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 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