NEW YORK — Is that 3-year-old child with a limp and a low-grade fever just another case of transient synovitis, or is it a much more serious but far rarer case of septic arthritis?
With published decision rules in conflict on how to distinguish one from the other, physicians need to apply clinical judgment appropriate to their available resources, Dr. Martin G. Hellman said at the meeting sponsored by the American College of Emergency Physicians.
“Even a very experienced clinician is not going to see many cases of septic arthritis on a routine or even a nonroutine basis,” said Dr. Hellman, clinical assistant professor of pediatrics at the University of Pittsburgh.
Findings from a study of children presenting to Children's Hospital Boston, between 1979 and 1996, identified four clinical predictors that, taken together, could reliably differentiate between septic arthritis and transient synovitis: history of fever, non-weight-bearing status, erythrocyte sedimentation rate (ESR) of at least 40 mm/hr, and serum white blood cell (WBC) count of more than 12,000 cells/mm
But researchers at St. Louis Children's Hospital asserted that a better set of variables would be to check for a history of fever, a serum total WBC count of greater than 12,000 cells/mm
A prospective study from Children's Hospital of Philadelphia described 53 children for whom the suspicion of septic arthritis was so strong that they had undergone hip taps. The researchers concluded that a C-reactive protein (CRP) level greater than 2 mg/dL was a strong risk factor for septic arthritis. Fever above 38.5° C was the most influential risk factor; no patients with transient synovitis had a fever above that temperature (J. Bone Joint Surg. Am. 2006;88:1251–7). “However, temperature less than 38.5° C had a false negative more than 50% of the time. And 12% of the septic arthritis cases had zero or one of the factors. That's a little scary,” he said.
Dr. Hellman proposed the following plan for evaluation and consultation of hip pain.
“Begin with a careful physical exam,” Dr. Hellman said. “Don't forget the possibility of abdominal problems.”
For an afebrile child who looks well aside from limited range of motion in the hip and refusal to bear weight, he recommended that physicians take plain x-rays of the pelvis and frog lateral. The physician could choose to stop testing at that point, or could consider obtaining lab tests for CRP, ESR, and WBC. Assuming all tests come up negative, parents should still be given strict instructions to return for immediate evaluation if symptoms worsen.
On the other hand, with a febrile child who does not look well, lab tests would be strongly advised.