Baldwin et al reported factors which can help to diagnose septic arthritis of the knee in pediatric patients in a region with endemic Lyme disease. The authors are from The Children's Hospital of Philadelphia.
Patient selection: age < 18 years of age with knee effusion
Criteria for septic arthritis: positive joint fluid culture, synovial WBC count > 60,000 per µL, negative serologic test for Lyme disease
Criteria for Lyme disease: positive anti-Lyme antibodies on Western blot analysis
Features seen with septic arthritis:
(1) pain with short arc motion (less than 30 degrees of motion)
(2) CRP > 4 mg/L
(3) patient reported history of fever
(4) age < 2 years
Number of Features
Percent Septic Arthritis
0
2%
1
18%
2
45%
3
84%
4
100%
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