<i>In vivo</i> relationship between the clinical epicondylar axis and the anterior pelvic plane in normal subjects

Abstract

Background: Several researchers consider the clinical epicondylar axis (CEA) as the functional flexion-extension axis of the knee. The anterior pelvic plane (APP) is commonly used as an anatomical reference plane of the pelvis. However, no study has investigated the relationship of the APP with the CEA and PCA. In this study, we aimed to investigate the relationship of the APP with the CEA and posterior condylar axis (PCA) in the standing and supine positions. Methods: We recruited 77 healthy Japanese subjects for this study, and carried out measurements using the Hip CAS ? system, a 3D system used for the assessment of lower extremity alignment. Results: The mean femoral neck anteversion was 16.33°. There was an approximate discrepancy of 6° between the male and the female in anatomy (15.73° and 21.15° in the male and female subjects, respectively). The mean condylar twist angle (CTA) was 6.86° and the mean APP-PCA value in the standing position was ﹣ 6.88°. The mean APP-CEA value in the standing position was 0.02°, and the discrepancy between males and females was only 0.21° (0.09° and ﹣ 0.13° for the male and female subjects, respectively). This meant that Xp axis of APP and CEA were almost parallel. On the other hand, the mean APP-CEA value in the supine position was 7.07° (male subjects = 9.48°; female subjects = 5.62°). Here, the CEA was approximately parallel to the horizontal axis of the APP, which was compatible with the neutral position of the knee and hip joint, and anatomically and kinesiologically justified in normal subjects. Conclusion: CEA was approximately parallel to the horizontal axis of the APP. These results are compatible with regard to the neutral position of the knee and hip joints, and anatomically and kinesiologically justified in normal subjects. Moreover, CEA is a potential reference axis for the insertion of the femoral component in THA.