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.
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
- Measurement 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.
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