The Myth of Leg Length Discrepancies

The Myth of Leg Length Discrepancies

The Myth of Leg Length Discrepancies

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One of the most frequently cited causes of biomechanical dysfunction in runners is leg-length discrepancy (LLD). This alleged problem is widely discussed in both the lay (i.e., Runner’s World) and medical literature and for two reasons it’s easy to see why. Number one, it is seen in the clinic all the time. Take any ten people (they don’t have to be runners), measure the length of their legs according to the accepted methods taught in medical, chiropractic or physical therapy schools, and you will most likely find a difference of 1/8 inch or greater in at least seven of the ten. Now, 1/8 of an inch does not sound terribly significant, but most of the running injury experts claim that in distance running this difference is very meaningful.

Which brings us to reason number two for differences in leg length being blamed for causing injuries: it’s so easy to understand the theory behind it! I mean, it just makes sense, doesn’t it? If you had one tire on your car an inch larger in diameter than the other three, surely you would expect to have problems with steering, alignment, bushing wear, etc., leading to eventual breakdown. Likewise, if your body is somehow unbalanced (tilted) due to a difference in the length of your legs, it just seems logical to assume that there will be too much stress on some structure, leading to injury. If this seems obvious, then so too must be the solution: Simply place a “lift” in the shoe for the short leg, of equal height as the discrepancy, to “balance out” the limbs. This is, in fact, the treatment of choice for many, if not most health professionals. But there are a few problems with this, as you might have suspected with such an easy answer.

First of all, there is the question of whether a discrepancy actually exists. The only truly accurate method of measuring the length of limbs is by x-ray, but this would be an expensive and hard-to-justify exposure to radiation, so clinicians rely on basically two “hands-on” methods to take these measurements. But these involve feeling for various bony landmarks of the pelvis and ankles, areas that are somewhat rounded and hardly pinpoint. The result is a rather inaccurate and unreliable assessment of leg length. This was demonstrated in a 1988 study of clinical versus x-ray measurements in 21 patients. Not only did the results indicate highly imprecise clinical measurements overall, of greater concern was the fact that in 13% of the measurements the testers erred in deciding which leg was longer!

Even if we could be assured that clinical measurements were accurate, the next problem is knowing for certain what it means. To assume that a difference in leg length means there is an actual difference in the length of the bones (femur and/or tibia) is most of the time a mistake. Most often what we are seeing is an apparent, or functional LLD. This is usually the result of a muscle imbalance somewhere in the lower extremities, most frequently at the hip. Here’s a prime example:

Most people seem to know where the gluteus maximus muscle is located, if not for physiological then at least for esthetic reasons. But it is another gluteus, the medius, that is a particularly significant muscle in terms of support and balance of the pelvis. This muscle runs from the pelvis to the upper femur on the outside area of the hip. When Jane Fonda lays on her side and lifts the top leg straight up, she’s using the gluteus medius. When standing on one leg, this muscle prevents your pelvis from tilting down on the opposite side. So, if the length of your right G. medius is, say, longer than your left because you habitually stand with most of your weight on your right leg while bending your left knee (think about it — it’s a very common posture), your pelvis will tilt down on the left and you will appear “cockeyed.” What’s more, your right leg will clinically measure longer than your left. Should this be treated with a shoe lift? Or should you be doing exercises to balance a weak or shortened muscle?

The point of all this is to forewarn you against apparently easy, simple solutions. Unless you know for sure that the length of your legs is different as the result of a childhood fracture, surgery or bony malformation, you should be a little skeptical of shoe lifts as the first line of treatment of running injuries. And be aware of your posture habits: stand on both legs evenly, or at least switch sides often, and don’t always cross the same leg over the other when sitting. You could be creating an imbalance that will cause you grief in the future.