I had snapped both ligaments in my ankle and had a similar procedure done. The doc "opened" the joint during xrays by turning the ankle. Anything over 5 degrees of separation would warrant consideration for surgery. He was able to open the ankle joint a full 13 degrees. My instability was so bad that when I would step off a curb onto a street, my foot would twist 90 degrees inward and I would actually step on the ankle instead of the foot (outside of the foot would be against the road).
My surgery was at least 12 years ago and I am happy to say that I have had very minimal problems since. I do not have full mobility - probably reduced by 10-20 percent (I can not turn the foot inward like I should be able to).
I do have some problems when it is cold. At times, it will feel as if someone is sticking a hot needle into my ankle. This usually passes after a couple of hours. I also experience some pain if I do some serious walking or standing on my feet for more than 4-5 hours at a time.
I won't get into the "gross" aspects of my surgery. If you want more info, feel free to PM me here.