Correlations of Alpha Angle on Preoperative Imaging with Intraoperative Fluoroscopy for the Evaluation of Cam...

Reliable preoperative imaging of femoroacetabular impingement is important for effective diagnosis and treatment. While numerous imaging techniques exist, their relative accuracy remains unclear. The purpose of this study was to evaluate the accuracy of preoperative standard hip radiographs and magnetic resonance imaging (MRI) axial and radial views compared to the gold standard of intraoperative fluoroscopy for cam-type femoroacetabular impingement. Data were collected from 93 patients who underwent femoroplasty for cam deformity between 2015 and 2020 by a single orthopedic surgeon. One-way analysis of variance with post-hoc pair-wise evaluation, Pearson correlation coefficients, and Bland-Altman plots were used to evaluate differences and agreement between the imaging modalities. The fluoroscopic alpha angle (62.3°±7°) was significantly different than the radiographic (58.5°±7.0°; P=.004) and MRI axial angles (52.0°±8.2°; P<.001) but was similar to the MRI radial angle (60.7°±7.9°; P=.9). MRI radial angles had the highest correlation with fluoroscopy (r=.876, P<.001). The analysis revealed a sensitivity of only 27% for radiographic evaluation and a specificity of 41% with MRI axial evaluation. However, MRI radial evaluation displayed a sensitivity of 87% and specificity of 91% for diagnosis of cam deformity in the study population. These findings suggest the alpha angle derived from radial MRI correlated most strongly with intraoperative fluoroscopy. Radial MRI should continue to be the gold standard for preoperative templating and diagnosis of femoroacetabular impingement in symptomatic patients without obvious deformity on radiographs.