Spanish King Juan Carlos has undergone successful knee replacement surgery that has prompted new concern about his overall health.

Doctors say there were no complications as the 73-year-old king had his right knee replaced with an artificial joint. They say the surgery was performed to alleviate pain from old sports injuries, and he is expected to make a full recovery.

There has been widespread speculation about the king's health since last year, when he had a benign tumor removed from his right lung. The news earlier this week of his impending knee surgery prompted new questions.

King Juan Carlos responded to the reports with sarcasm, saying he felt “terrible.” He added that he felt some in the media were determined to spread rumors he was about to die and “ready to be put in a box.”

The monarch is well respected in Spain for helping the transition to democracy after the 1975 death of long-time dictator Francisco Franco.