Spinopelvic alignment in asymptomatic adults: a global meta-analysis quantifying heterogeneity and proposing a...

Meta-analysis.

This PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses)-compliant meta-analysis aimed to quantify global variation in spinopelvic parameters among asymptomatic adults, distinguish population-invariant from adaptive components, and propose a clinically relevant parameter hierarchy.

High variability in sagittal spinal alignment is well established. However, a meta-analysis employing standardized methodology to quantify the heterogeneity and stratify findings by geographic region has not been conducted.

This systematic review identified 140 studies reporting 15 types of radiographic measurements in healthy 18-60-year-old individuals (n=1,229-15,251 subjects) from PubMed, Academia, and ResearchGate up to June 2025. The National Institutes of Health Quality Assessment Tool was used to assess the risk of bias. Parameters were regional spine curvatures, pelvic parameters, and global alignment measures. Random-effects models generated pooled estimates with 95% prediction intervals (95% pelvic incidence [PI]). Meta-regression was performed for geographic subgroup comparison.

All parameters demonstrated substantial heterogeneity (I2, 72%-98%), irreducible by demographic stratification. Pelvic tilt (PT) exhibited consistently low variability across populations (95% PI <5°). Bicoxofemoral axis-referenced angles-including T1 and T9 PT (T1PT and T9PT), and T1 pelvic angle (TPA)-demonstrated low variability in the available cohorts (95% PI <5°), indicating potential stability, but require further validation. The regional spine curvatures-including cervical lordosis, thoracic kyphosis, and lumbar lordosis- varied widely (95% PI >10°). PT was uniquely conserved across geographic subgroups (Δ<1°, p =0.58), with sacral slope (SS) and PI demonstrating population-specific adaptations. Major limitations include the high heterogeneity of data, measurement variability across the included studies, and the low number of included studies reporting T1PT, T9PT, and TPA.

We propose a functional hierarchy of spinopelvic parameters based on their observed heterogeneity-from stable "core" to variable "adaptive" components. Future research is warranted to validate the potential population-invariance of currently underreported bicoxofemoral axis-referenced parameters and to evaluate whether correction strategies focused on these stable elements improve surgical outcomes.