2008 Femoroacetabular impingement Can the alpha angle be estimated

Description: Femoroacetabular impingement is an important entity with well-described radiographic findings. One of the criteria of the cam type of femoroacetabular impingement is femoral head-neck dysplasia, denoted mathematically as the "alpha angle." Several observers have reported that direct measurement of the angle may not be necessary because subjective appraisal may yield similar results. We sought to scientifically determine the accuracy of a subjective assessment, using the calculated angle as the gold standard.
CONCLUSION: Subjective assessment of alpha angles is suboptimal unless one is quite confident of a bone abnormality.
Femoroacetabular impingement: can the alpha angle be estimated? Nouh MR, Schweitzer ME, Rybak L, Cohen J. AJR Am J Roentgenol. 2008 May;190(5):1260-2. Full text