Vertebral Body Wedge Geometry Predicts Lumbar Lordosis Beyond Pelvic Morphology in Chronic Low Back Pain

Objectives: Lumbar vertebral wedge angles reflect vertebral body geometry and may influence lordosis. Whether the total wedge index (TWI) and segmental wedge angles differ between asymptomatic individuals and chronic low back pain (CLBP) patients, and predict lordosis independently of pelvic morphology, remains unclear. Methods: Standing lateral full-spine radiographs from 72 volunteers (49 male; mean age 28.3 ± 7.7 years) and 72 CLBP patients (28 male; mean age 52.0 ± 17.9 years; NRS 4.5 ± 2.2; pain > 3 months) were digitized using a validated quadrilateral vertebral body model. L1–L5 wedge angles and TWI (L1 + L2 + L3 + L4 + L5; negative = net posterior taper) were calculated. Pearson correlations, hierarchical OLS regression, and centile distributions were assessed, following STROBE guidelines. Results: In CLBP, L1 wedge was lower (3.33 ± 4.32° vs. 4.87 ± 3.55°; p = 0.020; d = −0.39) and L5 wedge differed significantly (−6.50 ± 6.32° vs. −8.65 ± 6.30°; p = 0.043; d = +0.34). TWI correlated most strongly with lordosis in volunteers (r = +0.531) and CLBP (r = +0.478; both p < 0.001), and with sacral tilt in both groups. TWI added ΔR² = 0.183 over pelvic morphology (PTPIA) in volunteers and ΔR² = 0.210 in CLBP, where PTPIA alone explained <2% of lordosis variance. L1 wedge was greater in males (5.27 ± 3.64° vs. 2.76 ± 4.03°; p < 0.001; d = 0.67). T4-HA translation did not correlate with wedge variables. In CLBP, L1 and L5 lost lordosis correlations, while L2–L4 remained significant. TWI was the primary structural predictor of lumbar lordosis. Conclusions: In CLBP, the pelvic–lordosis relationship is disrupted, yet TWI remains predictive (ΔR² = +0.210), indicating that vertebral body geometry remains linked to lordosis when pelvic morphology does not. Normative TWI centiles may support radiographic outcome measurement.