Analysis of spinal alignment and pelvic parameters on upright radiographs: implications for acetabular development

The purpose of this study was to correlate measures of sagittal spinopelvic alignment [lumbar lordosis (LL), sacral slope (SS), pelvic tilt (PT) and pelvic incidence (PI)] and measures of acetabular coverage [lateral center edge angle (LCEA) and Tonnis angle] in asymptomatic adolescents on standing biplanar radiographs. We hypothesized that subjects with increased pelvic incidence and LL would have increased anterior PT and increased measures of acetabular coverage. Upright anteroposterior and lateral spinopelvic radiographs were obtained using EOS imaging technique. LCEA and Tonnis angle were calculated on the anteroposterior images and the lateral images were analyzed for LL, PI, PT and SS. LL was found to have a strong correlation with SS (r(s) = 0.786, P < 0.001), moderate correlation with PI (r(s) = 0.529, P < 0.001), and a poor inverse correlation with PT (r(s) = −0.167, P = 0.018). However, LCEA was not found to be significantly correlated with PT (r(s) = 0.084, P = 0.238) and Tonnis angle was not found to be correlated with any of the sagittal spinopelvic measures. Healthy, asymptomatic adolescents with increased pelvic incidence and lumbar lordosis did not have increased anterior PT or increased measures of acetabular coverage. The correlations identified in previous cadaveric studies or clinical studies evaluating changes between supine and standing radiographs are not supported in this healthy adolescent population. Our findings may suggest that an individual’s acetabulum develops as a dynamic adaptation to one's particular sagittal spinopelvic alignment to optimize femoral head coverage. Level III. Diagnostic – Investigating a diagnostic test.