Anatomical sacral slope, a new pelvic parameter, is associated with lumbar lordosis and pelvic incidence in healthy Japanese women: A retrospective cross-sectional study

Abstract

Purpose: Anatomical sacral slope (a-SS), a pelvic anatomical parameter that does not require the center of the femoral head, strongly correlates with pelvic incidence (PI) during three-dimensional measurements in normal subjects. Sagittal alignment of spinal and pelvic parameters is typically evaluated using two-dimensional radiographs; however, the relationship between a-SS and PI has not been evaluated using radiographs. This study aimed to evaluate the correlation between a-SS and other spinal and pelvic parameters using radiographs. Methods: We evaluated 144 healthy women. Using sagittal radiographs, we measured lumbar lordosis (LL), thoracic kyphosis, PI, SS, pelvic tilt, and a-SS, which were defined as the angle between the superior end plate of S1 and a line perpendicular to the anterior pelvic plane. Pearson coefficients were used to determine correlations, and intraobserver and interobserver intraclass correlation coefficients (ICCs) were used for validation. Results: There was a strong correlation between PI and a-SS (r ¼ 0.756). Moreover, correlations between a-SS and LL and between PI and LL were similar (r ¼ 0.661 and r ¼ 0.554, respectively). The intraobserver ICCs were 0.884 for a-SS and 0.840 for PI. The interobserver ICCs were 0.856 for a-SS and 0.653 for PI. Conclusion: a-SS was strongly correlated with PI. The correlation between a-SS and LL was equivalent to the correlation between PI and LL. Moreover, the ICC for a-SS was larger than that of PI. This study suggests that a-SS is a useful new pelvic anatomical parameter that can be used instead of PI.

Association of the Anatomical Sacral Slope With Lumbar Lordosis and Pelvic Incidence in Female Patients With Developmental Hip Dysplasia: A Retrospective Cross-sectional Study

“…Moreover, the association between a-SS and LL was similar to that between PI and LL (r=0.661, p < 0.001, and r 0.554, p < 0.001, respectively). These results were similar to those of a study in patients with DDH using 3D measurements [1] and to results in normal healthy subjects, obtained by 2D measurements [3]. Consequently, the relationships between a-SS and LL and between PI and LL were similar between patients with DDH and normal subjects.…”

“…We recently described a similar correlation between PI and a-SS in normal healthy subjects using 2D measurements [3]. Therefore, a-SS is considered useful for estimating PI.…”

“…From these results, PI could be estimated from a-SS with the following regression formula: PI = 0.8 × a-SS + 21. Moreover, this formula is similar to that used in normal subjects: PI = 0.8 × a-SS + 18 [3].…”

“…The anatomical sacral slope (a-SS) was established as the angle formed by the straight line of the superior endplate of S1 and a line at a right angle to the anterior pelvic plane (APP), which was established according to the line connecting the middle point of the anterior superior iliac spine (ASIS) of both sides and the pubic symphysis [1][2][3] (Fig. 1).…”

“…In sagittal spinal malalignment, maintaining suitable balance is considered di cult, and it may lead to "hip-spine syndrome" [7]. Several previous studies have described PI and other thoracolumbar spinal and pelvic parameters, such as lumbar lordosis (LL) and sacral slope (SS), as signi cantly associated on plane radiographs [3,8,9]. A larger PI is considered a risk factor for spondylolisthesis, because it seems to lead to anterior deviation of the sagittal vertical axis [10,11].…”