AP or Frog-leg Radiograph for Children with Hip Dysplasia: How Can We Decrease Radiation?

AP or Frog-leg Radiograph for Children with Hip Dysplasia: How Can We Decrease Radiation?

It is common for pediatric patients with a history of hip dysplasia to undergo anteroposterior (AP) and frog-leg (FL) radiographs to monitor development of the hip. The choice may depend on the preferences of the physician and the routine of the institution. Fortunately, radiation exposure from today’s x-ray machines is very low because of computer enhancements and special techniques compared to the old days of regular x-rays. However, it’s always good to limit the amount of x-ray exposure whenever possible.

Both x-ray views may be helpful for the initial diagnosis of hip dysplasia. However, after initial treatment, it is common to follow a measurement called the acetabular index. One view may be enough to determine the acetabular index for those children who are being followed.

A recent study in North America conducted by Hudak et al sought to document the relationship between AP and FL radiographs and to determine which image was better to assess acetabular dysplasia. 33 patients screened for hip dysplasia were reviewed where patients had both the AP and FL x-rays. Average age of the children was approximately 2 years suggesting that they were in the follow-up phase of care.

Authors concluded that there is little clinical difference in variability of positioning and interpretation between AP and FL radiographs for hip dysplasia. These results indicate that a single image could be used assess to acetabular dysplasia thus decreasing risks of ionizing radiation.

Comments: Although Ultrasound can be used in young infants with DDH both for diagnosis and management, the older infants and children need x-ray assessment for diagnosis and follow-up. One view, usually the AP view may be adequate for most follow-up x-rays. This data may be useful for both clinicians who manage patients with DDH as well as awareness for parents regarding the potential for limiting ionizing radiation.


Hudak KE, Faulkner ND, Guite K, Muchow R, Narotam V, Nemeth B, Halanski M, Noonan K. Variations in AP and Frog-Leg Pelvic Radiographs in a Pediatric Population. J Pediatr Orthop. 2013 Mar;33(2):212-5