Triage Considerations The patient with limp or localized musculoskeletal symptoms is often triaged as urgent Those with a question of neurovascular compromise, severe pain, or who appear systemically ill should be evaluated more immediately These patients should have their degree of pain documented and should receive analgesics on arrival Initial Assessment/H&P Physical signs of osteomyelitis are age dependent and recognition requires patience and diligence on the part of the clinician The older child is more likely to have localized infection and is more capable of expressing or identifying a specific site of pain and point tenderness The neonate or young infant may present with a pseudoparalysis of the affected limb Another common, although nonspecific, finding in this age group is paradoxical irritability in which the infant exhibits pain or distress upon handling and is more comfortable when left alone Fever and pain are classic findings but are not universally present Fever is described in up to 90% of children with acute hematogenous osteomyelitis upon presentation and may be quite elevated Signs of pain may include limp, refusal to bear weight, or a decreased range of motion when a limb is involved Erythema and swelling are less frequent but can also be observed at the site, and usually suggest more advanced periosteal involvement Osteomyelitis typically follows an indolent course and is less likely to present with the acute onset of symptoms that is more typical of traumatic injuries A history of minor trauma is common and often coincidental in an active child A history of sickle cell disease, prior surgery or skeletal manipulation places the patient at higher risk for osteomyelitis Management/Diagnostic Testing In addition to clinical findings, the diagnosis of osteomyelitis depends on culture results A blood culture and bone aspirate should be obtained in suspected cases of osteomyelitis Isolation of the causative organism is important not only for diagnosis, but also in antibiotic selection and determining the length of therapy Reports of positive blood cultures in the setting of osteomyelitis range from 30% to 57% An organism is recovered from a bone aspirate in 51% to 90% of cases The combination will identify a pathogen in 75% to 80% of cases Although blood cultures are often sterile within 24 hours of the initiation of antibiotics, bone aspirates may remain positive for several days after medication administration Therefore, therapy should not be withheld if the patient’s condition warrants immediate treatment A culture and PCR for Kingella kingae should be obtained in patients between months and years of age in regions with high incidence or in the setting of negative blood and bone aspirate cultures Laboratory tests vary in sensitivity The white blood cell (WBC) count rises in only one-third of the cases of osteomyelitis, whereas both the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are elevated in more than 90% of the cases The latter tests are useful in diagnosis and in monitoring the response to therapy The CRP peaks at days and gradually returns to normal over to 10 days of appropriate therapy The ESR may remain elevated for several weeks despite adequate treatment In the setting of a low clinical suspicion for osteomyelitis, a normal CRP, ESR, and plain radiograph suggests an alternative diagnosis The plain radiograph is useful both in detecting early signs of osteomyelitis and excluding other potential diagnoses The earliest radiographic changes suggestive of osteomyelitis include deep soft tissue swelling with elevation of the muscle planes from the adjacent bone These may be seen as early as to days after the onset of symptoms Lytic bone changes are not detectable until 10 to 14 days Periosteal elevation, when present, is not generally visible until 10 to 21 days after infection ( Fig 121.1 ) A negative radiograph in the first 10 days of illness does not rule out osteomyelitis When suspicion remains high in the setting of a negative radiograph, further imaging studies should be obtained The triple-phase technetium bone scan has a reported sensitivity and specificity of more than 90%, and is the test of choice when osteomyelitis is suspected but a specific site of concern cannot be identified by physical examination or when multiple foci of infection are possible MRI is also highly sensitive in detecting osteomyelitis and does not expose the child to ionizing radiation In addition, MRI provides a higher degree of detail than the bone scan ( Fig 121.2 ) This is useful in detecting suspected complications of osteomyelitis such as a subperiosteal abscess or bone sequestrum Many orthopedic surgeons prefer this high degree of resolution to guide a bone aspirate or biopsy Both imaging studies commonly require sedation of the young child, but the bone scan is not as affected by small movements A bone aspirate preceding a bone scan or MRI does not alter the imaging results and should not be delayed because of this concern Organisms responsible for osteomyelitis vary according to age of the patient, the route of infection, and any underlying comorbid conditions S aureus is the most common pathogen across all age groups accounting for 70% to 90% of cases The incidence of community-acquired methicillin-resistant S aureus (CAMRSA) has increased dramatically in most areas of the United States Some studies have found over 70% of cases due to MRSA Osteomyelitis due to MRSA has been associated with a longer duration of fever, extended hospitalization, and increased frequency of complications Group A β-hemolytic streptococcus and Streptococcus pneumoniae are the next most common organisms isolated in childhood osteomyelitis and together account for 10% of cases outside of the neonatal period The frequency of K kingae has been increasing and is most commonly reported in the toddler and preschool age group It is difficult to culture and the increased incidence may be due to improved success in identification through polymerase chain reaction (PCR) and improved culture techniques It is a gram-negative organism and therefore resistant to vancomycin and clindamycin, but sensitive to cephalosporins and β-lactam antibiotics Bacterial isolates from neonates younger than months include S aureus, group B streptococcus, and Escherichia coli ( Table 121.1 ) FIGURE 121.1 Periosteal activity in distal fibula in a child with Staphylococcus aureus osteomyelitis; day 20 of illness