A recent report from Sweden asked the question whether babies treated for hip instability had normal hips at one year of age. The first problem they encountered was the definition of normal. It’s is customary to consider the hips normal if they are within a range that includes 95% of the population. This means that 5% of babies – approximately one in twenty – are outside that range of normal but that 5% is split between babies with a very shallow socket and babies with a very deep socket. This means that 2.5% would have a very shallow socket and would be at risk for arthritis from dysplasia as adults.
Let’s use height as a similar example where 95% of men are between 5’4” and 6’3” in height. Men shorter than 5’4” make up 2.5% of the population, while men taller than 6’3” make up 2.5% of the population. By this reasoning, approximately 2.5% of the population has a shallow socket when healthy babies are measured at one year of age, but this does not mean that all of them will develop arthritis. It is just a way of showing when to start getting worried.
The question is: how do babies treated for hip dysplasia compare to babies that were considered stable and did not need treatment? Are more or less than 2.5% of them outside the “normal” range for dysplasia? The authors took x-rays at one year of age and compared them to babies with stable hips who were not treated. All of the babies had improved after treatment and all of them had stable, reduced hips. However, the researchers found that 9% of babies treated for mildly unstable hips still had a shallow socket, and 23% of the babies treated for completely dislocated hips had a shallow socket at one year of age in spite of successful treatment when the brace was stopped.
This study raises concern that babies treated for hip dysplasia may not fully recover by one year of age. One factor may be that these babies were treated with the von Rosen splint instead of the Pavlik harness, but this may or may not be important. Also, babies with dislocated hips were treated for 12 weeks while babies with mildly unstable hips were treated for six weeks. It is possible that longer treatment would have improved the results.
This research study, like many studies, answers some questions and raises even more questions. This study shows that some babies still have shallow sockets even after successful treatment for hip instability or hip dislocation. Perhaps a more cautious approach with night time brace wear until an older age would help hips develop better.
The research study we discussed in July showed that night time splinting helps the socket continue to develop. https://hipdysplasia.org/news/scientific-literature-reviews/bracing-for-dysplasia-that-remains-after-initial-treatment/. Parents often question continued splinting on the basis of x-rays that look almost normal, but these two research studies seem to support a more cautious approach with continued splinting when in doubt. This recent study also serves as a comparison for researchers who use the Pavlik harness instead of the von Rosen splint. It will also serve as a comparison for researchers who treat infants longer than 6 to 12 weeks, or when night time splinting is continued for a longer period of time.
The best answers may never be known because there are so many variables, and each child is different, but this recent study suggests that longer periods of splinting may be needed even after the initial treatment seems successful.
Wenger D, Dϋppe H, Tiderius C-J, “Acetabular dysplasia at the age of 1 year in children with neonatal hip instability: a cohort study of 243 infants.” Acta Orthopaedica 2013;84(5):483-8