Standing versus supine pelvic incidence in adult lumbar spondylolisthesis

Pelvic incidence (PI) has been considered a morphological spinopelvic parameter, but this has been questioned by some experts in recent years. There is little research on whether PI changes with posture in patients with spondylolisthesis. This study thus examined the variation of PI in patients with lumbar spondylolisthesis under different postures.

This cross-sectional retrospective analysis included 110 patients with spondylolisthesis meeting the inclusion and exclusion criteria and hospitalized in Sichuan Province Orthopedic Hospital between January 2023 and January 2024. Patients' PI, pelvic tilt (PT), sacral slope (SS), and lumbar lordosis (LL) were measured on standing full spinal X-ray and supine X-ray [or scout computed tomography (CT)] and divided into two groups according to the supine and standing position. The difference between the two data groups was compared.

A total of 110 patients were included, with a mean age of 64.22±9.98 years. Supine PI was significantly lower than standing PI (58.22°±12.369° vs. 55.67°±11.694°; P<0.001), and the mean absolute difference was 4.11°±3.370°. Among the patients, 28 (25.5%) had an increase in PI of 6° or more, 32 (29.1%) an increase of 3° or more, and 50 (45.5%) remained within ±3°. Supine PT was significantly lower than standing PT (20.64°±9.079° vs. 14.03°±7.489°; P<0.001), while supine SS was significantly higher than standing SS (37.61°±10.157° vs. 41.65°±9.168°; P<0.001). There was no significant difference between supine LL and standing LL (50.20°±12.791° vs. 50.44°±11.658°; P=0.734).

The imaging analysis of adult patients with spondylolisthesis revealed obvious differences in the sagittal sequence between the standing and supine positions. PI and PT were significantly greater in in the standing position than in the supine position, while SS was significantly lower in the supine position than in the standing position. The variation in PI in different postures suggests that PI is not a fixed anatomical parameter and may change according to posture.