Reliability of plain radiographic parameters for developmental dysplasia of the hip in children.

INTRODUCTION: Few studies have evaluated the reliability and reproducibility of the femoral neck-shaft angle (NSA), center-edge angle (CEA), and acetabular index (AI) in young children with developmental dysplasia of the hip (DDH). We wanted to determine whether these parameters could be used reliably by practitioners.
METHODS: Fifty radiographs from 21 children with DDH were reviewed. Analysis was performed by three observers, at two time periods. The intra- and inter-observer reliability for each measure was assessed.
RESULTS: At time period one, we noted a "high" level of agreement between observers when measuring the NSA, a "low" level when measuring the CEA, and a "moderate" level when measuring the AI. At time period two, we noted a "very high" level of agreement between observers when measuring the NSA and a "high" level when measuring the CEA and AI. When comparing the measurements of observer 1 at the two different time periods, we noted nearly "very high" agreement when measuring the NSA, a "moderate" agreement when measuring the CEA, and a "high" agreement for the AI. In comparing the measurements of observer 2, we noted "very high" agreement for the NSA and "high" agreement for the CEA and AI. In comparing the measurements for observer 3, we noted nearly "very high" agreement for the NSA, nearly "high" agreement for the CEA, and "high" agreement for the AI.
CONCLUSION: It is difficult to reliably measure three-dimensional pelvic morphology on a frontal plane radiograph, especially when important pelvic landmarks have yet to ossify.