Purpose or Case Report: Developmental dysplasia of the hip (DDH) results from the abnormal development of the acetabulum, femoral head and mechanical instability of the hip joint. DDH often presents at birth, and if diagnosed early and treated successfully, children are able to develop a normal hip joint without functional limitation. If left untreated, DDH can lead to pain and osteoarthritis by early adulthood as well as discrepancy in leg length and functional disability. DDH risk factors include breech position in utero, oligohydramnios, female sex, primigravida, family history of DDH and improper swaddling. While there are recommendation for ultrasound screening in breech infants, only a few studies have dealt with the influence of gestational age on the development of DDH. Optimal timing of hip US and identification of patients who need follow-up are important to reduce unnecessary treatment and to avoid overtreatment. We aim to evaluate whether extremely premature infants (<28 weeks gestational age) warrant ultrasound screening for DDH in the absence of other risk factors.
Methods & Materials: We performed a retrospective review of 1528 consecutive patients who had a dynamic infant hip ultrasound at our institution from 2014-2019. Gestational age at birth, the position of in utero fetal lie, delivery method, evidence of hip instability, acetabular alpha angle, types of treatments pursued, and long-term outcome were evaluated based on medical records.
Results: Among 882 patients with known gestational age, 66 patients met the criteria for extreme prematurity. Within the study group, 1 patient had hip dysplasia. As our control group, there were 816 patients were born at 28 WGA or greater. Within this control group, 74 patients had hip dysplasia. The incidence of hip dysplasia in extremely premature infants was significantly lower than patients born at 28 weeks or greater (1.5% compared to 9.1% respectively, p=0.036).
Conclusions: Our findings are in agreement with other published literature that reported a lower incidence of DDH in premature infants. The one extremely premature infant in our study group who developed complete right hip dislocation and clubfoot deformity had preterm premature rupture of membranes with prolonged severe oligohydramnios. We propose that extremely premature infants do not need ultrasound screening for hip dysplasia in the absence of certain risk factors. Further study is needed to expand our knowledge on the extremely premature infants and the associations of individual risk factors with DDH.