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SUMMARY
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Osteomyelitis in the pediatric population is most often the result of hematogenous seeding of bacteria to the metaphyseal region of bone.
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Diagnosis is generally made with MRI studies to evaluate for bone marrow edema or subperiosteal abscess.
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Treatment is nonoperative with antibiotics in the absence of an abscess. Surgical debridement is indicated in the presence of an abscess.
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EPIDEMIOLOGY
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Incidence
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1 in 5000 children younger than 13 years old
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Demographics
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mean age 6.6 years
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2.5 times more common in boys
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more common in the first decade of life due to the rich metaphyseal blood supply and immature immune system
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not uncommon in healthy children
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Anatomic location
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typically metaphyseal via hematogenous seeding
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Risk factors
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diabetes mellitus
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hemoglobinopathy
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juvenile rheumatoid arthritis
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chronic renal disease
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immune compromise
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varicella infection
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ETIOLOGY
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Pathophysiology
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mechanism
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local trauma and bacteremia lead to increased susceptibility to bacterial seeding of the metaphysis
- history of trauma is reported in 30% of patients
- history of trauma is reported in 30% of patients
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microbiology
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Staph aureus
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is the most common organism in all children
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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
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Group B Strep
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is most common organism in neonates
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Kingella kingae
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becoming more common in younger age groups
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Pseudomonas
- is associated with direct puncture wounds to the foot
- is associated with direct puncture wounds to the foot
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H. influenza
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has become much less common with the advent of the Haemophilus influenza vaccine
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Mycobacteria tuberculosis
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children are more likely to have extrapulmonary involvement
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biopsy with stains and culture for acid-fast bacilli is diagnostic
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Salmonella
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more common in sickle cell patients
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pathoanatomy
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acute osteomyelitis
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most cases are hematogenous
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initial bacteremia may occur from a skin lesion, infection, or even trauma from tooth brushing
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microscopic activity
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sluggish blood flow in metaphyseal capillaries due to sharp turns results in venous sinusoids which give bacteria time to lodge in this region
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the low pH and low oxygen tension around the growth plate assist in the bacterial growth
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infection occurs after the local bone defenses have been overwhelmed by bacteria
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spread through bone occurs via Haversian and Volkmann canal systems
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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)
- a subperiosteal abscess develops when the purulence breaks through the metaphyseal cortex
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Infants <1 year of age can have infection spread across the growth plate via capillaries causing osteomyelitis in the epiphysis and septic arthritis
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chronic osteomyelitis
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periosteal elevation deprives the underlying cortical bone of blood supply leading to necrotic bone (sequestrum)
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sequestrum
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the necrotic bone which has become walled off from its blood supply and can present as a nidus for chronic osteomyelitis
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an outer layer of new bone is formed by the periosteum (involucrum)
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involucrum
- a layer of new bone growth outside existing bone seen in osteomyelitis
- a layer of new bone growth outside existing bone seen in osteomyelitis
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- chronic abscesses may become surrounded by sclerotic bone and fibrous tissue leading to a Brodie's abscess
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ANATOMY
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Blood supply
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the metaphyseal blood capillaries undergo sharp turns prior to entering venous sinusoids leading to turbulent flow and predisposition of bacterial deposition
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CLASSIFICATION
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Acute osteomyelitis
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see pathoanatomy above
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Subacute osteomyelitis
- uncommon infection with bone pain and radiographic changes without systemic symptoms
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increased host resistance, decreased organism virulence, and/or prior antibiotic exposure
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radiographic classification
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types IA and IB show lucency
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type II is a metaphyseal lesion with cortical bone loss
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type III is a diaphyseal lesion
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type IV shows onion skinning
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type V is an epiphyseal lesion
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type VI is a spinal lesion
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- uncommon infection with bone pain and radiographic changes without systemic symptoms
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Chronic osteomyelitis
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see pathoanatomy above
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PRESENTATION
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History
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limb pain
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recent local infection or trauma
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obtain immunization history regarding H. influenza
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ask about prior antibiotic use, as it may mask symptoms
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Symptoms
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limp or refusal to bear weight
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generally not toxic appearing
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+/- fever
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Physical exam
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inspection & palpation
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edematous, warm, swollen, tender limb
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evaluate for point tenderness in pelvis, spine, or limbs
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range of motion
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restricted motion due to pain
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IMAGING
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Radiographs
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recommended views
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obtain AP and lateral of the suspected area
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findings
- early films may be normal or show loss of soft tissue planes and soft tissue edema
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new periosteal bone formation (5-7 days)
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osteolysis (10-14 days)
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late films (1-2 weeks) show metaphyseal rarefaction (reduction in metaphyseal bone density) or possible abscess
- early films may be normal or show loss of soft tissue planes and soft tissue edema
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CT
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indication
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more helpful later in the disease course to demonstrate bone changes or abscesses
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MRI
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detects abscesses and early marrow and soft tissue edema
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indications
- can assist with decision making when a poor clinical response to antibiotics or surgical drainage considered
- can assist with decision making when a poor clinical response to antibiotics or surgical drainage considered
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views
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T1 signal decreased
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T1 with gadolinium signal increased
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T2 signal increased
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88% to 100% sensitivity, sensitivity increased by Gadolinium contrast
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Bone scan
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indications
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nondiagnostic x-ray
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need to localize pathology in infant or toddler with non-focal exam
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technetium-99m can localize the focus of infection and show a multifocal infection
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92% sensitivity
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a cold bone scan may be associated with more aggressive infections
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STUDIES
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Serum labs
- WBC count
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elevated in 25% of patients and correlates poorly with treatment response
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C-reactive protein
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elevated in 98% of patients with acute hematogenous osteomyelitis
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becomes elevated within 6 hours
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most sensitive to monitor therapeutic response
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declines rapidly as the clinical picture improves
- CRP is the best indicator of early treatment success and normalizes within a week
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failure of the C-reactive protein to decline after 48 to 72 hours of treatment should indicate that treatment may need to be altered
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ESR
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elevated in 90% of patients with osteomyelitis
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rises rapidly and peaks in three to five days, but declines too slowly to guide treatment
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less reliable in neonates and sickle cell patients
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plasma procalcitonin
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new serologic test that rises rapidly with a bacterial infection, but remains low in viral infections and other inflammatory situations
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elevated in 58% of pediatric osteomyelitis cases
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bone aspiration
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helps establish a definitive diagnosis
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50% to 70% of affected patients have positive cultures
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blood culture
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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
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- WBC count
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Aspiration
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assists in diagnosis and management
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helps guide antibiotic selection when organism identified (50% of the time)
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proceed with surgical drainage if pus is aspirated
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technique
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large bore needle utilized to aspirate the subperiosteal and intraosseous spaces under fluoroscopic or CT-guidance
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start antibiotics after aspiration
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Biopsy and culture
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consider when diagnosis not clear (i.e. subacute osteomyelitis) and need to rule out malignancy
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TREATMENT
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Nonoperative treatment
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antibiotic therapy alone
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indications
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early disease with no subperiosteal abscess or abscess within the bone
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surgery is not indicated if clinical improvement obtained within 48 hours
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modalities
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antibiotics
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begin with empiric therapy
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generally, nafcillin or oxacillin, unless high local prevalence of MRSA (then use clindamycin or vancomycin)
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mechanism of action for vancomycin involves binding to the D-Ala D-Ala moiety in bacterial cell walls
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if gram stain shows gram-negative bacilli - add a third generation cephalosporin
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convert to organism-specific antibiotics if organism identified
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mycobacterium tuberculosis
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treatment for initial 1 year is multiagent antibiotics and rarely surgical debridement due to risk of chronic sinus formation
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duration
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typically treat with IV antibiotics for four to six weeks
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controversial duration
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- intravenous versus oral
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often a case by case decision with input from infectious disease consultation
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Operative treatment
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surgical drainage, debridement, and antibiotic therapy
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indications
- deep or subperiosteal abscess
- failure to respond to antibiotics
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chronic infection
- deep or subperiosteal abscess
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contraindications
- hemodynamic instability, as patients should be stabilized first - however sometimes operative treatment of the underlying infection helps stabilize the patient
- hemodynamic instability, as patients should be stabilized first - however sometimes operative treatment of the underlying infection helps stabilize the patient
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example of institution algorithm treatment pathway
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TECHNIQUE
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Surgical drainage, debridement, and antibiotic therapy
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soft tissue
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evacuate all purulence, debride devitalized tissue, and drill as needed into intraosseous collections
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send tissue for culture and pathology to rule out neoplasm
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close wound over drains or pack and return to OR in two to three days
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bone work
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remove the sequestrum in chronic cases
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COMPLICATIONS
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DVT
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incidence
- is an infrequent complication in children
- is an infrequent complication in children
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risk factors
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CRP > 6 mg/dL
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surgical treatment
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age > 8-years-old
- MRSA
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Coagulase (+)
- Causes activation of thrombin and fibrin clot formation
- Causes activation of thrombin and fibrin clot formation
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treatment
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therapeutic anticoagulation
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Meningitis
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Septic arthritis
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risk factors
- bones with intra-articular metaphysis are at risk (shoulder, elbow, hip, ankle)
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neonates
- bones with intra-articular metaphysis are at risk (shoulder, elbow, hip, ankle)
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treatment
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irrigation and debridement
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- Growth disturbances and limb-length discrepancies from growth plate involvement
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treatment
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observation and possible corrective surgery depending on severity or projected severity
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Pathologic fractures
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PROGNOSIS
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Mortality decreased from 50% to <1% with development of antibiotics
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