Introduction: Sagittal balance appraisal and surgical planning rely heavily on the interpretation of spinopelvic parameters. Pelvic tilt (PT), a dynamic parameter that reflects pelvic retroversion resulting from sagittal plus-balance, has gained special importance for its strong association with pain and surgical outcomes. However, poor imaging techniques and incorrect patient positioning frequently hamper PT interpretation in lateral films. To overcome image-quality issues and simplify spinopelvic assessment, the authors propose a novel parameter measurable in anteroposterior radiographs that correlates with PT and indirectly estimates pelvic retroversion.
Methods: Conventional spinopelvic parameters (SVA, PI, LL, PT, SS) and BSA were retrospectively measured in lateral and anteroposterior radiographs of 105 consecutive patients. The BSA measured in AP x-rays is defined as the angle formed at the intersection of a line that connects the inferior margin of the sacroiliac joint to the midpoint of a horizontal line joining both femoral heads. Intra-class correlation coefficient was used to assess a quantitative correlation between PT and BSA as an indirect measure of pelvic retroversion.
Results: Average values for PI, LL, SS, PT and BSA were 46.5° (±10.23), 48.56° (±12.30), 29.97° (±9.77), 16.94° (±8.03) and 54.47° (±4.05) respectively. No statistically significant difference was observed with regards to sex. We encountered a moderately strong correlation (r=-0.66) between PT and BSA. ROC plot analysis revealed that a BSA threshold of 46° has a sensitivity of 90% to identify pathologic PT values (>20°), while a BSA =60° has a specificity of 90% to rule out pelvic retroversion using anteroposterior radiographs.
Conclusions: This study found a moderately strong correlation between the BSA, an innovative spinopelvic parameter measurable in anteroposterior radiographs, and PT. BSA seems to show great promise in simplifying spinopelvic appraisal by easily estimating pelvic retroversion associated with sagittal malalignment, while avoiding image-quality issues often encountered in lateral x-rays.
Patient Care: Sagittal deformity assessment and surgical planning rely heavily on radiographical analysis. An increased pelvic tilt reflects pelvic retroversion and correlates with increased pain and disability but it is not always measurable in lateral x-rays due to frequent technical difficulties; hence, causing patient reirradiation and delaying treatment to obtain adequate films or poor decision-making due to lack of information. With the BSA caregivers will be able to easily screen for abnormal pelvic tilt and retroversion, aiding in sagittal imbalance analysis and surgical planning.
Learning Objectives: By the conclusion of this session, participants should be able to recognize the importance of spinopelvic parameters in patient care and decision-making. Also they will be able to easily use the BSA in anteroposterior x-rays to identify patients with altered PT and increased pelvic retroversion as a compensatory mechanism for sagittal imbalance.