridement, and antibiotic therapy
        • indications
          • failure to respond to antibiotics
          • chronic infection
        • contraindications
          • hemodynamic instability, as patients should be stabilized first - however sometimes operative treatment of the underlying infection helps stabilize the patient
        • example of institution algorithm treatment pathway
  • Technique
    • Surgical drainage, debridement, and antibiotic therapy
      • soft tissue
        • evacuate all purulence, debride devitalized tissue, and drill as needed into intraosseous collections
        • send tissue for culture and pathology to rule out neoplasm
        • close wound over drains or pack and return to OR in two to three days
      • bone work
        • remove the sequestrum in chronic cases
  • Complications
    • DVT
      • incidence
        • is an infrequent complication in children
      • risk factors
        • CRP > 6 mg/dL
        • surgical treatment
        • age > 8-years-old
          • Coagulase (+) 
            • Causes activation of thrombin and fibrin clot formation
      • treatment
        • therapeutic anticoagulation
    • Meningitis
    • Septic arthritis
      • risk factors
        • bones with intra-articular metaphysis are at risk (shoulder, elbow, hip, ankle)
        • neonates
      • treatment
        • irrigation and debridement
    • Growth disturbances and limb-length discrepancies from growth plate involvement
      • treatment
        • observation and possible corrective surgery depending on severity or projected severity
    • Pathologic fractures
  • Prognosis
    • Mortality decreased from 50% to <1% with development of antibiotics
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