An operation to remove a torn cartilage from the Queen's left knee has been successful, says Buckingham Palace.
The Queen is expected to leave hospital at the weekend
A spokesman said some minor "benign skin lesions" were also removed from her face during the operation at King Edward VII hospital in London.
Roger Vickers, who operated on the Queen's right knee in January, carried out the keyhole surgery.
She has regained consciousness and is expected to leave the private hospital at the weekend.
The surgery was completed in about an hour and a quarter and involved two teams of surgeons.
Mr Vickers, the Queen's orthopaedic surgeon, and Adrian Fairbank worked on her knee.
And, while she was under general anaesthetic, Adam Searle and Dr Richard Staughton operated on her face.
It is likely she will spend the next few weeks recuperating, returning to Buckingham Palace before spending Christmas at Sandringham.
Former royal press secretary Dickie Arbiter told BBC News he was not surprised to hear the Queen had undergone additional surgery to remove the skin lesions.
"They are the sort of things which appear with age," he said.
"It's quite an exercise, not just getting the Queen to hospital, but all the security involved and the disruption, so rather than do it twice, they have done it in one go."
Professor Bill Cunliffe, of the British Skin Foundation, said in most cases they were not a major cause for concern.
They were usually removed for cosmetic reasons or because they caused some discomfort, he added.
The knee surgery was arranged after the operation on the Queen's right knee and was not the result of a fall.
The 77-year-old has enjoyed robust health throughout her life.
The right knee surgery was undertaken after the Queen jarred her knee while walking on uneven ground during a private visit to Newmarket last Christmas.
The Queen's commitments planned for next week, including receiving credentials from two new ambassadors, have been postponed or cancelled.