MADRID (AFP) - Surgeons successfully operated Friday on Spain's 73-year-old king, Juan Carlos I, to replace a badly damaged right knee with an artificial joint in a Madrid clinic, the surgeon said. In a 90-minute operation, they replaced the right knee joint after the widely loved Spanish king complained of pain from old sporting injuries that hampered his usual activities. "It was a complete success," surgeon Angel Villamor told a news conference at the private San Jose Clininc in Madrid after the operation, carried out while the king was under epidural anaesthesia. Surgeons polished the "severely deteriorated" surfaces of the knee joint and replaced them with a synthetic implant, he said, adding that the joint damage was typical for a sportsman. The king is a great lover of sailing and has had skiing accidents in the past. "When we opened the knee we saw severe injuries. The patient did not complain much when you consider what we found, he is very tough, very enduring," the surgeon said. "There were areas of the joint with very deteriorated cartilage, even with bone exposed," he added. The king will remain three or four days in hospital, followed by four to six weeks of recovery time including intensive physiotherapy to allow him to regain normal movement, Villamor said. "His majesty feels just fine, very animated," he said. There has been widespread speculation about his health since he had a benign tumour removed from a lung in May 2010 when he was kept four days in hospital and then had 10 days' rest at a private Barcelona clinic. In September last year the royal household said he had completely recovered from the lung operation and would not require further tests. News of the planned knee surgery led to a flurry of new questions about the king's health, provoking an outburst from the monarch that was widely reported in the Spanish press. "I am feeling terrible, as you can see," the king said when asked how he felt by journalists the day after plans for the knee operation had been announced on May 30. "What you like to do is kill me," said Juan Carlos. "This what you in the press are doing." Born January 5, 1938, in Rome, Juan Carlos was proclaimed king November 22 1975, two days after the death of General Francisco Franco who had designated him as successor since 1969.