Side note, I came to this conclusion because of certain issues I was having in my hip, and that I was seeing in other colleagues of mine. Here are some of my personal symptoms, which may or may not be yours:
1. My left hip has consistently turned out more than my right, whether I'm in music mode, standing, cooking, walking, running, etc. This can simply manifest as the foot turning out, at least in appearance. Both hips want to turn out in standing though. I've been working on gently bringing the legs back to neutral, and found that to be helpful.
2. This in turn can cause my left external rotators of the hip and the low back muscles to be unruly. (Muscles include my gluteus medius, TFL, Quadratus lumborum, and the iliotibial band of fascia.
3. I also have the beginnings of a baby bunion on my left foot which may be impacted by the external rotation of the hip.
4. From a combination of asymmetrical music-making, left side dominance, and a host of other things, my entire left side is loads tighter (less range of motion from sole of the foot up to the shoulder!) than my right, which means that I sometimes have back pain and other issues on just the left side.
So what's the solution? Start to get curious. It's also important to remember that correlation does not imply causation- my left hip/back issues aren't inherently caused by the turn out, but I would venture to say that the perpetual external rotation has impacted things. I will say that my pain has diminished exponentially since I've been doing pilates and other movement activities that have challenged my hip range of motion and stability.
-How do you stand when you're playing? Where are your feet, knees, and pelvis? What sort of shoes do you normally wear? How might those be affecting your lower body?
-How do you teach your students to stand? If you have a specific way of teaching stance, why do you teach what you do?
-Try standing differently. Maybe feet closer together, more parallel, right leg in front, both legs in the same orientation...give yourself permission to experiment, and perhaps that will change how you teach.
-Do you sit when you practice at home, and if so, what are your legs doing?
-If you photograph yourself (or video) while playing, what does your standing look like in context?
-Do your feet turn out when you walk/run/play/sit/etc? Start experimenting with changing that setup gradually and see if it changes how you feel. It can have ramifications all around the lower body, specifically feet/knees/hips/spine, but maybe affects other aspects as well.
Playing an instrument requires movement within the body- it's not meant to be a static endeavor, but repeating the same position in perpetuity for twenty plus years may not be the best.