@Peter **********
The VISA you has allows you to stay no longer than 90 days at a time. Then you either bounce out and back into the country to get another 90 days
OR
You apply for the 60 day visit family extension (WITH your wife present)
Those are your choices on that visa.
Now that you have a medical condition where you can't walk, you either get lugged to the border and bounce out and back in when you're supposed to, you get a medical extension of stay, OR you end up on overstay and pay 500 baht a day fine when you finally CAN bounce out of the country and back in