The frog-leg lateral radiograph accurately visualized hip cam impingement abnormalities

Area of Science:

• Orthopedic surgery
• Radiology
• Sports medicine

Background:

• Cam femoroacetabular impingement (FAI) is a hip condition characterized by abnormal contact between the femoral head-neck junction and the acetabulum.
• Accurate radiographic assessment of the anterolateral femoral head-neck junction is critical for diagnosing cam FAI.
• Traditional radiographic views may not always provide sufficient detail of the head-neck offset.

Purpose of the Study:

• To evaluate the accuracy of the frog-leg lateral radiograph in assessing femoral head-neck offset abnormalities in cam FAI.
• To compare measurements of femoral head sphericity, alpha-angle, and head-neck offset between hips with cam FAI and asymptomatic controls using various radiographic views.

Main Methods:

• Retrospective review of radiographs from 61 hips treated for cam FAI and 24 asymptomatic control hips.
• Measurement of femoral head sphericity, alpha-angle (Nötzli et al.), and head-neck offset on all radiographs.
• Comparison of measurements between the cam FAI group and the control group across different radiographic views.

Main Results:

• Asphericity of the femoral head was more frequent in hips with cam FAI compared to controls.
• The average alpha-angle was significantly greater in the cam FAI group across all views, with the largest difference observed on the frog-leg lateral view (65° vs. 47°).
• The average head-neck offset was decreased in the cam FAI group, with the most pronounced difference seen on the frog-leg lateral view (6.6 mm vs. 9.3 mm).

Conclusions:

• The frog-leg lateral radiograph provides accurate visualization of the femoral head-neck offset.
• This radiographic view is effective in identifying abnormalities associated with cam femoroacetabular impingement.
• The frog-leg lateral view demonstrates significant differences in key impingement parameters between affected and asymptomatic hips.