I really don't know what caused mine. I used to do a lot of exercise, especially aerobics, in my 20s and 30s so general wear and tear may have been the reason. I also have high arches - which I read somewhere could contribute to this condition.
I am now 58 and luckily my husband was able to walk our dogs. I am now completely pain free which is a huge relief. Good luck whatever you decide to do.
Retiring and living frugally in money from downsizing after years of stress
