An operation to insert a pin into Lady Thatcher's broken upper arm was a success, her son said today.
Sir Mark Thatcher said he was "relieved" and "delighted" that today's operation went so well and praised surgeons at the Chelsea and Westminster Hospital, in central London.
Lady Thatcher is expected to remain in hospital until Wednesday at the earliest, Sir Mark said, speaking outside the hospital this afternoon.
The 83-year-old former prime minister has been recovering in hospital since last week after breaking her upper left arm in a fall.
Doctors decided to insert the pin after the injury failed to heal as quickly as they would have liked.
Sir Mark said the procedure was to hold together the two sides of the fracture which had been "moving about a little bit".
He said general anaesthesia was a concern for anyone of Lady Thatcher's age and added that both he and his sister Carol were "relieved" the operation had been a success.
Miss Thatcher visited her mother yesterday afternoon, he said, and he had spoken to her by telephone before addressing reporters as he left the hospital.
"I shall be coming back to see my mother when she comes out of recovery," he added.
Sir Mark added: "There is no prospect of her leaving at the weekend.
"She wants to go home as quickly as possible but that's in the hands of the people in charge of her aftercare."
Sir Mark said the surgeons had described the operation as "a complete success".
"She will probably be going back to the ward this evening," he added. "We are all delighted.
"The surgical team and everyone here has done a fantastic job.
"We are relieved it has gone so well."
He said the fracture had struggled to repair due to its position, under the deltoid muscle.
"Every time she moved her shoulder the fracture site was moving, which prevented proper union."
He said his sister Carol was herself recovering from eye surgery and was under doctors' orders "to take it extremely gently".
"She is extremely interested in what's going on and extremely concerned," he said.
He said Lady Thatcher's first concern would be when she could go home.
"The second thing she will want to know is what has happened to the Speaker's election, I expect," he added.
Lady Thatcher has suffered a number of health scares in recent years, including a series of minor strokes.
In March last year, she spent a night in hospital after feeling unwell while having dinner with friends.
Last summer, her daughter spoke for the first time about the ex-premier's battle with dementia.
She revealed that her mother struggled to finish sentences, did not know where she lived and even forgot that her husband Denis was dead.
Lady Thatcher cut down her commitments - all but stopping speaking in public - on the advice of doctors several years ago but she continues to attend ceremonial functions.