Review Question - QID 454

This question is describing a scenario in which you must rule out a septic hip, and therefore the most appropriate next step in management is aspiration.

Prematurity and c-section are both risk factors for a septic hip in the new born.While there is no fever in this case, there is swelling, pain with passive motion, no active motion secondary to pain, and a radiograph which indicates an effusion in the hip as seen by lateral displacement of the left proximal femur. Suspicion for a septic hip should be high, and the next most appropriate step is a hip aspiration. If no fluid is obtained, arthrography should be performed to confirm intra-articular position of the needle. The aspirate should be sent for a stat CBC with diff, culture (aerobic, anaerobic and acid-fast bacilli +/- fungal), and gram stain. A WBC greater than 50,000/uL or a positive gram stain suggest septic arthritis and are an indication for surgical incision and drainage and initiation of IV antibiotics.

Kocher et al identified four independent multivariate clinical predictors of septic arthritis. These were fever, non-weight-bearing (not applicable in this case because the infant is not of ambulatory age), ESR greater than 40 ml/hr, and WBC greater than 12,000. The predicted probability of septic arthritis was 0.2% for 0 predictors, 3.0% for 1 predictor, 40.0% for 2 predictors, 93.1% for 3 predictors, and 99.6% for 4 predictors.

Incorrect Answers:
Answer 1: MRI may reveal an effusion or associated osteomyelitis abscess, but this is not appropriate because the additional hours spent obtaining an MRI could potentially lead to severe articular cartilage destruction (as an aside ultrasound would be a reasonable choice in some institutions when readily available since it is an easy, quick and noninvasive technique that can detect an effusion and guide aspiration of the hip if an effusion is present).
Answer 2: A CT scan would not be sensitive for an effusion or osteomyeletis, and therefore is not the most appropriate imaging modality.
Answer 3: Observation is not appropriate because septic arthritis of the hip constitutes a surgical emergency; the release of proteolytic enzymes by polymorphonuclear cells and bacteria in conjunction with increased intra-articular pressure can result in rapid irreversible hyaline cartilage degradation in as little as 6 hours in animal studies, with resultant joint destruction, deformity and lifelong arthritis & disability.
Answer 5: A Pavlick harness would be appropriate if there was any indication of hip dysplasia, including a positive Ortolani or Barlow sign, a Galeazzi sign or ultrasound evidence of hip dysplasia, none of which were described.