Reliability of assessing patellar alignment: the A angle.

Abstract

Anterior knee pain syndrome is a complex problem for clinicians and patients. One possible etiological factor that has been identified is malalignment of the patella. Recently, a clinical method to assess patellar malalignment has been proposed--the A angle. However, no reliability of this technique was reported. Therefore, the purpose of this study was to determine intrarater and interrater reliability for the A angle. Thirty-six subjects participated in this study. Three raters measured each knee twice (N = 70). Interclass correlation coefficients (ICC) and standard error of measurements (SEM) were determined for the A angle and component measurements. Intrarater A-angle values ranged from 11.8 to 23.5 degrees. Intrarater A-angle ICCs were poor (0.20-0.32, SEM = 5.30-7.95 degrees). Interrater A-angle ICC was poor (-0.01, SEM = 7.82 degrees). Results indicated that the A angle as determined in this study was not reproducible. Therefore, further study is needed before the A angle can be used as a reliable assessment tool for patellar position.