Comparative analysis of hip joint development abnormalities and risk factors in preterm and term infants

Abstract

Objective: To investigate the risk factors affecting hip joint development in infants and to compare abnormalities in hip joint development between preterm and term infants.

Methods: This retrospective cohort study reviewed the medical records of newborns admitted to the neonatology department of our hospital between January 2019 and January 2020. Hip joint ultrasound screening and follow-up data were collected for each newborn. The enrolled newborns were categorized into two groups: preterm (<37 weeks) and term (≥37 weeks). Hip joint ultrasounds were assessed using the Graf classification criteria.

Results: A total of 955 newborns were included in the study, comprising 393 preterm and 562 term infants. All preterm infants were born at a gestational age over 28 weeks. Among term infants, the proportion of abnormal hip joints during the first and second screenings was significantly higher in singletons than twins (p < 0.05), in non-small for gestational age (non-SGA) infants than SGA infants (p < 0.05), and in females than males (p < 0.0001). By the third screening, the proportion of abnormal hip joints remained significantly higher in females than in males (p < 0.01). In newborns with birth weight percentiles above the 50th percentile (P50), term infants showed a significantly higher proportion of abnormal hip joints than preterm infants during the first screening (P50-P75: 32.1 vs. 15.8%, P75-P90: 36.0 vs. 16.7%, p < 0.01; >P90: 32.1 vs. 15.8%, p < 0.05). During the second screening, term infants in the P50-P75 and P75-P90 percentiles exhibited abnormal hip joint proportions of 27.6 and 34.8%, respectively, which were significantly higher than those in preterm infants (13.9%, p < 0.05; 12.1%, p < 0.01). By the third screening, the proportion of abnormal hip joints in term infants within the P75-P90 percentile was 11.2%, which was significantly higher than that of preterm infants (1.5%, p < 0.05). Overall, preterm infants demonstrated a significantly lower proportion of abnormal hip joints compared to term infants across all four screening time points. By the fourth screening, all abnormal hips in preterm infants had evolved into normal ones according to Graf classification criteria. In contrast, although most abnormal hips in term infants had also resolved, with only 6 of them persisted.

Conclusion: Term singletons, female, and non-SGA infants demonstrated a higher proportion of abnormal hip joints during the early postnatal period. Among neonates born after 28 weeks of gestation, there is no difference in hip development between preterm infants with a birth weight percentile <P50 and term infants. Most abnormal hip joints in both preterm and term infants are due to physiological immaturity and tend to resolve by themselves as natural growth and development. The timing of hip ultrasound screening for preterm infants born after 28 weeks of gestation may not require correction for gestational age.

Keywords: Developmental dysplasia of the hip; Preterm infants; Risk factors; Term infants; Ultrasound screening.

Fig. 1

Images of Type I and Type IIa hips in preterm infants during the four screening sessions. A shows the Type I hip in a preterm infant on the first day after birth. B and C demonstrates the screenings at 7 and 42 days, respectively. D shows the 90-day screening, where the hip remains as Type I. E shows the Type IIa hip in a preterm infant on the first day after birth. F and G demonstrates the screenings at 7 and 42 days, respectively. H shows the 90-day screening, where the hip has transitioned to Type I

Fig. 2

Flowchart of subjects’ inclusion of this study. Between January 2019 and January 2020, a total of 1,064 newborns were admitted to the neonatology department. Of these, 27 were excluded due to guardians not consenting to hip joint ultrasound screening, 34 had other associated deformities or diseases, and 48 were lost to follow-up. Ultimately, 955 newborns were included in the study, comprising 393 preterm infants and 562 term infants

Fig. 3

The Comparison of Hip Joint Ultrasound Screening Results Between Preterm and Term Infants with Different Birth Weight Percentiles. A During the first screening, the proportion of abnormal hip joints was significantly higher in term infants compared to preterm infants (P50–P75: 32.1 vs. 15.8%, P75–P90: 36.0 vs. 16.7%, p < 0.01; >P90: 32.1 vs. 15.8%, p < 0.05). B In the second screening, the proportions of abnormal hip joints in term infants with P50–P75 and P75–P90 were 27.6 and 34.8%, respectively, significantly exceeding those in preterm infants (13.9%, p < 0.05; 12.1%, p < 0.01). C For the third screening, term infants with P75–P90 had a significantly higher rate of abnormal hip joints at 11.2%, compared to 1.5% in preterm infants (p < 0.05). D By the fourth screening, there was no significant difference in the proportion of abnormal hip joints between preterm and term infants across different birth weight percentiles. ^*: p < 0.05, ^**: p < 0.01, chi-squared test

Fig. 4

The Comparison of Hip Joint Ultrasound Screening Results Between Preterm and Term Infants Across Four Screenings. A The first screening results showed that the abnormality rates of hip joints in preterm infants (19.1%) were significantly lower than those in term infants (31.7%) (p < 0.0001). B The second screening results indicated that preterm infants (16.3%) continued to have significantly lower abnormality rates compared to term infants (28.1%) (p < 0.0001). C In the third screening, the abnormality rates in preterm infants (2.5%) remained significantly lower than in term infants (6.2%) (p < 0.01). D By the fourth screening, the rates of hip joint abnormalities in preterm infants (0%) were still significantly lower than those in term infants (1.1%) (p < 0.05). ^*: p < 0.05, ^**: p < 0.01, ^****: p < 0.0001, chi-squared test