Background: A lateral radiograph of the proximal femur is critical in the evaluation of patients with suspected femoroacetabular impingement. Positioning patients for a cross-table lateral (XTL) image is difficult, which may result in repeat exposures and increased cumulative radiation. Alternatively, the 45-degree Dunn (Dunn) and single frog lateral (SFL) views have been shown to accurately reveal proximal femoral abnormalities in femoroacetabular impingement. The purpose of this study was to compare the effective radiation doses (ERD) for 3 lateral hip projections that provide similar diagnostic information.
Methods: Patients presenting to the adolescent hip clinic with indicated examinations were evaluated with a standard anteroposterior (AP) pelvic radiograph and one of 3 lateral hip radiographs: XTL (n=16), Dunn (n=17), or SFL (n=27). Technical exposure parameters and published reference data for an AP pelvic radiograph were used to extrapolate the ERD. A simple Pearson r correlation test determined the relationships between body mass index, age, and ERD. The rate of repeat exposures per study was calculated.
Results: Body mass index positively correlated (r=0.34) and age and negatively correlated (r=-0.27) with ERD. ERD was increased for the XTL (0.83±0.98 mSv) over the Dunn (0.37±0.15 mSv) and SFL (0.22±0.11 mSv; P<0.05). Repeat exposures were performed in 10.4%, 4%, and 6% of XTL, Dunn, and SFL studies, respectively.
Conclusions: The ERD for a single projection is highest for the XTL, and the examination is more likely to be repeated. The XTL radiograph should be avoided whenever possible and substituted with alternative images providing similar diagnostic information, such as the Dunn or SFL, to minimize lifetime cumulative radiation exposure to the patient.
Level of evidence: Level II.