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

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 to 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 intrareader agreement (k = 0.38-0.93) and similar inter-reader agreement between the 2-view and 5-view (k = 0.33 vs 0.37).

Conclusions: 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.