Objective To analyze the results of ultrasonic examinations of hip joints in preterm infants, clarify the developmental characteristics of hip joints across different gestational ages.

Methods A total of 881 preterm infants who attended the Child Healthcare Outpatient Clinic of Nanjing Maternity and Child Health Care Hospital between January 2023 and April 2024 were enrolled. The first ultrasonic examination of the hip joints was performed at a corrected gestational age of 4 to 6 weeks. The Graf classification method was employed to categorize the ultrasonic findings. Differences in hip joint development among preterm infants of varying gestational ages were compared, and relevant influencing factors were statistically analyzed.

Results A total of 1, 762 hip joints were examined, with 30 cases of abnormal hip joints detected, yielding an abnormality detection rate of 3.4% (30/881). Among these, 26 hips were classified as type IIa and 8 as type IIb. Statistically significant differences were observed in the detection of left-sided abnormal hip joints between preterm infants of other gestational age groups and late preterm infants (P < 0.05). A statistically significant difference was found in the classification of right-sided hip joints between preterm infants of different genders (P < 0.05), while no significant difference was observed for left-sided hip joints (P>0.05). Statistically significant differences were noted in the detection rates of bilateral abnormal hip joints among preterm infants with varying birth weights (P < 0.05). Advanced maternal age was found to influence the development of left-sided hip joints inpreterm infants, whereas factors such as assisted reproductive technology, breech presentation, and nulliparity had no significant impacts on abnormal hip joint development in preterm infants.

Conclusion Ultrasonic technology demonstrates significant advantages in screening for developmental dysplasia of the hip (DDH) in preterm infants. Different gestational ages exert a notable influence on the development of left-sided hip joints in preterm infants. Female preterm infants exhibit a higher risk of right-sided hip joint abnormalities compared to the left side. Breech presentation, assisted reproductive technology, and nulliparity are not risk factors for DDH in preterm infants. However, higher birth weight in preterm infants and advanced maternal age are associated with abnormal hip joint development. Clinical attention should focus on high-risk factors, and enhanced dynamic ultrasonic monitoring of hip joints in preterm infants is warranted to facilitate early intervention and treatment.