Identifying Cam Lesions on the False Profile View

OBJECTIVES: Recently the AP, Dunn and Frog Leg Lateral radiographic views have been verified to accurately reflect the findings of three dimensional imaging while assessing for cam lesions. The false profile radiographic view is traditionally used to measure acetabular coverage in the setting of femoroacetabular impingement. We believe it should also be used to assess the femoral head neck junction. Our objective is to verify the accuracy of this view with respect to 3D CT scan findings. METHODS: We retrospectively reviewed 37 consecutive surgical patients between May 2012 and September 2012 with preoperative radial oblique reformatted CT scans and plain radiographs. Alpha angles were measured on plain radiographs (AP, Dunn, False Profile) and CT reformats. Abnormal alpha angles were considered greater than 55 degrees and the CT scans were considered gold standard. Post-operative radiographs were also measured. Two physicians independently measured the images and the results were compared. RESULTS: The false profile view was 70.6% sensitive and 95.0% specific for diagnosing a cam lesion. It was noted that the false profile view was 1.31 times better than other views at visualizing the anterior head-neck junction at a 3 o’clock position (See image 1). The false profile view pre-operative mean alpha angle was 53.4° versus its post-operative mean alpha angle was 41.9°, Δ = 11.5° (t = 0.001). The interclass correlation coefficient (ICC) was found to be 0.81. CONCLUSION: This is the first study to suggest using the false profile view to assess the femoral head neck junction. For diagnostic and treatment purposes, the false profile view effectively characterizes cam lesions, particularly anterior 3 o’clock lesions. Further, it shows promising results as a peri-operative assessment tool to verify adequate osteoplasty. Measuring the alpha angle on this view also appears to be a reproducible with a significant ICC. We believe this view should be used for both acetabular coverage measurements as well as for femoral head neck junction measurements.