Sacro-pelvic Tilt as a Predictor for Optimal Lumbar Lordosis

Abstract

Introduction Spino-pelvic parameters are crucial to address the spinal sagittal balance; such measurements require standardized lateral x-ray views that include the spine as well as the hips, which are not always available upon referral of cases, where instead, shorter films for the lumbo-sacral spine are requested. We aimed to describe a pelvic radiological reference points that could provide comparatively sound sagittal balance estimates, from conventional lumbo- sacral lateral x-ray views. The iliopectineal line was addressed as a radiological reference in the pelvis, that along with the horizontal line, and the upper endplate of the first sacral vertebra, provide two angles, the Iliopectineal inclination (Doha angle; DA), and the Sacro-pelvic tilt (Baco angle; BA), respectively. Material and Method: Radiological images for 96 adult subjects, aged between 20 – 80 years, with suspected or established diagnosis for spine problem. Readings were taken from the institute's digital radiology library, blinded to personal and clinical data. Frequency tables, correlations and test of difference were tested, taking (p-value < 0.05) as cut-off for significance. Correlation to the conventional Pelvic Incidence (PI), Pelvic tilt (PT), and the Sacral slope (SS), measured for the same patients, and from the same standardized standing lateral views that include the femoral heads. Results Readings of the new angles were found to be practically easy and reproducible. The iliopectineal inclination (Doha angle) readings averaged 61 +/- 9 degrees, indirectly proportional to the pelvic tilt (r = −0.46, P-value 0.000), along with its averaged 7 degree difference from the mean Pelvic incidence (54 +/- 8.9 degrees), DA (practically the sum of SS + BA) corresponded to the described lumbar lordosis values in the literature, as well as the estimated lumbar lordosis by Schwab's formula for the study sample. On the other hand; the Sacro-pelvic tilt (BA) had readings of 24 +/- 8 degrees, and a highly significant, yet weak negative correlation with the sacral slope (P-value = 0.001, r = −0.266). Having the Sacral slope as a common component for both DA and PI; those 7 degrees difference seem to reflect an actual upper sacrum retroversion, relative to the pelvis, which had a significant difference in age terms; those with sacral retroversion >7 and <7, for average age of 31 yrs, 40 yrs, respectively (P-value = 0.000) and seem to contribute to maintaining the spinal sagittal balance, that becomes more profound by the age of 50 years (averaged 2 degrees for over 50 years, in comparison to 8 degrees for youngers). Conclusion The iliopectineal lines provide reproducible readings, closer values to the lumbar lordosis, and addresses sacroiliac contribution to the sagittal balance, that regresses by middle age.