Let’s take a look at leg length inequality (LLI) AKA: Anisomelia or Leg Length Discrepency).
None of us are built straight; we might have a nose that points slightly to the left, an ear that’s lower than the other, or a breast that’s larger than its twin. In about 90% of us, one leg is longer that the other; and the vast majority of the time, this is not a problem. Sometimes that LLI can be functional – caused by other things such as a collapsed arch in the foot, or a muscle imbalance; whilst other times that LLI can be structural – one bone longer than the other, but accommodated by the body so that it has little or no impact upon the individual.
However, a long-standing LLI can cause secondary problems elsewhere, especially the pelvis and spine, as you want your eyes level to the horizon. These problems will tend to be low-grade overuse injuries, and often misdiagnosed to start with; typically responding to treatment of the secondary issue, but recurring; or responding but not resolving.
In the case of a functional LLI the best course of action is to identify why the LLI exists, and treat that root cause; in the case of a structural LLI (that is symptomatic), then an artificial lengthening of the short leg may be worthwhile; by the use of a heel lift, foot lift, or building up the sole of one shoe.
Establishing how great the inequality is can be difficult, expensive, and often pointless; given that your body can adapt and accommodate it, it often just needs a little help. One of the best (and cheapest) ways of establishing the extent of any LLI is to simply stand on flat ground, with you pelvis and lower back freely mobile (which may or may not require treatment to achieve); and then stand with one foot raised by a pile of paper; repeat on the other side; and decide which felt more comfortable. If you do notice a beneficial difference; then alter the size of the pile of paper until it feels most “right”; and that would indicate the size of any correction you can trial to see if it works. Basic orthotics to raise the heel or foot can be bought in most pharmacists, or on Amazon; for anything more complicated we would advise consulting a podiatrist.