Given concerns about cost and pediatric radiation exposure, we questioned if long-term radiographic follow-up was beneficial for infants with developmental dysplasia of the hip (DDH) who have achieved normal clinical and sonographic exams,” said Eric J. Sarkissian, BS, during his presentation on “Hip Dysplasia Follow-up After Six Months: Why Order X-rays Later if Ultrasound has Normalized?” at the 2014 AAOS Annual Meeting. “We hypothesized that infants with normalized hip instability, acetabular dysplasia, or both may not require further radiographic monitoring.”

“This is a very common condition in pediatric orthopaedics,” explained coauthor Wudbhav N. Sankar, MD. “For cost containment and safety reasons, we are reviewing many of our protocols and the evidence behind them.”

On one hand, radiographic surveillance may be warranted, because the risk for residual dysplasia cannot be ignored and may lead to premature degenerative joint disease that would require progressively more complicated corrective surgeries of the pelvis as the patient ages. On the other hand, long-term radiographic follow-up of DDH in infants raises concerns about the risks of radiation exposure in a susceptible patient population. Compared to adult patients, pediatric patients have increased sensitivity to radiation and a higher probability of late radiation effects due to their longer life expectancy.

The researchers reviewed data on 115 “normalized” infant patients who had presented with idiopathic DDH at a single institution between January 2008 and January 2012. They defined infants as normalized if they had achieved a stable clinical exam (defined as a negative Barlow maneuver and Ortolani click) as well as an ultrasound revealing no signs of either hip instability or acetabular dysplasia. The research team excluded infants with persistently abnormal sonographic indices or clinical exams by 6 months of age.

A single, blinded observer then analyzed anteroposterior pelvic radiographs at approximately 6 months and 1 year of age for evidence of residual radiographic acetabular dysplasia. An absolute acetabular index greater than 30 degrees on the 6-month radiograph or greater than 28 degrees on the 12-month radiograph was defined as acetabular dysplasia.

“The mean patient age at which an ultrasound showed stable-appearing hips with no signs of acetabular dysplasia was 3.1 months,” said Mr. Sarkissian. “However, at a mean age of 6.6 months, 17 percent of all patients showed radiographic signs of acetabular dysplasia, and of patients left untreated after 6 months, 33 percent had acetabular dysplasia on subsequent radiographs at an average age of 12.5 ± 1.2 months.”

The researchers then measured the radiation effect that infants would experience. The computed ionizing radiation-effective dose for an anteroposterior (AP) pelvic radiograph at 6 and 12 months of age were 0.003 mSv and 0.006 mSv, respectively. The combined cancer risk of induced death from a single-view AP radiograph of the pelvis at 6 and 12 months of age was less than 1 per million.

Although the study had some limitations, including its retrospective design and short length of follow-up, the authors noted the following strengths: the use of a consecutive series of patients to represent the general pool of infants with DDH without bias to outcome, the definition they used for acetabular dysplasia, and their use of digital radiographs and picture archiving and communication system measurements, which have been shown to maximize accuracy and reproducibility.

“Our initial hypothesis was incorrect,” admitted Dr. Sankar. “There is a very real instance of persistent disease at 6 months and 1 year of age, and our findings support the need for serial radiographic monitoring through at least walking age. Radiographic follow-up at 6 months and 1 year of age may help identify residual acetabular dysplasia.

“We often have preconceived notions about what a study is going to show,” he continued, “but if results don’t follow the initial hypotheses, it doesn’t necessarily mean that the data is not worth publishing. We thought that our data would demonstrate that we could reduce radiation exposure, streamline care, and save money for the healthcare industry, but it turns out that it’s important to follow these patients because there is a fair amount of residual disease that needs to be addressed.”

John M. Flynn, MD, is a coauthor on this study.

Disclosure information: Dr. Flynn—Biomet, Wolters-Kluwer Health/Lippincott Williams & Wilkins, Orthopedics Today. Dr. Sankar—Wolters-Kluwer Health/Lippincott Williams & Wilkins. Mr. Sarkissian—no conflicts.

Peter Pollack is electronic content specialist for AAOS Now. He can be reached at ppollack@aaos.org

Bottom Line

• Infants with developmental dysplasia of the hip (DDH) are at risk for residual dysplasia that may lead to premature degenerative joint disease and progressively more complicated corrective surgeries of the pelvis as the patient ages.
• However, pediatric patients have increased sensitivity to radiation and have a higher probability of late radiation effects, requiring physicians to balance the impact of ongoing exposure after “normalization” is attained.
• This study of 115 infants with DDH found that the disease persisted at 6 months and 1 year of age, thus supporting the need for serial radiographic monitoring through at least walking age to help identify residual acetabular dysplasia.

Additional Information
Presentation Abstract