I was explaining to a Hungarian ex-gymnast patient about her slight leg-length inequality and the problems this was causing her low-back and she got me with the testing ‘Why?’ question – and, as you all know, this is the best question, and so I took a deep breath and started:

 

Firstly, leg length inequality (LLI) is really common.  A bloke called Knutson found:

 

“Using data on leg-length inequality obtained by accurate and reliable x-ray methods, the prevalence of anatomic inequality was found to be 90%, the mean magnitude of anatomic inequality was 5.2 mm (SD 4.1).”

So that’s all of us; but, as he adds:

 

“The evidence suggests that, for most people, anatomic leg-length inequality does not appear to be clinically significant until the magnitude reaches ~ 20 mm (~3/4").”

 

So it has got to be about 2 cm to be clinically important. 

 

However, for most of our patients it is not anatomical differences in leg–length that actually cause the change but pelvic rotation.  Rarely do people’s arms grow to be different lengths so why should their legs.  What really happens is that their pelvises get rotated.  Due to the cunning anatomy of the pelvis the bones do not rotate around the middle of the sacroiliac joints but about a point just below the bottom of the joint.  This means that if the bone rotates it does so like a cam with it getting higher as it rotates forward and lower as it rotates backwards – trust me on this one, it just does. 

 

Now a good way to test this if you have such a thing happening to you is to look in a mirror and see if your iliac crests are level, if they aren’t and your belt/pants are lopsided and one trouser hem and one shoe is wearing more that the other and then you may well have a leg-length inequality.  However, this doesn’t tell you what’s causing it.  To do this we need to look at the height of your hips without the legs in the equation, so sit down.  Now you are sitting on your ischeal tuberosities – the bits you sit on when you are on a bike and your legs are taken out of the equation.  If your iliac crest is still high when you are sitting then it must be a pelvis issue and we need to sort something out.

 

But how does it happen – well I recon for most of my patients it’s all to do with falling off the swings/tree/bike/footy/gymnastics and all that stuff as a child and it going unnoticed as the change was too small to see.  However, school screenings have shown that LLI is pretty common and I recon should be tackled at this point to prevent them from becoming a problem later because:

 

“The overwhelming majority of patients examined for low back pain of uncertain origin had LLI with asymmetric load distribution.  Furthermore, the overload at the lumbosacral level may produce muscular stress, premature degenerative diseases of the disc-somatic and the interapophyseal joints L4-L5 and/or L5-S1, as well as dysfunction (sometimes subluxation) of the sacroiliac joint, which might give rise to low pelvic pain.  The pain, with or without sciatica, if non caused by herniary pathology, almost always affects the side of the greater load.

Leg Length Inequality, Scoliosis And Low Back Pain.  A. Manganiello.

 

And then I took a breath in.