The high-low condition is mostly identified in the front feet, where it seems to be exaggerated the most, but usually also affects the hinds.
For some horses, that will translate in a club foot, for others, it can be an extremely flat, run forward foot. It can also be a very mild difference between the 2 fronts.

To illustrate the article, the high foot is the white one, and the low foot is the black one.

We mostly tend to think the “abnormal” looking foot (too clubby or too flat) as the problem foot. When this is not true in most cases.
Hi/Lo or High Low or HLS (High Low Syndrome) is mainly a whole body problem that is most visible in the feet.

Here are the most common causes identified:
Teeth problems, chiro imbalances, how the foal is placed in the mare’s womb, trimming problems, saddle fitting issues, rider’s asymmetrical body, and so on 😅

It can be helped by treating the causes but of course, the body will have adapted to this crookedness. So give it time to evolve without over stressing the body.

Here I highlighted in orange how the extensor branch of the suspensory ligament is being strained. It doesn’t mean a huge immediate correction of the “high heels” is beneficial though. On the contrary, by taking off too much heels, it can lead to serious soft tissues damage.