Background data: 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.
Purpose: To bring out the effect of the age and of a sagittal imbalance in the variability of the value of PI.
Materials and methods: 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.
Results: 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.
Discussion: 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.
Conclusion: 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.