Defining "Normal" Static and Dynamic Spinopelvic Characteristics: A Cross-Sectional Study

Methods: This was a cross-sectional cohort study of 112 asymptomatic volunteers (age, 47.4 ± 17.7 years; 50.0% female; BMI, 27.3 ± 4.9 kg/m). All participants underwent lateral spinopelvic radiography in the standing and deep-seated positions to determine maximum hip and lumbar flexion. Lumbar flexion (change in lumbar lordosis, ∆LL), hip flexion (change in pelvic-femoral angle, ∆PFA), and pelvic movement (change in pelvic tilt, ΔPT) were determined. The hip user index, which quantifies the relative contribution of the hip to overall sagittal movement, was calculated as (∆PFA/[∆PFA + ∆LL]) × 100%.

Results: There were decreases of 4.5° (9%) per decade of age in lumbar flexion (rho, -0.576; p < 0.001) and 3.6° (4%) per decade in hip flexion (rho, -0.365; p < 0.001). ∆LL could be predicted by younger age, low standing PFA, and high standing LL. Standing spinopelvic characteristics were similar between sexes. There was a trend toward men having less hip flexion (90.3° ± 16.4° versus 96.4° ± 18.1°; p = 0.065) and a lower hip user index (62.9% ± 8.2% versus 66.7% ± 8.3%; p = 0.015). BMI weakly correlated with ∆LL (rho, -0.307; p = 0.011) and ∆PFA (rho, -0.253; p = 0.039).

Conclusions: Spinopelvic characteristics were found to be age, sex, and BMI-dependent. The changes in the lumbar spine during aging (loss of lumbar lordosis and flexion) were greater than the changes in the hip, and as a result, the hip's relative contribution to overall sagittal movement increased. Men had a greater change in posterior pelvic tilt when moving from a standing to a deep-seated position in comparison with women, secondary to less hip flexion. The influence of BMI on spinopelvic parameters was low.