Does Swaddling Influence Developmental Dysplasia of the Hip? An Experimental Study of the Traditional Straight-Leg Swaddling Model in Neonatal Rats

Background: 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. In our experiment, the influence of straight-leg swaddling in an animal model was observed radiographically and histologically. Methods: One hundred and twelve neonatal rats were divided 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 anteroposterior pelvic radiographs, and histological studies were performed to further observe the morphology of the hips. Results: 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. Differences between the sexes were significant only in the early swaddling group, and differences between sides were not significant in any group. Appositional growth of the acetabular cartilage and deformity of the triradiate cartilage complex were observed in the dislocated and subluxated hips. Conclusions: Straight-leg swaddling was demonstrated to increase 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. Sex differences also existed but a side preference was not observed. Appositional growth of acetabular cartilage and a deformed triradiate cartilage complex were the pathological basis of the hip dysplasia in this animal model. Clinical Relevance: Traditional swaddling in human infants should be avoided to allow normal hip development; more modern alternatives that do less harm to hip development in human infants are available.