Pediatric emergency medicine trisk 2295 2295
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Septic arthritis is a bacterial infection of the joint space. The etiologies vary by age. In the neonatal period and
early infancy, GBS and S. aureus are the predominant pathogens, with gram-negative bacilli and Candida seen
sporadically, especially in hospitalized infants. Beyond this time period, S. aureus overwhelmingly is the most
common pathogen causing septic arthritis. Pneumococcus, GAS, gonococcus, and K. kingae also are associated
with septic arthritis in children. Salmonella can be seen in children with hemoglobinopathies. Brucella septic
arthritis can be associated with consumption of unpasteurized milk products and has a predilection for the
sacroiliac joint. Neisseria gonorrhea can cause a monoarticular arthritis can be seen in sexually active adolescents.
Hib is a rare cause of septic arthritis in the modern era. Lyme arthritis and tuberculosis arthritis are discussed
elsewhere.
Goals of Treatment
The goal of treatment is to rapidly identify children with septic arthritis so that prompt arthrocentesis can be
performed and antibiotics administered. Clinical outcomes include orthopedic sequelae (e.g., chondrolysis,
osteonecrosis) and differentiation of septic arthritis from other orthopedic complaints of childhood.
Clinical Considerations
Clinical recognition: The most common manifestation is limp, as 90% of children with septic arthritis have
monoarticular involvement of a lower extremity joint. In the child who is limping or refusing to ambulate,
occasionally it will be difficult to determine a focal lesion after manipulation of the lower extremity joints and
palpation of the long bones. Clinicians should be sure to evaluate the sole of the foot for foreign bodies and also to
palpate over the sacroiliac joint to assess for tenderness. Pain may be referred to other areas (e.g., hip septic
arthritis presenting as knee pain). The child with a septic hip often lies quite still with the leg abducted and in
external rotation. Fever is present in almost two-thirds of children with septic arthritis, but can be absent in
adolescents with gonococcal infections or in neonates. An erythematous swelling may surround a superficial joint
that is infected. Although a temperature difference exists between the affected and unaffected sites, it can be
difficult to discern in the febrile child. Inflammation within the joint distends the capsule and produces pain with
movement. If a child allows the physician to manipulate an extremity through a full range of motion, septic
arthritis is unlikely.
Triage considerations: Any child with fever and a limp or other joint complaint should be promptly evaluated
for septic arthritis. The most urgent of locations is septic arthritis of the hip, as this can result in compromised
vascular flow to the femoral capitis. Associated tachycardia and/or hypotension can imply sepsis and would
require fluid resuscitation.
Clinical assessment: Septic arthritis is diagnosed via aspiration and culture of joint fluid. Arthrocentesis is not
only diagnostic, it is therapeutic; many children report decreased pain after synovial fluid is aspirated. As such,
early consultation with orthopedic surgery is critical. Most children with pyogenic septic arthritis have synovial
fluid white blood cell count (WBC) of >50,000 cells/mm3 and a neutrophilic predominance. However, cell counts
may be lower with Brucella or tuberculosis arthritis and may exceed 50,000 cells/mm3 with some noninfectious
causes of arthritis, such as juvenile idiopathic arthritis. A Gram stain should be sent, as some organisms may be
seen in the synovial fluid and not grown in culture, even in children without antibiotic pretreatment, as synovial
fluid has some bacteriostatic properties. Approximately 50% of children with septic arthritis will have positive
synovial fluid cultures. Culture yield is enhanced for certain pathogens with appropriate specimen handling. If
Kingella is suspected, synovial fluid should be injected into a blood culture bottle to increase yield. If Brucella is
suspected, the laboratory should be notified so that the cultures can be kept far beyond the usual protocol, as it
often takes weeks for this organism to grow. Acid-fast cultures and M. tuberculosis PCR should be sent in
immunocompromised hosts or children with epidemiologic risk factors for tuberculosis. Fungal, anaerobic, and
acid-fast cultures (the latter for nontuberculous mycobacteria) should be obtained in children with penetrating
trauma, as these infections often are polymicrobial and can be caused by a broad spectrum of pathogens.
Ancillary laboratory evaluation should include a blood culture, complete blood count, ESR, and CRP. The ESR
and CRP are the most consistent abnormal laboratory studies and can be used to monitor response to therapy.
Radiographic studies (e.g., MRI) can be used to evaluate for contiguous osteomyelitis. This is particularly common
in the first year of life, because at this time, the metaphysis is located within the joint capsule. Recognition of
osteomyelitis in association with septic arthritis is an important consideration when determining the duration of
therapy.
