Morphological description of sagittal lumbar spinal alignment using curve magnitude, span, and apex—the multiethnic alignment normative study (MEANS)

Abstract

Current definition of lumbar lordosis uses the L1-S1 angle. Prevailing classification of sagittal spinal morphology, derived from a young adult population, classifies the spine into four subtypes defined by their sacral slope (SS) and curve morphology. To describe physiological sagittal alignment of the lumbar spine across age groups using three main parameters that dictate the lumbar curve: angular magnitude, span, and apex. A large, multicenter, cross-sectional radiographic comparison study. Four hundred sixty-eight healthy, asymptomatic subjects aged 18 to 80 years from five countries (184 males, 284 females; 98 France, 119 Japan, 79 Singapore, 80 Tunisia, 92 USA, mean age 40.61±14.99 years). Sagittal lumbar profile subtypes clustered based on lumbar curve angular magnitude (ie, Cobb angle of the lumbar lordosis), span, and apex, and described by sagittal radiographic parameters. Subjects underwent whole-body low-dose EOS stereoradiographs. Comparisons between conventional L1-S1 lumbar lordosis (cLL) and true lumbar lordosis (tLL, defined by the inflection-S1 angle) were conducted. Using the K-means clustering algorithm, lumbar curve angular magnitude, span and apex were used to classify sagittal spinal morphology into subtypes, stratified across age groups. Further univariate and multivariate analyses were conducted to compare radiographic parameters across subtypes, and identify predictors for the lumbar curve's angular magnitude, span and apex. Mean cLL was -57.27±11.37°, and tLL was -62.62±10.76°. Using tLL, instead of cLL, to describe sagittal spinal morphology, we found significant differences in terms of angular magnitude of the lumbar curve, the median thoracolumbar inflection vertebral level and pelvic incidence-lumbar lordosis mismatch Multivariate analysis found a larger SS, more positive T9 tilt, and more kyphotic T4-T12 predictive for a more lordotic tLL, while a larger overhang distance predicted for a less lordotic tLL (p-values<.001). In addition, a larger T9 tilt, less lordotic L1-L5 and smaller PT were predictors of a more caudal thoracolumbar inflection and lumbar apical vertebral levels (p-values<.001). Sagittal lumbar profiles of subjects age<30 years, 30≤age<60 years and age≥60 years, could be classified into 4, 6, and 3 subtypes, respectively. Sagittal lumbar profile subtypes vary across age groups, with more homogenous morphologies at the extremes of ages. Improved understanding of the morphological evolution of sagittal spinal profiles with age in asymptomatic individuals will help guide future individualized surgical treatment.