Pelvic and sacral morphology and their correlation with pelvic incidence, lumbar lordosis, and lumbar alignment changes between standing and sitting postures

Study design: Retrospective Cross-Sectional Radiographic Study. Objective: This study aims to describe novel radiographic markers of sacropelvic morphology to further define the static and dynamic relationship between the pelvis and the spine, via the analysis of two postures - standing and sitting. Summary of background data: There is increasing evidence underlining the importance of spinopelvic radiographic parameters in the holistic management of sagittal spinal deformity given the close relationship between pelvic morphology and spinal profile. Methods: This is a retrospective radiographic study of patients who presented with the first episode of isolated mechanical, low back pain of fewer than 3 months' duration. All patients underwent whole spine radiographs using EOS technology in both standing and relaxed sitting postures. Six novel distance measurements (H1, H2, H3, V1, V2, DD) to determine pelvic dimensions, and 3 novel angles (A, B, C) to determine sacral morphology were described. Results: A total of 64 males (58.2%) and 46 females (41.8%) with a mean age of 42.8 +/- 18.6 (range:17-81) years old was studied. Between standing and relaxed sitting postures, differences were observed in all sagittal radiographic parameters. Multivariate analysis showed that standing LL< 500 (p = 0.008), standing V1 > 13 cm(p = 0.040), and angle B> 800(p = 0.002) are predictive of PI< 500, standing TK< 300 (p = 0.003) and PI< 500 (p = 0.006) are predictive of LL< 500, and standing PT< 170(p = 0.034), standing H3 > 4 cm (p = 0.030), standing angle C< 420 (p = 0.003), sitting SS> 60 (p = 0.002), and sitting PT < 450 (p = 0.013) are predictive of change in LL below mean difference of 420 between standing and relaxed sitting. Conclusions: Apart from the known correlation between TK, LL and PI, low PI was found to be associated with a tall pelvis and a straight sacrum (angle B). Association between a small coccygeal inclination angle (angle C) and smaller change in LL between standing and relaxed sitting may have clinical relevance.

Automated summary

The study aimed to describe novel radiographic markers of sacropelvic morphology and analyze the relationship between the pelvis and spine in standing and sitting postures. Significant differences were observed in sagittal radiographic parameters between the two postures. Multivariate analysis identified predictive parameters for different spinal deformities in relation to pelvic and sacral morphology.