The operation she has been waiting for since March 1992 is very painful. Mrs Johnson knows this because she underwent the same surgery on her right knee in 1984, after a wait of two months.
None the less, she is desperate for the operation. 'The pain has got a lot worse in the past few months. I get about a little with my stick. I do the best I can. I try to persevere.'
Mrs Johnson, who lives in Muswell Hill, north London, believed that by now her mobility would have been restored.
In summer, she was given a date for the operation: 23 August - 17 months after her consultant out-patient appointment. The operation, which was to have been at University College London Hospital (UCLH), was then cancelled.
In September, she received a letter from the hospital to say that as the New River Health Authority no longer had a contract with UCLH, the hospital could not treat her.
Mrs Johnson appears to have been caught in an administrative time warp caused by the transfer of waiting lists to other, cheaper hospitals.
In April New River decided to reduce the number of patients it sent to UCLH, which as as a central London teaching hospital has prices 10 per cent higher than hospitals in the suburbs.
Last week, after loud and public protests, Mrs Johnson's GP, Dr Margaret Safranek, succeeded - through an extra-contractual referral - in winning her patient a bed at UCLH, where she had been treated previously. UCLH has now given Mrs Johnson a date in November. She is crossing her fingers that this time she will be treated.