Check the health plans of the private hospitals - especially the Hospital Aleman and the Hospital Italiano. They both offer plans with coverage similar to OSDE's, at lower prices, but without access to the wide cartilla of hospitals and providers. And I think I recall that their waiting periods are more manageable.
The other viable pregago for health care is Galeno. Although I have OSDE, I was in one of their hospitals for an emergency apendectomy last summer and enjoyed care at a level that sbsolutely astonished me. They may have a better policy for pre-existing conditions.
Still, you have to realize that it would take some time for your premiums to amortize the cost of hip surgery, so it's understandable that these companies don't want to risk you signing up for one month, paying one month's premium, and quitting after the surgery. You might ask about pre-paying a year's premiums, to see if they would waive the waiting period.
Good luck!
