UNITED HEALTH CARE?????
I think it depends on the type of coverage you have with United. They have several different plans. My assumption is that if you meet your deductible, the rest is covered 80% or 100%, however your plan works.
Call United Healthcare directly and ask to speak to Care Coordination. They should be able to tell you.
Good Luck!
That person probably used a provider that is not contracted with United Healthcare. Chances are if they were their co-pay would not have been nearly as much even with an 80/20 policy. Check with United and see who their providers are for the surgery in your area and check with them before going to someone that charges so much out of pocket.