The standardized sonographic hip screening according to Graf has increased reliability and comparability of measurements in the screening of developmental dysplasia of the hip (DDH). However, examiner dependent factors have been discussed to influence sonographic measurements. The objectives of this study were to examine the tolerance of the transducer positioning and to analyse the impact of transducer inclinations on Grafs hip grading system.
Materials and methods
Twenty-four hips in consecutive newborns were screened sonographically in combination with an optoelectronic motion capture system to trace transducer positions in space. Subsequently five defined inclinations of the transducer relative to Grafs neutral transducer position were analysed, giving a total of 144 sonographic images.
We found a permissible transducer inclination in the axial plane of 8.8 to anterior and 8.1 to posterior. In the frontal plane we found a permissible inclination of 15.4 to caudal and 7.2 to cranial. The impact on the -angle was significant for posterior-cranial (p < 0.001), cranial (p = 0.009), and caudal (p < 0.001) inclined transducer positions. The effect on the results according to Grafs grading system was significant for the caudal inclination of the transducer position (p < 0.001).
Our findings show that the standardized plane defined by Grafs criteria allows notable inclinations of the transducer positions. Transducer inclinations show an impact on measurement results, which are clinically relevant. Those effects cannot be ruled out using Grafs ultrasound criteria alone. The examiner should pay attention to avoid transducer inclinations in the frontal plane and a combination of posterior and cranial inclination.