Purpose: The purpose of this study was to simplify and enhance the ultrasound (US) analysis of the infant's hip by introducing a novel parameter named "L value" into the widely used Graf method.
Methods: We analysed 508 ultrasonographic images of the hips in infants aged three months. The images were first evaluated using the Graf measurements. On the same images, two additional measurements were performed in order to define the new parameter that was named L value. The threshold values of the new L value were identified based on the highest specificity as well as sensitivity for discrimination between the Graf groups. Those values were then used in order to reclassify the hips into three simplified groups. Inter-observer agreement was estimated by Cohen's kappa coefficient.
Results: The threshold values for the L value between Graf groups Ia and Ib was 0.46, between Ib and IIb was 0.68 and between IIb and IIc was 0.92. Correlation analysis between Graf's classification and the values of the L value was performed and was proved to be statistically significant, r = 0.49; p < 0.001. After simplifying the classification into three newly defined groups of patients depending on the degree of hip development, the correlation coefficient was much higher, r = 0.94, r (2) = 0.88 for p < 0.001. Inter-observer agreement for the L value was substantial.
Conclusions: The new L value parameter in Graf's ultrasound hip evaluation enables a faster, simpler, more reliable and more unbiased classification for developmental dysplasia of the hip as the L value changes proportionally with the hip maturity.