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