The overall effect of swaddling has been controversial for centuries. Its positive effect on the psychological development of the infant has popularized it in European and North American countries, but its negative effect on the development of the hip is of great concern.
Wang et al conducted a prospective study on 112 neonatal rats dividing them into a control group and three experimental groups that were swaddled with use of surgical tape in a manner simulating the human practice for the first five days of life (early swaddling), the second five days (late swaddling), and the first ten days (prolonged swaddling).
Hip dislocation and subluxation were evaluated on pelvic radiographs, and histological studies were performed to further observe the morphology of the hips.
Rats in the prolonged swaddling group had the highest prevalence of hip dysplasia (thirty-six of forty-four), followed by the early swaddling group (twenty-one of forty-four). Most of the dysplastic hips in the prolonged swaddling group were dislocated, whereas subluxation dominated in the late swaddling group.
This study demonstrates that straight-leg swaddling increases the prevalence of developmental dysplasia of the hip in this animal model, especially if the swaddling was early or prolonged. The severity of hip impairment varied, with early and prolonged swaddling both leading to more dislocations than subluxations.
The paper by Wang et al. is timely because of the rising popularity of infant swaddling in Western societies. Swaddling involves wrapping or bundling babies in cloth blankets with the arms restrained to dampen the startle response and provide a sense of comfort. Approximately 90% of infants in the United States are swaddled during the first few months of life.
This practice should be discouraged because it increases the risk of developmental dysplasia of the hip and hip dislocation. The paper by Wang et al. adds new information regarding the potential effects of swaddling on immature hips while further defining the pathomechanics of hip dysplasia. Although genetics and hormonal factors influence the development of hip dysplasia, this study confirms that abnormal mechanical factors are detrimental during early hip development.
The clinical relevance of the paper by Wang et al. is that it calls attention to the potential harmful effects of traditional infant swaddling with the lower extremities extended and adducted. The authors recommend that a less harmful method of swaddling should be substituted for the traditional straight-leg method.
This further validates the efforts of the International Hip Dysplasia Institute to promote safe swaddling that promotes hip healthy positioning.