Pediatric emergency medicine trisk 2296 2296
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Clinical algorithms have been developed for septic arthritis. The best known is the Kocher criteria for septic
arthritis of the hip. The risk factors assessed were nonweight bearing on the affected side, ESR >40 mm/hr, fever,
and WBC >12,000/mm3. When all four criteria are met, there is a 99% chance that the child has septic arthritis.
However, the negative predictive value is not as robust; 40% of cases with only 2/4 criteria have a septic joint.
Management: Prompt surgical intervention is typically advocated for septic arthritis of the hip. All children with
suspected septic arthritis should be admitted to the hospital for parenteral antibiotics. Antistaphylococcal coverage
should be initiated in children of any age with suspected septic arthritis. The selection of vancomycin over
clindamycin depends upon local antibiotic susceptibility patterns, illness severity, and any prior culture results
available for the child. Coverage should be expanded beyond staphylococcal coverage if the Gram stain
demonstrates organisms other than gram-positive cocci in clusters, if gonococcal arthritis is suspected based upon
history or cultures from nonjoint sites (e.g., oropharynx, rectum), or in immunocompromised children or children
whose arthritis is due to penetrating trauma to the joint. In neonates and young infants, ampicillin and a thirdgeneration cephalosporin should be added to augment coverage for GBS and gram-negative rods. Standard
precautions should be used unless draining lesions exist, in which case contact precautions should be implemented.
Lyme Disease Arthritis
A common cause of septic arthritis in Lyme-endemic regions (northeastern, mid-Atlantic, and Great Lakes states in
the United States) is B. burgdorferi. Lyme arthritis is a monoarticular or pauciarticular (affecting 2 to 4 joints)
arthritis that most often affects the large joints, especially the knees, which are involved in over 90% of cases.
After the knee, the shoulder, ankle, and elbow are the most commonly affected joints. It affects approximately 7%
of children with Lyme disease. The symptoms mimic those of septic arthritis caused by pyogenic organisms (acute
bacterial septic arthritis). There are some features that can enable the provider to differentiate the two entities (
e-Table 94.13 ). One clinical prediction rule derived and validated in a Lyme-endemic region showed that children
were at low risk for septic arthritis if the ANC was <10,000/mm3 and the ESR was <40 mm/hr. Serologic tests are
insensitive in the first month after Lyme infection, but are always positive when arthritis exists. Tiered screening,
beginning with an enzyme immunoassay (EIA) or immunofluorescent antibody (IFA) assay, with confirmation of
positive results by a Western blot, is recommended. Two-step screening is needed because false positives on EIA
or IFA can occur due to other spirochete infections, varicella, EBV, and some collagen vascular disorders. Lyme
serologies should not be sent in children who have not lived in or traveled to Lyme-endemic regions, as any
positive results in these children are far more likely to represent false positives. The treatment of initial and
recurrent arthritis due to Lyme disease is summarized in e-Table 94.14 . Macrolides are less effective than other
antibiotics, and as such are recommended only for patients who cannot tolerate cephalosporins, penicillins, or
tetracyclines. Standard precautions are used for children with suspected Lyme disease.
Osteomyelitis
CLINICAL PEARLS AND PITFALLS
Children with osteomyelitis usually present with fever and focal bone pain. Range of motion may be
limited by pain, and findings can thus mimic septic arthritis.
The most common cause of osteomyelitis is S. aureus.
Blood cultures are positive in approximately 50% of children, as such, bone biopsy should be
attempted. Under optimal circumstances, the biopsy would occur prior to the child receiving
antibiotics, if the child is nontoxic and immunocompetent.
Current Evidence
Osteomyelitis is a bacterial infection of the bone. In 90% of cases, only one bone (most commonly in the lower
extremity) is involved. The upper extremity is involved in approximately 25% of cases. The most common cause,
across all age groups, is S. aureus. There is substantial overlap between the organisms causing septic arthritis and
those causing osteomyelitis. P. aeruginosa may infect the bones of the foot after a puncture wound. In children
with sickle cell disease and other hemoglobinopathies, Salmonella species account for almost half the cases of
osteomyelitis. Atypical pathogens may be recovered from immunocompromised children.
Goals of Treatment
