Betty Frances Harrison, 87, lived at Tweedsmuir, a sheltered housing scheme in Vicars Cross, a Chester inquest was told.

Cheshire coroner Nicholas Rheinberg heard that Mrs Harrison died on November 15, 2007 at the Countess of Chester Hospital.

On September 13, Mrs Harrison had a fall and fractured her femur. She had an operation in hospital and went into rehabilitation at Ellesmere Port Hospital.

Her friend of 35 years, Eileen Brenda Davies, told the hearing Mrs Harrison had suffered from knee problems in the past and had had two knee replacements.

She said: "At Ellesmere Port Hospital she had been complaining of her right knee being very painful. We could never get her on her feet and she seemed to be getting worse. Before the fall she was quite active and went into town twice a week to play bridge."

It was decided an operation on her right knee would be organised even though a surgeon agreed it was "technically extremely difficult".

Mrs Harrison, who was described by consultant orthopaedic surgeon Dr Janardhan Rao as "a bright, intelligent and articulate woman," had the operation on November 15.

During the operation shattered bone marrow from the knee got into Mrs Harrison's circulation. A bone marrow embolism meant vessels were obstructed by marrow following the fracture of a bone.

The operation began at 10.15am and at 12.45pm her blood pressure dropped and she collapsed and had a cardiac arrest.

She survived the operation but had very low blood pressure and continued to deteriorate until she was pronounced dead at 3.25pm.

It was found that Mrs Harrison had a lung tumour which had spread to her liver.

A report by consultant histopathologist Dr William Kenyon said: "Several pulmonary arteries containing bone marrow from the knee ended up in her circulation.

"The tumour could have weakened her. She would have died of the tumour in weeks or months."

Recording a narrative verdict Cheshire coroner Nicholas Rheinberg said Mrs Harrison had died as a consequence of a lung tumour on which orthopaedic surgery had had an effect.

He agreed the bone marrow embolism had been the cause of her death but said the "size and quantity" of it was unusual.