Influence of age and sagittal balance of the spine on the value of the pelvic incidence.

Abstract

The pelvic incidence (PI) was recognized as the key factor of the sagittal balance of the spine. Its value was described own for each individual and unchanged during adulthood. To bring out the effect of the age and of a sagittal imbalance in the variability of the value of PI. 200 subjects with chronic low back pain due to sagittal imbalance were compared to 89 normal subjects. For each groups, the cases were divided according to the age (19-40, 6-40 years, over 60 years). The PI and the sagittal positional parameters were measured on large radiographs in standardized standing position. The correlation between age and PI was observed significant only for the >60 years cases. The mean values of PI were significantly greater for these cases. An increase of the value of PI was attributable to a twisting mobilization within the sacroiliac joint. It results from a forward projection of the gravity due to a sagittal disturbance and a pelvic compensatory backward rotation. This twisting into the sacroiliac joint was incriminated in the origin of chronic low back pain. The sagittal pelvi-spinal imbalance may be incriminated in the increasing of the value of PI by a painful destabilization sacro-iliac, with leads to an increasing of the value of PI.