November 24, 2011

Assessing structural leg length difference


There is much discussion in the literature regarding the difference between *induced* vs. *structural* leg length difference (LLD). Many mechanisms for induced LLD are offered by the different professions, including ilium up-or down-slip, or movements of the ilia in the anterior--posterior direction (rotation of an ilium in either direction in the sagittal plane).

All are possible—but the existence of an *actual* LLD (that is, where there is a cumulative difference in the leg bones' lengths, or when one ankle is pronated and the other is not, or small hemi-pelvis) often gets lost in the details of possible causal mechanisms in the discussions.

The radiological research from 11 sources (each cited in the book Overcome neck & back pain) tells us that skeletal LLD of 5mm or more (about 1/4") is found in about 50% of the general population, and this fraction is probably higher in the back and neck pain suffering population.

Actual, structural, leg-length difference is common. And because we live in an invisible sea of gravity, our body has to adjust to these asymmetries. We are the only mammals whose spines must align in the same plane as gravity, after all.

Why not try this "quick and dirty" 'provocation test'? This video shows you how. Do not be concerned about the absolute measure of the difference—just establish whether there is one first. 

Read transcription


Hi. Today Olivia, who's holding the boom and Sharon who will be helping me and myself will be showing you how to assess someone else's leg length difference at home or in your clinic. We need very simple equipment. So first are these little blocks and we'll talk about those in a moment, but the most important bit of equipment is having a light out to the side that will shine across your patient or your friend's back, so that you can see all the contours of the muscles. We made these little blocks here for leg length testing. You'll see that they're about six millimeters thick. And so two of them make 12 millimeters. And I recommend for use in the clinic that a six millimeter difference and a 12 millimeter difference is all you need. Let's show you what that looks like.


I've taken my shirt off and I'm standing facing away from me with the light out to the side here shining across my back so that the shapes of the muscles and the spine underneath the muscles can be seen quite clearly. Then if you're testing and working with someone else as Sharon and I are, you ask the person who's doing the test to move their feet so that the inside edges of the feet are parallel as mine are now. And then ask the person to move the hips subtly from side to side like this and ask them to stand in such a way that the weight of the body is being pressed up by the floor equally underneath both feet. That's the first part of the test. And then you look at the body to see whether there's anything to be seen. And for most people who are not trained to look this way, the curves in the spine left or right are not obvious. 


So what we do is we use the blocks to provoke an increase or a decrease like this. I'll lift my left heel first and ask Sharon to put the blocks underneath the left heel. Then I put my left heel down like this and then move the weight from side to side in my hips so that I can feel the floor pressing about the same left and right, which is about this point here. Lift the shoulders up and down like this. Let them drop down to normal and then ask the person who's testing you to look at the back and to make any note of the shapes that they see. You can also ask the person how that feels.


Now take a close look at the shape of my spine, and then we'll show you what it looks like when we put the block underneath the other foot. So I'll lift the left heel off the ground now, and then put it back down. And Sharon will put the block underneath the right heel. We once again move the hips and the weight from side to side until they're the same. You ask yourself when you're looking at your person, "Has anything changed?" And I think you can see that both hips are more level now and the spine is looking straighter. Let me put the blocks over underneath the left-hand foot once again to see the difference.


And you can probably see that it looks completely wrong now. Now I'm using 12 millimeter block underneath both feet, but we actually repeat the test with only six milliliters. And if the person that you're working with has a shorter leg length difference than mine, then even the six millimeter blocks will make the same change to the shape of the spine. So let us just demonstrate that for you now. Sharon's going to take away one block. So there's only one block underneath my left heel, but you can probably still see that those curves that were induced by the larger amount is still there. And we can show you by transferring the block across to the other side, that even though I'm only using a six millimeter block, the spine looks straighter. And refer to the book Overcome Neck & Back Pain for details of what sort of inserts to use if you actually find this kind of difference in the person you're working with.


Most people without quite a bit of training can't actually see the height in the hips by eye. So use a tactile technique like this. Sharon is going to bring her hands in from the side above my hips and then press her hands in towards my spine and then down onto the hips themselves. Then when I move my legs from side to side like this very slightly, she can feel where the hips themselves are. Now she takes her hands away from the hips. We put the block underneath the left heel as before. I redistribute my weight and she puts her hands back on the hips and then press straight down on the hips. And you should be able to see that the left hip is quite a bit higher than the right now.


Now we'll change over to the other side and show you what that looks like with the blocks underneath the right foot. And again, shift the weight backwards and forwards in this subtle sideways movement. She goes straight into towards the spine and then down on top of the hips. And if we've got this right, the hip should look roughly level now. Just to show you the difference, we'll put the blocks underneath the left side once more. So take your hands away, Shaz. Change the blocks over. Put the hands back in again. And I think it should be obvious to everyone that the left hip is considerably higher than the right hip. That means we have an actual leg length difference.

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