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Introduction
  • 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
    • location
      • typically metaphyseal via hematogenous seeding
    • risk factors
      • diabetes mellitus
      • hemoglobinopathy
      • rheumatoid arthritis
      • chronic renal disease
      • immune compromise
      • varicella infection
  • Pathophysiology
    • mechanism
      • local trauma and bacteremia lead to increased susceptibility to bacterial seeding
    • 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) 
        • 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)
        • an outer layer of new bone is formed by the periosteum (involucrum)
        • chronic abscesses may become surrounded by sclerotic bone and fibrous tissue leading to a Brodie's abscess 
    • definitions
      • involucrum 
        • a layer of new bone growth outside existing bone seen in osteomyelitis 
      • sequestrum
        • the necrotic bone which has become walled off from its blood supply and can present as a nidus for chronic osteomyelitis 
  • Prognosis
    • mortality has decreased from 50% to <1% due to new antibiotic treatment
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  
    • recommend 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 
      • 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 85% 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, no abscess
        • surgery is not indicated if clinical improvement obtained within 48 hours
      • 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.
  • Operative treatment
    • surgical drainage, debridement, and antibiotic therapy
      • indications
        • deep or subperiosteal abscess   
        • 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
        • evacuate all purulence, debride devitalized tissue, and drill as needed into intraosseous collections
        • remove the sequestrum in chronic cases
        • 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
        • follow with IV antibiotics and consider changing to PO antibiotics when ESR or CRP has returned to normal
Complications
  • DVT
    • is an infrequent complication in children    
      • risk factors
        • CRP > 6
        • surgical treatment
        • age > 8-years-old
        • MRSA 
  • Meningitis
  • Chronic osteomyelitis
  • Septic arthritis
    • bones with intra-articular metaphysis are at risk
    • hip, shoulder, elbow, ankle
  • Growth disturbances and limb-length discrepancies from growth plate involvement 
    • may result in gait abnormalities
  • Pathologic fractures
 

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