User's Guide to the Surgical Literature: How to Use an Article About a Diagnostic Test

Clinical Scenario You are an orthopaedic surgeon who is asked to evaluate a sixty-five-year-old woman in the emergency department because of new-onset right hip pain that started one week ago. Seven months previously, the patient had had a right total hip arthroplasty for the treatment of osteoarthritis. The pain radiates to the thigh and buttocks. The patient reports that she slipped on a kitchen floor a few days ago but did not think that she had sustained a serious injury. In addition, she has been recovering from a sinus infection (a viral illness) for the past ten days. She is otherwise healthy except that she takes oral bisphosphonates for the treatment of osteoporosis. On examination, she has a temperature of 39°C. She walks most comfortably with a flexed posture. The range of motion of the right hip is normal. There is no erythema or draining sinus over the right hip and thigh. Anteroposterior radiographs of the pelvis and the right hip reveal a press-fit acetabular component and a cemented femoral stem with no evidence of loosening. Laboratory evaluations show a white blood-cell count of 12.1 cells/μL, of which 85% are neutrophils. Blood cultures are negative. You wonder whether the new onset of hip pain is the result of a soft-tissue injury, back pain radiating to the hip, prosthetic loosening that is not apparent on radiographs, or an infection of the hip joint. If the hip is truly infected, the patient will require an operative procedure for débridement of the wound and removal of the implants. While some of your colleagues would take all such patients to the operating room for exploration of the hip, you have been impressed by the number of cases in which you have found no infection. Because of such concerns, your practice is to routinely aspirate the hip in patients in whom an infection is suspected. Just as you are thinking about placing your patient’s name on the next day’s procedures list for an aspiration, the result of the C-reactive protein test comes back as 8 mg/dL (normal, ≤10 mg/dL). This finding raises some question as to