Developmental retardation of femoral head size and femoral head ossification in mild and severe developmental dysplasia of the hip in infants: a preliminary cross-sectional study based on ultrasound images

Background: For infants up to 6 months, ultrasound (US) screening of developmental dysplasia of the hip (DDH) is recommended. This cross-sectional study investigated the developmental data of femoral head size and femoral head ossification in mature infant hips and the impact of mild and severe DDH on femoral head development based on US images.Methods: We reviewed all hip US studies performed from January 2018 to December 2019 to evaluate DDH in infants younger than 6 months at West China Hospital, Sichuan University. The femoral head diameter (FHD) and femoral head ossification center type of each hip were recorded. A total of 1,037 normal participants with 2,074 mature hips and 367 DDH participants with 456 dysplastic hips were included in this study.Results: For normal mature hips (Graf I), the FHD of mature male hips was significantly larger than that of female hips from the age of 2 months to 6 months (all P values <0.01), and the femoral head ossification center of males occurred significantly later than that of females at the same age from 3 months to 6 months (all P values <0.05). Compared with the matched mature hips, the FHDs of Graf IIa (-), IIb, IIc, and D, III or IV hips were significantly smaller (1.64 vs. 1.72 cm, 1.75 vs. 1.79 cm, 1.65 vs. 1.73 cm, 1.51 vs. 1.71 cm, respectively; all P values <0.05), and the occurrence of the femoral head ossification center was delayed in Graf IIa (-) and D, III or IV hips (both P values <0.05). However, no significant developmental retardation of the femoral head was observed in Graf IIa (+) hips.Conclusions: We identified a relatively normal range for the development of infants' hips from 1 month old to 6 months old and found significant developmental retardation of the femoral head in Graf IIa (-), IIb, IIc, and D, III or IV hips. This is a preliminary study of the developmental impact of DDH on the femoral head, and we will continue the follow-up study after treatment.