Has anyone else suffered from an ankle that hurts along the outside, think right above that circle bone projection on the outside of your foot, and makes putting weight on the outside edge of your foot seem impossible? I suffered through the workout as much as I could and when I got off had slight trouble walking. If I didn't concentrate on keeping my weight to the inside as I took a step my ankle would practically collapse and roll to the outside. I'm sure I could conjure up a diagram if need be, sorry lol!
Because this is unpleasant, I don't usually ride with short stirrups. Long gives a deeper seat anyway, and I don't bother shortening up for trails. Another idea: If you find your ankles getting even slightly uncomfortable, drop them out of the stirrups and make circles with your feet; this helps nip it in the bud. On long trails rides, this is one of many good reasons to periodically get off when your horse is walking, and walk with it. Improved circulation for you, and for your horse's back; both of you will be much refreshed after a 2-5 minute break like this, and ride more comfortably. My gelding likes to play games when we do this - like having me pick up a stick that he can take off me and walk around with in his mouth!