Adaptation of the Lumbar Spine From Orthostasis to Supine

Observational-ecologic study.

Spine and pelvis undergo modifications in alignment so that the individual can maintain an orthostatic position, but to date there is no evidence as to the contribution of each lumbar segment and the change that occurs in them when moving from orthostasis to supine position.

To identify the difference in the contribution of the lumbar segments and pelvis to the formation of lumbar lordosis in both positions (orthostasis and supine) and how each one alters in this change.

lumbar lordosis adapts to the individual's body position and can be physiological or pathologic.

Retrospective cohort study that included 174 patients: the segments total lumbar lordosis (LL), L1-L4, L4-S1, L4-L5, L5-S1, and sacral slope were measured on x-rays (orthostasis) and MRI (supine). We obtained the mean values, correlations and models proposed for the relationship between the values found.

The SS, LL, L1-L4, L4-S1, and L4-L5 had their angular value reduced, and L5-S1 had its contribution to lordosis significantly increased when lying down. Moderate and strong correlations were obtained between SS × LL, L1-L4 and L4-S1, and between LL versus L1-L4 and L4-S1 in both positions. When using linear regression, proposed models were obtained with a high coefficient of determination between LL versus SS, L1-L4 and L4-S1 in orthostasis, for the same measurements and SS versus L4-S1 in supine, as well as for lordosis when comparing the 2 positions.

The L5-S1 segment has no change in angular value when lying in supine and is thus the largest contributor to lordosis in supine. L1-L4 increases its angular value when standing in orthostasis, the position in which it is the greatest contributor to lordosis.