As I think Loosie was hinting at, a club foot doesn't affect the body, it's the body causing the club foot. Any imbalance that causes a horse to bear weight on one side more will cause a club, (or atrophied) hoof. It's narrower because weight's not spreading it out. Remember a horse's feet change shape according to how they bear weight.
Now if a horse had a dished foot with a high heel, without difference in width, I may believe it was a tendon-related problem. I'd say in my experience, that's only the case in maybe 10% of the horses. That's just my experience around here. When I see a club foot, it's usually on the front, and you can often figure out why it's happening if you look and ask questions. Could be grazing posture, injury that caused them to favor one side, rider's tendency to work one way more than they should, etc. Look hard at these modern-day barrel horses. Many are tall with short necks. Watch them graze and they'll tell you what's happening. Not hard to fix if that's the case. Remember too that many barrel horses are ridden to the left more. One turn to the right, two to the left. If they get stronger to the left, they'll even rest on that side more standing in a stall. It's more comfortable.