Agree that it's likely to by posterior tibial. Unfortunately the tendon, which wraps around the ankle bone, has a very poor blood supply so healing is slow. There -are- exercises that the physio can get you doing. Definitely get this sorted sooner rather than later or it will take much longer.
Oops. There is one other problem. Occasionally (about every 4-6 months) when I turn it on it "sticks"on the initial screen saying Garmin etc. I've tried (a) leaving it on for 10-60 minutes; (b) turning it off and on again several times. Eventually I turn it on again and it works. Anyone else ever had this? If so, any way you've worked out to make it work when it does this?