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Osteomyelitis - Pediatric

  • 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

          • 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

    • 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

        • MRSA 

           

          • 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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