Pelvic Incidence is defined as the angle between the line joining the middle of the sacral endplate to the middle axis of the femoral heads.
The pelvic incidence is unique anatomical parameter for each individual and is independent of position or spatial orientation. Pelvic incidence is closely related to Sacral Slope and pelvic tilt
How To Measure
- A line is drawn across the sacral end plate. [Yellow dashed straight line in the image below]
- A line is drawn perpendicular to the above line at the midpoint.
- Center of femoral head is noted [Dashed yellow circle]s
- Another line connects midpoint of sacral end plate to center of femoral head.
- Angle between 2 and 4 gives the value of pelvic incidence
Normal Values and Significance
Mean pelvic incidence in normal children is 47°, and in normal adults, 57°.
In patients with low-grade spondylolisthesis, mean pelvic incidence is 68.5°, and in those with high-grade spondylolisthesis, mean pelvic incidence is 79°.
A low pelvic incidence implies a low pelvic tilt and lower lumbar lordosis. Patients with greater lumbar lordosis, and thus a high pelvic incidence, have increased shear forces at the lumbosacral junction.
There is a correlation between the pelvic incidence, the lumbar lordosis and the risk of L5 splondylolysis. The risk of spondylolysis and spondylolisthesis is higher with a higher pelvic incidence.