07/29/2026
"As many of you know, Dr. Carrie and I do leg length checks as a part of our appointment. I can't speak for Dr. Carrie, but I will occasionally be asked the purpose of the leg check. I actually find it quite interesting, so I thought it might be a fun topic.
The leg length is almost never what is considered anatomical. That is, one leg isn't shorter due to the bones of one leg being longer. It does happen, but it is rare. Typically it's what we call a functional leg length.
When you're lying face-down and I check your pelvis, I may find that the back of your left pelvic bone is sitting higher, compared to your right. What I don't know, automatically, is whether that is because your left pelvis is rotated forward or your right is rotated back. The leg length indicates which side is being affected, making it a test of laterality. When you lie prone, it pulls on muscles that affect the hip joint, like the quadriceps and TFL, or the glutes and hamstring depending on which side is being affected. That, in turn, indicates the direction the pelvis is rotated. So if your right pelvis looks higher than left and the right leg is short, I have more certainty about how that pelvic bone needs to be moved.
When we bend the knees, it pulls on the piriformis and other tendons around the sacrum, which then helps indicate which direction the sacral apex (recall when I wrote about the sacrum a few weeks ago) is pointing so we then know where to put our driving forces with regard to that.
Like I said, the kinetic chain is quite interesting to me and it is a conversation I have with enough regularity that I thought it would be fun to write about. " - Dr. Erick Thompson
