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Diagnostic Variability in the Modified Kocher Criteria for Septic Arthritis of the Hip: Implications for Aspiration
Sean P Owens1, Emily Ho2, Sula Frausto2
1Division of Orthopedic Surgery, The Children's Hospital of Philadelphia.
Objective:
This study evaluates the clinical application of the modified Kocher criteria (MKC) in assessing septic arthritis of the hip (SAH) at a tertiary children's hospital.
Methods:
A retrospective cohort study was conducted on subjects presenting to the emergency department and receiving a hip ultrasound over a 1-year period. Those without a hip effusion were excluded. Patient demographics, symptoms, imaging, labs, treatment, and final diagnoses were collected. SAH was defined clinically by the treating team, supported by patient presentation, lab/imaging findings, operative intervention, and antibiotic therapy. Descriptive and bivariate statistics based on variable distribution were used during analysis.
Results:
A total of 326 subjects were identified, and 110 had effusion present on ultrasound. Eighteen (16.4%) underwent aspiration. Aspirated subjects had significantly higher cumulative MKC scores (P=0.001) and higher median values for all individual MKC components, including CRP, WBC, ESR, maximum temperature, and a higher prevalence of non-weight-bearing (P<0.05). SAH was diagnosed in 38.9% of the aspirated group (n=7), with MKC scores of 2 (n=2), 3 (n=3), and 5 (n=2). Aspiration rates increased across MKC scores 0 to 3, and synovial fluid inflammatory markers trended higher with increasing MKC scores. Thirteen subjects with an MKC score of 2 were not aspirated; final diagnoses included transient synovitis (n=9), hip effusion, osteomyelitis, sickle cell crisis, or limp (each n=1). Three subjects with an MKC score of 3 were not aspirated and later diagnosed with metastatic tumor, osteomyelitis, and rheumatic fever.
Conclusions:
Pediatric patients undergoing hip aspiration with a concern for SAH had significantly higher cumulative MKC scores and higher levels of all individual MKC components than their nonaspirated counterparts. However, nearly 15% of patients had MKC scores of 2 or 3 that were not aspirated in the ED, and SAH was identified even in lower-score subjects. While MKC scores appear to influence clinical decision-making, diagnostic variability remains. In patients with intermediate MKC scores of 2 to 3, the criteria should prompt further evaluation, taking into consideration the overall clinical context to guide aspiration decision-making.
