In this study, newborns with the Graf type IIa hips were selected as subjects as they are commonly observed to undergo maturation of the acetabular roof. Considering spontaneous resolution in most of the babies, double diapering resulted in greater increase of the alpha angle, and more babies soon recovered to having bilateral Graf type I hips in 1 month. The number of following clinic visits and hip ultrasounds was reduced due to the faster maturation of the hip in the first month of life.
The spectrum of DDH ranges from severe dislocation to mild ultrasonic dysplasia without clinical instability. We agree that double diapering cannot treat dislocated or dislocatable DDH because it could delay the golden time for other definite treatments, such as harness, spica cast, and open surgery . For stable hips with ultrasonic dysplasia in which the alpha angle is < 55°, treatments could be observation or harness depending on physicians’ decisions . For Graf type IIa hip without clinical instability, the so-called ‘physiological immature’ state, follow-up is still recommended until a type I hip is presented by sonographic examination before 3 months of age [10, 11]. One study reported that only 79% of babies developed normal hips at 6–7 weeks of age, and there was a high missing rate of required follow-up due to parents’ insensitivity to type IIa hip . In the observation period, double diapering could be one of the recommendations for early maturation and for reducing costs in clinical and ultrasound follow-up.
Hip positioning and swaddling have been regarded as post-natal risk factors for DDH. The incidence of DDH was very high in areas using swaddling with the baby’s hips in extension and adduction position . In a recent report from Malawi, flexion and abduction hip positioning by ‘back-carrying’ significantly reduced the surgeries for DDH . Double diapering aims to maintain babies’ hips in a more flexed and abducted position. Although our data do not prove that the hip abduction angle was greater in the double-diaper group, we believe that double diapering is a practical method to continuously remind parents of proper hip positioning. The study results showed that instructions for parents to carry out a task like double diapering could work better than oral instructions of hip positioning.
This study had a few limitations. One limitation is that the study subjects had immature state of the hips rather than true DDH. The results, thus, cannot be used as a treatment guideline for hips with positive Ortolani or Barlow tests or Graf type IIc, D, III, and IV hips. Second, the type IIa hips in the two groups had equally good results at 1 year of age. Almost all type IIa hips in the single-diaper group spontaneously resolved to mature hips, but double diapering enhanced hip maturation and reduced the requirement of further follow-up. Whether universal use of double diapering in early life can reduce surgeries for DDH, as the ‘back-carrying’ method did, requires further study. Third, the first ultrasound examination was performed in a newborn nursery for collecting study candidates of the same age. The protocol did not selectively screen by risk factors, and the results may be different when ultrasound examination was performed at 4–6 weeks of age. Further studies of babies with risk factors and of older babies with Graf type IIa hips are warranted. Fourth, inter-rater reliability was not a problem because in this study hip ultrasound examination was performed by the same doctor in the newborn nursery and outpatient clinic, but minor inconsistency from intra-rater variability may exist [14–17].