How Many Radiographs Does It Take to Screen for Femoral Cam Morphology?: A Noninferiority Study

Abstract Purpose To compare a 2-view radiograph series (AP of the pelvis and 45° Dunn of the hip) with a 5-view radiograph series for sensitivity in identifying femoral cam morphology. Materials and Methods This is a retrospective review of consecutive patients with a 5-view radiograph series (AP pelvis and AP, 45° Dunn, frog lateral, and false profile of the affected hip) from 2016-2017. Three fellowship trained radiologists blindly and independently evaluated 2 views (AP pelvis and Dunn) for a femoral cam lesion, acetabular rim calcification, Tonnis grade, and important incidental findings. Two weeks later, the same assessment was made on all 5 views. A noninferiority test of the 2-view series vs. the 5-view series for sensitivity in identifying femoral cam morphology was conducted. Individual reader sensitivity calculations were performed and agreement was determined with the kappa statistic. Results The 2-view series was noninferior to the 5-view series for cam identification (p-value = 0.010). In comparing the 2-view vs. 5-view series for individual readers, there was no difference in the sensitivities (84-100% vs. 85-98%, p = 0.85-1.0) or specificities (11-56% vs. 7-56%, p = 0.58-1.0) for cam identification. There was fair to excellent 2-view intra-reader agreement (k = 0.38-0.93) and similar inter-reader agreement between the 2-view and 5-view (k = 0.33 vs. 0.37). Conclusion A 2-view radiograph series (AP pelvis and Dunn hip) is noninferior to a 5-view radiograph series for sensitivity in identifying femoral cam morphology.