Dimensions of the 60 male human lumbar vertebrae were quantified on their digitalised lateral images, and related to them across the five vertebral levels (range of 20–40 years). Vertebra dimensions’ were defined and referred to the upper endplate. Linear dimensions (mm) were: the length of the whole vertebra and of the spinous process; the anterior/posterior body heights, and the upper/lower endplate lengths. For each of the measurements L3/L1, L3/l2, L3/L4, L3/L5 ratios were calculated. The inclination angle (°) of the lower-end-plate was further calculated.

Significant differences were shown by a randomized complete blocks design, post-hoc test (Student-Newman-Keuls), (α< .05). Anterior bodies’ heights ratios progressively decreased from L1 to L5 level, which means a relative increase of the anterior bodies’ heights. Posterior bodies’ heights ratios progressively increased from L1 to L5 level, which means a relative decrease of the posterior bodies’ heights. Lower-endplates inclination angle significantly and progressively increased from L1 to L5 vertebral level. For L1 and L2 (𝛉< 0°), it means that vertebrae are ventrally wedged, whereas L3, L4, L5 vertebrae are dorsally wedged (𝛉< 0°). It could be suggested that individual vertebra morphology contributes to shape the anterior convexity of the lumbar curvature along with the intervertebral discs. Spinous process and vertebral lengths ratios significantly decreased from L1 to L2, and significantly increased from L4 to L5, but no differences between L1vs. L5 neither for L2 vs. L4. It shows that lengths of the spinous process and vertebrae define two segments with same trends at the lumbar spine, the upper L1 and L2 segment; and the lower L4 and L5, which join together at L3 vertebra. This design allows to drawn the concavity of the lower back while standing upright and its convexity while flexing forward.