Introduction of a Novel “Segmentation Line” to Analyze the Variations in Segmental Lordosis, Location of the Lumbar Apex, and Their Correlation with Spinopelvic Parameters in Asymptomatic Adults

STUDY DESIGN: Cross-sectional study. PURPOSE: This study aimed to understand the sagittal spinopelvic parameters, segmental lumbar parameters, and lumbar apex location in asymptomatic adults and analyze their correlations with each other. OVERVIEW OF LITERATURE: Roussouly and his colleagues reported that pelvic incidence (PI) influences the lower arc of lumbar lordosis, whereas Pesenti and his colleagues reported that PI influences only the proximal part of lordosis and not the distal part. Both studies have their shortcomings. METHODS: One hundred asymptomatic adult volunteers (mean age, 29.1±7.9 years; 69 males, 31 females) who satisfied the selection criteria were enrolled in this study. Standing antero-posterior and lateral whole spine and pelvis X-rays were performed, and the radiographic parameters were analyzed. We introduced a “segmentation line” bisecting the apical vertebra/disk to divide the upper arc of lumbar lordosis (ULL) and lower arc of lumbar lordosis (LLL). RESULTS: The mean PI was 48.02°, ULL 29.12°, LLL 16.02°, total lumbar lordosis (TLL) 45.14°, lumbar tilt angle 4.73°, and location of the apex of lumbar lordosis (LLA) 4.11°. The location of the lumbar apex moved higher as the PI increased. The PI was strongly positively correlated with the LLL (r =0.582, p <0.001) and TLL (r =0.579, p <0.001) but not with the ULL (r =0.196, p =0.05). The LLA was strongly positively correlated with the ULL (r =0.349, p <0.001), negatively with the LLL (r =−0.63, p <0.001), and not correlated with the TLL (r =−0.177, p =0.078). CONCLUSIONS: The PI influences the location of the lumbar apex, the LLL, and the TLL but not the ULL. The location of the lumbar apex significantly influences the segmental lordosis but not the TLL.