BACKGROUND: Approximately 20-50% of children with juvenile idiopathic arthritis (JIA) have hip involvement within 6 years of diagnosis. Scoring systems for hip-related radiographic changes are lacking.
OBJECTIVE: To examine precision of potential radiographic variables and to suggest a scoring system.
MATERIALS AND METHODS: We reviewed a set of 75 pelvic radiographs from 75 children with JIA hip involvement across two European centres. We assessed findings of (1) destructive change and (2) growth abnormality, according to a pre-defined scoring system. All radiographs were scored independently by two sets of radiologists. One set scored the radiographs a second time. We used kappa statistics to rate inter- and intra-observer variability.
RESULTS: Assessment of erosions of the femoral head, femoral neck and the acetabulum showed moderate to good agreement for the same reader (kappa of 0.5-0.8). The inter-reader agreement was, however, low (kappa of 0.1-0.3). There was moderate to high agreement for the assessment of femoral head flattening (kappa of 0.6-0.7 for the same reader, 0.3-0.7 between readers). Joint space narrowing showed moderate to high agreement both within and between observers (kappa of 0.4-0.8). Femoral neck length and width measurements, the centrum-collum-diaphysis angle, and trochanteric-femoral head lengths were relatively precise, with 95% limits of agreement within 10-15% of the observer average.
CONCLUSION: Several radiographic variables of destructive and growth abnormalities in children with hip JIA have reasonable reproducibility. We suggest that future studies on clinical validity focus on assessing only reproducible radiographic variables.