The Accuracy and Reliability of the Photometric Method-A New Noninvasive Tool for Assessing Frontal Lower Limb...

Background/Objectives: The aim of this study was to establish the reliability and accuracy of a new noninvasive tool for FLLA (frontal plane lower limb alignment) assessment: a photometric method. Methods: Sixty-seven subjects (31 males, 36 females, age 11-47 years) participated in the study. Seventeen subjects with orthopedic disorders were marked with radiopaque markers over the anterior superior iliac spines and femoral condyles. One pelvis-to-floor radiograph and one photograph were taken in the same standardized standing position. The hip-knee-ankle (HKA) angle (radiography) and the pelvis-knee-ankle (PKA) angle (photography) were measured by one rater. In 50 healthy participants, anterior superior iliac spines and femoral condyles were marked, and two pelvis-to-floor photographs were taken in a standardized standing position. The PKA angle was measured two times by three raters. The accuracy of the photometric method was tested with Pearson's correlation coefficient, simple linear regression, and Bland-Altman analysis. The reliability was tested with ICC(2,k) and Bland-Altman analysis. Results: The HKA angle was on average 3.9° more varus than the PKA angle, with a high correlation between measures (r = 0.97, p < 0.0001) and limits of agreement between -1.300 and -6.482. Intrarater (ICC(2,k) > 0.972), interrater (ICC(2,k) = 0.991), and test-retest (ICC(2,k) = 0.980) reliability were excellent. Conclusions: The photometric method is promising as a reliable and accurate noninvasive tool for assessing FLLA. Its accuracy across different study groups has yet to be confirmed in a larger cohort. The advantage of the presented photometric method is the use of the easily palpable anterior superior iliac spine as the proximal femoral axis point.