I have a mare with not so pretty arthritis in a front ankle. She's on cortaflex, ACV, rosehips, and MSM. She stays sound on these, not sound without. She's had perfectly normal healthy foals for us so far.
Avoid any "no bute" type of pain relievers as they contain Devil's Claw and are no good for pregnant mares.
Also keep them out as much as possible and if you can, wrap the area with a standing bandage, if an ankle, at night to keep warm.