If you read many papers on spinal biomechanics you’ve no doubt encountered the term “pelvic incidence”.  The measurement has always been somewhat confusing to clinicians in spite of the fact that it has been widely used in spinal research for years. I think it’s fair to say that many chiropractors , especially those of  us “of a certain age”,  remain a little fuzzy as to what  pelvic incidence is,  how it’s measured or why it’s important.  (And yes, it IS important!)

My purpose here is to (hopefully) simplify this subject a bit. A sound understanding of the concept is crucial  to reading much of the current literature related to the effect of spinal posture on clinical outcomes. So without getting too far afield here let’s start with a simple description of how Pelvic Incidence is measured on the lateral radiograph. I hope you find it helpful.

Mark R. Payne DC

President, Matlin Mfg. Inc.   

 Five Easy Steps

Step 1:  Construct the sacral base line (shown as Black Dotted line)

Step 2:  Mark the center point of the sacral base.

Step 3:  Construct a line (shown in Blue) perpendicular to the sacral base line and extending inferiorly from the center of the sacral base. 

Step 4:  Construct a line (shown in Red) from the center of the femoral head extending superior to the center point of the sacral base.

Step 5: The angle of “Pelvic Incidence” is the measured angle of intersection between the blue and red lines.

   There’s more to cover here than I can do in the context of a single post. Until next time, just keep these four points in mind.

MRP

Four Key Points About Pelvic Incidence

 1.  Gives us the relationship of the sacral base to the femur heads and is generally considered to remain constant throughout life.

2.  Average value is around 55 degrees (+/- 10 degrees)

3.  The angle may possibly change by up to 3 degrees due to motion at the sacroiliac joint as a result of degeneration or trauma.

4.  Considered a fundamental parameter in terms of determining the status of the spinal sagittal curves.