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
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Classification |
- Acute osteomyelitis
- 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
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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
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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
- 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
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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
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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
- 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
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