I have often wondered if people who have a  slight difference in the length of their legs would wonder around in a circle if they got lost in a desert?.

I regularly see patients who, when they lie down, will appear to have one leg significantly shorter than the other. This is called leg length alignment asymmetry  (LLAA) or apparent leg length Inequality  (LLI) in the trade. This should not be confused with actual or anatomic leg length Inequality. Confused? I’m not surprised.

The Gold Standard to measure actual leg length is an x-ray and when applied to the normal population ie the first 100 or so folks you meet coming out of the supermarket, you will find that there is some discrepancy between the actual size of the legs in about 90% of us . That’s a whopping number. In fact it is quite rare to have legs that are the same length. However this difference is mostly small – estimated to be an average of 5mm.

Of the 90 % of us with uneven leg length, less than 5% will have what could be considered to be significant anatomic LLI of over 20 mm. In other words folks who have a longer leg on one side by at least 20 mm could possibly be suffering back pain, knee pain, hip pain and also have a terrible predilection for getting lost in deserts.

In fact it is quite rare to have legs that are the same length.

As we said earlier that there is an anatomic LLI and an apparent LLI; what’s the difference? Well, the apparent LLI is caused by tight muscles that attach to the pelvis principally the Quadratus Lumborum or QL. The QL attaches to the spine above and to the pelvis below and will hoik up the pelvis on one side if it is tight. It is this hypertonicity which causes much apparent LLI.

When there is an actual shortness of one leg of less than 20 mm the body does a neat little trick and compensates with some tight muscles but this does not usually cause any problems.

So don’t be too worried if you are told you have one leg shorter that the other – most people do. It is extremely unlikely to be the cause of any problems unless the difference is more than 20 mm. And in that case make sure you take a compass with you the next time you go for a walk in the Sahara.