Assessing Femoral Head Medialization in Developmental Hip Dysplasia Type 1 and Type 2 Hip Separation

Abstract

Background/objectives: The prevalence of developmental hip dysplasia is estimated to be 0.1-2 per 1000 infants. Hip imaging by ultrasonography is considered to be the gold standard method for screening and detecting developmental dysplasia of the hip (DDH), as per the Graf categorization. The classification of hip differentiation into type 1 and type 2 is determined by the alpha angle, as assessed by the Graf classification. Type 1 hips are defined as those with an alpha angle exceeding 60 degrees, whilst type 2 hips are defined as those with measurements falling within the range of 50 to 59 degrees.

Methods: The computerized patient card in our institution had a compilation of 208 hip photographs taken from 110 patients, with 98 of them being bilateral. The acquisition of these photos occurred from January 2020 to December 2020. A retrospective review was conducted on the ultrasound (US) scans, with a specific emphasis on the outcomes related to type 1 and type 2 hips.

Results: There were 108 high-resolution US photos in the type 1 hip group and 100 high-resolution US images in the type 2 hip group. In terms of unilateral or bilateral cases, gender, or age, no statistically significant differences were seen between the two groups (p > 0.05). The FMD model exhibited a sensitivity of 86% and specificity of 70% in effectively predicting the presence of type 1 mature hips when the values surpassed 2.9 mm. The AUC (area under the curve) value achieved was 0.628.

Conclusions: The process of diagnostic categorization may occasionally encounter challenges in accurately differentiating between type 1 and type 2 hip separation subsequent to a hip ultrasound examination. The findings of our analysis indicate that the assessment of the FMD is a highly successful method, demonstrating both high specificity and sensitivity in differentiating between various scenarios.

Keywords: Graf classification; developmental dysplasia; femur; hip; measurement.

Figure 1

The iliac bone (single arrow), iliac roof (double arrow), and femoral head (arrow head) demonstrated in picture form. The distance indicated by the star is the measurement between the femoral decapitation center and the horizontal line passing through the iliac bone.

Figure 2

The FMD value is measured as 3.3 mm in a 62-day-old type 1 mature hip with an alpha angle of 67 and a beta angle of 53 (FMD refers to the distance that remains between point B and the decussated A line, which is drawn parallel to the femur from the iliac bone. Point B refers to the center of the femoral head).

Figure 3

Alpha angle of 58 and beta angle of 55 measured in a 60-day-old type 2 physiological immature hip; the FMD value measured 2.1 mm (FMD refers to the distance that remains between point B and the decussated A line, which is drawn parallel to the femur from the iliac bone. Point B refers to the center of the femoral head).