Femoroacetabular cam-type impingement: diagnostic sensitivity and specificity of radiographic views compared to radial MRI

Purpose: To retrospectively assess the diagnostic sensitivity of 45° Dunn view and cross-table lateral radiographs for the assessment of cam deformity by comparison with radial MRI.

Materials and methods: 60 cases with radiographs (38 a-p and 45° Dunn views, 22 a-p and cross-table lateral views) and radial MRI were assessed. Alpha angle measurements were obtained both for radiographs and radial MRI. Statistics included frequency analysis, bivariate linear correlation analyses of MRI and radiograph measurements and cross-table analyses testing for the sensitivity and specificity of radiographs for the detection of an alpha angle larger than 55°.

Results: 53.3% had the maximum alpha angle in the superior-anterior aspect of the femoral head-neck junction. Cam deformity was found in 45/60 cases (75%) in radial MRI. Pearson correlation demonstrated the Dunn view was most accurate for the superior-anterior aspect (.772, P<.001). The cross-table lateral views were best suited for the anterior-superior aspect (.511, P<.05). The sensitivity for cam deformity in the Dunn view was 96.4% vs. 70.6% in the cross-table lateral view.

Conclusion: The 45° Dunn view can improve the first line of impingement diagnostics. Radial MRI however remains indispensable for pre-operative planning and the evaluation of symptomatic cases without obvious deformity.