Letters to the editor.

Abstract

I would like to share my comments on the article reporting two infants with initial normal hip ultrasonography at 6 weeks of age, who were then diagnosed with developmental dysplasia of the hip (DDH) at 9 months of age. Both cases were considered ‘late presenting DDH’.1 According to Graf, the main reason for deterioration of an initially normal considered hip (type I hip) to a pathologic hip by time is an incorrect initial diagnosis (never a normal hip).2 In this study, initial sonogram of one case was presented (Fig. 1 of Reference 1). Although the alpha angle was reported to be 60°, the drawing of the acetabular bony roof line according to Graf method3 is incorrect in Figure 1 of Reference 1. This line must run tangentially from the lower limb of the iliac bone to the bony roof, not through or above the bony roof.3 Otherwise, incorrect measurements can be done. Therefore, the bony acetabular roof is actually deficient, bony rim is rounded, the alpha angle is less than 60° if the bony roof line could have been drawn as originally defined and it is initially not a normal hip according to the Graf classification.3 A missed initial diagnosis may then be misinterpreted as late presenting DDH. It is mandatory to follow the well-defined technical rules of the Graf method, including the measurement of alpha angle in order to avoid false negative and false positive assessments.4