Abstract
Introduction: The radiographic evaluation of the antero-lateral femoral head is an essential tool for the assessment of cam type of femoroacetabular impingement. Computerised tomography (CT), magnetic resonance imaging and frog lateral plain radiograph views have all been suggested as imaging options for this type of lesion. The alpha angle is accepted as a reliable indicator of cam type of impingement and this may also be used as an assessment tool for successful operative correction of the cam lesion. The aim of our study was to analyse the reliability of The frog lateral view plain radiographs to analyse the alpha angle in cam femoroacetabular impingement.
Patients and Methods: Thirty two patients who presented with femoroacetabular impingement were studied. Interobserver reliability for assessment of alpha angles on frog lateral radiographic view was analysed using intraclass correlation coefficient. The alpha angles measured on frog lateral views using digital templating tools were compared to those measured on CT scans.
Results: A high interobserver reliability was noted for the assessment of alpha angles on frog lateral views with a correlation coefficient of 0.83. The average alpha angles measured on frog lateral views was 58.71 degrees (range 32 to 83.3). The average alpha angle measured on CT was 65.11 degrees (range 30 to 102). However, a poor correlation (Spearman r of 0.2) was noted between the measurements using the two systems.
Conclusions: Frog lateral plain radiographs are not reliable predictors of alpha angle. Various factors may be responsible for this such as the projection of the radiographs, patient positioning and quality of images. CT imaging may be necessary for accurate measurement of the alpha angle.
The abstracts were prepared by Mr Matt Costa and Mr Ben Ollivere. Correspondence should be addressed to Mr Costa at Clinical Sciences Research Institute, University of Warwick, Clifford Bridge Road, Coventry CV2 2DX, UK.
