Pelvic incidence is the quantification of the pelvis anatomical shape which has significant effect on the occurrence of various lumbar degenerative diseases. The aim of this study was to measure the in vivo dynamic motion characteristics of the lower lumbar spine in people with different pelvic incidence.

A total of 55 volunteers were included in the study. The participants were devided into 3 groups (A: pelvic incidence≤40°, B: 40° < pelvic incidence <60° and C: pelvic incidence ≥60°). The L3–S1 vertebrae of each subject was MRI scanned to construct 3D models. The lumbar spine was then imaged using a dual fluoroscopic imaging system as the subject performed physiological position. The 3D vertebral models and the fluoroscopic images were used to reproduce the in vivo vertebral positions along the motion path. The relative translations and rotations of each motion segment were analyzed.

At the L5-S1 segment, the primary ranges of motion for left-right axial rotation and flexion-extension of the patients with large pelvic incidence (3.28° ± 0.79°, 7.56° ± 1.81°) were significantly larger than normal pelvic incidence (2.61° ± 1.01°, 6.57° ± 2.18°) and small pelvic incidence (2.00° ± 0.60°, 5.83° ± 1.67°).

The anatomic variable pelvic incidence is associated with the ranges of motion in lower lumbar vertebrae, especially in the L4–5 and L5-S1 segments.